1
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Das A, Bysack A, Raghuraman H. Cholesterol modulates the structural dynamics of the paddle motif loop of KvAP voltage sensor. Curr Res Struct Biol 2024; 7:100137. [PMID: 38500801 PMCID: PMC10945132 DOI: 10.1016/j.crstbi.2024.100137] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2023] [Revised: 02/29/2024] [Accepted: 03/03/2024] [Indexed: 03/20/2024] Open
Abstract
KvAP is a prokaryotic Kv channel, which has been widely used as a model system to understand voltage- and lipid-dependent gating mechanisms. In phospholipid membranes, the KvAP-VSD adopts the activated/'Up' conformation, whereas the presence of non-phospholipids in membranes favours the structural transition to resting/'Down' state. The S3b-S4 paddle motif loop of KvAP-VSD is functionally important as this participates in protein-protein interactions and is the target for animal toxins. In this study, we have monitored the modulatory role of cholesterol - the physiologically-relevant non-phospholipid - on the organization and dynamics of the S3b-S4 loop of the isolated KvAP-VSD in membranes by site-directed fluorescence approaches using the environmental sensitivity of 7-nitrobenz-2-oxa-1,3-diazol-4-yl-ethylenediamine (NBD) fluorescence. Our results show that cholesterol alters the dynamic nature (rotational and hydration dynamics) of S3b-S4 loop in a segmental fashion, i.e., the residues 110 to 114 and 115 to 117 behave differently in the presence of cholesterol, which is accompanied by considerable change in conformational heterogeneity. Further, quantitative depth measurements using the parallax quenching method reveal that the sensor loop is located at the shallow interfacial region of cholesterol-containing membranes, suggesting that the sensor loop organization is not directly correlated with S4 helix movement. Our results clearly show that cholesterol-induced changes in bilayer properties may not be the predominant factor for the sensor loop's altered structural dynamics, but can be attributed to the conformational change of the KvAP-VSD in cholesterol-containing membranes. Overall, these results are relevant for gating mechanisms, particularly the lipid-dependent gating, of Kv channels in membranes.
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Affiliation(s)
- Anindita Das
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata, India
- Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai, 400 094, India
| | - Arpan Bysack
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata, India
- Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai, 400 094, India
| | - H. Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata, India
- Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai, 400 094, India
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2
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Sakuragi T, Kanai R, Otani M, Kikkawa M, Toyoshima C, Nagata S. The role of the C-terminal tail region as a plug to regulate XKR8 lipid scramblase. J Biol Chem 2024; 300:105755. [PMID: 38364890 PMCID: PMC10938166 DOI: 10.1016/j.jbc.2024.105755] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 01/27/2024] [Accepted: 02/10/2024] [Indexed: 02/18/2024] Open
Abstract
XK-related 8 (XKR8), in complex with the transmembrane glycoprotein basigin, functions as a phospholipid scramblase activated by the caspase-mediated cleavage or phosphorylation of its C-terminal tail. It carries a putative phospholipid translocation path of multiple hydrophobic and charged residues in the transmembrane region. It also has a crucial tryptophan at the exoplasmic end of the path that regulates its scrambling activity. We herein investigated the tertiary structure of the human XKR8-basigin complex embedded in lipid nanodiscs at an overall resolution of 3.66 Å. We found that the C-terminal tail engaged in intricate polar and van der Waals interactions with a groove at the cytoplasmic surface of XKR8. These interactions maintained the inactive state of XKR8. Point mutations to disrupt these interactions strongly enhanced the scrambling activity of XKR8, suggesting that the activation of XKR8 is mediated by releasing the C-terminal tail from the cytoplasmic groove. We speculate that the cytoplasmic tail region of XKR8 functions as a plug to prevent the scrambling of phospholipids.
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Affiliation(s)
- Takaharu Sakuragi
- Laboratory of Biochemistry and Immunology, World Premier International Immunology Frontier Research Center, Osaka University, Suita, Osaka, Japan
| | - Ryuta Kanai
- Institute for Quantitative Biosciences, The University of Tokyo, Tokyo, Japan
| | - Mayumi Otani
- Laboratory of Biochemistry and Immunology, World Premier International Immunology Frontier Research Center, Osaka University, Suita, Osaka, Japan
| | - Masahide Kikkawa
- Department of Cell Biology and Anatomy, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
| | - Chikashi Toyoshima
- Institute for Quantitative Biosciences, The University of Tokyo, Tokyo, Japan
| | - Shigekazu Nagata
- Laboratory of Biochemistry and Immunology, World Premier International Immunology Frontier Research Center, Osaka University, Suita, Osaka, Japan.
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3
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Hernandez CC, Gimenez LE, Dahir NS, Peisley A, Cone RD. The unique structural characteristics of the Kir 7.1 inward rectifier potassium channel: a novel player in energy homeostasis control. Am J Physiol Cell Physiol 2023; 324:C694-C706. [PMID: 36717105 PMCID: PMC10026989 DOI: 10.1152/ajpcell.00335.2022] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Revised: 01/12/2023] [Accepted: 01/13/2023] [Indexed: 02/01/2023]
Abstract
The inward rectifier potassium channel Kir7.1, encoded by the KCNJ13 gene, is a tetramer composed of two-transmembrane domain-spanning monomers, closer in homology to Kir channels associated with potassium transport such as Kir1.1, 1.2, and 1.3. Compared with other channels, Kir7.1 exhibits small unitary conductance and low dependence on external potassium. Kir7.1 channels also show a phosphatidylinositol 4,5-bisphosphate (PIP2) dependence for opening. Accordingly, retinopathy-associated Kir7.1 mutations mapped at the binding site for PIP2 resulted in channel gating defects leading to channelopathies such as snowflake vitreoretinal degeneration and Leber congenital amaurosis in blind patients. Lately, this channel's role in energy homeostasis was reported due to the direct interaction with the melanocortin type 4 receptor (MC4R) in the hypothalamus. As this channel seems to play a multipronged role in potassium homeostasis and neuronal excitability, we will discuss what is predicted from a structural viewpoint and its possible implications for hunger control.
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Affiliation(s)
- Ciria C Hernandez
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States
| | - Luis E Gimenez
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States
| | - Naima S Dahir
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States
| | - Alys Peisley
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States
| | - Roger D Cone
- Life Sciences Institute, University of Michigan, Ann Arbor, Michigan, United States
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan, United States
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4
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Pandey Y, Dondapati SK, Wüstenhagen D, Kubick S. Cell-Free Synthesis and Electrophysiological Analysis of Multipass Voltage-Gated Ion Channels Tethered in Microsomal Membranes. ADVANCES IN BIOCHEMICAL ENGINEERING/BIOTECHNOLOGY 2023; 186:103-120. [PMID: 37640910 DOI: 10.1007/10_2023_228] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/31/2023]
Abstract
Cell-free protein synthesis (CFPS) has emerged as a powerful tool for the rapid synthesis and analysis of various structurally and functionally distinct proteins. These include 'difficult-to-express' membrane proteins such as large multipass ion channel receptors. Owing to their membrane localization, eukaryotic CFPS supplemented with endoplasmic reticulum (ER)-derived microsomal vesicles has proven to be an efficient system for the synthesis of functional membrane proteins. Here we demonstrate the applicability of the eukaryotic cell-free systems based on lysates from the mammalian Chinese Hamster Ovary (CHO) and insect Spodoptera frugiperda (Sf21) cells. We demonstrate the efficiency of the systems in the de novo cell-free synthesis of the human cardiac ion channels: ether-a-go-go potassium channel (hERG) KV11.1 and the voltage-gated sodium channel hNaV1.5.
