記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.bpj.2013.12.034

担当区分：責任著者   記述言語：英語   出版者・発行元：Bioorganic and Medicinal Chemistry  

Ceramides, which are recognized as pivotal signaling agents in cell differentiation and proliferation, elicit apoptosis in response to anticancer drugs and stress. Although the 1-hydroxy group of ceramide is considered to play an important role in inducing apoptosis, the detailed mechanism underlying ceramide-induced apoptosis remains elusive. We previously synthesized ceramide derivatives by transforming the 1-hydroxy group into amino and carboxy groups, and assessed their ability to form domains in artificial membranes. In this study, we evaluated the apoptotic activities of these derivatives against living cells. Surprisingly, despite the lack of the 1-hydroxy group, most of the derivatives exhibited apoptotic activity, with some being more active than ceramide. Confocal microscopy using fluorescent-ceramide and coherent anti-Stokes Raman scattering microscopy utilizing deuterated ceramide suggested the formation of large domains on living cell membranes. These findings suggest a potential relationship between domain formation and apoptotic activity. Liquid chromatography-mass spectrometry showed that the differences in apoptotic activity among the derivatives were unlikely attributed to variations in cellular uptake. Consequently, we propose that these ceramide derivatives accumulate and form distinct domains within the cellular membranes, inducing apoptosis. Intracellular ceramides synthesized in response to external stimuli may trigger apoptosis through the same mechanism.

DOI： 10.1016/j.bmc.2025.118222

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その他リンク： https://www.sciencedirect.com/science/article/pii/S0968089625001634

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日本学士院  

<p>Structural studies of natural products have been a driving force in the development of organic chemistry throughout its long history, especially in the early years. Recently, structure determination based on new concepts has also gained momentum. In this review we will mainly discuss the functional structures of natural products that account for the mechanisms of action largely from our studies. The topics include marine natural products, amphidinols, and ladder-shaped polyether compounds, which are known as potent antifungal agents and important marine biotoxins, respectively. Nuclear magnetic resonance studies for determining the stereochemistry of amphidinol 3 and its conformation in lipid-bilayer membranes will be presented in detail.</p>

DOI： 10.2183/pjab.101.016

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Biochimica et Biophysica Acta - Biomembranes  

Ginsenoside Rh2 (Rh2) is a ginseng saponin comprising a triterpene core and one unit of glucose and has attracted much attention due to its diverse biological activities. In the present study, we used small-angle X-ray diffraction, solid-state NMR, fluorescence microscopy, and MD simulations to investigate the molecular interaction of Rh2 with membrane lipids in the liquid-disordered (Ld) phase mainly composed of palmitoyloleoylphosphatidylcholine compared with those in liquid-ordered (Lo) phase mainly composed of sphingomyelin and cholesterol. The electron density profiles determined by X-ray diffraction patterns indicated that Rh2 tends to be present in the shallow interior of the bilayer in the Ld phase, while Rh2 accumulation was significantly smaller in the Lo phase. Order parameters at intermediate depths in the bilayer leaflet obtained from 2H NMR spectra and MD simulations indicated that Rh2 reduces the order of the acyl chains of lipids in the Ld phase. The dihydroxy group and glucose moiety at both ends of the hydrophobic triterpene core of Rh2 cause tilting of the molecular axis relative to the membrane normal, which may enhance membrane permeability by loosening the packing of lipid acyl chains. These features of Rh2 are distinct from steroidal saponins such as digitonin and dioscin, which exert strong membrane-disrupting activity.

DOI： 10.1016/j.bbamem.2024.184366

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Analytica Chimica Acta  

Background: N-Glycosylation is one of the most important post-translational modifications in proteins. As the N-glycan profiles in biological samples are diverse and change according to the pathological condition, various profiling methods have been developed, such as liquid chromatography (LC), capillary electrophoresis (CE), and mass spectrometry. However, conventional analytical methods have limitations in sensitivity and/or resolution, hindering the discovery of minor but specific N-glycans that are important both in the basic glycobiology research and in the medical application as biomarkers. Therefore, a highly sensitive and high-resolution N-glycan profiling method is required. Results: In this study, we developed a novel two-dimensional (2D) separation system, which couples hydrophilic interaction liquid chromatography (HILIC) with capillary gel electrophoresis (CGE) via large-volume dual preconcentration by isotachophoresis and stacking (LDIS). Owing to the efficient preconcentration efficiency of LDIS, limit of detection reached 12 pM (60 amol, S/N = 3) with good calibration curve linearity (R2 > 0.999) in the 2D analysis of maltoheptaose. Finally, 2D profiling of N-glycans obtained from standard glycoproteins and cell lysates were demonstrated. High-resolution 2D profiles were successfully obtained by data alignment using triple internal standards. N-glycans were well distributed on the HILIC/CGE 2D plane based on the glycan size, number of sialic acids, linkage type, and so on. As a result, specific minor glycans were successfully identified in HepG2 and HeLa cell lysates. Significance and novelty: In conclusion, the HILIC/CGE 2D analysis method showed sufficient sensitivity and resolution for identifying minor but specific N-glycans from complicated cellular samples, indicating the potential as a next-generation N-glycomics tool. Our novel approach for coupling LC and CE can also dramatically improve the sensitivity in other separation modes, which can be a new standard of 2D bioanalysis applicable not only to glycans, but also to other diverse biomolecules such as metabolites, proteins, and nucleic acids.

DOI： 10.1016/j.aca.2024.342990

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Analyst  

In biological membranes, lipids often interact with membrane proteins (MPs), regulating the localization and activity of MPs in cells. Although elucidating lipid-MP interactions is critical to comprehend the physiological roles of lipids, a systematic and comprehensive identification of lipid-binding proteins has not been adequately established. Therefore, we report the development of lipid-immobilized beads where lipid molecules were covalently immobilized. Owing to the detergent tolerance, these beads enable screening of water-soluble proteins and MPs, the latter of which typically necessitate surfactants for solubilization. Herein, two sphingolipid species—ceramide and sphingomyelin—which are major constituents of lipid rafts, were immobilized on the beads. We first showed that the density of immobilized lipid molecules on the beads was as high as that of biological lipid membranes. Subsequently, we confirmed that these beads enabled the selective pulldown of known sphingomyelin- or ceramide-binding proteins (lysenin, p24, and CERT) from protein mixtures, including cell lysates. In contrast, commercial sphingomyelin beads, on which lipid molecules are sparsely immobilized through biotin-streptavidin linkage, failed to capture lysenin, a well-known protein that recognizes clustered sphingomyelin molecules. This clearly demonstrates the applicability of our beads for obtaining proteins that recognize not only a single lipid molecule but also lipid clusters or lipid membranes. Finally, we demonstrated the screening of lipid-binding proteins from Neuro2a cell lysates using these beads. This method is expected to significantly contribute to the understanding of interactions between lipids and proteins and to unravel the complexities of lipid diversity.

DOI： 10.1039/d4an00579a

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Analytical Biochemistry  

Membrane proteins (MPs) are affected by binding of specific lipids. We previously developed a methodology for systematically analyzing MP-lipid interactions leveraging surface plasmon resonance (SPR). In this method, the gold sensor chip surface was modified with a self-assembled monolayer (SAM), which allowed for a larger amount of MP-immobilization. However, the laborious lipid purification step remained a bottleneck. To address this issue, a new strategy has been developed utilizing gold nanoparticles (AuNPs) instead of the gold sensor chip. AuNPs were coated with SAM, on which MP was covalently anchored. The MP-immobilized AuNPs were mixed with a lipid mixture, and the recovered lipids were quantified by LC–MS. Bacteriorhodopsin (bR) was used as an MP to demonstrate this concept. We optimized immobilization conditions and confirmed the efficient immobilization of bR by dynamic light scattering and electron micrographs. Washing conditions for pulldown experiments were optimized to efficiently remove non-specific lipids. A new binding index was introduced to qualitatively reproduce the known affinity of lipids for bR. Consequently, the low-abundant and least-studied lipid S-TeGD was identified as a candidate for bR-specific lipids. This technique can skip the laborious lipid purification process, accelerating the screening of MP-specific lipids from complex lipid mixtures.

DOI： 10.1016/j.ab.2023.115447

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Bioorganic and Medicinal Chemistry Letters  

Here we examined the membrane binding and pore formation of amphidinol 3 (AM3) and its truncated synthetic derivatives. Importantly, both of the membrane affinity and pore formation activity were well correlated with the reported antifungal activity. Our data clearly demonstrated that the C1-C30 moiety of AM3 plays essential roles both in sterol recognition and stable pore formation. Based on the current findings, we updated the interacting model between AM3 and sterol, in which the moiety encompassing from C21 to C67 accommodates a sterol molecule with forming hydrogen bonds with the sterol hydroxy group and van der Waals contact between AM3 polyol and sterol skeleton. Although the conformation of the C1-C20 moiety of AM3 is hard to specify due to its flexibility, the region likely contributes to stabilization of pore structure.

DOI： 10.1016/j.bmcl.2023.129594

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：iScience  

KcsA is a potassium channel with a plethora of structural and functional information, but its activity in the KcsA-producing actinomycete membranes remains elusive. To determine lipid species involved in channel-modulation, a surface plasmon resonance (SPR)-based methodology, characterized by immobilization of membrane proteins under a membrane environment, was applied. Dianionic cardiolipin (CL) showed extremely higher affinity for KcsA than monoanionic lipids. The SPR experiments further demonstrated that CL bound not only to the N-terminal M0 helix, a lipid-sensor domain, but to the M0 helix-deleted mutant. In contrast, monoanionic lipids interacted primarily with the M0 helix. This indicates the presence of an alternative CL-binding site, plausibly in the transmembrane domain. Single-channel recordings demonstrated that CL enhanced channel opening in an M0-independent manner. Taken together, the action of monoanionic lipids is exclusively mediated by the M0 helix, while CL binds both the M0 helix and its specific site, further enhancing the channel activity.

DOI： 10.1016/j.isci.2023.108471

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Communications Chemistry  

The structural diversity of chemical libraries, which are systematic collections of compounds that have potential to bind to biomolecules, can be represented by chemical latent space. A chemical latent space is a projection of a compound structure into a mathematical space based on several molecular features, and it can express structural diversity within a compound library in order to explore a broader chemical space and generate novel compound structures for drug candidates. In this study, we developed a deep-learning method, called NP-VAE (Natural Product-oriented Variational Autoencoder), based on variational autoencoder for managing hard-to-analyze datasets from DrugBank and large molecular structures such as natural compounds with chirality, an essential factor in the 3D complexity of compounds. NP-VAE was successful in constructing the chemical latent space from large-sized compounds that were unable to be handled in existing methods, achieving higher reconstruction accuracy, and demonstrating stable performance as a generative model across various indices. Furthermore, by exploring the acquired latent space, we succeeded in comprehensively analyzing a compound library containing natural compounds and generating novel compound structures with optimized functions.

DOI： 10.1038/s42004-023-01054-6

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Biochimica et Biophysica Acta - Biomembranes  

Sphingomyelin (SM) is a main component of lipid rafts and characteristic of abundance of long and saturated acyl chains. Recently, we reported that fluorescence-labeled lipids including C16:0 and C18:0SMs retained membrane behaviors of inherent lipids. Here, we newly prepared fluorescent SMs with longer acyl chains, C22:0 and C24:1, for observing their partition and diffusion in SM/cholesterol (chol)/dioleoylphosphatidylcholine (DOPC) bilayers. Although fluorescent C24:1SM underwent a uniform distribution between ordered (Lo) and disordered (Ld) phases, other fluorescent SMs with saturated acyl chains were preferentially distributed in the Lo phase. Interestingly, when the acyl chains of fluorescent and membrane SMs are different, distribution of fluorescent SM to the Lo phase was reduced compared to when the acyl chains are the same. This tendency was also observed for C16:0SM/C22:0SM/chol/DOPC quaternary bilayers, where the minor SM was more excluded out of the Lo phase than the major SM. We also found that the coexistence of SMs induces SM efflux out of the Lo phase and simultaneous DOPC influx to the Lo phase, consequently reducing the difference in fluidity between the two phases. These results suggest that physicochemical properties of lipid rafts are regulated by the acyl chain heterogeneity of SMs.

DOI： 10.1016/j.bbamem.2022.184036

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Bulletin of the Chemical Society of Japan  

The exploration of molecular recognition in lipid bilayers is still extremely difficult. In this report, we leveraged short-range energy transfer (ET) that enabled detection of close contacts within 1 nm distance, and applied it to the interaction of natural products with sterols in lipid bilayers. Amphidinol 3 (AM3), a polyhydroxypolyene metabolite from a marine dinoflagellate, possesses potent antifungal activity by forming membrane pores in a sterol-dependent manner. Although AM3 was shown to interact directly with membrane sterols, the mode of interaction is yet to be fully elucidated. Herein, we found that AM3 and cholestatrienol (CTL), a fluorescent sterol, can be an ET pair because the emission spectrum of the former overlaps with the excitation of the latter. We further confirmed that CTL exerts the sterol-dependent pore formation of AM3 as in the case of cholesterol. Then, titration using intermolecular ET in bilayers revealed that AM3 and CTL form a 1:1 complex with a dissociation constant of 1.4 © 1015 M. The distance between the AM3 polyene and CTL triene was estimated to be less than 1 nm. Based on this information, we proposed a tight binding model between AM3 and the sterol in lipid bilayers.

DOI： 10.1246/bcsj.20220273

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Langmuir  

The ginsenoside Rh2 (Rh2) is a saponin of medicinal ginseng, and it has attracted much attention for its pharmacological activities. In this study, we investigated the interaction of Rh2 with biological membranes using model membranes. We examined the effects of various lipids on the membrane-disrupting activity of Rh2 and found that cholesterol and sphingomyelin (SM) had no significant effect. Furthermore, the effects of Rh2 on acyl chain packing (DPH anisotropy) and water molecule permeability (GP340 values) did not differ significantly between bilayers containing SM and saturated phosphatidylcholine. These results suggest that the formation of the liquid-ordered (Lo) phase affects the behavior of Rh2 in the membrane rather than a specific interaction of Rh2 with a particular lipid. We investigated the effects of Rh2 on the Lo and liquid-disordered (Ld) phases using surface tension measurements and fluorescence experiments. In the surface tension-area isotherms, we compared the monolayers of the Ld and Lo lipid compositions and found that Rh2 is abundantly bound to both monolayers, with the amount being greater in the Ld phase than in the Lo phase. In addition, the hydration state of the bilayers, mainly consisting of the Lo or Ld phase, showed that Rh2 tends to bind to the surface of the bilayer in both phases. At higher concentrations, Rh2 tends to bind more abundantly to the relatively shallow interior of the Ld phase than the Lo phase. The phase-dependent membrane behavior of Rh2 is probably due to the phase-selective affinity and binding mode of Rh2.

DOI： 10.1021/acs.langmuir.2c01261

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Membranes  

Ceramide is the simplest precursor of sphingolipids and is involved in a variety of biological functions ranging from apoptosis to the immune responses. Although ceramide is a minor constituent of plasma membranes, it drastically increases upon cellular stimulation. However, the mechanistic link between ceramide generation and signal transduction remains unknown. To address this issue, the effect of ceramide on phospholipid membranes has been examined in numerous studies. One of the most remarkable findings of these studies is that ceramide induces the coalescence of membrane domains termed lipid rafts. Thus, it has been hypothesised that ceramide exerts its biological activity through the structural alteration of lipid rafts. In the present article, we first discuss the characteristic hydrogen bond functionality of ceramides. Then, we showed the impact of ceramide on the structures of artificial and cell membranes, including the coalescence of the pre-existing lipid raft into a large patch called a signal platform. Moreover, we proposed a possible structure of the signal platform, in which sphingomyelin/cholesterol-rich and sphingomyelin/ceramide-rich domains coexist. This structure is considered to be beneficial because membrane proteins and their inhibitors are separately compartmentalised in those domains. Considering the fact that ceramide/cholesterol content regulates the miscibility of those two domains in model membranes, the association and dissociation of membrane proteins and their inhibitors might be controlled by the contents of ceramide and cholesterol in the signal platform.

DOI： 10.3390/membranes12080727

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記述言語：その他   掲載種別：研究論文（学術雑誌）   出版者・発行元：Biophysical Reviews  

As a model of lipid rafts, the liquid-ordered (Lo) phase formed by sphingomyelin (SM) and cholesterol (Cho) in bilayer membranes has long attracted the attention of biophysics researchers. New approaches and methodologies have led to a better understanding of the molecular basis of the Lo domain structure. This review summarizes studies on model membrane systems consisting of SM/unsaturated phospholipid/Cho implying that the Lo phase contains SM-based nanodomains (or nano-subdomains). Some of the Lo phase properties may be attributed to these nanodomains. Several studies suggest that the nanodomains contain clustered SM molecules packed densely to form gel-phase-like subdomains of single-digit nanometer size at physiological temperatures. Cho and unsaturated lipids located in the Lo phase are likely to be concentrated at the boundaries between the subdomains. These subdomains are not readily detected in the Lo phase formed by saturated phosphatidylcholine (PC) molecules, suggesting that they are strongly stabilized by homophilic interactions specific to SM, e.g., between SM amide groups. This model for the Lo phase is supported by experiments using dihydro-SM, which is thought to have stronger homophilic interactions than SM, as well as by studies using the enantiomer of SM having opposite stereochemistry to SM at the 2 and 3 positions and by some molecular dynamics (MD) simulations of lipid bilayers containing Lo-lipids. Nanosized gel subdomains seem to play an important role in controlling membrane organization and function in biological membranes.

