担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

Photoactivated adenylyl cyclase (PAC) is a unique protein that, upon blue light exposure, catalyzes cAMP production. The crystal structures of two PACs, from Oscillatoria acuminata (OaPAC) and Beggiatoa sp. (bPAC), have been solved, and they show a high degree of similarity. However, the photoactivity of OaPAC is much lower than that of bPAC, and the regulatory mechanism of PAC photoactivity, which induces the difference in activity between OaPAC and bPAC, has not yet been clarified. Here, we investigated the role of the C-terminal region in OaPAC, the length of which is the only notable difference from bPAC. We found that the photoactivity of OaPAC was inversely proportional to the C-terminal length. However, the deletion of more than nine amino acids did not further increase the activity, indicating that the nine amino acids at the C-terminal critically affect the photoactivity. Besides, absorption spectral features of light-sensing domains (BLUF domains) of the C-terminal deletion mutants showed similar light-dependent spectral shifts as in WT, indicating that the C-terminal region influences the activity without interacting with the BLUF domain. The study characterizes new PAC mutants with modified photoactivities, which could be useful as optogenetics tools.

DOI： 10.1038/s41598-019-56721-3

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

KcsA is a proton-activated K+ channel that is regulated at two gates: an activation gate located in the inner entrance of the pore and an inactivation gate at the selectivity filter. Previously, we revealed that the cytoplasmic domain (CPD) of KcsA senses proton and that electrostatic changes of the CPD influences the opening and closing of the activation gate. However, our previous studies did not reveal the effect of CPD on the inactivation gate because we used a non-inactivating mutant (E71A). In the present study, we used mutants that did not harbor the E71A mutation, and showed that the electrostatic state of the CPD influences the inactivation gate. Three novel CPD mutants were generated in which some negatively charged amino acids were replaced with neutral amino acids. These CPD mutants conducted K+, but showed various inactivation properties. Mutants carrying the D149N mutation showed high open probability and slow inactivation, whereas those without the D149N mutation showed low open probability and fast inactivation, similar to wild-type KcsA. In addition, mutants with D149N showed poor K+ selectivity, and permitted Na+ to flow. These results indicated that electrostatic changes in the CPD by D149N mutation triggered the loss of fast inactivation and changes in the conformation of selectivity filter. Additionally, the loss of fast inactivation induced by D149N was reversed by R153A mutation, suggesting that not only the electrostatic state of D149, but also that of R153 affects inactivation.

DOI： 10.1016/j.bbamem.2018.07.011

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

The artificial bilayer single channel recording technique is commonly used to observe the detailed physiological properties of various ion channel proteins. It permits easy control of the solution and membrane lipid composition, and is also compatible with pharmacological screening devices. However, its use is limited due to low measurement efficiency. Here, we developed a novel artificial bilayer single channel recording technique in which solubilized ion channel proteins immobilized on a gold nano-electrode are directly incorporated into a lipid bilayer at the same time as the bilayer is formed at the tip of it on coming in contact with an aqueous-oil interface. Using this technique, we measured the single channel currents of several types of channels including KcsA, MthK, hBK and P2X4. This technique requires only one action to simultaneously form the bilayers and reconstitute the channels into the membranes. This simplicity greatly increases the measurement efficiency and allows the technique to potentially be combined with high-throughput screening devices.

DOI： 10.1039/c7nr08098k

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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：Royal Society of Chemistry  

Chaperoning functions of liposomes were investigated using cell-free membrane protein synthesis. KcsA potassium channel-reconstituted liposomes were prepared directly using cell-free protein synthesis. In the absence of liposomes, all synthesized KcsA protein aggregated. In the presence of liposomes, however, synthesized KcsA spontaneously integrated into the liposome membrane. The KscA-reconstituted liposomes were transferred to the planar bilayer across a small hole in a thin plastic sheet and the channel function of KcsA was examined. The original electrophysiological activities, such as voltage- and pH-dependence, were observed. These results suggested that in cell-free membrane protein synthesis, liposomes act as chaperones, preventing aggregation and assisting in folding and tetrameric formation, thereby allowing full channel activity.

DOI： 10.1039/c5bm00285k

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

The artificial bilayer single-channel recording technique is commonly used to observe detailed pharmacological properties of various ion channel proteins. It permits easy control of the solution and membrane lipid composition, and is also compatible with pharmacological screening devices. However, its use is limited due to low measurement efficiency. Here, we develop a novel artificial bilayer single-channel recording technique in which bilayers are made and channels are reconstituted into the membranes by contacting a gold electrode to the lipid-solution interface. Using this technique, we measured the single-channel currents of two channel-forming peptides, gramicidin and alamethicin, and a channel-forming protein, α-hemolysin. This technique requires only one action, allowing the technique to potentially be combined with high-throughput screening devices.

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

The KcsA channel is a proton-activated potassium channel. We have previously shown that the cytoplasmic domain (CPD) acts as a pH-sensor, and the charged states of certain negatively charged amino acids in the CPD play an important role in regulating the pH-dependent gating. Here, we demonstrate the KcsA channel is constitutively open independent of pH upon mutating E146 to a neutrally charged amino acid. In addition, we found that rearrangement of the CPD following this mutation was not large. Our results indicate that minimal rearrangement of the CPD, particularly around E146, is sufficient for opening of the KcsA channel.