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Affiliation(s)
- Yogesh Pandey
- Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Potsdam, Germany
- Institut für Biochemie und Biologie, University of Potsdam, Potsdam, OT Golm, Germany
| | - Srujan Kumar Dondapati
- Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Potsdam, Germany.
| | - Doreen Wüstenhagen
- Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Potsdam, Germany
| | - Stefan Kubick
- Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Potsdam, Germany
- Institute of Biotechnology, Technische Universität Berlin, Berlin, Germany
- Institute of Chemistry and Biochemistry-Biochemistry, Freie Universität Berlin, Berlin, Germany
- Faculty of Health Science, Joint Faculty of the Brandenburg University of Technology Cottbus-Senftenberg, The Brandenburg Medical School Theodor Fontane and the University of Potsdam, Potsdam, Germany
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5
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Malik C, Ghosh S. A mutation in the S6 segment of the KvAP channel changes the secondary structure and alters ion channel activity in a lipid bilayer membrane. Amino Acids 2022; 54:1461-1475. [PMID: 35896819 DOI: 10.1007/s00726-022-03188-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Accepted: 07/04/2022] [Indexed: 11/01/2022]
Abstract
The peptide segment S6 is known to form the inner lining of the voltage-gated K+ channel KvAP (potassium channel of archaea-bacterium, Aeropyrum pernix). In our previous work, it has been demonstrated that S6 itself can form an ion channel on a bilayer lipid membrane (BLM). In the present work, the role of a specific amino acid sequence 'LIG' in determining the secondary structure of S6 has been investigated. For this purpose, 22-residue synthetic peptides named S6-Wild (S6W) and S6-Mutant (S6M) were used. Sequences of these peptides are similar except that the two amino acids isoleucine and glycine of the wild peptide interchanged in the mutant peptide. Channel forming capabilities of both the peptides were checked electro-physiologically on BLM composed of DPhPC and cholesterol. Bilayer electrophysiological experiments showed that the conductance of S6M is higher than that of S6W. Significant differences in the current versus voltage (I-V) plot, open probability, and gating characteristics were observed. Interestingly, two sub-types of channels, S6M Type 1 and Type 2, were identified in S6M differing in conductances and open probability patterns. Circular dichroism (CD) spectroscopy indicated that the secondary structures of the two peptides are different in phosphatidyl choline/asolectin liposomes and 1% SDS detergent. Reduced helicity of S6M was also noticed in membrane mimetic liposomes and 1% SDS detergent micelles. These results are interpreted in view of the difference in hydrophobicity of the two amino acids, isoleucine and glycine. It is concluded that the 'LIG' stretch regulates the structure and pore-forming ability of the S6 peptide.
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Affiliation(s)
- Chetan Malik
- Department of Biophysics, University of Delhi South Campus, Benito Juarez Road, New Delhi, 110021, India
| | - Subhendu Ghosh
- Department of Biophysics, University of Delhi South Campus, Benito Juarez Road, New Delhi, 110021, India.
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Catacuzzeno L, Franciolini F. The 70-year search for the voltage sensing mechanism of ion channels. J Physiol 2022; 600:3227-3247. [PMID: 35665931 PMCID: PMC9545881 DOI: 10.1113/jp282780] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2022] [Accepted: 04/25/2022] [Indexed: 01/10/2023] Open
Abstract
This retrospective on the voltage‐sensing mechanisms and gating models of ion channels begins in 1952 with the charged gating particles postulated by Hodgkin and Huxley, viewed as charges moving across the membrane and controlling its permeability to Na+ and K+ ions. Hodgkin and Huxley postulated that their movement should generate small and fast capacitive currents, which were recorded 20 years later as gating currents. In the early 1980s, several voltage‐dependent channels were cloned and found to share a common architecture: four homologous domains or subunits, each displaying six transmembrane α‐helical segments, with the fourth segment (S4) displaying four to seven positive charges invariably separated by two non‐charged residues. This immediately suggested that this segment was serving as the voltage sensor of the channel (the molecular counterpart of the charged gating particle postulated by Hodgkin and Huxley) and led to the development of the sliding helix model. Twenty years later, the X‐ray crystallographic structures of many voltage‐dependent channels allowed investigation of their gating by molecular dynamics. Further understanding of how channels gate will benefit greatly from the acquisition of high‐resolution structures of each of their relevant functional or structural states. This will allow the application of molecular dynamics and other approaches. It will also be key to investigate the energetics of channel gating, permitting an understanding of the physical and molecular determinants of gating. The use of multiscale hierarchical approaches might finally prove to be a rewarding strategy to overcome the limits of the various single approaches to the study of channel gating.
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Affiliation(s)
- Luigi Catacuzzeno
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Italy
| | - Fabio Franciolini
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Italy
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7
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Kacher YG, Karlova MG, Glukhov GS, Zhang H, Zaklyazminskaya EV, Loussouarn G, Sokolova OS. The Integrative Approach to Study of the Structure and Functions of Cardiac Voltage-Dependent Ion Channels. CRYSTALLOGR REP+ 2021. [DOI: 10.1134/s1063774521050072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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CNG channel structure, function, and gating: a tale of conformational flexibility. Pflugers Arch 2021; 473:1423-1435. [PMID: 34357442 DOI: 10.1007/s00424-021-02610-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Revised: 03/10/2021] [Accepted: 03/11/2021] [Indexed: 10/20/2022]
Abstract
Cyclic nucleotide-gated (CNG) channels are key to the signal transduction machinery of certain sensory modalities both in vertebrate and invertebrate organisms. They translate a chemical change in cyclic nucleotide concentration into an electrical signal that can spread through sensory cells. Despite CNG and voltage-gated potassium channels sharing a remarkable amino acid sequence homology and basic architectural plan, their functional properties are dramatically different. While voltage-gated potassium channels are highly selective and require membrane depolarization to open, CNG channels have low ion selectivity and are not very sensitive to voltage. In the last few years, many high-resolution structures of intact CNG channels have been released. This wealth of new structural information has provided enormous progress toward the understanding of the molecular mechanisms and driving forces underpinning CNG channel activation. In this review, we report on the current understanding and controversies surrounding the gating mechanism in CNG channels, as well as the deep intertwining existing between gating, the ion permeation process, and its modulation by membrane voltage. While the existence of this powerful coupling was recognized many decades ago, its direct structural demonstration, and ties to the CNG channel inherent pore flexibility, is a recent achievement.