DOI： 10.1007/s12551-022-00967-1

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その他リンク： https://link.springer.com/article/10.1007/s12551-022-00967-1/fulltext.html

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Science Advances  

Amphotericin B, an antifungal drug with a long history of use, forms fungicidal ion-permeable channels across cell membranes. Using solid-state nuclear magnetic resonance spectroscopy and molecular dynamics simulations, we experimentally elucidated the three-dimensional structure of the molecular assemblies formed by this drug in membranes in the presence of the fungal sterol ergosterol. A stable assembly consisting of seven drug molecules was observed to form an ion conductive channel. The structure is somewhat similar to the upper half of the barrel-stave model proposed in the 1970s but substantially different in the number of molecules and in their arrangement. The present structure explains many previous findings, including structure-activity relationships of the drug, which will be useful for improving drug efficacy and reducing adverse effects.

DOI： 10.1126/sciadv.abo2658

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Cold Spring Harbor Laboratory  

DOI： 10.1101/2022.02.08.479071

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

This review paper highlights the recent research on liquid-phase microscale separation techniques for lipidome analysis over the last 10 years, mainly focusing on capillary liquid chromatography (LC) and capillary electrophoresis (CE) coupled with mass spectrometry (MS). Lipids are one of the most important classes of biomolecules which are involved in the cell membrane, energy storage, signal transduction, and so on. Since lipids include a variety of hydrophobic compounds including numerous structural isomers, lipidomes are a challenging target in bioanalytical chemistry. MS is the key technology that comprehensively identifies lipids; however, separation techniques like LC and CE are necessary prior to MS detection in order to avoid ionization suppression and resolve structural isomers. Separation techniques using μm-scale columns, such as a fused silica capillary and microfluidic device, are effective at realizing high-resolution separation. Microscale separation usually employs a nL-scale flow, which is also compatible with nanoelectrospray ionization-MS that achieves high sensitivity. Owing to such analytical advantages, microscale separation techniques like capillary/microchip LC and CE have been employed for more than 100 lipidome studies. Such techniques are still being evolved and achieving further higher resolution and wider coverage of lipidomes. Therefore, microscale separation techniques are promising as the fundamental technology in next-generation lipidome analysis.

DOI： 10.1039/d1an00967b

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ceramides can regulate biological processes probably through the formation of laterally segregated and highly packed ceramide-rich domains in lipid bilayers. In the course of preparation of its analogues, we found that a hydrogen-bond-competent functional group in the C1 position is necessary to form ceramide-rich domains in lipid bilayers [Matsufuji; Langmuir 2018]. Hence, in the present study, we newly synthesized three ceramide analogues: CerN3, CerNH2, and CerNHAc, in which the 1-OH group of ceramide is substituted with a nitrogen functionality. CerNH2 and CerNHAc are capable of forming hydrogen bonds in their headgroups, whereas CerN3 is not. Fluorescent microscopy observation and differential scanning calorimetry analysis disclosed that these ceramide analogues formed ceramide-rich phases in sphingomyelin bilayers, although their thermal stability was slightly inferior to that of normal ceramides. Moreover, wide-angle X-ray diffraction analysis showed that the chain packing structure of ceramide-rich phases of CerNHAc and CerN3 was similar to that of normal ceramide, while the CerNH2-rich phase showed a slightly looser chain packing due to the formation of CerNH3+. Although the domain formation of CerN3 was unexpected because of the lack of hydrogen-bond capability in the headgroup, it may become a promising tool for investigating the mechanistic link between the ceramide-rich phase and the ceramide-related biological functions owing to its Raman activity and applicability to click chemistry.

DOI： 10.1021/acs.langmuir.1c02101

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphidinol 3 (AM3), a polyhydroxy-polyene metabolite from the dinoflagellate Amphidinium klebsii, possesses potent antifungal activity. AM3 is known to interact directly with membrane sterols and permeabilize membranes by forming pores. Because AM3 binds to sterols such as cholesterol and ergosterol, it can be assumed that AM3 has some impact on lipid rafts, which are membrane domains rich in sphingolipids and cholesterol. Hence, we first examined the effect of AM3 on phase-separated liposomes, in which raft-like ordered and non-raft-like disordered domains are segregated. Consequently, AM3 disrupted the phase separation at 22 μM, as in the case of methyl-β-cyclodextrin, a well-known raft-disrupter that extracts sterol from membranes. The surface plasmon resonance measurements and dye leakage assays show that AM3 preferentially recognizes cholesterol in the disordered membrane, which may reflect a weaker lipid-cholesterol interaction in disordered membrane than in ordered membrane. Finally, to gain insight into the AM3-induced coalescence of membrane phases, we measured membrane fluidity using fluorescence correlation spectroscopy, demonstrating that AM3 significantly increases the order of disordered phase. Together, AM3 preferentially binds to the disordered phase rather than the ordered phase, and enhances the order of the disordered phase, consequently blending the separated phases.

DOI： 10.1016/j.bbrep.2021.100941

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We demonstrate a fluid-fluid phase separation in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membranes using a metal complex lipid of type [Mn(L1)] (1; HL1=1-(2-hydroxybenzamide)-2-(2-hydroxy-3-formyl-5-hexadecyloxybenzylideneamino)ethane). Small amount of 1 produces two separated domains in DMPC, whose phase transition temperatures of lipids (Tc ) are both lower than that of the pristine DMPC. Variable temperature fluorescent microscopy for giant-unilamellar vesicles of DMPC/1 hybrids demonstrates that visible phase separations remain in fluid phases up to 37 °C, which is clearly over the Tc of DMPC. This provides a new dimension for the application of metal complex lipids toward controlling lipid distributions in fluid membranes.

DOI： 10.1002/anie.202102774

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ordered/disordered phase separation occurring in bio-membranes has piqued researchers' interest because these ordered domains, called lipid rafts, regulate important biological functions. The structure of the ordered domain has been examined with artificial membranes, which undergo macroscopic ordered/disordered phase separation. However, owing to technical difficulties, the local structure inside ordered domains remains unknown. In this study, we employed electron diffraction to examine the packing structure of the lipid carbon chains in the ordered domain. First, we prepared dehydrated monolayer samples using a rapid-freezing and sublimation protocol, which attenuates the shrinkage of the chain-packing lattice in the dehydration process. Then, we optimised the electron flux to minimise beam damage to the monolayer sample. Finally, we developed low-flux scanning electron diffraction and assessed the chain packing structure inside the ordered domain formed in a distearoylphosphatidylcholine/dioleoylphosphatidylcholine binary monolayer. Consequently, we discovered that the ordered domain contains multiple subdomains with different crystallographic axes. Moreover, the size of the subdomain is larger in the domain centre than that near the phase boundary. To our knowledge, this is the first study to reveal the chain packing structures inside an ordered domain.

DOI： 10.1038/s41598-020-79083-7

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Cell membranes contain lateral systems that consist of various lipid compositions and actin cytoskeleton, providing two-dimensional (2D) platforms for chemical reactions. However, such complex 2D environments have not yet been used as a synthetic platform for artificial 2D nanomaterials. Herein, we demonstrate the direct synthesis of 2D coordination polymers (CPs) at the liquid-cell interface of the plasma membrane of living cells. The coordination-driven self-assembly of networking metal complex lipids produces cyanide-bridged CP layers with metal ions, enabling “pseudo-membrane jackets” that produce long-lived micro-domains with a size of 1–5 μm. The resultant artificial and visible phase separation systems remain stable even in the absence of actin skeletons in cells. Moreover, we show the cell application of the jackets by demonstrating the enhancement of cellular calcium response to ATP.

DOI： 10.1002/anie.202006600

記述言語：日本語  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The lipidome of mammalian cells not only contain sphingomyelin (SM) but also, as a minor component, dihydrosphongomyelin (DHSM), in which the double bond at C4-C5 in the sphingosine base is reduced to a single-bond linkage. It has been indicated that DHSM forms ordered domains more effectively than SM due to its greater potential to induce intermolecular hydrogen bonds. However, direct information on partition and dynamic behaviors of DHSM in raft-like liquid-ordered (Lo) and non-raft-like liquid-disordered (Ld) phase-segregated membranes has been lacking. In the present study, we prepared fluorescent derivatives of DHSM and compared their behaviors to those of fluorescent SM and phosphatidylcholine (PC) derivatives. Fluorescence microscopy showed that DHSM is more preferentially localized to the Lo domains in the Lo/Ld phase-segregated giant unilamellar vesicles than SM and PC. Most importantly, diffusion coefficient measurements indicated that DHSM molecules form DHSM-condensed assembly inside the SM-rich Lo domain of the SM/dioleoylphosphatidylcholine/cholesterol system even when DHSM accounts for 1-3.3 mol% of total lipids. Such heterogeneous distribution of DHSM in the SM-rich Lo domains was further confirmed by inter-lipid FRET experiments. This study provides new insights into the biological functions and significance of minor component DHSM in lipid rafts.

DOI： 10.1038/s41598-020-68688-7

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Covering: Up to 2019 Nature furnishes bioactive compounds (natural products) with complex chemical structures, yet with simple, sophisticated molecular mechanisms. When natural products exhibit their activities in cells or bodies, they first have to bind or react with a target molecule in/on the cell. The cell membrane is a major target for bioactive compounds. Recently, our understanding of the molecular mechanism of interactions between natural products and membrane lipids progressed with the aid of newly-developed analytical methods. New technology reconnects old compounds with membrane lipids, while new membrane-targeting molecules are being discovered through the screening for antimicrobial potential of natural products. This review article focuses on natural products that bind to eukaryotic membrane lipids, and includes clinically important molecules and key research tools. The chemical diversity of membrane-targeting natural products and the molecular basis of lipid recognition are described. The history of how their mechanism was unveiled, and how these natural products are used in research are also mentioned.

DOI： 10.1039/c9np00059c

記述言語：英語  

DOI： 10.1007/s12551-020-00643-2

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphidinol 3 (AM3) is a potent antifungal produced by the dinoflagellate Amphidinium klebsii. It was difficult to determine the absolute configuration of AM3 by using the scarce natural product due to the presence of numerous stereogenic centers on the acyclic carbon chain. Since the absolute configuration was partially determined on the basis of insufficient evidence, the originally proposed structure has been revised three times. Although recent progress on structure determination by computational analysis is remarkable, total synthesis is still the most reliable way to confirm structures. The first total synthesis of AM3 was achieved via expeditious assembly of three components in five steps, confirming the revised structure of AM3 after more than 20 years since its first discovery. The established synthetic route would be a general strategy for synthesizing amphidinol congeners. An artificial and simplified analogue of AM3, which elicited antifungal activity comparable to that of AM3, was designed and synthesized. This is the first example of a biologically active artificial analogue possessing a shorter polyol moiety, providing insight on the antifungal mode-of-action.

DOI： 10.1021/jacs.9b11789

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The influence of ceramide and its dihydro analog (Cer and DHCer, respectively; inclusively termed Cers) on sphingomyelin (SM) bilayers was examined. Fluorescent microscopy showed that SM/Cers binary bilayers undergo phase separation between Cers-rich and Cers-poor phases. Based on calorimetry, the content of Cers in the Cers-rich phase was estimated and the results show that DHCer in the DHCer-rich phase (17.5 mol%) is more condensed than Cer in the Cer-rich phase (15 mol%), likely due to a stronger intermolecular interaction of DHCer than that of Cer. Furthermore, the Cers-poor phase consists of almost pure SM. X-ray diffraction and water permeability measurements disclosed that the size of crystallites—lipid nano-clusters formed inside the Cers-rich phase—are larger for the DHCer-rich phase than those for the Cer-rich phase. Due to its stronger intermolecular interactions, DHCer could effectively suppress the inter-crystallite packing gaps to avoid the energetic disadvantage, resulting in formation of larger crystallites.

DOI： 10.1016/j.chemphyslip.2019.104835

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Copyright © 2019 American Chemical Society. Although it has been demonstrated that membrane proteins (MPs) require lipids to ensure their structural and functional integrity, details on how lipid-MP interactions regulate MPs are still unclear. Recently, we developed a concise method for quantitatively evaluating lipid-MP interactions and applied it to bacteriorhodopsin (bR), a halobacterial MP that forms trimers and acts as a light-driven proton pump. Consequently, we found that the halobacterial glycolipid, S-TGA-1, has the highest affinity for bR, among other lipids. In this study, we examined the effects of S-TGA-1 on bR via visible circular dichroism spectroscopy, flash photolysis, and proton influx measurement. The results showed that S-TGA-1 efficiently promotes trimer formation, photocycle, and proton pumping in bR. Our data also suggested that the bR photocycle is restored as a consequence of the trimerization induced by the lipid. This study demonstrates clearly that lipids specifically interacting with MPs can have significant impacts on MP structure and/or function. The methodology adopted in our studies can be applied to other MPs and will help elucidate the physiological functions of lipids in terms of lipid-MP interactions, thus accelerating "lipid chemical biology" studies.

DOI： 10.1021/acschembio.9b00756

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Many plasma membrane (PM) functions depend on the cholesterol concentration in the PM in strikingly nonlinear, cooperative ways: fully functional in the presence of physiological cholesterol levels (35~45 mol%), and nonfunctional below 25 mol% cholesterol; namely, still in the presence of high concentrations of cholesterol. This suggests the involvement of cholesterol-based complexes/domains formed cooperatively. In this review, by examining the results obtained by using fluorescent lipid analogs and avoiding the trap of circular logic, often found in the raft literature, we point out the fundamental similarities of liquid-ordered (Lo)-phase domains in giant unilamellar vesicles, Lo-phase-like domains formed at lower temperatures in giant PM vesicles, and detergent-resistant membranes: these domains are formed by cooperative interactions of cholesterol, saturated acyl chains, and unsaturated acyl chains, in the presence of >25 mol% cholesterol. The literature contains evidence, indicating that the domains formed by the same basic cooperative molecular interactions exist and play essential roles in signal transduction in the PM. Therefore, as a working definition, we propose that raft domains in the PM are liquid-like molecular complexes/domains formed by cooperative interactions of cholesterol with saturated acyl chains as well as unsaturated acyl chains, due to saturated acyl chains' weak multiple accommodating interactions with cholesterol and cholesterol's low miscibility with unsaturated acyl chains and TM proteins. Molecules move within raft domains and exchange with those in the bulk PM. We provide a logically established collection of fluorescent lipid probes that preferentially partition into raft and non-raft domains, as defined here, in the PM.

DOI： 10.1111/tra.12718

記述言語：その他   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.biochem.9b00835

記述言語：日本語  

天然物のNMR研究―立体化学決定および溶液中と膜中における配座解析

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Background: Because ordered membrane domains, called lipid rafts, regulate activation of ion channels related to the nerve pulse, lipids rafts are thought to be a possible target for anesthetic molecules. To understand the mechanism of anesthetic action, we examined influence of representative local anesthetics (LAs); dibucaine, tetracaine, and lidocaine, on raft-like liquid-ordered (L_o)/non-raft-like liquid-disordered (L_d) phase separation. Methods: Impact of LAs on the phase separation was observed by fluorescent microscopy. LA-induced perturbation of the L_o and L_d membranes was examined by DPH anisotropy measurements. Incorporation of LAs to the membranes was examined by fluorescent anisotropy of LAs. The biding location of the LAs was indicated by small angle x-ray diffraction (SAXD). Results: Fluorescent experiments showed that dibucaine eliminated the phase separation the most effectively, followed by tetracaine and lidocaine. The disruption of the phase separation can be explained by their disordering effects on the L_o membrane. SAXD and other experiments further suggested that dibucaine's most potent perturbation of the L_o membrane is attributable to its deeper immersion and bulky molecular structure. Tetracaine, albeit immersed in the L_o membrane as deeply as dibucaine, less perturbs the L_o membrane probably because of its smaller bulkiness. Lidocaine hardly reaches the hydrophobic region, resulting in the weakest L_o membrane perturbation. Conclusion: Dibcaine perturbs the L_o membrane the most effectively, followed by tetracaine and lidocaine. This ranking correlates with their anesthetic potency. General significance: This study suggests a possible mechanistic link between anesthetic action and perturbation of lipid rafts.

DOI： 10.1016/j.bbagen.2019.06.008

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Sphingomyelin (SM) and cholesterol (Cho) are the important lipids for the formation of biologically functional membrane domains, lipid rafts. However, the interaction between Cho and the headgroup of SM remains unclear. In this study, we performed solid-state NMR experiments to reveal the Cho effects on the headgroup conformation using ²H-labeled stearoyl-SM (SSM). Deuterated SSMs at the Cα, Cβ, and Cγ positions of a choline moiety were separately prepared and subjected to NMR measurements to determine the quadrupolar splitting of ²H signals in hydrated SSM unitary and SSM/Cho (1:1) bilayers. Using ²H NMR and ¹³C-³¹P REDOR data, the conformation and orientation of the choline moiety were deduced and compared with those derived from molecular dynamics simulations. In SSM unitary bilayers, three torsional angles in the phosphocholine moiety, P-O-Cα-Cβ, were found to be consecutive +gauche(g)/+g/+g or −g/−g/−g. The orientation and conformation of the SSM headgroup were consistent with the results of our molecular dynamics simulations and the previous results on phosphatidylcholines. The quadrupolar coupling at the α methylene group slightly increased in the presence of Cho, and those at the Cβ and Cγ decreased more significantly, thus suggesting that Cho reduced the gauche conformation at the Cα-Cβ torsion. The conformational ensemble in the presence of Cho may enhance the so-called umbrella effect of the SSM headgroup, resulting in the stabilization of Cho near the SM molecules by concealing the hydrophobic Cho core from interfacial water. We also examined the effect of the chiral centers at the sphingosine chain to the headgroup conformation by determining the enantiomeric excess between the diastereomeric +g/+g/+g and −g/−g/−g conformers using (S)-Cα-deuterated and (R)-Cα-deuterated SSMs. Their ²H NMR measurements showed that the chiral centers induced the slight diastereomeric excess in the SM headgroup conformation.