DOI： 10.1016/j.bbrc.2014.07.032

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Chloroplasts require protein translocons at the outer and inner envelope membranes, termed TOC and TIC, respectively, to import thousands of cytoplasmically synthesized preproteins. However, the molecular identity of the TIC translocon remains controversial. Tic20 forms a 1-megadalton complex at the inner membrane and directly interacts with translocating preproteins. We purified the 1-megadalton complex from Arabidopsis, comprising Tic20 and three other essential components, one of which is encoded by the enigmatic open reading frame ycf1 in the chloroplast genome. All four components, together with well-known TOC components, were found stoichiometrically associated with different translocating preproteins. When reconstituted into planar lipid bilayers, the purified complex formed a preprotein-sensitive channel. Thus, this complex constitutes a general TIC translocon.

DOI： 10.1126/science.1229262

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Although ion channels are attractive targets for drug discovery, the systematic screening of ion channel-targeted drugs remains challenging. To facilitate automated single ion-channel recordings for the analysis of drug interactions with the intra- and extracellular domain, we have developed a parallel recording methodology using artificial cell membranes. The use of stable lipid bilayer formation in droplet chamber arrays facilitated automated, parallel, single-channel recording from reconstituted native and mutated ion channels. Using this system, several types of ion channels, including mutated forms, were characterised by determining the protein orientation. In addition, we provide evidence that both intra- and extracellular amyloid-beta fragments directly inhibit the channel open probability of the hBK channel. This automated methodology provides a high-throughput drug screening system for the targeting of ion channels and a data-intensive analysis technique for studying ion channel gating mechanisms.

DOI： 10.1038/srep01995

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

The KcsA channel is a representative potassium channel that is activated by changes in pH. Previous studies suggested that the region that senses pH is entirely within its transmembrane segments. However, we recently revealed that the cytoplasmic domain also has an important role, because its conformation was observed to change dramatically in response to pH changes. Here, to investigate the effects of the cytoplasmic domain on pH-dependent gating, we made a chimera mutant channel consisting of the cytoplasmic domain of the KcsA channel and the transmembrane region of the MthK channel. The chimera showed a pH dependency similar to that of KcsA, indicating that the cytoplasmic domain can act as a pH sensor. To identify how this region detects pH, we substituted certain cytoplasmic domain amino acids that are normally negatively charged at pH 7 for neutral ones in the KcsA channels. These mutants opened independently of pH, suggesting that electrostatic charges have a major role in the cytoplasmic domain's ability to sense and respond to pH.

DOI： 10.1016/j.bpj.2011.09.024

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ion channels are membrane proteins that regulate cell functions by controlling the ion permeability of cell membranes. An ion channel contains an ion-selective pore that permeates ions and a sensor that senses a specific stimulus such as ligand binding to regulate the permeability. The detailed molecular mechanisms of this regulation, or gating, are unknown. Gating is thought to occur from conformational changes in the sensor domain in response to the stimulus, which results in opening the gate to permit ion conduction. Using an atomic force microscope and artificial bilayer system, a mechanical stimulus is applied to a potassium channel, and its gating is monitored in real time. The channel-open probability increases greatly when pushing the cytoplasmic domain toward the membrane. This result shows that a mechanical stimulus at the cytoplasmic domain causes changes in the gating and is the first to show direct evidence of coupling between conformational changes in the cytoplasmic domain and channel gating. This novel technology has the potential to be a powerful tool for investigating the activation dynamics in channel proteins.

DOI： 10.1002/smll.201002337

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担当区分：筆頭著者   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

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記述言語：英語   掲載種別：論文集(書籍)内論文   出版者・発行元：Springer Netherlands  

There has been much interest in imaging single drug bindings to ion channel proteins while simultaneously recording single channel current. We developed an experimental apparatus for simultaneous optical and electrical measurement of single channel proteins by combining the single molecule imaging technique and the artificial bilayer technique. However, one major problem is that single molecule imaging of drug bindings is limited by the innate thermal diffusion of channel proteins in the artificial bilayer. Therefore, immobilizing channel proteins in the bilayers is imperative for stable measurements of channel-drug interactions. For future studies on channel-drug interactions, we describe here three different methods for simultaneous optical and electrical observation of single channels in which channel proteins are immobilized. (i) Membrane binding protein annexin V reduces the lateral diffusion of single channel proteins in a concentration-dependent manner. (ii) Channel proteins are immobilized by anchorage through a polyethylene glycol (PEG) molecule to the glass substrate. (iii) Channels immobilized on a gel bead can be directly incorporated into artificial bilayers. © Springer Science+Business Media B.V. 2011.