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9
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Structure of membrane diacylglycerol kinase in lipid bilayers. Commun Biol 2021; 4:282. [PMID: 33674677 PMCID: PMC7935881 DOI: 10.1038/s42003-021-01802-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Accepted: 02/05/2021] [Indexed: 12/17/2022] Open
Abstract
Diacylglycerol kinase (DgkA) is a small integral membrane protein, responsible for the ATP-dependent phosphorylation of diacylglycerol to phosphatidic acid. Its structures reported in previous studies, determined in detergent micelles by solution NMR and in monoolein cubic phase by X-ray crystallography, differ significantly. These differences point to the need to validate these detergent-based structures in phospholipid bilayers. Here, we present a well-defined homo-trimeric structure of DgkA in phospholipid bilayers determined by magic angle spinning solid-state NMR (ssNMR) spectroscopy, using an approach combining intra-, inter-molecular paramagnetic relaxation enhancement (PRE)-derived distance restraints and CS-Rosetta calculations. The DgkA structure determined in lipid bilayers is different from the solution NMR structure. In addition, although ssNMR structure of DgkA shows a global folding similar to that determined by X-ray, these two structures differ in monomeric symmetry and dynamics. A comparative analysis of DgkA structures determined in three different detergent/lipid environments provides a meaningful demonstration of the influence of membrane mimetic environments on the structure and dynamics of membrane proteins. Jianping Li et al. present the homo-trimeric structure of the small integral membrane protein diacylglycerol kinase (DgkA) in phospholipid bilayers determined by magic angle spinning solid-state NMR spectroscopy. They compare the structure with structures solved by solution NMR and X-ray crystallography and provide insights into the influence of membrane mimetic environments on membrane proteins.
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10
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Schmidt M, Schroeder I, Bauer D, Thiel G, Hamacher K. Inferring functional units in ion channel pores via relative entropy. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2021; 50:37-57. [PMID: 33523249 PMCID: PMC7872957 DOI: 10.1007/s00249-020-01480-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Revised: 10/11/2020] [Accepted: 11/09/2020] [Indexed: 11/25/2022]
Abstract
Coarse-grained protein models approximate the first-principle physical potentials. Among those modeling approaches, the relative entropy framework yields promising and physically sound results, in which a mapping from the target protein structure and dynamics to a model is defined and subsequently adjusted by an entropy minimization of the model parameters. Minimization of the relative entropy is equivalent to maximization of the likelihood of reproduction of (configurational ensemble) observations by the model. In this study, we extend the relative entropy minimization procedure beyond parameter fitting by a second optimization level, which identifies the optimal mapping to a (dimension-reduced) topology. We consider anisotropic network models of a diverse set of ion channels and assess our findings by comparison to experimental results.
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Affiliation(s)
- Michael Schmidt
- Department of Physics, TU Darmstadt, Karolinenpl. 5, 64289 Darmstadt, Germany
| | - Indra Schroeder
- Department of Biology, TU Darmstadt, Schnittspahnstr. 10, 64287 Darmstadt, Germany
| | - Daniel Bauer
- Department of Biology, TU Darmstadt, Schnittspahnstr. 10, 64287 Darmstadt, Germany
| | - Gerhard Thiel
- Department of Biology, TU Darmstadt, Schnittspahnstr. 10, 64287 Darmstadt, Germany
| | - Kay Hamacher
- Department of Physics, Department of Biology, Department of Computer Science, TU Darmstadt, Schnittspahnstr. 10, 64287 Darmstadt, Germany
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11
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Das A, Raghuraman H. Conformational heterogeneity of the voltage sensor loop of KvAP in micelles and membranes: A fluorescence approach. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2021; 1863:183568. [PMID: 33529577 DOI: 10.1016/j.bbamem.2021.183568] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 01/06/2021] [Accepted: 01/27/2021] [Indexed: 12/14/2022]
Abstract
KvAP is a tetrameric voltage-gated potassium channel that is composed of a pore domain and a voltage-sensing domain (VSD). The VSD is crucial for sensing transmembrane potential and gating. At 0 mV, the VSD adopts an activated conformation in both n-octylglucoside (OG) micelles and phospholipid membranes. Importantly, gating-modifier toxins that bind at S3b-S4 loop of KvAP-VSD exhibit pronounced differences in binding affinity in these membrane-mimetic systems. However, the conformational heterogeneity of this functionally-important sensor loop in membrane mimetics is poorly understood, and is the focus of this work. In this paper, we establish, using intrinsic fluorescence of the uniquely positioned W70 in KvAP-VSD and environment-sensitive NBD (7-nitrobenz-2-oxa-1,3-diazol-4-yl-ethylenediamine) fluorescence of the labelled S3b-S4 loop, that the surface charge of the membrane does not significantly affect the topology and structural dynamics of the sensor loop in membranes. Importantly, the dynamic variability of the sensor loop is preserved in both zwitterionic (POPC) and anionic (POPC/POPG) membranes. Further, the lifetime distribution analysis for the NBD-labelled residues by maximum entropy method (MEM) demonstrates that, in contrast to micelles, the membrane environment not only reduces the relative discrete population of sensor loop conformations, but also broadens the lifetime distribution peaks. Overall, our results strongly suggest that the conformational heterogeneity of the sensor loop is significantly altered in membranes and this correlates well with its environmental heterogeneity. This constitutes the first report demonstrating that MEM-lifetime distribution could be a powerful tool to distinguish changes in conformational heterogeneity in potassium channels with similar architecture and topology.
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Affiliation(s)
- Anindita Das
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India
| | - H Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India.
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12
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Zecchi KA, Heimburg T. Non-linear Conductance, Rectification, and Mechanosensitive Channel Formation of Lipid Membranes. Front Cell Dev Biol 2021; 8:592520. [PMID: 33575253 PMCID: PMC7870788 DOI: 10.3389/fcell.2020.592520] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Accepted: 12/10/2020] [Indexed: 01/04/2023] Open
Abstract
There is mounting evidence that lipid bilayers display conductive properties. However, when interpreting the electrical response of biological membranes to voltage changes, they are commonly considered as inert insulators. Lipid bilayers under voltage-clamp conditions display current traces with discrete conduction-steps, which are indistinguishable from those attributed to the presence of protein channels. In current-voltage (I-V) plots they may also display outward rectification, i.e., voltage-gating. Surprisingly, this has even been observed in chemically symmetric lipid bilayers. Here, we investigate this phenomenon using a theoretical framework that models the electrostrictive effect of voltage on lipid membranes in the presence of a spontaneous polarization, which can be recognized by a voltage offset in electrical measurements. It can arise from an asymmetry of the membrane, for example from a non-zero spontaneous curvature of the membrane. This curvature can be caused by voltage via the flexoelectric effect, or by hydrostatic pressure differences across the membrane. Here, we describe I-V relations for lipid membranes formed at the tip of patch pipettes situated close to an aqueous surface. We measured at different depths relative to air/water surface, resulting in different pressure gradients across the membrane. Both linear and non-linear I-V profiles were observed. Non-linear conduction consistently takes the form of outward rectified currents. We explain the conductance properties by two mechanisms: One leak current with constant conductance without pores, and a second process that is due to voltage-gated pore opening correlating with the appearance of channel-like conduction steps. In some instances, these non-linear I-V relations display a voltage regime in which dI/dV is negative. This has also been previously observed in the presence of sodium channels. Experiments at different depths reveal channel formation that depends on pressure gradients. Therefore, we find that the channels in the lipid membrane are both voltage-gated and mechanosensitive. We also report measurements on black lipid membranes that also display rectification. In contrast to the patch experiments they are always symmetric and do not display a voltage offset.