DOI： 10.1016/j.bpj.2019.06.019

記述言語：英語  

Although interactions between lipids and membrane proteins (MPs) have been considered crucially important for understanding the functions of lipids, lack of useful and convincing experimental methods has hampered the analysis of the interactions. Here, we developed a surface plasmon resonance (SPR)-based concise method for quantitative analysis of lipid-MP interactions, coating the sensor chip surface with self-assembled monolayer (SAM) with C6-chain. To develop this method, we used bacteriorhodopsin (bR) as an MP, and examined its interaction with various types of lipids. The merits of using C6-SAM-modified sensor chip are as follows: (1) alkyl-chains of SAM confer a better immobilization of MPs because of the efficient preconcentration due to hydrophobic contacts; (2) SAM provides immobilized MPs with a partial membranous environment, which is important for the stabilization of MPs; and (3) a thinner C6-SAM layer (1 nm) compared with MP size forces the MP to bulge outward from the SAM surface, allowing extraneously injected lipids to be accessible to the hydrophobic transmembrane regions. Actually, the amount of bR immobilized on C6-SAM is 10 times higher than that on a hydrophilic CM5 sensor chip, and AFM observations confirmed that bR molecules are exposed on the SAM surface. Of the lipids tested, S-TGA-1, a halobacterium-derived glycolipid, had the highest specificity to bR with a nanomolar dissociation constant. This is consistent with the reported co-crystal structure that indicates the formation of several intermolecular hydrogen bonds. Therefore, we not only reproduced the specific lipid-bR recognition, but also succeeded in its quantitative evaluation, demonstrating the validity and utility of this method.

DOI： 10.1016/j.aca.2019.01.042

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The clinically important antibiotic amphotericin B (AmB) is a membrane-active natural product that targets membrane sterol. The antimicrobial activity of AmB is generally attributed to its membrane permeabilization, which occurs when a pore is formed across a lipid bilayer. In this study, the molecular orientation of AmB was investigated using solid-state nuclear magnetic resonance (NMR) to better understand the mechanism of antifungal activity. The methyl ester of AmB (AME) labeled with NMR isotopes, d₃-AME, and its fluorinated and/or ¹³C-labeled derivatives were prepared. All of the AmB derivatives showed similar membrane-disrupting activities and ultraviolet spectra in phospholipid liposomes, suggesting that their molecular assemblies in membranes closely mimic those of AmB. Solid-state ²H NMR measurements of d₃-AME in a hydrated membrane showed that the mobility of AME molecules depends on concentration and temperature. At a 1:5:45 AME:Erg:dimyristoylphosphatidylcholine ratio, AME became sufficiently mobilized to observe the motional averaging of quadrupole coupling. On the basis of the rotational averaging effect of ¹⁹F chemical shift anisotropy, ²H quadrupolar splitting, and ¹³C-¹⁹F dipolar coupling of 14β-F-AMEs, we deduced that the molecular axis of AME is predominantly parallel to the normal of a lipid bilayer. This result supports the barrel-stave model as a molecular assembly of AmB in membranes. ©

DOI： 10.1021/acs.biochem.9b00180

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ceramide is a bioactive lipid with significant roles in several biological processes including cell proliferation, apoptosis, and raft formation. Although fluorescent derivatives of ceramide are required to probe the behavior of ceramide in cells and cell membranes, commercial fluorescent ceramide derivatives do not reproduce the membrane behavior of native ceramide because of the introduction of bulky fluorophores in the acyl chain. Recently, we developed novel fluorescent analogs of sphingomyelin in which the hydrophilic fluorophores, ATTO488 and ATTO594, are attached to the polar head of sphingomyelin via a nonaethylene glycol linker and demonstrated that their partition and dynamic behaviors in bilayer membranes are similar to native sphingomyelin. In this report, by extending the concept used for the development of fluorescent analogs of sphingomyelin, we prepared novel fluorescent ceramides that exhibit membrane behaviors similar to native ceramide and succeeded in visualizing ceramide-rich membrane domains segregated from ceramide-poor domains.

DOI： 10.1021/acs.langmuir.8b03176

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ceramides are important intermediates in sphingolipid biosynthesis (and degradation) and are normally present in only small amounts in unstressed cells. However, following the receptor-mediated activation of neutral sphingomyelinase, sphingomyelin can acutely give rise to substantial amounts of ceramides, which dramatically alter membrane properties. In this study, we have examined the role of the 1-OH and 3-OH functional groups of ceramide for its membrane properties. We have specifically examined how the oxidation of the primary alcohol to COOH or COOMe in palmitoyl ceramide (PCer) or the removal of either the primary alcohol or C(3)-OH (deoxy analogs) affected ceramides' interlipid interactions in fluid phosphatidylcholine bilayers. Measuring the time-resolved fluorescence emission of trans-parinaric acid, or its steady-state anisotropy, we have obtained information about the propensity of the ceramide analogs to form ceramide-rich domains and the thermostability of the formed domains. We observed that the oxidation of the primary alcohol to COOH shifted the ceramide's gel-phase onset concentration to slightly higher values in 1-palmitoyl-2-oleoyl-sn-3-glycero-3-phosphocholine (POPC) bilayers. Methylation of the COOH function of the ceramide did not change the segregation tendency further. The complete removal of the primary alcohol dramatically reduced the ability of 1-deoxy-PCer to form ceramide-rich ordered domains. However, the removal 3-OH (in 3-deoxy-PCer) had only small effects on the lateral segregation of the ceramide analog. The thermostability of the ceramide-rich domains in the POPC bilayers decreased in the following order: 1-OH > COOH > COOMe = 3-deoxy > 1-deoxy. We conclude that ceramide needs a hydrogen-bonding-competent functional group in the C(1) position to be able to form laterally segregated ceramide-rich domains of high packing density in POPC bilayers. The presence or absence of 3-OH was not functionally critical for ceramide's lateral segregation properties.

DOI： 10.1021/acs.langmuir.8b03237

記述言語：日本語  

Excellent Fluorescent Sphingomyelin Analog Reveals the Existence of Lipid Rafts

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Sphingomyelin is an abundant lipid in some cellular membrane domains, such as lipid rafts. Hydrogen bonding and hydrophobic interactions of the lipid with surrounding components such as neighboring sphingomyelin and cholesterol (Cho) are widely considered to stabilize the raft-like liquid-ordered (Lo) domains in membrane bilayers. However, details of their interactions responsible for the formation of Lo domains remain largely unknown. In this study, the enantiomer of stearoyl sphingomyelin (ent-SSM) was prepared, and its physicochemical properties were compared with the natural SSM and the diastereomer of SSM to examine possible stereoselective lipid-lipid interactions. Interestingly, differential scanning calorimetry experiments demonstrated that palmitoyl sphingomyelin, with natural stereochemistry, exhibited higher miscibility with SSM bilayers than with ent-SSM bilayers, indicating that the homophilic sphingomyelin interactions occurred in a stereoselective manner. Solid-state ²H NMR revealed that Cho elicited its ordering effect very similarly on SSM and ent-SSM (and even on the diastereomer of SSM), suggesting that SSM-Cho interactions are not significantly affected by stereospecific hydrogen bonding. SSM and ent-SSM formed gel-like domains with very similar lateral packing in SSM/Cho/palmitoyloleoyl phosphatidylcholine membranes, as shown by fluorescence lifetime experiments. This observation can be explained by a homophilic hydrogen-bond network, which was largely responsible for the formation of gel-like nanodomains of SSMs (or ent-SSM). Our previous study revealed that Cho-poor gel-like domains contributed significantly to the formation of an Lo phase in sphingomyelin/Cho membranes. The results of the study presented here further show that SSM-SSM interactions occur near the headgroup region, whereas hydrophobic SSM-Cho interactions appeared important in the bilayer interior for Lo domain formation. The homophilic interactions of sphingomyelins could be mainly responsible for the formation of the domains of nanometer size, which may correspond to the small sphingomyelin/Cho-based rafts that temporally occur in biological membranes.

DOI： 10.1016/j.bpj.2018.08.042

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Sphingomyelin (SM)-rich membrane nano-domains, called lipid rafts, have attracted the interest of researchers due to their potential involvement in the formation of signaling platform. Although there are many studies on lipid rafts, the direct observation of lipid rafts is still challenging owing to two critical reasons. One is the lack of an appropriate fluorescent probe mimicking the native behavior of raft lipids; fluorescent labeling often alters the intrinsic disposition of raft lipids. The other is their spatio-temporal stability; the size of lipid rafts is much smaller than the optical resolution of usual microscopy and their lifetime is much shorter than image acquisition duration. These issues are hampering the visualization of lipid rafts. Our review highlights the recent advances in microscopic techniques to visualize the partition and dynamic behavior of SMs, disclosing the detailed structure of lipid rafts. Moreover, we will elucidate the importance of SM-SM interactions in the stabilization of signaling platforms as lipid rafts.

DOI： 10.1016/j.chemphyslip.2018.07.002

記述言語：日本語  

生体膜を標的にする天然有機化合物 天然物による厳密な脂質認識とそれに基づく表現型

記述言語：その他   掲載種別：研究論文（学術雑誌）  

Theonellamide A, a marine-sponge-derived bicyclic peptide, binds to cholesterol in aqueous DMSO: Solution NMR-based analysis of peptide-sterol interactions using hydroxylated sterol.

DOI： 10.1016/j.bbamem.2018.07.010

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphidinol 3 (AM3) is a marine natural product produced by the dinoflagellate Amphidinium klebsii. Although the absolute configuration of AM3 was determined in 1999 by extensive NMR analysis and degradation of the natural product, it was a daunting task because of the presence of numerous stereogenic centers on the acyclic carbon chain and the limited availability from natural sources. Thereafter, revisions of the absolute configurations at C2 and C51 were reported in 2008 and 2013, respectively. Reported herein is the revised absolute configuration of AM3: 32S, 33R, 34S, 35S, 36S, and 38S based on the chemical synthesis of partial structures corresponding to the C31–C67 fragment of AM3 in combination with degradation of the natural product. The revised structure is unique in that both antipodal tetrahydropyran counterparts exist on a single carbon chain. The structural revision of AM3 may affect proposed structures of congeners related to the amphidinols.

DOI： 10.1002/anie.201712167

記述言語：その他  

Synthesis and Stereochemical Revision of the C31-C67 Fragment of Amphidinol 3

DOI： 10.1002/ange.201712167

記述言語：英語   掲載種別：研究論文（学術雑誌）  

For the complete structure elucidation of an endogenous sperm-activating and -attracting factor isolated from eggs of the ascidian Ascidia sydneiensis (Assydn-SAAF), its two possible diastereomers with respect to C-25 were synthesized. Starting from ergosterol, the characteristic steroid backbone was constructed by using an intramolecular pinacol coupling reaction and stereoselective reduction of a hydroxy ketone as key steps, and the side chain was introduced by Julia-Kocienski olefination. Comparison of the NMR data of the two diastereomers with those of the natural product led to the elucidation of the absolute configuration as 25S; thus the complete structure was determined and the first synthesis of Assydn-SAAF was achieved.

DOI： 10.1021/acs.jnatprod.7b01052

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A variety of biomolecules acting on the cell membrane folds into a biologically active structure in the membrane environment. It is, therefore, important to determine the structures and dynamics of such biomolecules in a membrane environment. While several biophysical techniques are used to obtain low-resolution information, solid-state NMR spectroscopy is one of the most powerful means for determining the structure and dynamics of membrane bound biomolecules such as antibacterial biomolecules and amyloidogenic proteins; unlike X-ray crystallography and solution NMR spectroscopy, applications of solid-state NMR spectroscopy are not limited by non-crystalline, non-soluble nature or molecular size of membrane-associated biomolecules. This review article focuses on the applications of solid-state NMR techniques to study a few selected antibacterial and amyloid peptides. Solid-state NMR studies revealing the membrane inserted bent α-helical structure associated with the hemolytic activity of bee venom melittin and the chemical shift oscillation analysis used to determine the transmembrane structure (with α-helix and 3₁₀-helix in the N- and C-termini, respectively) of antibiotic peptide alamethicin are discussed in detail. Oligomerization of an amyloidogenic islet amyloid polypeptide (IAPP, or also known as amylin) resulting from its aggregation in a membrane environment, molecular interactions of the antifungal natural product amphotericin B with ergosterol in lipid bilayers, and the mechanism of lipid raft formation by sphingomyelin studied using solid state NMR methods are also discussed in this review article. This article is part of a Special Issue entitled “Biophysical Exploration of Dynamical Ordering of Biomolecular Systems” edited by Dr. Koichi Kato.

DOI： 10.1016/j.bbagen.2017.06.004

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ceramide is a bioactive lipid with important roles in several biological processes including cell proliferation and apoptosis. Although 3-ketoceramides that contain a keto group in place of the 3-OH group of ceramide occur naturally, ceramide derivatives oxidized at the primary 1-OH group have not been identified to date. To evaluate how the oxidative state of the 1-OH group affects the physical properties of membranes, we prepared novel ceramide derivatives in which the 1-OH group was oxidized to a carboxylic acid (PCerCOOH) or methylester (PCerCOOMe) and examined the rigidity of their monolayers and the formation of gel domains in palmitoyloleoylphosphatidylcholine (POPC) or sphingomyelin (SM) bilayers. As a result, PCerCOOH and PCerCOOMe exhibited membrane properties similar to those of native ceramide, although the deprotonated form of PCerCOOH, PCerCOO^-, exhibited markedly lower rigidity and higher miscibility with POPC and SM. This was attributed to the electrostatic repulsion of the negative charge, which hampered the formation of the ceramide-enriched gel domain. The similarities in the properties of PCerCOOMe and ceramide revealed the potential to introduce various functional groups onto PCerCOOH via ester or amide linkages; therefore, these derivatives will also provide a new strategy for developing molecular probes, such as fluorescent ceramides, and inhibitors of ceramide-related enzymes.

DOI： 10.1021/acs.langmuir.7b02654

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Interactional and structural analyses of lipids in hydrated biomembranes are at the frontier of membrane physics and biology. Recently, solid-state NMR has emerged as a frequently used technique for the investigation of biomembrane systems, leading to particularly remarkable advances in the study of the structural biology of membrane proteins. However, conformational and interactional analyses of lipid molecules and membrane-active small compounds remain challenging. This chapter highlights recent applications of solid-state NMR to membrane lipids and nonpeptidic molecules such as membrane-active natural products. Lipid rafts are microdomains in cellular membranes formed by sphingomyelin and cholesterol and are thought to constitute a platform for signal transduction. Amphotericin B, theonellamide-A, and amphidinol 3 exert their activities by interacting with lipid membranes. Deuterium quadrupole coupling combined with dipole-dipole interactions has been used to evaluate the interaction modes and dynamic properties of membrane lipids and small membrane-active compounds. Herein, we review the recent advances in these topics using our recent research studies as examples of solid-state NMR investigations of hydrated lipid bilayers.

DOI： 10.1016/bs.arnmr.2017.12.003

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphidinol 3 (AM3) is an anti-fungal polyene extracted from a marine dinoflagellate. Here, we examined the ion channel activity and membrane-embedded structure of AM3 using a lipid bilayer method and atomic force microscopy (AFM). AM3 exhibited large-conductance (∼1 nS) and non-selective single-channel activity only when sterols were present in the membrane leaflet of the AM3-added side. The variable conductance suggests the formation of a multimeric barrel-stave pore. At high AM3 concentrations, giant-conductance "jumbo" channels (∼40 nS) emerged. AFM revealed a thicker raft-like membrane phase with the appearance of a wrinkled surface, in which phase pores (diameter: ∼10 nm) were observed. The flip-flop of ergosterol occurred only after the appearance of the jumbo channel, indicating that the jumbo channel induced a continuity between the outer and inner leaflets of the membrane: a feature characteristic of toroidal-like pores. Thus, AM3 forms different types of sterol-aided polymorphic channels in a concentration dependent manner.

DOI： 10.1038/s41598-017-11135-x

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A morphology transformation of hybrid liposomes was shown to occur from spherical vesicles to tubular micelles when increasing the ratio of the metal complex lipid present. Phase transition temperatures increased while viscosities decreased, indicating that the hybrids exhibit stronger interaction between heads but weaker interaction between alkyl chains than occurs in pristine liposomes.