DOI： 10.1007/978-90-481-9864-1_5

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

A change of cytosolic pH 7 to 4 opens the bacterial potassium channel KcsA. However, the overall gating mechanism leading to channel opening, especially the contribution of the cytoplasmic domain, remains unsolved. Here we report that deletion of the cytoplasmic domain resulted in changes in channel conductance and gating behavior at pH 4 without channel opening at pH 7. To probe for rearrangements in the cytoplasmic domain during channel opening, amino acid residues were substituted with cysteines and labeled with a fluorophore (tetramethylrhodamine maleimide) that exhibits increased fluorescence intensity upon transfer from a hydrophilic to hydrophobic environment. In all cases channel open probability (P(o)) was approximately 1 at pH 4 and approximately 0 at pH 7. Major increases in fluorescence intensity were observed for tetramethylrhodamine maleimide-labeled residues in the cytoplasmic domain as pH changed from 7 to 4, which suggests the fluorophores shifted from a hydrophilic to hydrophobic environment. Dipicrylamide, a lipid soluble quencher, reduced the fluorescence intensities of labeled residues in the cytosolic domain at pH 4. These results reveal that a decrease in pH introduces major conformational rearrangements associated with channel opening in the KcsA cytoplasmic domain.

DOI： 10.1074/jbc.M109.084368

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/anie.200904909

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Single channel currents of lysenin were measured using artificial lipid bilayers formed on a glass micropipette tip. The single channel conductance for KCl, NaCl, CaCl(2), and Trimethylammonium-Cl were 474 ± 87, 537 ± 66, 210 ± 14, and 274 ± 10 pS, respectively, while the permeability ratio P(Na)/P(Cl) was 5.8. By adding poly(deoxy adenine) or poly(L-lysine) to one side of the bilayer, channel currents were influenced when membrane voltages were applied to pass the charged molecules through the channel pores. Current inhibition process was concentration-dependent with applied DNA. As the current fluctuations of α-hemolysin channels is often cited as the detector in a molecular sensor, these results suggest that by monitoring channel current changes, the lysenin channel has possibilities to detect interactions between it and certain biomolecules by its current fluctuations.

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記述言語：英語   出版者・発行元：一般社団法人 日本生物物理学会  

DOI： 10.2142/biophys.50.S139_4

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

Current ion channel current measurement techniques are cumbersome, as they require many steps and much time. This is especially true when reconstituting channels into liposomes and incorporating them into lipid bilayers. Here, we report a novel method that measures ion channel current more efficiently than current methods. We applied our method to KcsA and MthK channels by binding them to cobalt affinity gel beads with histidine tags and then forming a lipid bilayer membrane on the bead. This allowed channels to incorporate into the bilayer and channel currents to be measured quickly and easily. The efficiency was such that currents could be recorded with extremely low amounts of protein. In addition, the channel direction could be determined by the histidine tag. This method has the potential to be applied to various channel proteins and channel research in general.

DOI： 10.1021/ac900286z

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記述言語：英語   掲載種別：論文集(書籍)内論文   出版者・発行元：Wiley-VCH Verlag GmbH & Co. KGaA  

DOI： 10.1002/9783527626137.ch4

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Single-channel recording using artificial lipid bilayers is along with the patch-clamp technique a very powerful tool to physiologically and pharmacologically study ion channels. It is particularly advantageous in studying channels that are technically difficult to access with a patch pipet. However, the fragility of the bilayers and the difficulty to incorporate ion channels into them significantly compromises measurement efficiency. We have developed a novel method for forming artificial lipid bilayers on a hydrogel surface that significantly improves the measurement efficiency. Bilayers formed almost instantly (<1 s) and were able to incorporate various types of ion channel proteins within a short time (<30 s) enabling multichannel measurements. These results indicate that this method can potentially be applied to developing high-throughput screening devices for drug design.

DOI： 10.1021/ac801224a

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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：Surface Science Society Japan  

We have developed a practical method to produce durable artificial lipid bilayers using a hydrogel-hydrogel interface for ion channel measurements. Bilayers were formed by forcing a hydrogel-bead into contact with the hydrogel layer (hydrogel plate) in a lipid solution. The immediate formation of a bilayer was observed (&lt
1 s). This allows channel recordings to be repeated more easily and quickly as compared to conventional methods. Currents of various types of channel such as gramicidin, hemolysin and BK-channel have been recorded. Our channel property results mirrored those of other techniques and were reproducible. Hydrogel solutions containing gramicidin were extremely stable and could be used months after preparation for bilayer experiments. © 2008 The Surface Science Society of Japan.

DOI： 10.1380/ejssnt.2008.130

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記述言語：日本語   掲載種別：記事・総説・解説・論説等（学術雑誌）  

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This paper describes an automated drug screening system for Ca 2+-activated K+ channel proteins (BK channel). BK channels are pharmacological targets for the treatment of stroke. We have been developing multiple lipid bilayer membranes (BLMs) system for reconstituting the membrane proteins [1]. In this study, the osmotic pressure in the proteoliposomes was controlled to induce the vesicle fusion. As a result, we succeeded in simultaneous reconstitution of BK channels in the BLMs array using an injection robot (Fig. 1). Moreover, the channel inhibition behavior was examined using a K+ channel blocker. Since our method is applicable for multi-type of proteoliposomes, we believe that the system can be used as a high-throughput screening (HTS) system for membrane-protein-based drug discovery. Copyright © (2011) by the Chemical and Biological Microsystems Society.

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