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Affiliation(s)
- Karis Amata Zecchi
- Membrane Biophysics Group, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
| | - Thomas Heimburg
- Membrane Biophysics Group, Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
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13
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Zhou Y, Assmann SM, Jegla T. External Cd2+ and protons activate the hyperpolarization-gated K+ channel KAT1 at the voltage sensor. J Gen Physiol 2021; 153:211573. [PMID: 33275659 PMCID: PMC7721907 DOI: 10.1085/jgp.202012647] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2020] [Revised: 10/21/2020] [Accepted: 11/10/2020] [Indexed: 11/20/2022] Open
Abstract
The functionally diverse cyclic nucleotide binding domain (CNBD) superfamily of cation channels contains both depolarization-gated (e.g., metazoan EAG family K+ channels) and hyperpolarization-gated channels (e.g., metazoan HCN pacemaker cation channels and the plant K+ channel KAT1). In both types of CNBD channels, the S4 transmembrane helix of the voltage sensor domain (VSD) moves outward in response to depolarization. This movement opens depolarization-gated channels and closes hyperpolarization-gated channels. External divalent cations and protons prevent or slow movement of S4 by binding to a cluster of acidic charges on the S2 and S3 transmembrane domains of the VSD and therefore inhibit activation of EAG family channels. However, a similar divalent ion/proton binding pocket has not been described for hyperpolarization-gated CNBD family channels. We examined the effects of external Cd2+ and protons on Arabidopsisthaliana KAT1 expressed in Xenopus oocytes and found that these ions strongly potentiate voltage activation. Cd2+ at 300 µM depolarizes the V50 of KAT1 by 150 mV, while acidification from pH 7.0 to 4.0 depolarizes the V50 by 49 mV. Regulation of KAT1 by Cd2+ is state dependent and consistent with Cd2+ binding to an S4-down state of the VSD. Neutralization of a conserved acidic charge in the S2 helix in KAT1 (D95N) eliminates Cd2+ and pH sensitivity. Conversely, introduction of acidic residues into KAT1 at additional S2 and S3 cluster positions that are charged in EAG family channels (N99D and Q149E in KAT1) decreases Cd2+ sensitivity and increases proton potentiation. These results suggest that KAT1, and presumably other hyperpolarization-gated plant CNBD channels, can open from an S4-down VSD conformation homologous to the divalent/proton-inhibited conformation of EAG family K+ channels.
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Affiliation(s)
- Yunqing Zhou
- Department of Biology, Penn State University, University Park, PA.,Huck Institutes of the Life Sciences, Penn State University, University Park, PA
| | - Sarah M Assmann
- Department of Biology, Penn State University, University Park, PA
| | - Timothy Jegla
- Department of Biology, Penn State University, University Park, PA.,Huck Institutes of the Life Sciences, Penn State University, University Park, PA
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14
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Abstract
Potassium channels are present in every living cell and essential to setting up a stable, non-zero transmembrane electrostatic potential which manifests the off-equilibrium livelihood of the cell. They are involved in other cellular activities and regulation, such as the controlled release of hormones, the activation of T-cells for immune response, the firing of action potential in muscle cells and neurons, etc. Pharmacological reagents targeting potassium channels are important for treating various human diseases linked to dysfunction of the channels. High-resolution structures of these channels are very useful tools for delineating the detailed chemical basis underlying channel functions and for structure-based design and optimization of their pharmacological and pharmaceutical agents. Structural studies of potassium channels have revolutionized biophysical understandings of key concepts in the field - ion selectivity, conduction, channel gating, and modulation, making them multi-modality targets of pharmacological regulation. In this chapter, I will select a few high-resolution structures to illustrate key structural insights, proposed allostery behind channel functions, disagreements still open to debate, and channel-lipid interactions and co-evolution. The known structural consensus allows the inference of conserved molecular mechanisms shared among subfamilies of K+ channels and makes it possible to develop channel-specific pharmaceutical agents.
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Affiliation(s)
- Qiu-Xing Jiang
- Laboratory of Molecular Physiology and Biophysics and the Cryo-EM Center, Hauptmann-Woodward Medical Research Institute, Buffalo, NY, USA.
- Department of Medicinal Chemistry, University of Florida, Gainesville, FL, USA.
- Departments of Materials Design and Invention and Physiology and Biophysics, University of Buffalo (SUNY), Buffalo, NY, USA.
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15
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The membrane protein KCNQ1 potassium ion channel: Functional diversity and current structural insights. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2019; 1862:183148. [PMID: 31825788 DOI: 10.1016/j.bbamem.2019.183148] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2019] [Revised: 11/15/2019] [Accepted: 12/04/2019] [Indexed: 12/19/2022]
Abstract
BACKGROUND Ion channels play crucial roles in cellular biology, physiology, and communication including sensory perception. Voltage-gated potassium (Kv) channels execute their function by sensor activation, pore-coupling, and pore opening leading to K+ conductance. SCOPE OF REVIEW This review focuses on a voltage-gated K+ ion channel KCNQ1 (Kv 7.1). Firstly, discussing its positioning in the human ion chanome, and the role of KCNQ1 in the multitude of cellular processes. Next, we discuss the overall channel architecture and current structural insights on KCNQ1. Finally, the gating mechanism involving members of the KCNE family and its interaction with non-KCNE partners. MAJOR CONCLUSIONS KCNQ1 executes its important physiological functions via interacting with KCNE1 and non-KCNE1 proteins/molecules: calmodulin, PIP2, PKA. Although, KCNQ1 has been studied in great detail, several aspects of the channel structure and function still remain unexplored. This review emphasizes the structural and biophysical studies of KCNQ1, its interaction with KCNE1 and non-KCNE1 proteins and focuses on several seminal findings showing the role of VSD and the pore domain in the channel activation and gating properties. GENERAL SIGNIFICANCE KCNQ1 mutations can result in channel defects and lead to several diseases including atrial fibrillation and long QT syndrome. Therefore, a thorough structure-function understanding of this channel complex is essential to understand its role in both normal and disease biology. Moreover, unraveling the molecular mechanisms underlying the regulation of this channel complex will help to find therapeutic strategies for several diseases.