DOI： 10.1039/c7cc07944c

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Imaging the distribution of sphingomyelin (SM) in membranes is an important issue in lipid-raft research. Recently we developed novel fluorescent SM analogs that exhibit partition and dynamic behaviors similar to native SM, and succeeded in visualizing lateral domain-segregation between SM-rich liquid-ordered (L_o) and SM-poor liquid-disordered (L_d) domains. However, because the fluorescent contrast between these two domains depends directly on their partition ratio for the fluorescent SMs, domain-separation becomes indeterminate when the distribution difference is not great enough. In this study, we propose the use of inter-lipid Förster resonance energy transfer (FRET) imaging between fluorescent SMs to enhance the contrast of the two domains in cases in which the inter-domain difference in SM distribution is inadequate for conventional monochromic imaging. Our results demonstrate that inter-lipid FRET intensity was significantly higher in the L_o domain than in the L_d domain, resulting in a clear and distinguishable contrast between the two domains even in poorly phase-separated giant unilamellar vesicles. In addition, we show that inter-lipid FRET imaging is useful for selective visualization of highly condensed assemblies and/or clusters of SM molecules in living cell membranes. Thus, the inter-lipid FRET imaging technique can selectively emphasize the SM-condensed domains in both artificial and biological membranes.

DOI： 10.1038/s41598-017-16361-x

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphidinols are polyketide metabolites produced by marine dinoflagellates and are chiefly composed of a long linear chain with polyol groups and polyolefins. Two new homologues, amphidinols 20 (AM20, 1) and 21 (AM21, 2), were isolated from Amphidinium carterae collected in Korea. Their structures were elucidated by detailed NMR analyses as amphidinol 6-type compounds with remarkably long polyol chains. Amphidinol 21 (2) has the longest linear structure among the amphidinol homologues reported so far. The congeners, particularly amphidinol 21 (2), showed weaker activity in hemolysis and antifungal assays compared to known amphidinols.

DOI： 10.1021/acs.jnatprod.7b00345

記述言語：英語  

In this chapter we overview two topics on NMR methodologies for small molecules, mostly natural products; one is about the solution NMR-based methods used for stereochemical determination of natural products, and the other is on the solid-state and other techniques for investigating natural product-membrane interactions. Since important two methods for stereochemical analysis of natural products, namely the J-based configuration analysis (JBCA) and universal NMR database (UDB) methods, were reported in the 1990s, both methods have been widely used in the field of natural products. The newly coming RDC method is not the major method in the field of natural products yet, but will surely be an important tool for the stereochemical correlation between distant stereogenic centers, which could provide invaluable information as to the whole shape of natural products in solution. In the latter part of this chapter, we discuss the application of solid-state and other NMR techniques to membrane interaction analysis of natural products. In particular, we describe three examples of natural products that interact with biological membranes such as amphotericin B, erythromycin A, and theonellamide A. As shown in NMR studies of amphotericin B, natural products often reveal very high affinities for phospholipids and sterols in bilayer membranes. Solid-state NMR, therefore, provides a very promising approach toward the structure study of membrane-active complexes formed by natural products that have high affinity to lipids. In addition, solution NMR techniques can be applied to elucidate the structural features of membrane-bound small molecules such as antibiotic erythromycin A and membrane-disrupting cyclic peptide theonellamide A. Standard 2D ¹H-¹H experiments such as COSY (correlation spectroscopy), NOESY (nuclear Overhauser effect spectroscopy), and DOSY (diffusion-ordered spectroscopy) are often helpful in elucidating the membrane interaction between natural products and lipids.

DOI： 10.1007/978-981-10-5966-7_14

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The 3D structure determination of biological macromolecules by X-ray crystallography suffers from a phase problem: to perform Fourier transformation to calculate real space density maps, both intensities and phases of structure factors are necessary; however, measured diffraction patterns give only intensities. Although serial femtosecond crystallography (SFX) using X-ray free electron lasers (XFELs) has been steadily developed since 2009, experimental phasing still remains challenging. Here, using 7.0-keV (1.771 Å) X-ray pulses from the SPring-8 Angstrom Compact Free Electron Laser (SACLA), iodine single-wavelength anomalous diffraction (SAD), single isomorphous replacement (SIR), and single isomorphous replacement with anomalous scattering (SIRAS) phasing were performed in an SFX regime for a model membrane protein bacteriorhodopsin (bR). The crystals grown in bicelles were derivatized with an iodine-labeled detergent heavy-atom additive 13a (HAD13a), which contains the magic triangle, I3C head group with three iodine atoms. The alkyl tail was essential for binding of the detergent to the surface of bR. Strong anomalous and isomorphous difference signals from HAD13a enabled successful phasing using reflections up to 2.1-Å resolution from only 3,000 and 4,000 indexed images from native and derivative crystals, respectively. When more images were merged, structure solution was possible with data truncated at 3.3-Å resolution, which is the lowest resolution among the reported cases of SFX phasing. Moreover, preliminary SFX experiment showed that HAD13a successfully derivatized the G protein-coupled A2a adenosine receptor crystallized in lipidic cubic phases. These results pave the way for de novo structure determination of membrane proteins, which often diffract poorly, even with the brightest XFEL beams.

DOI： 10.1073/pnas.1602531113

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphotericin B (AmB) is a polyene macrolide antibiotic isolated from Streptomyces nodosus. The antifungal activity of AmB can be attributed to the formation of an ion-channel assembly in the presence of ergosterol (Erg), in which there are two different AmB-Erg orientations, parallel and antiparallel, as reported previously. In this study, to elucidate the structures of those AmB-Erg complexes based on solid-state nuclear magnetic resonance, a ¹⁹F-labeled AmB derivative was newly prepared by a hybrid synthesis that utilized degradation products from the drug. Using the 2-(trimethylsilyl)ethoxymethyl (SEM) group as the protecting group for the carboxylic acid moiety of AmB, the fully deprotected labeled AmB compounds were obtained successfully. Then, these labeled AmBs were subjected to ¹³C{¹⁹F} rotational-echo double-resonance (REDOR) experiments in hydrated lipid bilayers. The results indicated the coexistence of parallel and antiparallel orientations for AmB and Erg pairing, at a ratio of 7:3. A total of six distances between AmB and Erg were successfully obtained. Geometry analysis using the distance constraints derived from the REDOR experiments provided the plausible AmB-Erg complex structure for both the parallel and antiparallel interactions. The flat macrolide of AmB and the tetracyclic core of Erg closely contacted in a face-to-face manner, thus maximizing the van der Waals interaction between the two molecules. This interaction can be attributed to the coexistence of both the parallel and antiparallel orientations.

DOI： 10.1021/acs.biochem.6b00193

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Theonellamides (TNMs) are antifungal and cytotoxic bicyclic dodecapeptides derived from the marine sponge Theonella sp. These peptides specifically bind to 3β-hydroxysterols, resulting in 1,3-β-d-glucan overproduction and membrane damage in yeasts. The inclusion of cholesterol or ergosterol in phosphatidylcholine membranes significantly enhanced the membrane affinity of theonellamide A (TNM-A) because of its direct interaction with 3β-hydroxyl groups of sterols. To better understand TNM-induced membrane alterations, we investigated the effects of TNM-A on liposome morphology. ³¹P nuclear magnetic resonance (NMR) and dynamic light scattering (DLS) measurements revealed that the premixing of TNM-A with lipids induced smaller vesicle formation. When giant unilamellar vesicles were incubated with exogenously added TNM-A, confocal micrographs showed dynamic changes in membrane morphology, which were more frequently observed in cholesterol-containing than sterol-free liposomes. In conjunction with our previous data, these results suggest that the membrane action of TNM-A proceeds in two steps: 1) TNM-A binds to the membrane surface through direct interaction with sterols and 2) accumulated TNM-A modifies the local membrane curvature in a concentration-dependent manner, resulting in dramatic membrane morphological changes and membrane disruption.

DOI： 10.1016/j.bbamem.2016.03.019

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Bilayer lipids influence the lateral structure of the membranes, but the relationship between lipid properties and the lateral structure formed is not always understood. Model membrane studies on bilayers containing cholesterol and various phospholipids (PLs) suggest that high and low temperature melting PLs may segregate, especially in the presence of cholesterol. The effect of different PL headgroups on lateral structure of bilayers is also not clear. Here, we have examined the formation of lateral heterogeneity in increasingly complex (up to five-component) multilamellar bilayers. We have used time-resolved fluorescence spectroscopy with domain-selective fluorescent probes (PL-conjugated trans-parinaric acid), and ²H NMR spectroscopy with site or perdeuterated PLs. We have measured changes in bilayer order using such domain-selective probes both as a function of temperature and composition. Our results from time-resolved fluorescence and ²H NMR showed that in ternary bilayers, acyl chain order and thermostability in sphingomyelin-rich domains were not affected to any greater extent by the headgroup structure of the monounsaturated PLs (phosphatidylcholine, phosphatidylethanolamine, or phosphatidylserine) in the bilayer. In the complex five-component bilayers, we could not detect major differences between the different monounsaturated PLs regarding cholesterol-induced ordering. However, cholesterol clearly influenced deuterated N-palmitoyl sphingomyelin differently than the other deuterated PLs, suggesting that cholesterol favored N-palmitoyl sphingomyelin over the other PLs. Taken together, both the fluorescence spectroscopy and ²H NMR data suggest that the complex five-component membranes displayed lateral heterogeneity, at least in the lower temperature regimen examined.

DOI： 10.1016/j.bpj.2015.12.043

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Recent advances in solid-state nuclear magnetic resonance (NMR) techniques, such as magic angle spinning and high-power decoupling, have dramatically increased the sensitivity and resolution of NMR. However, these NMR techniques generate extra heat, causing a temperature difference between the sample in the rotor and the variable temperature gas. This extra heating is a particularly crucial problem for hydrated lipid membrane samples. Thus, to develop an NMR thermometer that is suitable for hydrated lipid samples, thulium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate (TmDOTA) was synthesized and labeled with ¹³C (i.e., ¹³C-TmDOTA) to increase the NMR sensitivity. The complex was mixed with a hydrated lipid membrane, and the system was subjected to solid-state NMR and differential scanning calorimetric analyses. The physical properties of the lipid bilayer and the quality of the NMR spectra of the membrane were negligibly affected by the presence of ¹³C-TmDOTA, and the ¹³C chemical shift of the complex exhibited a large-temperature dependence. The results demonstrated that ¹³C-TmDOTA could be successfully used as a thermometer to accurately monitor temperature changes induced by ¹H decoupling pulses and/or by magic angle spinning and the temperature distribution of the sample inside the rotor. Thus, ¹³C-TmDOTA was shown to be a versatile thermometer for hydrated lipid assemblies.

DOI： 10.1002/mrc.4371

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Theonellamide A (TNM-A) is an antifungal bicyclic dodecapeptide isolated from a marine sponge Theonella sp. Previous studies have shown that TNM-A preferentially binds to 3β-hydroxysterol-containing membranes and disrupts membrane integrity. In this study, several¹H NMR-based experiments were performed to investigate the interaction mode of TNM-A with model membranes. First, the aggregation propensities of TNM-A were examined using diffusion ordered spectroscopy; the results indicate that TNM-A tends to form oligomeric aggregates of 2–9 molecules (depending on peptide concentration) in an aqueous environment, and this aggregation potentially influences the membrane-disrupting activity of the peptide. Subsequently, we measured the¹H NMR spectra of TNM-A with sodium dodecyl sulfate-d₂₅(SDS-d₂₅) micelles and small dimyristoylphosphatidylcholine (DMPC)-d₅₄/dihexanoylphosphatidylcholine (DHPC)-d₂₂bicelles in the presence of a paramagnetic quencher Mn²⁺. These spectra indicate that TNM-A poorly binds to these membrane mimics without sterol and mostly remains in the aqueous media. In contrast, broader¹H signals of TNM-A were observed in 10 mol % cholesterol-containing bicelles, indicating that the peptide efficiently binds to sterol-containing bilayers. The addition of Mn²⁺to these bicelles also led to a decrease in the relative intensity and further line-broadening of TNM-A signals, indicating that the peptide stays near the surface of the bilayers. A comparison of the relative signal intensities with those of phospholipids showed that TNM-A resides in the lipid–water interface (close to the C2′ portion of the phospholipid acyl chain). This shallow penetration of TNM-A to lipid bilayers induces an uneven membrane curvature and eventually disrupts membrane integrity. These results shed light on the atomistic mechanism accounting for the membrane-disrupting activity of TNM-A and the important role of cholesterol in its mechanism of action.

DOI： 10.1016/j.bmc.2016.08.043

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this study, we measured the time-resolved fluorescence of trans-parinaric acid (tPA), steady-state fluorescence anisotropy of diphenylhexatriene (DPH), and ²H NMR of 10,10-d₂-stearoyl lipids in stearoyl sphingomyelin with cholesterol (SSM/Chol) and l-palmitoyl-2-stearoyl-sn-glycero-3-phosphocholine with Chol (PSPC/Chol) binary membranes. The results suggest that the membrane order obtained from the fluorescence experiments shows a similar temperature dependency as those of the ²H NMR data. More importantly, the time-resolved fluorescence data implied the presence of at least two types of domains, cholesterol-poor gel-like domains (CPGLD) and cholesterol-enriched liquid-ordered (L_o) domains. These domains appear on a nano-to-micro second time scale for both SSM-Chol and PSPC-Chol membranes. The relative size of the gel-like domain was also estimated from the temperature-dependent lifetime measurements and ²H NMR spectral changes. The results imply that the size of the gel-like domains is very small, probably on the nanometer scale, and smaller in SSM-Chol membrane than those in PSPC-Chol bilayers, which could account for the higher thermal stability of SM-Chol membranes. The present study demonstrates that gel-like nanodomains occur in SM-Chol binary membrane even with Chol content of over 33 mol %, which has been thought to consist exclusively of L_o phase, implying that not only L_o domains but also gel-like nanodomains are important for formation of lipid-ordered phase in SM-Chol and PC-Chol membranes.

DOI： 10.1021/acs.langmuir.5b03566

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.bmc.2015.07.009

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Determining the bioactive structure of membrane lipids is a new concept, which aims to examine the functions of lipids with respect to their three-dimensional structures. As lipids are dynamic by nature, their "structure" does not refer solely to a static picture but also to the local and global motions of the lipid molecules. We consider that interactions with lipids, which are completely defined by their structures, are controlled by the chemical, functional, and conformational matching between lipids and between lipid and protein. In this review, we describe recent advances in understanding the bioactive structures of membrane lipids bound to proteins and related molecules, including some of our recent results. By examining recent works on lipid-raft-related molecules, lipid-protein interactions, and membrane-active natural products, we discuss current perspectives on membrane structural biology. Information on the bioactive structure of lipids is essential to gain deeper insight into biological membranes. As lipids are dynamic by nature, their "structure" does not refer solely to a static picture but also to the local and global motions of the lipid molecules. By examining recent work on lipid-raft-related molecules, lipid-protein interactions, and membrane-active natural products, we discuss current perspectives on membrane structural biology.

DOI： 10.1002/tcr.201402097

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.bmc.2015.05.014

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.bmc.2015.05.014

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/c5ob01252j

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Sphingomyelin (SM) and cholesterol (Chol) are considered essential for the formation of lipid rafts; however, the types of molecular interactions involved in this process, such as intermolecular hydrogen bonding, are not well understood. Since, unlike other phospholipids, SM is characterized by the presence of an amide group, it is essential to determine the orientation of the amide and its order in the lipid bilayers to understand the nature of the hydrogen bonds in lipid rafts. For this study, 1′-¹³C-2-¹⁵N-labeled and 2′-¹³C-2-¹⁵N-labeled SMs were prepared, and the rotational-axis direction and order parameters of the SM amide in bilayers were determined based on ¹³C and ¹⁵N chemical-shift anisotropies and intramolecular ¹³C-¹⁵N dipole coupling constants. Results revealed that the amide orientation was minimally affected by Chol, whereas the order was enhanced significantly in its presence. Thus, Chol likely promotes the formation of an intermolecular hydrogen-bond network involving the SM amide without significantly changing its orientation, providing a higher order to the SM amide. To our knowledge, this study offers new insight into the significance of the SM amide orientation with regard to molecular recognition in lipid rafts, and therefore provides a deeper understanding of the mechanism of their formation.

DOI： 10.1016/j.bpj.2015.05.011

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In this report, we applied site-specifically deuterated N-stearoylsphingomyelins (SSMs) to raft-exhibiting ternary mixtures containing SSM, 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), and cholesterol (Chol) and successfully acquired deuterium quadrupole coupling profiles of SSM from liquid-ordered (L_o) and liquid-disordered (L_d) domains. To our knowledge, this is the first report that shows detailed lipid chain dynamics separately and simultaneously obtained from coexisting L_o and L_d domains. We also found that the quadrupole profile of the L_o phase in the ternary system was almost identical to that in the SSM-Chol binary mixture, suggesting that the order profile of the binary system is essentially applicable to more complicated membrane systems in terms of the acyl chain order. We also demonstrated that ²H NMR spectroscopy, in combination with organic synthesis of deuterated components, could be used to reveal the accurate mole fractions of each component distributed in the L_o and L_d domains. As compared with the reported tie-line analysis of phase diagrams, the merit of our ²H NMR analysis is that the domain-specific compositional fractions are directly attainable without experimental complexity and ambiguity. The accurate compositional distributions as well as lipid order profiles in ternary mixtures are relevant to understanding the molecular mechanism of lipid raft formation.

DOI： 10.1016/j.bpj.2015.04.008

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/asia.201403299

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphotericin B (AmB) is a polyene macrolide antibiotic widely used to treat mycotic infections. In this paper, we focus on the role of the polyol moiety of AmB in sterol selectivity using 7-oxo-AmB, 7α-OH-AmB, and 7β-OH-AmB. The 7-OH analogs were prepared from 7-oxo-AmB. Their K⁺ flux activity in liposomes showed that introduction of an additional ketone or hydroxy group on the polyol moiety reduces the original activity. Conformational analyses of these derivatives indicated that intramolecular hydrogen-bonding network possibly influenced the conformational rigidity of the macrolactone ring, and stabilized the active conformation in the membrane. Additionally, the flexible polyol leads to destabilization of the whole macrolactone ring conformation, resulting in a loss of sterol selectivity.

DOI： 10.1016/j.bmc.2015.07.009

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.bmcl.2014.11.072

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1039/c5ob90166a

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The interaction of amphotericin B (AmB) with fungal ergosterol (Erg) is stronger than its interaction with mammalian cholesterol (Cho), and this property of AmB as an antifungal drug is thought to be responsible for its selective toxicity toward fungi. However, the mechanism by which AmB recognizes the structural differences between sterols, particularly minor difference in the sterol alicyclic portion, is largely unknown. Thus, to investigate the mode of interaction between AmB and the sterol core, we assessed the affinity of AmB to various sterols with different alicyclic structures. Ion flux assays and UV spectral measurements clearly revealed the importance of the Δ7-double bond of the sterol B-ring for interaction with the drug. AmB showed lower affinity for triene sterols, which have double bonds at the Δ5, Δ7, and Δ9 positions. Intermolecular distance measurements by ¹³C{¹⁹F} rotational echo double resonance (REDOR) revealed that the AmB macrolide ring is in closer contact with the steroid core of Erg than it is with the Cho core in the membrane. Conformational analysis suggested that an axial hydrogen atom at C7 of Δ5-sterol (2, 6) and the protruded A-ring of Δ5,7,9-sterol (4, 8) sterically hampered face-to-face contact between the van der Waals surface of the sterol core and the macrolide of AmB. These results further suggest that the α-face of sterol alicycle interacts with the flat macrolide structure of AmB.

DOI： 10.1021/bi5012942

記述言語：英語  

DOI： 10.1021/bi5002932

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/bi500122c

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.bbamem.2014.01.017

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1246/cl.131099

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/ja500128u

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Although many non-peptidic drugs target biological membrane and membrane proteins, it is still difficult to determine the membrane-bound conformation of the drugs. To solve those problems, we have utilized bicelles as a membrane model, since the bicelles, which have planar lipid bilayer portions, are thought to be a more appropriate membrane model than micelles. Small-sized bicelles allow for liquid NMR measurements due to isotropic fast tumbling in solution. We have applied small bicelles to erythromycin A, salinomycin, and amphidinol 3, and determined their membrane-bound structures as well as their positions and orientations in the membranes using coupling constants, NOEs, and paramagnetic relaxation methods. Recently, we found that sphingomyelin, a major lipid constituent of lipid rafts, also forms bicelles, and established its conformation in the bicelles. These studies show the general utility of small bicelles for detailed conformation and orientation analysis of membrane-associated drugs and lipid molecules. We are now developing a bicelle-based crystallization method for membrane proteins, which will facilitate the cocrystalization of membrane proteins and hydrophobic drugs.

DOI： 10.5059/yukigoseikyokaishi.72.596

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Stereoselective synthesis of the C43-C67 part of amphidinol 3 (AM3) and its C51-epimer was achieved starting from a common intermediate corresponding to the tetrahydropyran moiety of AM3, via asymmetric oxidations and Julia-Kocienski olefination. By comparing NMR data of the synthetic specimens with those of AM3, the absolute configuration at C51 of AM3 was revised from R to S.

DOI： 10.1021/ol401176a

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The influences of structural alterations of sphingomyelin (SM) on its interactions with cholesterol (chol) and on ordered phase formation were examined by density measurements and surface pressure vs. molecular area isotherm measurements. In addition, we quantitatively characterized the ordered phase formed in each SM and chol binary mixture on the basis of the molecular compressional modulus of SM (C_mol^-1). Density measurements demonstrated that the ordered phase formation in threo- SM (tSM)/chol and dihydrosphingomyelin (DHSM)/chol binary bilayers shows similar chol concentration-dependency to that of natural erythro-SM (eSM)/chol bilayers; the ordered phase formation was completed in the presence of 25 mol% chol. In contrast, SM bearing a triple bond in the place of a double bond (tripleSM) required a greater concentration of chol to completely transform the bilayer into the ordered phase (at 40mol% chol). Surface pressure vs. molecular area isotherms showed that the DHSM molecule (C_mol^-1=290mN/m) is more rigid than eSM (C_mol^-1=240mN/m) above 30 mol% chol (in the ordered phase), although these values are similar (140- 150mN/m) in the absence of chol (liquid condensed phase). Most likely, the DHSM/chol mixture forms a more ordered membrane than the eSM/chol mixture does. Moreover, in the absence of chol, the rigidity of the tripleSM molecule (C_mol^-1=250mN/m) is significantly higher as compared with that of the eSM molecule (C_mol^-1=150mN/m), which is probably due to the presence of a triple bond.

DOI： 10.2142/biophysics.9.37

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Theonellamides (TNMs) are members of a distinctive family of antifungal and cytotoxic bicyclic dodecapeptides isolated from the marine sponge Theonella sp. Recently, it has been shown that TNMs recognize 3β-hydroxysterol- containing membranes, induce glucan overproduction, and damage cellular membranes. However, to date, the detailed mode of sterol binding at a molecular level has not been determined. In this study, to gain insight into the mechanism of sterol recognition of TNM in lipid bilayers, surface plasmon resonance (SPR) experiments and solid-state deuterium nuclear magnetic resonance (²H NMR) measurements were performed on theonellamide A (TNM-A). SPR results revealed that the incorporation of 10 mol % cholesterol or ergosterol into 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes significantly enhances the affinity of the peptide for the membrane, particularly in the initial binding to the membrane surface. These findings, together with the fact that binding of TNM-A to epicholesterol (3α-cholesterol)-containing liposomes and pure POPC liposomes was comparably weak, confirmed the preference of the peptide for the 3β-hydroxysterol-containing membranes. To further establish the formation of the complex of TNM-A with 3β-hydroxysterols in lipid bilayers, solid-state ²H NMR measurements were conducted using deuterium-labeled cholesterol, ergosterol, or epicholesterol. The ²H NMR spectra showed that TNM-A significantly inhibits the fast rotational motion of cholesterol and ergosterol, but not epicholesterol, therefore verifying the direct complexation between TNM-A and 3β-hydroxysterols in lipid bilayers. This study demonstrates that TNM-A directly recognizes the 3β-OH moiety of sterols, which greatly facilitates its binding to bilayer membranes.

DOI： 10.1021/bi4000854

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A novel SAAF was isolated from the title ascidian. The structure was elucidated using the entire sample of 4 nmol, suggesting that the position of the OH group confers genus-specificity to sperm chemotaxis in ascidians. This study not only provides insight into the chemical tactics in sperm chemotaxis but demonstrates that the innovative techniques allow structure determination of natural products in trace amounts.

DOI： 10.1021/ol303172n

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphidinol 3 (AM3), a membrane-active agent isolated from the dinoflagellate Amphidinium klebsii, consists of a long carbon chain containing 25 stereogenic centers. Although the absolute configuration of AM3 was determined by extensive NMR analysis and degradation of the natural product, the partial structure corresponding to the tetrahydropyran ring system was found to be antipodal to that of karlotoxin 2, a structurally related compound recently isolated from the dinoflagellate Karlodinium veneficum. By extensive degradation of the natural product and conversion of the resulting alcohol to an MTPA ester, the absolute configuration at C45 of AM3 was confirmed to be R, supporting the originally proposed structure.

DOI： 10.1021/np300604w

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Aiming for structural analysis of amphotericin B (AmB) ion-channel assemblies in membrane, a covalent dimer was synthesized between ¹³C-labled AmB methyl ester and ¹⁹F-labled AmB. The dimer showed slightly weaker but significant biological activities against fungi and red blood cells compared with those of monomeric AmB. Then the dimer was subjected to ¹³C{¹⁹F}REDOR (Rotational-Echo Double Resonance) experiments in hydrated lipid bilayers. The obtained REDOR dephasing effects were explained by two components; a short ¹³C/¹⁹F distance (6.9 Å) accounting for 23% of the REDOR dephasing, and a longer one (14 Å) comprising the rest of the dephasing. The shorter distance is likely to reflect the formation of barrel-stave ion channel.

DOI： 10.1016/j.bmc.2012.08.016

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Sphingomyelin (SM) and cholesterol form microdomains called lipid rafts in cellular membranes. To develop a versatile fluorescent lipid probe, chemical modifications to both the hydrophobic and hydrophilic portions of SM are essential. Few reports describing SM probes with a fluorophore at the polar head group have been published. This study examined the effect of substitution on an ammonium moiety of SM on the membrane properties of SM. Two SM analogs with small propargyl and allyl groups on the quaternary nitrogen atom were synthesized and subjected to analysis using differential scanning calorimetry, fluorescent anisotropy, detergent solubilization, surface pressure, and density measurements. Results demonstrated that the two SM analogs retained the membrane properties of SM, including formation of an ordered phase and the ability to interact with cholesterol. A dansyl-substituted SM was prepared for fluorescent measurements. Dansyl-SM showed less of a propensity to form microdomains. These findings imply the potential application of N-substituted SMs as a raft-specific molecular probe.

DOI： 10.1016/j.bmc.2012.05.015

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Maitotoxin (MTX) is a ladder-shaped polyether produced by the epiphytic dinoflagellate Gambierdiscus toxicus. It is known to elicit potent toxicity against mammals and induce influx of Ca²⁺ into cells. An artificial ladder-shaped polyether possessing a 6/7/6/6/7/6/6 heptacyclic ring system, which was designed for elucidating interactions with transmembrane proteins, was found to be the most potent inhibitor against MTX-induced Ca²⁺ influx that has ever been reported.

DOI： 10.1016/j.bmcl.2012.04.053

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphotericin B (AmB) is thought to exert its antifungal activity by forming an ion-channel assembly in the presence of ergosterol. In the present study we aimed to elucidate the mode of molecular interactions between AmB and ergosterol in hydrated phospholipid bilayers using the rotational echo double resonance (REDOR) spectra. We first performed ¹³C{ ¹⁹F}REDOR experiments with C14-19F-labeled AmB and biosynthetically ¹³C-labeled ergosterol and implied that both "head-to-head" and "head-to-tail" orientations occur for AmB-ergosterol interaction in the bilayers. To further confirm the "head-to-tail" pairing, ¹³C-labeled ergosterol at the dimethyl terminus (C26/C27) was synthesized and subjected to the REDOR measurements. The spectra unambiguously demonstrated the presence of a "head-to-tail" orientation for AmB-ergosterol pairing. In order to obtain information on the position of the dimethyl terminus of ergosterol in membrane, ¹³C{ ³¹P}REDOR were carried out using the labeled ergosterol and the phosphorus atom of a POPC headgroup. Significant REDOR dephasing was observed at the C26/C27 signal of ergosterol in the presence of AmB, but not in the absence of AmB, clearly indicating that the side-chain terminus of ergosterol in the AmB complex comes close to the bilayer surface.

DOI： 10.1021/bi2012542

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Sphingomyelin (SM) is a common sphingolipid in mammalian membranes and is known to be substantially involved in cellular events such as the formation of lipid rafts. Despite its biological significance, conformation of SM in a membrane environment remains unclear because the noncrystalline property and anisotropic environment of lipid bilayers hampers the application of X-ray crystallography and NMR measurements. In this study, to elucidate the conformation of SM in membranes, we utilized bicelles as a substitute for a lipid bilayer membrane. First, we demonstrated through ³¹P NMR, ²H NMR, and dynamic light scattering experiments that SM forms both oriented and isotropic bicelles by changing the ratio of SM/dihexanoyl phosphatidylcholine. Then, we determined the conformation of SM in isotropic bicelles on the basis of coupling constants and NOE correlations in ¹H NMR and found that the C2-C6 and amide groups of SM take a relatively rigid conformation in bicelles.

DOI： 10.1016/j.bmc.2011.11.001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A lipid raft is a cholesterol (Chol)-rich microdomain floating in a sea of lipid bilayers. Although Chol is thought to interact preferentially with sphingolipids such as sphingomyelin (SM), rather than with glycerophospholipids, the origin of the specific interaction has remained unresolved, primarily because of the high mobility of lipid molecules and weak intermolecular interactions. In this study, we synthesized SM-Chol conjugates with functionally designed linker portions to restrain Chol mobility and examined their formation of ordered membranes by a detergent insolubility assay, fluorescence anisotropy experiments, and fluorescence-quenching assay. In all of the tests, membranes prepared from the conjugates showed properties of ordered domains comparable to a SM-Chol (1:1) membrane. To gain insight into the structure of bilayers composed from the conjugates, we performed molecular dynamics simulations with 64 molecules of the conjugates, which suggested that the conjugates form a stable bilayer structure by bending at the linker portion and, mostly, reproduce the hydrogen bonds between the SM and Chol portions. These results imply that the molecular recognition between SM and Chol in an ordered domain is essentially reproduced by the conjugated molecules and, thus, demonstrates that these conjugate molecules could potentially serve as molecular probes for understanding molecular recognition in lipid rafts.

DOI： 10.1002/chem.201100849

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphotericin B (AmB) is a widely used antifungal antibiotic with high specificity for fungi. We previously synthesized several covalently conjugated AmB dimers to clarify the AmB channel structure. Among these dimers, that with an aminoalkyl linker was found to exhibit potent hemolytic activity. We continue this work by investigating the channel activity of the dimer, finding that all channels comprised of AmB dimers show rectification. The direction of the dimer channel in the membrane depended on the electric potential at which the dimer channel was formed. On the other hand, only about half the monomer channels showed rectification. In addition, these channels were easily switched from a rectified to a nonrectified state following voltage stimulation, indicating instability. We propose a model to describe the AmB channel structure that explains why AmB dimer channels necessarily show rectification.

DOI： 10.1007/s00232-011-9354-x

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Advanced glycation end products (AGE) are known to cause diabetes complications in hyperglycemia patients. In this study we prepared hetero-trimers of collagen model peptides comprising Ac-(Pro-Hyp-Gly) ₅-Pro-Lys-Gly-(Pro-Hyp-Gly)₅-Ala-NH₂ (4) and Ac-(Pro-Hyp-Gly)₁₁-Ala-NH₂ (5) to investigate the clustering effect of lysine on AGE formation. The formation rate of carboxymethyllysine over several months was determined for the mixtures of peptides 4 and 5 at (3:0), (2:1) and (1:2) in the presence of glucose. The contents of carboxymethyllysine were significantly enhanced for (3:0) and (2:1) as compared with (1:2), suggesting that the proximity of lysine residues in the trimers accelerated formation of the AGE. Furthermore, a lysine dimerization moiety (GOLD) was identified for the first time from AGEs of glucose origin, which implied the significance of GOLD in oligomerization of collagens and other long-life proteins.

DOI： 10.1016/j.bmc.2011.02.048

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Selectively ²H- and ¹³C-labeled spermines (SPM) were efficiently synthesized and analyzed by NMR spectroscopy to determine the spin-spin coupling constants for six conformationally relevant bonds. SPM that is composed of three alkyl moieties, a butanylene, and two propanylene chains undergoes a conformational change when interacting with multivalent anions (e.g., adenosine triphosphate (ATP), ATP-Mg²⁺, and tripolyphosphate). Upon interaction with ATP, the C-C bonds, which affect the distance between the neighboring pairs of ammonium groups (i.e., N1/N5 and N5/N5′), increase the population of gauche rotamers by 17-20 % relative to those in the 4 HCl salt of SPM. However, the trend in increments of the gauche conformers for the SPM-ATP complex profoundly differs from that of the spermidine (SPD)-ATP complex. This implies that SPM may preferentially recognize the adenyl group of ATP rather than the tripolyphosphate moiety. This may account for the higher affinity of SPM to ATP-Mg²⁺ than with that of SPD, which chiefly interacts with β- and Î-phosphates and is easily replaced by Mg ²⁺. These results may provide a clue for the further understanding of the structural basis of polyamine biological functions. Spermines and spin: Spermines (SPM) labeled selectively with ²H and ¹³C were used to determine the spin-spin coupling constants for six conformationally relevant bonds. SPM revealed diverse conformational changes upon interaction with adenosine triphosphate (ATP), ATP-Mg²⁺, and tripolyphosphate (TPP, see graph).

DOI： 10.1002/chem.201002759

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Two well-known antifungals, amphotericin B (AmB) and amphodinol 3 (AM3), are thought to exert antifungal activity by forming ion-permeable channels or pores together with sterol molecules. However, detailed molecular recognitions for AmB-sterol and AM3-sterol in lipid bilayers have yet to be determined. Toward ¹⁹F NMR-based investigation of the molecular recognition underlying their potent antifungal activity, we synthesized 6-fluoro-ergosterol in five steps via ring opening of (5α,6α)-epoxide of ergosterol acetate with using novel combination of TiF₄ and n-Bu ₄N⁺Ph₃SiF₂^-. Then we evaluated its activity of promoting pore formation of AmB and AM3, and found that pore formation of AmB was barely promoted by 6-F-ergosterol in clear contrast to the dramatic promotion effect of unmodified ergosterol, whereas AM3 activity was markedly enhanced in the presence of 6-F-ergosterol, which was comparable to that of unmodified ergosterol. These results indicate that the introduction of an F atom at C6 position of ergosterol plays an inhibitory role in interacting with AmB, but it is not the case with AM3.