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16
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Tao X, MacKinnon R. Cryo-EM structure of the KvAP channel reveals a non-domain-swapped voltage sensor topology. eLife 2019; 8:e52164. [PMID: 31755864 PMCID: PMC6882556 DOI: 10.7554/elife.52164] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2019] [Accepted: 11/20/2019] [Indexed: 11/13/2022] Open
Abstract
Conductance in voltage-gated ion channels is regulated by membrane voltage through structural domains known as voltage sensors. A single structural class of voltage sensor domain exists, but two different modes of voltage sensor attachment to the pore occur in nature: domain-swapped and non-domain-swapped. Since the more thoroughly studied Kv1-7, Nav and Cav channels have domain-swapped voltage sensors, much less is known about non-domain-swapped voltage-gated ion channels. In this paper, using cryo-EM, we show that KvAP from Aeropyrum pernix has non-domain-swapped voltage sensors as well as other unusual features. The new structure, together with previous functional data, suggests that KvAP and the Shaker channel, to which KvAP is most often compared, probably undergo rather different voltage-dependent conformational changes when they open.
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Affiliation(s)
- Xiao Tao
- Laboratory of Molecular Neurobiology and BiophysicsThe Rockefeller University, Howard Hughes Medical InstituteNew YorkUnited States
| | - Roderick MacKinnon
- Laboratory of Molecular Neurobiology and BiophysicsThe Rockefeller University, Howard Hughes Medical InstituteNew YorkUnited States
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17
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Torbeev V. Illuminating Voltage Sensor Paddling in Different Membrane Milieu. Biophys J 2019; 118:781-782. [PMID: 31623888 DOI: 10.1016/j.bpj.2019.09.032] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2019] [Accepted: 09/25/2019] [Indexed: 01/31/2023] Open
Affiliation(s)
- Vladimir Torbeev
- Institut de Science et d'Ingénierie Supramoléculaires, International Center for Frontier Research in Chemistry, University of Strasbourg and CNRS (UMR 7006), Strasbourg, France.
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18
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Hu B, Zheng X, Wang Y, Wang J, Zhang F. Computational Approaches for Elucidating Protein-Protein Interactions in Cation Channel Signaling. Curr Drug Targets 2019; 21:179-192. [PMID: 31490747 DOI: 10.2174/1389450120666190906154412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 08/10/2019] [Accepted: 08/23/2019] [Indexed: 11/22/2022]
Abstract
BACKGROUND The lipid bilayer of the plasma membrane is impermeable to ions, yet changes in the flux of ions across the cell membrane are critical regulatory events in cells. Because of their regulatory roles in a range of physiological processes, such as electrical signaling in muscles and neurons, to name a few, these proteins are one of the most important drug targets. OBJECTIVE This review mainly focused on the computational approaches for elucidating proteinprotein interactions in cation channel signaling. DISCUSSION Due to continuously advanced facilities and technologies in computer sciences, the physical contacts of macromolecules of channel structures have been virtually visualized. Indeed, techniques like protein-protein docking, homology modeling, and molecular dynamics simulation are valuable tools for predicting the protein complex and refining channels with unreleased structures. Undoubtedly, these approaches will greatly expand the cation channel signaling research, thereby speeding up structure-based drug design and discovery. CONCLUSION We introduced a series of valuable computational tools for elucidating protein-protein interactions in cation channel signaling, including molecular graphics, protein-protein docking, homology modeling, and molecular dynamics simulation.
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Affiliation(s)
- Baichun Hu
- Key Laboratory of Structure-Based Drug Design & Discovery of Ministry of Education, Shenyang Pharmaceutical University, Shenyang 110016, China.,School of Pharmaceutical Engineering, Shenyang Pharmaceutical University, Shenyang, China
| | - Xiaoming Zheng
- Key Laboratory of Structure-Based Drug Design & Discovery of Ministry of Education, Shenyang Pharmaceutical University, Shenyang 110016, China.,School of Pharmaceutical Engineering, Shenyang Pharmaceutical University, Shenyang, China
| | - Ying Wang
- Key Laboratory of Structure-Based Drug Design & Discovery of Ministry of Education, Shenyang Pharmaceutical University, Shenyang 110016, China.,School of Pharmaceutical Engineering, Shenyang Pharmaceutical University, Shenyang, China.,Wuya College of Innovation, Shenyang Pharmaceutical University, Shenyang, Liaoning, 110016, China.,School of Traditional Chinese Materia Medica, Shenyang Pharmaceutical University, Shenyang, 110016, China
| | - Jian Wang
- Key Laboratory of Structure-Based Drug Design & Discovery of Ministry of Education, Shenyang Pharmaceutical University, Shenyang 110016, China.,School of Pharmaceutical Engineering, Shenyang Pharmaceutical University, Shenyang, China
| | - Fengjiao Zhang
- Wuya College of Innovation, Shenyang Pharmaceutical University, Shenyang, Liaoning, 110016, China
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19
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Das A, Chatterjee S, Raghuraman H. Structural Dynamics of the Paddle Motif Loop in the Activated Conformation of KvAP Voltage Sensor. Biophys J 2019; 118:873-884. [PMID: 31547975 DOI: 10.1016/j.bpj.2019.08.017] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2019] [Revised: 07/31/2019] [Accepted: 08/06/2019] [Indexed: 02/07/2023] Open
Abstract
Voltage-dependent potassium (Kv) channels play a fundamental role in neuronal and cardiac excitability and are potential therapeutic targets. They assemble as tetramers with a centrally located pore domain surrounded by a voltage-sensing domain (VSD), which is critical for sensing transmembrane potential and subsequent gating. Although the sensor is supposed to be in "Up" conformation in both n-octylglucoside (OG) micelles and phospholipid membranes in the absence of membrane potential, toxins that bind VSD and modulate the gating behavior of Kv channels exhibit dramatic affinity differences in these membrane-mimetic systems. In this study, we have monitored the structural dynamics of the S3b-S4 loop of the paddle motif in activated conformation of KvAP-VSD by site-directed fluorescence approaches, using the environment-sensitive fluorescent probe 7-nitrobenz-2-oxa-1,3-diazol-4-yl-ethylenediamine (NBD). Emission maximum of NBD-labeled loop region of KvAP-VSD (residues 110-117) suggests a significant change in the polarity of local environment in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) membranes compared to OG micelles. This indicates that S3b-S4 loop residues might be partitioning to membrane interface, which is supported by an overall increased mean fluorescence lifetimes and significantly reduced water accessibility in membranes. Further, the magnitude of red edge excitation shift (REES) supports the presence of restricted/bound water molecules in the loop region of the VSD in micelles and membranes. Quantitative analysis of REES data using Gaussian probability distribution function clearly indicates that the sensor loop has fewer discrete equilibrium conformational states when reconstituted in membranes. Interestingly, this reduced molecular heterogeneity is consistent with the site-specific NBD polarization results, which suggest that the membrane environment offers a relaxed/dynamic organization for most of the S3b-S4 loop residues of the sensor. Overall, our results are relevant for understanding toxin-VSD interaction and gating mechanisms of Kv channels in membranes.
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Affiliation(s)
- Anindita Das
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India
| | - Satyaki Chatterjee
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India
| | - H Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, 1/AF Bidhannagar, Kolkata, India.