DOI： 10.1039/c0ob00685h

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Lipid rafts are cholesterol (Chol)-rich microdomains floating in a sea of lipid bilayers. Chol is thought to interact preferentially with sphingolipids such as sphingomyelin (SM) rather than with glycerophospholipids, and this putative SM-Chol interaction is generally recognized as a requirement for raft formation. However, the presence of the specific interaction is still controversial, primarily because of the lack of useful molecular probes for scrutinizing this interaction. Recently, we reported that the dynamic properties of 6-F-Chol in DMPC bilayers are similar to those of unmodified Chol. Hence, in the present study, we first compared the roles of 6-F-Chol and Chol in SM bilayers through detergent insolubility, fluorescence polarization, and 2H NMR experiments. The results demonstrated that 6-F-Chol and Chol behave similarly in SM bilayers, whereas, in SM-DOPC membranes, 6-F-Chol is less effective in domain formation. Then, we analyzed the molecular orientation of 6-F-Chol in SM bilayers using solid-state NMR, and found that the dynamics and orientation of 6-F-Chol in SM bilayers are almost identical to those in DMPC bilayers. This supports the notion of the lack of a putative specific interaction between SM and Chol. Thus, this study demonstrates the utility of 6-F-Chol as a molecular probe for understanding molecular recognition in lipid rafts.

DOI： 10.1016/j.chemphyslip.2011.05.007

記述言語：英語   掲載種別：研究論文（学術雑誌）  

As is the case with other ladder-shaped polyether compounds, yessotoxin is produced by marine dinoflagellate, and possesses various biological activities beside potent toxicity. To gain a better understanding of the molecular mechanism for high affinity between these polyethers and their binding proteins, which accounts for their powerful biological activities, we searched for its binding proteins from human blood cells by using the biotin-conjugate of desulfated YTX as a ligand. By a protein pull-down protocol with use of streptavidin beads, a band of specifically binding proteins was detected in SDS-PAGE. HPLC-tandem mass spectrometry (MS/MS) indicated that Rap 1A, one of Ras superfamily proteins, binds to the YTX-linked resins. Western blotting and surface plasmon resonance experiments further confirmed that Rap1A specifically binds to YTX with the K_D value around 4 μM.

DOI： 10.1016/j.bmcl.2010.09.080

記述言語：英語   掲載種別：研究論文（学術雑誌）  

About half of known bioactive organic molecules, including drugs, are known to target biological membranes and membrane proteins. Despite this, it has proven difficult to define the membrane-bound conformations of these molecules. In recent years, bicelles have been recognized as a more appropriate membrane model than micelles because their planar portion is composed of a lipid bilayer. Bicelles with a small diameter, termed isotropic or fast-tumbling bicelles, allow for high-resolution NMR measurements due to their high mobility in suspension, and therefore have become a versatile tool for structure studies of membrane-associated molecules. Following a brief description of the morphology and preparation of isotropic bicelles, we summarize their application to structural studies of membrane-bound peptides and small molecules, and then highlight our recent studies on the 3D structures of erythromycin A, salinomycin and amphidinol 3 using isotropic bicelles.

DOI： 10.1039/c0np00002g

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The affinity of amphidinol 3 (AM3) to phospholipid membranes in the presence and absence of sterol was examined by surface plasmon resonance (SPR) experiments. The results showed that AM3 has 1000 and 5300 times higher affinity for cholesterol- and ergosterol-containing liposomes, respectively, than those without sterol. The two-state reaction model well reproduced the sensor grams, which indicated that the interaction is composed of two steps, which correspond to binding to the membrane and internalization to form stable complexes.

DOI： 10.1016/j.bmcl.2010.02.025

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Among other homologues, amphidinol 3 (AM3) is the most potent antifungal compound isolated from the dinoflagellate Amphidinium klebsii. AM3 undergoes conformational changes in organic solvents while it takes relatively fixed configuration in a membrane model. By using NMR data of peracetyl AM3, we were able to confirm the configuration of C50-C51 of AM3 which remained uncertain in our previous study.

DOI： 10.3987/COM-10-S(E)86

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The effect of phospholipid head group on the membrane-permeabilizing activity of amphotericin B (AmB) was examined using 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposomes and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG) liposomes. The activity of AmB was evaluated as K⁺ influx measured as pH change inside liposomes by fluorescent measurements of 2′,7′-bis(carboxyethyl)-4 or 5-carboxyfluorescein (BCECF). AmB showed prominent permeability in POPC liposomes, whereas hardly inducing ion flux in POPG membrane. POPC added to POPG liposomes as a minor constituent markedly enhanced membrane permeability, indicating the importance of a phosphonocholine group of PC for the drug's activity.

DOI： 10.1016/j.bmc.2009.07.036

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Although amphotericin B (AmB) is thought to exert its antifungal activity by forming transmembrane ion-permeable self-assemblies together with ergosterol, no previous study has directly proven AmB-ergosterol interaction. To establish the interaction, we measured ²H NMR using deuterium-labeled sterols and AmB. The ²H NMR spectra of deuterated ergosterol in palmitoyloleoylphosphatidylcholine (POPC) bilayers showed that fast axial diffusion of erogosterol was almost completely inhibited by the coexistence of AmB. Conversely, cholesterol mobility in POPC membrane was essentially unchanged with or without AmB. These results unequivocally demonstrate that ergosterol has significant interaction with AmB in POPC bilayers. In addition, we examined the mobility of AmB using deuterium-labeled AmB, and found that, although AmB is almost immobilized in sterol-free and cholesterol-containing POPC membranes, a certain ratio of AmB molecules acquires mobility in the presence of ergosterol. The similar mobility of AmB and ergosterol in POPC bilayers confirmed the idea of the direct intermolecular interaction between ergosterol and AmB.

DOI： 10.1021/ja9033473

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphotericin B (AmB) exerts its pharmacological effects by forming a barrel-stave assembly in fungal membranes. To examine the interaction between AmB and ergosterol or cholesterol, ¹³C- and ¹⁹F-labeled covalent conjugates were prepared and subjected to solidstate NMR measurements. Using rotor-synchronous double-resonance experiments such as rotational echo double resonance (REDOR) and RDX, we estimated the distance between the fluorine atom and its nearest carbon in the heptaene moiety to be less than 8.6 A ̊, indicating that the B ring of ergosterol comes close to the AmB polyene moiety. Conformational search of the AmB-ergosterol conjugate using the NMR-derived constraints suggested that ergosterol molecules surround the AmB assembly in contrast to the conventional image where ergosterol is inserted into AmB molecules. AmB-AmB bimolecular interaction was examined by using ¹³C- and ¹⁹F-labeled AmBs in dimyritoylphosphatidylcholine (DMPC) membrane without sterols. ¹³C- and ¹⁹F dipolar interactions deriving from both head-to-head and head-to-tail orientations were observed in the REDOR experiments. The interactions between AmB and acyl chains of the phospholipid were also detected.

DOI： 10.1351/PAC-CON-08-08-37

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ladder-shaped polyether (LSP) compounds represented by brevetoxins and ciguatoxins were largely discovered in association with seafood poisoning. Thus, a quick quantification method for LSPs is potentially important. We examined a surface plasmon resonance method using desulfated-yessotoxin (dsYTX) immobilized on a sensor chip and phosphodiesterase PDEII in a inhibition detection mode. Yessotoxin, brevetoxin B and synthetic LSP derivatives showed clear inhibition against PDEII binding to the immobilized dsYTX, by which their half inhibitory concentrations were successfully estimated. This inhibition method appeared to be superior in specificity to direct binding assays where binding proteins to LSP was immobilized on a sensor chip.

DOI： 10.1016/j.bmcl.2009.03.103

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Endogenous polyamines, represented by putrescine, spermidine, and spermine, are known to exert their physiological functions by interacting with polyanionic biomolecules such as DNA, RNA, adenosine triphosphate (ATP), and phospholipids. Very few examples of conformation analysis have been reported for these highly flexible polymethylene compounds, mainly due to the lack of appropriate methodologies. To understand the molecular basis of the weak interaction between polyamines and polyanions that underlies their physiological functions, we aimed to elucidate the solution conformation of spermidine by using diastereospecifically deuterated and
¹³
C-labeled derivatives (1-7), which were designed to diagnose the orientation of seven conformationally relevant bonds in spermidine. 1H-1H and
¹³
C-1H NMR coupling constants (
³
J
_H,H
and
³
J
_C,H
) were successfully determined for a spermidine-ATP complex. The relevant coupling constants markedly decreased upon complexation. The results reveal that spermidine, when interacting with ATP, undergoes changes that make the conformation more bent and forms the complex with the triphosphate part of ATP in an orientation-sensitive manner.

DOI： 10.1002/chem.200801961

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A ¹³C-labeled amphotericin B (AmB) derivative was synthesized based on a hybrid strategy combining chemical synthesis with degradation of a natural product through successive cross-coupling reactions and macrolactonization. The specimen regiospecifically ¹³C-labeled (99% enrichment) at C25 position corresponding to the polyene moiety would be a powerful tool for structural analysis of the molecular assembly formed by AmB based on solid-state NMR measurements.

DOI： 10.1246/cl.2009.114

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Vicinal spin-spin coupling constants frequently used for conformation analysis were determined for ammonium-containing ¹³C-N-C- ¹H systems by using HMBC. 1-Deoxynojirimycin hydrochloride provided an appropriate system for measuring the antiperiplanar and gauche interactions, which were determined to be 7.3 and 1.6 Hz, respectively.

DOI： 10.1246/cl.2008.1172

記述言語：英語   掲載種別：研究論文（学術雑誌）  

(Chemical Equation Presented) Amphidinol 3 (AM3) exhibits a potent membrane permeabilizing activity by forming pores in biological membranes. We examined the conformation and location of AM3 using Isotropic bicelles, a more natural membrane model than micelles. The results show that AM3 takes turn structures at the two tetrahydropyran rings. Most of the hydrophilic region of the molecule is predominantly present in the surface, while the hydrophobic polyolefin penetrates in the bicelle interior.

DOI： 10.1021/ol8016337

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Marine dinoflagellates are a rich source of structurally and biologically intriguing secondary metabolites. Among those, maitotoxin may be one of the best known examples, which is the largest natural product known to date and possesses the most potent toxicity known amongst non-proteinaceous compounds. Structural studies of maitotoxin are reviewed with a particular focus on the configuration and mode of action of this unique toxin. In addition, there are many marine natural products which bind to biomembranes to exert their biological activities. To gain a better understanding of their mode of action, conformation, and bimoleeular interaction occurring in biomembranes are particularly important. Recent results from NMR studies of membrane systems in the authors' group are reviewed briefly.

DOI： 10.1246/bcsj.81.307

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ladder-shaped polyether (LSP) compounds are thought to interact with transmembrane α-helices, but direct evidence has scarcely obtained for these interactions. We adopted a transmembrane α-helix of glycophorin A, and quantitatively evaluated its interaction with LSPs such as yessotoxin (YTX), desulfated YTX and artificial LSPs, using surface plasmon resonance and saturation transfer difference NMR. As a result, dissociation constants (K_D) of YTX and desulfated YTX to a transmembrane domain peptide of glycophorin A were determined to be in the submillimolar range. Furthermore, in saturation transfer difference NMR, the signals at the polyene side chain and the angular methyl groups of YTX were significantly attenuated, which probably comprised an interacting interface of LSPs with a transmembrane α-helix. These results suggest that hydrophobic interaction plays an important role in molecular recognition of the α-helix peptide by LSPs.

DOI： 10.1016/j.bmcl.2008.10.020

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphotericin B (AmB) exerts its antifungal activity by forming ion-permeable assemblies across lipid bilayers. To investigate AmB-AmB bimolecular interactions in the assembly, we carried out ¹³C{ ¹⁹F}REDOR experiments using 14-¹⁹F- and ¹³C41-labeled AmBs in sterol-containing and sterol-free palmitoyloleoylphosphatidylcholine (POPC) membranes and measured the average distance between the labeled sites of AmBs in membrane-bound forms. The REDOR results suggested that the intermolecular distance of AmB molecules is significantly increased in the ergosterol membrane as compared with the cholesterol membrane. This sterol-dependent change was supported by the UV spectra of AmB in lipid bilayers, in which the excitonic absorption band arising from the aggregated state of AmB shifted to longer wavelength in ergosterol-containing POPC membrane. The REDOR experiments also disclosed that the head-to-head orientation of AmB is predominant in both of the sterol-containing membranes and AmB-POPC interaction was detected only in the ergosterol membrane. Ergosterol significantly influences the interactions between AmB molecules as well as those between AmB and POPC, which may facilitate formation of ion-permeable channels in ergosterol-containing membrane.

DOI： 10.1021/bi801875y

記述言語：英語   掲載種別：研究論文（学術雑誌）  

(Chemical Equation Presented) The WXYZA′B′C′ ring system (1) of maitotoxin (MTX) was synthesized in a convergent manner via successive coupling of the W, Z, and C′ ring fragments through construction of the XY and A′B′ ring systems. The synthetic segment 1 blocked the hemolytic activity elicited by MTX.

DOI： 10.1021/ol801369g

記述言語：英語   掲載種別：研究論文（学術雑誌）  

(Chemical Equation Presented) Combinatorial synthesis of a 1,5-polyol system corresponding to the C1-C14 unit of amphidinol 3 (AM3) and its diastereomers was achieved via chemoselective cross metathesis as the key step. Comparison of ¹³C NMR data of the synthetic specimens with that of AM3 led to a controversy regarding the originally proposed structure. From GC-MS analysis of the degradation product, the absolute configuration at C2 of AM3 has been revised to be R.

DOI： 10.1021/ol802168r

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ladder-shaped polyether (LSP) toxins represented by brevetoxins and Ciguatoxins are thought to bind to transmembrane (TM) proteins. To elucidate the interactions of LSPs with TM proteins, we have synthesized artificial ladder-shaped polyethers (ALPs) containing 6/7/6/6 tetracyclic, 6/7/6/6/7/6/6 heptacyclic, and 6/7/6/6/7/6/6/7/6/6 decacyclic systems, based on the convergent method via α-cyano ethers. The ALPs possessing the simple iterative structure with different numbers of rings would be useful for structure-activity relationship studies on the molecular length, which is supposed to be important when naturally occurring LSPs elicit their toxicity. Two series of ALPs were prepared to evaluate the hydrophilic or hydrophobic effects of the side chains: (i) both sides were functionalized as diols (A series), and (ii) one side remained as diol and the other side was protected as benzyl ethers (B series). To examine the interaction of these ALPs with TM proteins, dissociation of glycophorin A (GpA) dimers into monomers was evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The heptacyclic ether (ALP7B) elicited the most potent activity in the presence of 2% SDS buffer, whereas the decacyclic ether (ALP10A) exhibited an intriguing phenomenon to induce precipitation of GpA in a dose-dependent manner, under the low concentration of SDS (0.03%). ALP10A also induced precipitation of integrin α ₁β₁, a TM protein known to form heterodimers in the lipid bilayer membranes. The different activities among the ALPs can be accounted for by the concept of "hydrophobic matching" that is, lengths of the hydrophobic region including the side chains of ALP7B and ALP10A are ca. 25 Å, which match the lengths of the hydrophobic region of α-helical TM proteins, as well as the hydrophobic thickness of lipid bilayer membranes. The concept of the hydrophobic matching would be a clue to understanding the interaction between LSPs and TM proteins, and also a guiding principle to design ALPs possessing potent affinities with TM proteins.

DOI： 10.1021/ja801576v

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphotericin B (AmB) is a membrane-active antibiotic that increases the permeability of fungal membranes. Thus, the dynamic process of its interaction with membranes poses intriguing questions, which prompted us to elaborate a quick and reliable method for real-time observation of the drug's binding to phospholipid liposomes. We focused on surface plasmon resonance (SPR) and devised a new modification method of sensor chips, which led to a significant reduction in the level of nonspecific binding of the drug in a control lane. With this method in hand, we examined the affinity of AmB for various membrane preparations. As expected, AmB exhibited much higher affinity for sterol-containing palmitoyloleoylphosphatidylcholine membranes than those without sterol. The sensorgrams recorded under various conditions partly fitted theoretical curves, which were based on three interaction models. Among those, a two-state reaction model reproduced well the sensorgram of AmB binding to an ergosterol-containing membrane; in this model, two states of membrane-bound complexes, AB and AB*, are assumed, which correspond to a simple binding to the surface of the membrane (AB) and formation of another assembly in the membrane (AB*) such as an ion channel complex. Kinetic analysis demonstrated that the association constant in ergosterol-containing POPC liposomes is larger by 1 order of magnitude than that in the cholesterol-containing counterpart. These findings support the previous notion that ergosterol stabilizes the membrane-bound assembly of AmB.