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20
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Tronin AY, Maciunas LJ, Grasty KC, Loll PJ, Ambaye HA, Parizzi AA, Lauter V, Geragotelis AD, Freites JA, Tobias DJ, Blasie JK. Voltage-Dependent Profile Structures of a Kv-Channel via Time-Resolved Neutron Interferometry. Biophys J 2019; 117:751-766. [PMID: 31378315 PMCID: PMC6712512 DOI: 10.1016/j.bpj.2019.07.011] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Revised: 06/27/2019] [Accepted: 07/09/2019] [Indexed: 10/26/2022] Open
Abstract
Available experimental techniques cannot determine high-resolution three-dimensional structures of membrane proteins under a transmembrane voltage. Hence, the mechanism by which voltage-gated cation channels couple conformational changes within the four voltage sensor domains, in response to either depolarizing or polarizing transmembrane voltages, to opening or closing of the pore domain's ion channel remains unresolved. Single-membrane specimens, composed of a phospholipid bilayer containing a vectorially oriented voltage-gated K+ channel protein at high in-plane density tethered to the surface of an inorganic multilayer substrate, were developed to allow the application of transmembrane voltages in an electrochemical cell. Time-resolved neutron reflectivity experiments, enhanced by interferometry enabled by the multilayer substrate, were employed to provide directly the low-resolution profile structures of the membrane containing the vectorially oriented voltage-gated K+ channel for the activated, open and deactivated, closed states of the channel under depolarizing and hyperpolarizing transmembrane voltages applied cyclically. The profile structures of these single membranes were dominated by the voltage-gated K+ channel protein because of the high in-plane density. Importantly, the use of neutrons allowed the determination of the voltage-dependent changes in both the profile structure of the membrane and the distribution of water within the profile structure. These two key experimental results were then compared to those predicted by three computational modeling approaches for the activated, open and deactivated, closed states of three different voltage-gated K+ channels in hydrated phospholipid bilayer membrane environments. Of the three modeling approaches investigated, only one state-of-the-art molecular dynamics simulation that directly predicted the response of a voltage-gated K+ channel within a phospholipid bilayer membrane to applied transmembrane voltages by utilizing very long trajectories was found to be in agreement with the two key experimental results provided by the time-resolved neutron interferometry experiments.
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Affiliation(s)
- Andrey Y Tronin
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania
| | - Lina J Maciunas
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Kimberly C Grasty
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Patrick J Loll
- Department of Biochemistry and Molecular Biology, Drexel University College of Medicine, Philadelphia, Pennsylvania
| | - Haile A Ambaye
- Neutron Scattering Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - Andre A Parizzi
- Neutron Scattering Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - Valeria Lauter
- Neutron Scattering Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | | | - J Alfredo Freites
- Department of Chemistry, University of California Irvine, Irvine, California
| | - Douglas J Tobias
- Department of Chemistry, University of California Irvine, Irvine, California
| | - J Kent Blasie
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania.
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21
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Chen H, Pan J, Gandhi DM, Dockendorff C, Cui Q, Chanda B, Henzler-Wildman KA. NMR Structural Analysis of Isolated Shaker Voltage-Sensing Domain in LPPG Micelles. Biophys J 2019; 117:388-398. [PMID: 31301804 DOI: 10.1016/j.bpj.2019.06.020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2019] [Accepted: 06/20/2019] [Indexed: 11/25/2022] Open
Abstract
The voltage-sensing domain (VSD) is a conserved structural module that regulates the gating of voltage-dependent ion channels in response to a change in membrane potential. Although the structures of many VSD-containing ion channels are now available, our understanding of the structural dynamics associated with gating transitions remains limited. To probe dynamics with site-specific resolution, we utilized NMR spectroscopy to characterize the VSD derived from Shaker potassium channel in 1-palmitoyl-2-hydroxy-sn-glycero-3-phospho-(1'-rac-glycerol) (LPPG) micelles. The backbone dihedral angles predicted based on secondary chemical shifts using torsion angle likeliness obtained from shift (TALOS+) showed that the Shaker-VSD shares many structural features with the homologous Kv1.2/2.1 chimera, including a transition from α-helix to 310 helix in the C-terminal portion of the fourth transmembrane helix. Nevertheless, there are clear differences between the Shaker-VSD and Kv1.2/2.1 chimera in the S2-S3 linker and S3 transmembrane region, where the organization of secondary structure elements in Shaker-VSD appears to more closely resemble the KvAP-VSD. Comparison of microsecond-long molecular dynamics simulations of Kv 1.2-VSD in LPPG micelles and a 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) bilayer showed that LPPG micelles do not induce significant structural distortion in the isolated voltage sensor. To assess the integrity of the tertiary fold, we directly probed the binding of BrMT analog 2-[2-({[3-(2-amino-ethyl)-6-bromo-1H-indol-2-yl]methoxy}k7methyl)-6-bromo-1H-indol-3-yl]ethan-1-amine (BrET), a gating modifier toxin, and identified the location of the putative binding site. Our results suggest that the Shaker-VSD in LPPG micelles is in a native-like fold and is likely to provide valuable insights into the dynamics of voltage-gating and its regulation.
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Affiliation(s)
- Hongbo Chen
- Graduate Program in Biophysics, Madison, Wisconsin; Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin
| | - Junkun Pan
- Department of Neuroscience, Madison, Wisconsin; Department of Biomolecular Chemistry, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin
| | - Disha M Gandhi
- Departments of Chemistry, Marquette University, Milwaukee, Wisconsin
| | - Chris Dockendorff
- Departments of Chemistry, Marquette University, Milwaukee, Wisconsin
| | - Qiang Cui
- Departments of Chemistry, Physics, Biomedical Engineering, Boston University, Boston, Massachusetts
| | - Baron Chanda
- Graduate Program in Biophysics, Madison, Wisconsin; Department of Neuroscience, Madison, Wisconsin; Department of Biomolecular Chemistry, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin.
| | - Katherine A Henzler-Wildman
- Graduate Program in Biophysics, Madison, Wisconsin; Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin.