DOI： 10.1021/bi800334p

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphidinols (AMs) are a group of dinoflagellate metabolites with potent antifungal activity. As is the case with polyene macrolide antibiotics, the mode of action of AMs is accounted for by direct interaction with lipid bilayers, which leads to formation of pores or lesions in biomembranes. However, it was revealed that AMs induce hemolysis with significantly lower concentrations than those necessary to permeabilize artificial liposomes, suggesting that a certain factor(s) in erythrocyte membrane potentiates AM activity. Glycophorin A (GpA), a major erythrocyte protein, was chosen as a model protein to investigate interaction between peptides and AMs such as AM2, AM3 and AM6 by using SDS-PAGE, surface plasmon resonance, and fluorescent-dye leakages from GpA-reconstituted liposomes. The results unambiguously demonstrated that AMs have an affinity to the transmembrane domain of GpA, and their membrane-permeabilizing activity is significantly potentiated by GpA. Surface plasmon resonance experiments revealed that their interaction has a dissociation constant of the order of 10 μM, which is significantly larger than efficacious concentrations of hemolysis by AMs. These results imply that the potentiation action by GpA or membrane integral peptides may be due to a higher affinity of AMs to protein-containing membranes than that to pure lipid bilayers.

DOI： 10.1016/j.bbamem.2008.01.018

記述言語：英語   掲載種別：研究論文（学術雑誌）  

6-F-cholesterol was reported to exhibit biological and interfacial properties similar to unmodified cholesterol. We have also found that 6-F-cholesterol mimicked the cholesterol activity observed in the systems of amphotericin B and lipid rafts. However, to use 6-F-cholesterol as a molecular probe to explore molecular recognition in membranes, it is indispensable to have detailed knowledge of the dynamic and orientation properties of the molecule in membrane environments. In this paper, we present the molecular orientation of 6-F-cholesterol (30 mol %) in dimyristoylphosphatidylcholine (DMPC) bilayers revealed by combined use of ¹⁹F chemical shift anisotropy (CSA), ²H NMR, and C-F rotational echo double resonance (REDOR) experiments. The axis of rotation of 6-F-cholesterol was shown to be in a similar direction to that of cholesterol in DMPC bilayers, which is almost parallel to the long axis of the molecular frame. The molecular order parameter of 6-F-cholesterol was determined to be ca. 0.85, which is within the range of reported values of cholesterol. These findings suggest that the dynamic properties of 6-F-cholesterol in DMPC are quite similar to those of unmodified cholesterol; therefore, the introduction of a fluorine atom at C6 has virtually no effect on cholesterol dynamics in membranes. In addition, this study demonstrates the practical utility of theoretical calculations for determining the ¹⁹F CSA principal axes, which would be extremely difficult to obtain experimentally. The combined use of quantum calculations and solid-state ¹⁹F NMR will make it possible to apply the orientation information of ¹⁹F CSA tensors to membrane systems.

DOI： 10.1021/ja077580l

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphidinols (AMs) are a new class of polyhydroxyl polyene compounds with potent antifungal activity. Membrane-permeabilizing activities of AM2, AM3, and AM6 were examined using fluorescent-dye leakage experiments with various phosphatidylcholines (PCs) and sterols. All the AMs tested showed the potent activity to cholesterol-containing liposomes. In the absence of the sterol, AM2, AM3, and AM6 had no membrane-permeabilizing activities to membranes of saturated PC. In liposomes consisting of unsaturated PC, AM2, which possesses an additional ether ring in a polyhydroxyl chain, showed membrane-permeabilizing activities with a moderate efficacy, while AM3 or AM6 did not. The potentiation by sterols was prominent even at 0.5% (wt/wt) and structure-dependent, which ruled out the possibility that alteration of the membrane physical properties induced by sterol was chiefly responsible for this sterol effect. The finding that their activity was not affected by membrane thickness implies that AMs permeabilized membrane by a different mechanism from that of polyene macrolide antibiotics.

DOI： 10.1016/j.bmc.2007.12.029

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphotericin B (AmB) is thought to exert its pharmacological effects by forming a barrel-stave assembly with ergosterol in fungal membranes. To examine the interaction between AmB and ergosterol (Erg) or cholesterol (Cho), ¹³C- and ¹⁹F-labelled covalent conjugales were prepared as reported previously (N. Matsumori et al. Chem. Biol. 2004, 11, 673-679). The CD spectra of the conjugates in a membrane-bound form suggested that the distance between the heptaene moieties of the ergosterol conjugates AmB-C ₂-(6-F)Erg 2 and AmB-C₂Erg 3 is similar to that of AmB in ergosterol-containing membranes, but significantly larger than that of AmB in nonsterol or cholesterol-containing mem branes. These observations suggest that, as is the case with ergosterol-containing membranes, the conjugated sterol moiety prevents the close contact between the heptaene moieties within the membrane that would reduce channel conductivity of the AmB assemblies. To further investigate this bimolecular interaction, we recorded the solid-state NMR spectra of conjugates 2 and AmB-C₂-(6-F)Cho 4. which are composed of uniformly ¹³C-labelled AmB and 6-fluorinuted ergosterol or cholesterol; the conjugates were expected to facilitate the estimation of distances between the fluorine and carbon atoms. By using rotor-synchronous double resonance (rotational echo double resonance of X cluster; RDX) experiments, we deduced the distance between the fluorine atom and its nearest carbon atom in the heptaene moiety of 2 to be less than 8.6 Å. This indicates that the B ring of ergosterol comes close to the AmB polyene moiety. A conformational search of the AmB-ergosterol conjugate by using distance constraints derived from the RDX results suggested that ergosterol molecules possibly surround the AmB assembly, which is in contrast with the conventional image in which ergosterol is inserted into AmB molecules.

DOI： 10.1002/chem.200701256

記述言語：英語   掲載種別：研究論文（学術雑誌）  

An ionophore antibiotic salinomycin was studied in a membrane environment consisting of isotropic bicelles, a better model for biological membranes than micelles, and its conformation and topological orientation in bicelles was determined. 2D NMR measurements and restrained conformational search revealed that salinomycin-sodium salt in bicelles adopts an open conformation in which the orientation of the E-ring is significantly different from that in crystal and solution structures. This conformational alteration breaks an intramolecular hydrogen bond between 28-OH and 1-O, dislocates the ether oxygen of the E-ring from a coordinated position to the sodium ion observed in the crystal, and consequently weakens the complexation between salinomycin and the sodium ion. Paramagnetic relaxation experiments using doxylphospholipids reveal that salinomycin is embedded shallowly in bicelles, with both terminals being closer to the water interface and the olefin portion facing the bicelle interior. Measurements of intermolecular NOEs between salinomycin and phospholipids further supported this orientation. Weaker complexation with sodium ion and positional preference in the membrane polar region may facilitate the catch-and-release of metal ions at the polar/nonpolar interface of bilayers. On the basis of these findings, a model for salinomycin-assisted transport of metal ions across biological membranes is proposed.

DOI： 10.1021/ja075024l

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Based on an amphotericin B (AmB) ion-channel model where the close proximity of neighboring molecules is effected by interaction between carboxyl and amino groups, we prepared covalent dimers of AmB connected between these functionalities. While directly connected and short-tethered derivatives (2 and 3) lacked the activities, dimer 4 with a longer linker revealed K⁺ ion flux activity, suggesting that some distance and/or flexibility between the carboxyl and amino groups in adjacent molecules is required for the formation of ion-permeable complex in biomembranes.

DOI： 10.1016/j.tetlet.2007.03.058

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The absolute configuration of blasticidin A, a strong inhibitor of aflatoxin production by Aspergillus parasiticus, was assigned by adding the data of relative configurations at its diol and pentaol moieties to previously known stereochemistry. Similarity of the NMR data of blasticidin A to those of aflastatin A allowed us to revise the stereochemistry of the diol and pentaol moieties of aflastatin A.

DOI： 10.1016/j.tetlet.2007.02.024

記述言語：英語   掲載種別：研究論文（学術雑誌）  

(Figure Presented) Amphotericin B (AmB) is known to self-assemble to form an ion channel across lipid bilayer membranes. To gain insight into the conformation of AmB in lipidic environments, AmB in SDS micelles was subjected to high-resolution NMR and CD measurements, and the NMR-derived conformation thus obtained was refined by molecular mechanics calculations. These results indicate that AmB in SDS micelles is conformationally fixed particularly for the macrolide moiety. Paramagnetic relaxation experiments with the use of Mn ²⁺ reveal that AmB is shallowly embedded in the micelle with the polyhydroxyl chain being close to the water interface and the side of polyene portion facing to the micelle interior. CD measurements demonstrate that AmB is in a monomeric form in SDS micelles. The structure of AmB in the micelles obtained in the present study may reproduce the initial stage of membrane interaction of AmB prior to the assembly formation in biomembranes.

DOI： 10.1021/jo061309p

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ladder-shaped polyether (LSP) compounds, such as brevetoxins and ciguatoxins, are thought to interact with transmembrane (TM) proteins. As a model LSP compound, we designed and synthesized an artificial tetracyclic ether (1) and evaluated its interaction with glycophorin A (GpA), a membrane protein known to dimerize or oligomerize between membrane-integral α-helical domains. Model compound 1 was found to induce the dissociation of oligomeric GpA in a similar manner to natural LSPs when examined by SDS-PAGE. The results suggest that even an artificial tetracyclic ether possesses the ability to interact with TM proteins, presumably through the intermolecular hydrogen bonds (C_α-H ⋯ O) with the GXXXG motif.

DOI： 10.1016/j.bmcl.2006.09.004

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The membrane interaction of amphotericin B (AmB), one of the most important anti-fungal drugs, was investigated by solid state NMR measurements of uniformly ¹³C-enriched AmB, which was prepared by the culture of the drug-producing microorganism in the presence of [u-¹³C₆]glucose. All the ¹³C NMR signals of AmB upon binding to DLPC membrane were successfully assigned on the basis of the ¹³C-¹³C correlation spectrum. ¹³C-³¹P RDX (Rotational-Echo Double Resonance for X-clusters) experiments clearly revealed the REDOR dephasing effects for carbon atoms residing in the both terminal parts, whereas no dephasing was observed for the middle parts including polyolefinic C20-C33 and hydroxyl-bearing C8/C9 parts. These observations suggest that AmB binds to DLPC membrane with a high affinity to the phospholipid and spans the membrane with a single molecular length.

DOI： 10.1016/j.bmc.2006.06.001

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Two new homologues of amphidinols (AM14 and AM15) were isolated from the cultured dinoflagellate Amphidinium klebsii. The structures were elucidated on the basis of 2D NMR and collision-induced dissociation MS/MS and turned out to be closely related homologues of AM7. Their weak membrane-disrupting activity indicates that the hydrophobic polyene chain is essential for the potent biological activities. Structure-activity relationship for the polyhydroxyl part was then examined with use of AM homologues possessing various chain lengths, indicating that the pore size of the channel/lesion formed by AMs was not greatly affected by the length of the polyhydroxyl chain.

DOI： 10.1016/j.bmc.2006.06.012

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphotericin B (AmB 1) is known to assemble and form an ion channel across biomembranes. We have recently reported that conformation-restricted derivatives of AmB 2-4 show different ergosterol preferences in ion-channel assays, which suggested that the orientation of the mycosamine strongly affects the sterol selectivity of AmB. The data allowed us to assume that compound 3 showing the highest selectivity would reflect the active conformation of AmB in the channel assembly. In this study, to gain further insight into the active conformation of AmB, we prepared a new intramolecular-bridged derivative 5, where the linker encompassed a hydrophilic glycine moiety. The derivative has almost equivalent ion-channel activity to those of AmB and 3. The antifungal activity of 5 compared with 3 improves significantly, possibly because the increasing hydrophilicity in the linker enhances the penetrability through the fungal cell wall. Conformation of 5 was well converged and very similar to that of 3, thus further supporting the notion that the conformations of these derivatives reproduce the active structure of AmB in the channel complex. Then we used the derivative to probe the mobility of AmB in the membrane by solid-state NMR. To measure dipolar couplings and chemical shift anisotropies, we incorporated [1-¹³C,¹⁵N]glycine into the linker. The results indicate that 5 is mostly immobilized in ergosterol-containing DMPC bilayers, implying formation of large aggregates of 5. Meanwhile some fraction of 5 remains mobile in sterol-free DMPC bilayers, suggesting promotion of Amb aggregation by ergosterol.

DOI： 10.1021/ja063433w

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A fluorinated amphotericin B (AmB) derivative, 28-¹⁹F-AmB methyl ester (3), labeled at the polyene moiety, was synthesized by combining chemical synthesis with degradation of a natural product via cross-coupling reactions and macrolactonization. The fluorinated derivative 3 showed antifungal activity similar to that of AmB, and is expected to be a powerful tool for NMR-based investigation of the mechanism of ion-channel formation.

DOI： 10.1016/j.tetlet.2006.06.159

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Although many nonpeptidic drugs target biological membrane and membrane proteins, it is still difficult to define the membrane-bound structure of the drugs. In this study, we utilized bicelles as a membrane model, since the bicelles, which have planar lipid bilayer portions, are thought to be a more appropriate and practical membrane model than micelles. Bicelles with a small diameter allow for measurements of liquid NMR due to fast tumbling in solution. We targeted erythromycin A (EA) as a membrane-binding compound because it is pointed out that the drug interacts with lysosomal membranes, inhibits phospholipase A, and consequently induces phospholipidosis as a side effect. The conformation of EA in the bicelle was successfully determined on the basis of coupling constants and NOEs. Measurements of intermolecular NOEs and paramagnetic relaxation times revealed that the drug is located shallowly in the membrane surface, with the dimethylamino group being close to the phosphate, and the macrolide portion adjacent to upper sides of the acyl chains. This study shows the general utility of isotropic bicelles for detailed conformational and orientational studies of membrane-associated nonpeptidic drugs.

DOI： 10.1021/jm051210v

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphotericin B (AmB) is known to assemble together and form an ion channel across biomembranes. The selective toxicity is generally accounted for by its higher affinity for ergosterol than cholesterol. To better understand the ion-channel structure and intermolecular interactions, we prepared various AmB derivatives and measured their activities. AmB dimers which are covalently linked between the amino groups by short chains showed more potent ion-channel activity than that of AmB, indicating that the mutual topology of AmB molecules is a head-to-head orientation. AmB-sterol conjugates were also designed and examined for ion-channel activities. AmB-ergosterol conjugates showed more powerful ion-channel activity than AmB-cholesterol congeners, suggesting that stronger van der Waals interaction between AmB and ergosterol contributes to the higher ion-channel activity. Finally, we prepared conformation-restricted derivatives of AmB, in which the amino and carboxyl groups were bridged with various lengths of alkyl chains. The derivatives successfully gave us information on the active-conformation of the sugar moiety of AmB in membrane. These derivatives are now labeled by ¹³C and/or ¹⁹F to probe the molecular structure of AmB ion channel using solid-state NMR.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ladder-shaped polyether compounds, represented by brevetoxins, ciguatoxins, maitotoxin, and prymnesins, are thought to possess the high affinity to transmembrane proteins. As a model compound of ladder-shaped polyethers, we adopted desulfated yessotoxin (2) and examined its interaction with glycopholin A, a membrane protein known to form a dimer or oligomer. Desulfated yessotoxin turned out to interact with the α-helix so as to induce the dissociation of glycopholin oligomers when examined by SDS and PFO gel electrophoresis. The results provided the first evidence that lapper-shaped polyethers interact with transmembrane helix domains.

DOI： 10.1016/j.bmc.2005.05.039

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A new member of amphidinols (AM7) possessing a polyene-polyhydroxyl structure with the shortest carbon backbone and sulfate ester was isolated from the cultured dinoflagellate, Amphidinium klebsii. AM7 showed hemolytic and antifungal activities. The structure was elucidated on the basis of 2D NMR data in combination with CID MS/MS experiments.

DOI： 10.1016/j.tet.2005.07.004

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The first stably fluorinated derivative of amphotericin B (2) with a fluorine atom in the macrolide skeleton was synthesized using an electrophilic fluorination reagent, Selectfluor®. The derivative 2 showed hemolytic, K⁺ permeable, and antifungal activities similar to those of AmB and thus was expected to be a powerful tool for NMR-based investigations on the mechanism of ion-channel formation by amphotericin B.

DOI： 10.1016/j.bmcl.2005.05.058

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphotericin B (AmB 1) is known to assemble together and form an ion channel across biomembranes. The antibiotic consists of mycosamine and macrolactone moieties, whose relative geometry is speculated to be determinant for the drug's channel activity and sterol selectivity. To better understand the relationship between the amino-sugar orientation and drug's activity, we prepared conformation-restricted derivatives 2-4, in which the amino and carboxyl groups were bridged together with various lengths of alkyl chains. K⁺ influx assays across the lipid-bilayer membrane revealed that ergosterol selectivity was markedly different among derivatives; short-bridged derivative 2 almost lost the selectivity, while 3 showed higher ergosterol preference than AmB itself. Monte Carlo conformational analysis of 2-4 based on NOE-derived distances indicated that the amino-sugar moiety of 2 comes close to C41 because of the short bridge, whereas those of 3 and 4 are pointing outward. The mutual orientation of the amino-sugar moiety and macrolide ring is so rigid in derivatives 2 and 3 that these conformations should be unchanged upon complex formation in lipid membranes. These results strongly suggest that the large difference in sterol preference between derivatives 2 and 3 is ascribed to the different orientation of amino-sugar moieties. These findings allowed us to propose a simple model accounting for AmB-sterol interactions, in which hydrogen bonding between 2′-OH of AmB and 3β-OH of ergosterol plays an important role.

DOI： 10.1021/ja051597r

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphidinols are a unique dinoflagellate metabolite with potent antifungal activity. We examined membrane permeabilizing action by amphidinol analogues with structural variations in polyhydroxy and polyene moieties. Consequently, the polyene and polyhydroxy moieties turned out to play important roles in binding to lipid bilayer membrane and in forming ion-permeable pore/lesion across membrane, respectively. NMR-constrained modeling experiments have revealed for the fist time that amphidinols in membrane generally take a hairpin configuration, which plausibly accounts for their potent antifungal and other membrane permeabilizing activities.

DOI： 10.1016/j.tet.2005.01.069

記述言語：英語   掲載種別：研究論文（学術雑誌）  

¹³C-Labeled amphotericin B (AmB) was prepared by feeding the producing organism Streptomyces nodosus with [3-¹³C]propionate. The REDOR experiments for dimyristoylphosphatidylcholine (DMPC) membrane using the ¹³C-labeled AmB showed the prominent dephasing effects between the phosphate group in PC and C41 carboxyl carbon in the polar head. In addition, C39/C40 methyl carbons also gave rise to the significant reduction of their ¹³C NMR signals, implying that both terminal parts of AmB reside close to the surface of the DMPC membrane. Conversely, the same REDOR experiments with use of distearoylphosphatidylcholine (DSPC) showed no dephasing for the C39/C40 methyl signals while a marked reduction of the C41 carbonyl signal was again observed. These findings should be most reasonably accounted for by the notion that AmB can span across the DMPC membrane with a single-length interaction but cannot span the DSPC membrane due to its greater thickness. To our knowledge, the results provide the first direct spectroscopic evidence for the formation of a single-length channel across a biomembrane, which was previously suggested by channel current recording experiments.

DOI： 10.1021/bi049001k

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphotericin B (AmB, 1) is known to assemble together and form an ion channel across biomembranes, by which the drug presumably exerts its antimicrobial activity. To access the whole architecture of this channel assemblage, the understanding of binary interaction between AmB molecules is of prime importance because the dimeric interaction is the basis of the assemblage. In this context, we have recently reported covalently conjugated AmB dimers such as 2 and 3 with a long linker, which show prominent hemolytic potency and ion-channel activity. To evaluate the effect of the length and hydrophilicity of linker parts on the activity, we prepared new dimers bearing tartarate linkages (4 and 5). Especially, 5 exhibited potent hemolytic activity (EC₅₀, 0.03 μm) surpassing those of AmB, 2, and 3. Measurements of UV and CD spectra of 5 in liposomes indicated that AmB portions of 5 could adopt appropriate arrangements in molecular assemblage in spite of the short linkage, and also indicated that the assemblage formed by 5 appeared more stable than AmB. These short-tethered dimers are expected to be a promising tool to reveal the mechanism of dimeric interaction in the ion channel formed by AmB.

DOI： 10.1002/cbdv.200490030

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphidinols, which are polyene-polyhydroxy metabolites produced by the marine dinoflagellate Amphidinium klebsii, possess potent antifungal and hemolytic activities. The membrane permeabilizing actions of amphidinol 3, the most potent homologue, were compared with those of polyene antibiotics, amphotericin B (AmB) and filipin, in hemolytic tests, ²³Na nuclear magnetic resonance (NMR)-based membrane permeabilizing assays, and UV spectroscopy for liposome-bound forms. In Na ⁺ flux experiments using large unilamellar vesicles (LUVs), ion efflux by amphidinol 3 was inhibited by cholesterol or ergosterol, which was opposed to previous results [J. Mar. Biotechnol., 5 (1997) 124]. When the effect of the agents on the size of vesicles was examined by light scattering experiments, amphidinol 3 did not significantly alter their size while filipin and synthetic detergent Triton X-100 did. The observations implied that the activity of amphidinol 3 was mainly due to formation of large pores/lesions in liposomes rather than detergent-like disruption of membrane. The pore/lesion size was estimated to be 2.0-2.9 nm in diameter on the basis of osmotic protection experiments using blood cells. The UV spectra in liposomes, which revealed the close interaction of polyene moieties in a lipid bilayer, further implied that the membrane activity of amphidinol 3 is caused by the molecular assemblage formed in biomembrane. These results disclose that amphidinol 3 is one of few non-ionic compounds that possess potent membrane permeabilizing activity with non-detergent mechanism.

DOI： 10.1016/j.bbamem.2004.09.002

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Polyamines such as spermidine and spermine are known to interact with polyanionic biomolecules under physiological conditions. Conformation analysis of these highly flexible acycles is virtually unprecedented due to the lack of appropriate methodologies. Spin-spin coupling constants, which are often utilized for acyclic systems, are rather uninformative for polyamines due to unresolved ¹H NMR signals of their tri- and tetra-methylene moieties. We attempted to solve this problem by synthesizing diastereospecifically deuterated spermidine, (1S^*,2S^*)-1,8-diamino- 4-azaoctane-1,2,3,3,5,5,6,6,7,7,8,8-d₁₂. To evaluate its utility, ¹H-¹H spin coupling constants were measured as trihydrochloride or tripolyphosphate salt. The relevant coupling constant markedly decreased upon complexation to tripolyphosphate. Under neutral pH, where the net charge of tripolyphosphate became tetravalent, the coupling constant was small; as pH was lowered to 1.4, where the charge was divalent, the constant increased significantly. These data clearly indicate that, when interacting with polyanions, spermidine undergoes conformational changes to increase bent conformation, which could be effectively monitored by the deuterated spermidine.

DOI： 10.1016/j.tet.2004.04.056

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Amphotericin B-sterol conjugates were synthesized and examined for their membrane permeabilizing activity. Ergosterol and cholesterol, each connected with amphotericin B via an ethylenecarbamate or hexamethylenecarbamate linker, were examined by K⁺ flux assays using liposomes and by single-channel recording across phospholipid membrane. Among four conjugates tested, AmB-ergosterol bearing an ethylenecarbamate linker exhibited the most powerful activity, which substantially exceeded that of the cholesterol homolog. Single-channel recording clearly exhibited that the ergosterol conjugate elicited channel current with the conductance of 28 pS, which was comparable with those by AmB, and revealed a higher channel open probability than the cholesterol conjugate. These results imply that direct interaction between amphotericin B and ergosterol is reproduced by their conjugate, which may serve as a model compound for understanding the drug's selective toxicity.

DOI： 10.1016/j.chembiol.2004.02.027

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The interaction between amphotericin B and phospholipid upon forming ion channels across a biomembrane was investigated using their covalent conjugates. The membrane permeabilizing activity was greatly affected by the chain length of the fatty acyl groups, suggesting that their interaction is involved in ion channel assemblages.

DOI： 10.1039/b306801c

記述言語：英語   掲載種別：研究論文（学術雑誌）  

(Matrix Presented) Covalently linked dimers of amphotericin B were prepared by cross-linking its carboxylic acid. Among these, a dimer with a linkage of 1,6-hexanediamine revealed potent hemolytic activity (EC₅₀,0.25 μM) while its N-acetyl derivative gave rise to large K⁺ ion flux in phosphatidylcholine liposomes, regardless of the presence or absence of sterols, suggesting that the dimers may serve as a tool for elucidating the structure of the ion channel assemblage formed by amphotericin B.

DOI： 10.1021/ol025982m

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Polyenemacrolides such as amphotericin B (AmB) were thought to assemble together and form an ion channel across plasma membranes. Their antimicrobial activity has been accounted for by this assemblage, whose stability and activity are dependent on sterol constituents of lipid bilayer membranes. The structure of this channel-like assemblage formed in biomembranes has been a target of extensive investigations for a long time. For the first step to this goal, we prepared several AmB dimers with various linkers and tested for their channel-forming activity. Among these, AmB dimers that bore an aminoalkyl-dicarboxylate tether covalently linked between amino groups of AmB showed potent hemolytic activity. Furthermore, K⁺ influx actions monitored by measuring the pH of the liposome lumen by ³¹P NMR revealed that the dimers formed the molecular assemblage similar to that of AmB in phospholipid membrane. Judging from changes in ³¹P NMR spectra, the dimers appeared to induce "all-or-none"-type ion flux across the liposome membrane in the presence of ergosterol, which suggested that the ion channel formed by ergosterol/dimer is similar to that of AmB. With these data in hand, we are now trying to elucidate the structure of the ion-channel complex by making the labeled conjugates of AmB for NMR measurements.

DOI： 10.1021/ja012026b

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Aflastatin A (1) is a specific inhibitor of aflatoxin production by Aspergillus parasiticus. It has the novel structure of a tetramic acid derivative with a long alkyl side chain. The absolute configurations of 29 chiral centers contained in I were chemically elucidated in this study. First, four small fragment molecules were prepared from I or its methyl ether (2), and their absolute structures were assigned as N-methyl-D-alanine, (2S,4R)-2,4-dimethyl-1,6-hexanediol dibenzoate, (R)-3-hydroxydodecanoic acid, and (R)-1,2,4-butanetriol tribenzoate. Next, an acyclic fragment molecule 3 with 13 chiral centers was obtained from I by NaIO₄ oxidation, and its relative stereochemistry was elucidated by J-based configuration analysis. By analyzing coupling constants of ³J(H,H) and ^2,3J(C,H) and ROE data, the relative configuration of 3 was verified. Finally, by further J-based configuration analysis using a fragment molecule 7 prepared from 2 with 28 chiral carbons, all relative configurations in the alkyl side chain of I were clarified. By connecting these relative configurations with the absolute configurations of first four fragment molecules, the absolute stereochemistry of 1 was fully determined.

DOI： 10.1021/jo991284c

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The cellular target of leptomycin B (LMB), a nuclear export inhibitor, has been identified as CRM1 (exportin 1), an evolutionarily conserved receptor for the nuclear export signal of proteins. However, the mechanism by which LMB inhibits CRM1 still remains unclear. CRM1 in a Schizo-saccharomyces pombe mutant showing extremely high resistance to LMB had a single amino acid replacement at Cys-529 with Ser. The mutant gene, named crm1-K1, conferred LMB resistance on wild-type S. pombe, and Crm1-K1 no longer bound biotinylated LMB. ¹H NMR analysis showed that LMB bound N-acetyl-L-cysteine methyl ester through a Michael-type addition, consistent with the idea that LMB binds covalently via its α,β-unsaturated δ-lactone to the sulfhydryl group of Cys-529. When HeLa cells were cultured with biotinylated LMB, the only cellular protein bound covalently was CRM1. Inhibition by N- ethylmaleimide (NEM), an alkylating agent, of CRM1-mediated nuclear export probably was caused by covalent binding of the electrophilic structure in NEM to the sulfhydryl group of Cys-529, because the crm1-K1 mutant showed the normal rate for the export of Rev nuclear export signal-bearing proteins in the presence of not only LMB but also NEM. These results show that the single cysteine residue determines LMB sensitivity and is selectively alkylated by LMB, leading to CRM1 inactivation.

DOI： 10.1073/pnas.96.16.9112

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/ja983655x

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A method for elucidating the relative configuration of acyclic organic compounds was developed on the basis of carbon-proton spin-coupling constants (^2,3J(C,H)) and interproton spin-coupling constants (³J(H,H)). This method is based on the theory that, in acyclic systems, the conformation of adjacent asymmetric centers is represented by staggered rotamers, and their relative stereochemistry can be determined using ^2,3J(C,H) and ³J(H,H), because the combined use of these J values enables the identification of the predominant staggered rotamer(s) out of the six possible derived from threo and erythro configurations. Detailed conformational analysis for model compounds 1-4 revealed that this method is useful in most cases for assignment of the configuration of acyclic structures occurring in natural products, in which stereogenic methine carbons are often substituted with a methyl or a hydroxy (alkoxy) group. This J-based configuration analysis was applied to the stereochemical elucidation of carboxylic acid 5 derived from zooxanthellatoxin and proven to be a practical method even for natural products with complicated structures.

DOI： 10.1021/jo981810k

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Lipogrammistin-A (1b) was isolated as an ichthyotoxic and hemolytic constituent of the skin mucus of the grammistid fish Aulacocephalus temmincki. Its absolute stereochemistry was established by chemical degradation and total synthesis. The stereochemistry of the 2-methylbutyryl moieties attached to N9 and N15 was determined to be S by HPLC analysis of a diastereomeric derivative. The stereochemistry of the remaining C4 position was elucidated to be S by a total synthesis of the two diastereomers (4S)- and (4R)-1.

DOI： 10.1021/jo9722461

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A new NMR methodology was devised for configurational assignments of acyclic structures in natural products or synthetic compounds. Conventional methods based on NOEs often suffer from the ambiguity in assigning the configurations of compounds with acyclic structures and conformational alternation. Unlike these NOE analyses, the new methodology is based on the dihedral angle dependency of long-range carbon-proton coupling constants (^2,3J^C.H). The combination of the coupling constants (^2,3J_C.H, ³J_H,H) which are categorized to large, medium, or small allows to determine the relative stereochemistry among adjacent asymmetric centers or those separated by a methylene group. Hetero half-filter TOCSY (HETLOC) was shown to be the most effective for measuring ^2,3J_C,H of protonated carbon system. For structures with quaternary carbons or weakly coupling protons, in which TOCSY in HETLOC fails to correlate relevant protons, phase-sensitive HMBC (HMQC optimized for long-range coupling) worked effectively. To evaluate the utility of the method in structural analysis of natural products, the relative configurations of acyclic portions of maitotoxin, the largest secondary metabolite known to date, were assigned by this method, which evidently demonstrated the validity of ^2,3J_C,H in the configurational and conformational analysis of organic compounds.

DOI： 10.1246/nikkashi.1997.749

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The afsA gene of Streptomyces griseus has been postulated to encode a key enzyme for A-factor biosynthesis from primary metabolites commonly present in Streptomyces strains. Escherichia coli cells harboring afsA under the control of the T7 promoter specified distinct A-factor activity in the culture broth, as determined by induction of streptomycin production and aerial mycelium and spore formation in an A-factor-deficient S. griseus mutant strain. Production of the substance(s) having A-factor activity was inhibited by cerulenin, an inhibitor of fatty acid biosynthesis. These observations suggest that afsA encodes a key enzyme in the A-factor biosynthetic pathway in which a β-keto acid derived from fatty acid biosynthesis and a glycerol derivative serve as precursors.

DOI： 10.7164/antibiotics.50.847

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A series of polyhydroxy-polyene compounds were isolated from the cultured dinoflagellate Amphidinium klebsii as well as from its surrounding media. Amphidinol 5 (AM 5) and 6 (AM 6) were found to be potent antifungal and hemolytic agents. Their permeabilizing activity towards phospholipid liposomes was markedly enhanced by the presence of cholesterol within the bilayer, indicating that the mechanism of action involved interaction with membranal cholesterol.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Long-range carbon-proton coupling constants (^2,3J(C,H)) were measured for maitotoxin (MTX), one of the largest natural non-biopolymers, by hetero-half filter experiments and phase-sensitive HMBC with use of 9 mg of a 4% ¹³C-enriched sample. The necessary coupling constants within the terminal acyclic portions of MTX, where NOE analysis was not successful owing to the presumed coexistence of multiple conformers, were thus obtained for the resultant elucidation of relative configurations for the acyclic stereogenic centers to the 5R*, 7R*, 8R*, and 9S*.

DOI： 10.1016/0040-4039(95)02413-1

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/anie.199616751

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/anie.199616721

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The relative configuration of carbons within the C35-C39 acyclic linkage of maitotoxin (MTX) was assigned by synthesis of stereodefined model compound 1 and its comparison with MTX in ¹H and ¹³C NMR spectra. This result completed Stereochemical assignments of the whole molecule except for side chains.

DOI： 10.1016/0040-4039(95)01973-L

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Long-range carbon-proton coupling constants (^2,3J_C,H) are known to depend on the dihedral angles as is the well-known case with interproton couplings. The precise measurement of these J values were carried out using hetero half-filtered TOCSY and phase-sensitive HMBC on a marine natural product, okadaic acid. From the obtained values together with ³J_H,H we disclosed the conformations of okadaic acid in organic and aqueous solutions (CD₃OD-CDCl₃ or NaOD/D₂O), which resembled each other and that obtained for its crystalline o-bromobenzyl ester. The successful result in the present conformational study, even though as an exmaple, demonstrated this methodology to be powerful in elucidation of conformations and configurations of acyclic or macrocyclic portions in natural products of this size.

DOI： 10.1016/0040-4020(95)00790-F

記述言語：英語   掲載種別：研究論文（学術雑誌）  

A new polyene-polyhydroxy compound, amphidinol 2 (2), was isolated as a potent hemolytic and antifungal agent from a cultured strain of dinoflagellate Amphidinium klebsii. The structure elucidated by spectroscopic methods turned out to be partly analogous to amphidinol 1 (1), which had been reported from the different strain of A. klebsii.

DOI： 10.1016/0040-4039(95)01259-K

担当ページ：13章　1H NMRおよび13C NMR分光法   記述言語：日本語   著書種別：学術書

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フィンランドAbo Akademi大における博士審査主査

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https://www.kyushu-u.ac.jp/ja/researches/view/349

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