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22
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Li H, Xu J, Shen ZS, Wang GM, Tang M, Du XR, Lv YT, Wang JJ, Zhang FF, Qi Z, Zhang Z, Sokabe M, Tang QY. The neuropeptide GsMTx4 inhibits a mechanosensitive BK channel through the voltage-dependent modification specific to mechano-gating. J Biol Chem 2019; 294:11892-11909. [PMID: 31201274 DOI: 10.1074/jbc.ra118.005511] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2018] [Revised: 06/06/2019] [Indexed: 12/12/2022] Open
Abstract
The cardiac mechanosensitive BK (Slo1) channels are gated by Ca2+, voltage, and membrane stretch. The neuropeptide GsMTx4 is a selective inhibitor of mechanosensitive (MS) channels. It has been reported to suppress stretch-induced cardiac fibrillation in the heart, but the mechanism underlying the specificity and even the targeting channel(s) in the heart remain elusive. Here, we report that GsMTx4 inhibits a stretch-activated BK channel (SAKcaC) in the heart through a modulation specific to mechano-gating. We show that membrane stretching increases while GsMTx4 decreases the open probability (P o) of SAKcaC. These effects were mostly abolished by the deletion of the STREX axis-regulated (STREX) exon located between RCK1 and RCK2 domains in BK channels. Single-channel kinetics analysis revealed that membrane stretch activates SAKcaC by prolonging the open-time duration (τO) and shortening the closed-time constant (τC). In contrast, GsMTx4 reversed the effects of membrane stretch, suggesting that GsMTx4 inhibits SAKcaC activity by interfering with mechano-gating of the channel. Moreover, GsMTx4 exerted stronger efficacy on SAKcaC under membrane-hyperpolarized/resting conditions. Molecular dynamics simulation study revealed that GsMTx4 appeared to have the ability to penetrate deeply within the bilayer, thus generating strong membrane deformation under the hyperpolarizing/resting conditions. Immunostaining results indicate that BK variants containing STREX are also expressed in mouse ventricular cardiomyocytes. Our results provide common mechanisms of peptide actions on MS channels and may give clues to therapeutic suppression of cardiac arrhythmias caused by excitatory currents through MS channels under hyper-mechanical stress in the heart.
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Affiliation(s)
- Hui Li
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou, Jiangsu Province 221004, China
| | - Jie Xu
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou, Jiangsu Province 221004, China
| | - Zhong-Shan Shen
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou, Jiangsu Province 221004, China
| | - Guang-Ming Wang
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou, Jiangsu Province 221004, China
| | - Mingxi Tang
- Department of Pathology, Affiliated Hospital of Southwest Medical University, Luzhou, Sichuan Province 646000, China
| | - Xiang-Rong Du
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou, Jiangsu Province 221004, China
| | - Yan-Tian Lv
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou, Jiangsu Province 221004, China
| | - Jing-Jing Wang
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou, Jiangsu Province 221004, China
| | - Fei-Fei Zhang
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou, Jiangsu Province 221004, China
| | - Zhi Qi
- Department of Basic Medical Sciences, Medical College of Xiamen University, Xiamen 361102, China
| | - Zhe Zhang
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou, Jiangsu Province 221004, China
| | - Masahiro Sokabe
- ICORP Cell Mechanosensing, Japan Science and Technology Agency, Nagoya 466-8550, Japan .,Mechanobiology Laboratory, Nagoya University, Graduate School of Medicine, Nagoya 466-8550, Japan.,Department of Physiology, Nagoya University, Graduate School of Medicine, Nagoya 466-8550, Japan
| | - Qiong-Yao Tang
- Jiangsu Province Key Laboratory of Anesthesiology, Xuzhou Medical University, Xuzhou, Jiangsu Province 221004, China .,ICORP Cell Mechanosensing, Japan Science and Technology Agency, Nagoya 466-8550, Japan
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23
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McDonald SK, Levitz TS, Valiyaveetil FI. A Shared Mechanism for the Folding of Voltage-Gated K + Channels. Biochemistry 2019; 58:1660-1671. [PMID: 30793887 DOI: 10.1021/acs.biochem.9b00068] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
In this study, we probe the folding of KvAP, a voltage-gated K+ (Kv) channel. The KvAP channel, though of archaebacterial origin, is structurally and functionally similar to eukaryotic Kv channels. An advantage of the KvAP channel is that it can be folded in vitro from an extensively unfolded state and the folding can be controlled by temperature. We utilize these properties of the KvAP channel to separately study the membrane insertion and the tetramerization stages during folding. We use two quantitative assays: a Cys PEGylation assay to monitor membrane insertion and a cross-linking assay to monitor tetramerization. We show that during folding the KvAP polypeptide is rapidly inserted into the lipid bilayer with a "native-like" topology. We identify a segment at the C-terminus that is important for multimerization of the KvAP channel. We show that this C-terminal domain forms a dimer, which raises the possibility that the tetramerization of the KvAP channel proceeds through a dimer of dimers pathway. Our studies show that the in vitro folding of the KvAP channel mirrors aspects of the cellular assembly pathway for voltage-gated K+ channels and therefore suggest that evolutionarily distinct Kv channels share a common folding pathway. The pathway for the folding and assembly of a Kv channel is of central importance as defects in this pathway have been implicated in the etiology of several disease states. Our studies indicate that the KvAP channel provides an experimentally tractable system for elucidating the folding mechanism of Kv channels.
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Affiliation(s)
- Sarah K McDonald
- Program in Chemical Biology, Department of Physiology and Pharmacology , Oregon Health & Science University , 3181 Southwest Sam Jackson Park Road , Portland , Oregon 97239 , United States
| | - Talya S Levitz
- Program in Chemical Biology, Department of Physiology and Pharmacology , Oregon Health & Science University , 3181 Southwest Sam Jackson Park Road , Portland , Oregon 97239 , United States
| | - Francis I Valiyaveetil
- Program in Chemical Biology, Department of Physiology and Pharmacology , Oregon Health & Science University , 3181 Southwest Sam Jackson Park Road , Portland , Oregon 97239 , United States
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24
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Detergent-free solubilization of human Kv channels expressed in mammalian cells. Chem Phys Lipids 2019; 219:50-57. [DOI: 10.1016/j.chemphyslip.2019.01.013] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Revised: 01/30/2019] [Accepted: 01/30/2019] [Indexed: 12/13/2022]
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25
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Dixit G, Sahu ID, Reynolds WD, Wadsworth TM, Harding BD, Jaycox CK, Dabney-Smith C, Sanders CR, Lorigan GA. Probing the Dynamics and Structural Topology of the Reconstituted Human KCNQ1 Voltage Sensor Domain (Q1-VSD) in Lipid Bilayers Using Electron Paramagnetic Resonance Spectroscopy. Biochemistry 2019; 58:965-973. [PMID: 30620191 DOI: 10.1021/acs.biochem.8b01042] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
KCNQ1 (Kv7.1 or KvLQT1) is a potassium ion channel protein found in the heart, ear, and other tissues. In complex with the KCNE1 accessory protein, it plays a role during the repolarization phase of the cardiac action potential. Mutations in the channel have been associated with several diseases, including congenital deafness and long QT syndrome. Nuclear magnetic resonance (NMR) structural studies in detergent micelles and a cryo-electron microscopy structure of KCNQ1 from Xenopus laevis have shown that the voltage sensor domain (Q1-VSD) of the channel has four transmembrane helices, S1-S4, being overall structurally similar with other VSDs. In this study, we describe a reliable method for the reconstitution of Q1-VSD into (POPC/POPG) lipid bilayer vesicles. Site-directed spin labeling electron paramagnetic resonance spectroscopy was used to probe the structural dynamics and topology of several residues of Q1-VSD in POPC/POPG lipid bilayer vesicles. Several mutants were probed to determine their location and corresponding immersion depth (in angstroms) with respect to the membrane. The dynamics of the bilayer vesicles upon incorporation of Q1-VSD were studied using 31P solid-state NMR spectroscopy by varying the protein:lipid molar ratios confirming the interaction of the protein with the bilayer vesicles. Circular dichroism spectroscopic data showed that the α-helical content of Q1-VSD is higher for the protein reconstituted in vesicles than in previous studies using DPC detergent micelles. This study provides insight into the structural topology and dynamics of Q1-VSD reconstituted in a lipid bilayer environment, forming the basis for more advanced structural and functional studies.
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Affiliation(s)
- Gunjan Dixit
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
| | - Indra D Sahu
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
| | - Warren D Reynolds
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
| | - Tessa M Wadsworth
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
| | - Benjamin D Harding
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
| | - Colleen K Jaycox
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
| | - Carole Dabney-Smith
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
| | - Charles R Sanders
- Department of Biochemistry and Center for Structural Biology , Vanderbilt University , Nashville , Tennessee 37240 , United States
| | - Gary A Lorigan
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
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26
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Cholesterol-Dependent Gating Effects on Ion Channels. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1115:167-190. [PMID: 30649760 DOI: 10.1007/978-3-030-04278-3_8] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Biomembranes separate a live cell from its environment and keep it in an off-equilibrium, steady state. They contain both phospholipids and nonphospholipids, depending on whether there are phosphate groups in the headgroup regions. Cholesterol (CHOL) is one type of nonphospholipids, and one of the most abundant lipid molecules in humans. Its content in plasma membranes and intracellular membranes varies and is tightly regulated. Voltage-gated ion channels are universally present in every cell and are fairly diversified in the eukaryotic domain of life. Our lipid-dependent gating hypothesis postulates that the controlled switch of the voltage-sensor domains (VSDs) in a voltage-gated potassium (Kv) channel between the "down" and the "up" state (gating) is sensitive to the ratio of phospholipids:nonphospholipids in the annular layer around the channel. High CHOL content is found to exert strong inhibitory effects on Kv channels. Such effects have been observed in in vitro membranes, cultured cells, and animal models for cholesterol metabolic defects. Thermodynamic analysis of the CHOL-dependent gating suggests that the inhibitory effects of CHOL result from collective interactions between annular CHOL molecules and the channel, which appear to be a more generic principle behind the CHOL effects on other ion channels and transporters. We will review the recent progress in the CHOL-dependent gating of voltage-gated ion channels, discuss the current technical limitations, and then expand briefly the learned principles to other ion channels that are known to be sensitive to the CHOL-channel interactions.
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27
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DeMarco KR, Bekker S, Vorobyov I. Challenges and advances in atomistic simulations of potassium and sodium ion channel gating and permeation. J Physiol 2018; 597:679-698. [PMID: 30471114 DOI: 10.1113/jp277088] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2018] [Accepted: 10/15/2018] [Indexed: 12/19/2022] Open
Abstract
Ion channels are implicated in many essential physiological events such as electrical signal propagation and cellular communication. The advent of K+ and Na+ ion channel structure determination has facilitated numerous investigations of molecular determinants of their behaviour. At the same time, rapid development of computer hardware and molecular simulation methodologies has made computational studies of large biological molecules in all-atom representation tractable. The concurrent evolution of experimental structural biology with biomolecular computer modelling has yielded mechanistic details of fundamental processes unavailable through experiments alone, such as ion conduction and ion channel gating. This review is a short survey of the atomistic computational investigations of K+ and Na+ ion channels, focusing on KcsA and several voltage-gated channels from the KV and NaV families, which have garnered many successes and engendered several long-standing controversies regarding the nature of their structure-function relationship. We review the latest advancements and challenges facing the field of molecular modelling and simulation regarding the structural and energetic determinants of ion channel function and their agreement with experimental observations.
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Affiliation(s)
- Kevin R DeMarco
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA, USA.,Department of Pharmacology, School of Medicine, University of California, Davis, CA, USA
| | - Slava Bekker
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA, USA.,Chemistry Department, American River College, Sacramento, CA, USA
| | - Igor Vorobyov
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA, USA.,Department of Pharmacology, School of Medicine, University of California, Davis, CA, USA
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28
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Jegla T, Busey G, Assmann SM. Evolution and Structural Characteristics of Plant Voltage-Gated K + Channels. THE PLANT CELL 2018; 30:2898-2909. [PMID: 30389753 PMCID: PMC6354262 DOI: 10.1105/tpc.18.00523] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2018] [Revised: 10/09/2018] [Accepted: 10/30/2018] [Indexed: 05/18/2023]
Abstract
Plant voltage-gated K+ channels have been referred to as "plant Shakers" in reference to animal Shaker channels, the first K+ channels identified. Recent advances in our knowledge of K+ channel evolution and structure have significantly deepened the divide between these plant and animal K+ channels, suggesting that it is time to completely retire the "plant Shaker" designation. Evolutionary genomics reveals that plant voltage-gated K+ channels and metazoan Shakers derive from distinct prokaryotic ancestors. The plant channels belong to a lineage that includes cyclic nucleotide-gated channels and metazoan ether-à-go-go and hyperpolarization-activated, cyclic nucleotide-gated channels. We refer to this lineage as the CNBD channel superfamily, because all these channels share a cytoplasmic gating domain homologous to cyclic nucleotide binding domains. The first structures of CNBD superfamily channels reveal marked differences in coupling between the voltage sensor and ion-conducting pore relative to metazoan Shaker channels. Viewing plant voltage-gated K+ channel function through the lens of CNBD superfamily structures should lead to insights into how these channels are regulated.
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Affiliation(s)
- Timothy Jegla
- Department of Biology and Huck Institute for the Life Sciences, Penn State University, 230 Life Sciences Building, University Park, Pennsylvania 16802
| | - Gregory Busey
- Department of Biology, Penn State University, 225 Life Sciences Building, University Park, Pennsylvania 16802
| | - Sarah M Assmann
- Department of Biology, Penn State University, 354 North Frear, University Park, Pennsylvania 16802
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29
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Abstract
Cell-free production is a valuable and alternative method for the synthesis of membrane proteins. This system offers openness allowing the researchers to modify the reaction conditions without any boundaries. Additionally, the cell-free reactions are scalable from 20 μL up to several mL, faster and suitable for the high-throughput protein production. Here, we present two cell-free systems derived from Escherichia coli (E. coli) and Spodoptera frugiperda (Sf21) lysates. In the case of the E. coli cell-free system, nanodiscs are used for the solubilization and purification of membrane proteins. In the case of the Sf21 system, endogenous microsomes with an active translocon complex are present within the lysates which facilitate the incorporation of the bacterial potassium channel KcsA within the microsomal membranes. Following cell-free synthesis, these microsomes are directly used for the functional analysis of membrane proteins.
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30
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Shenkarev ZO, Karlova MG, Kulbatskii DS, Kirpichnikov MP, Lyukmanova EN, Sokolova OS. Recombinant Production, Reconstruction in Lipid-Protein Nanodiscs, and Electron Microscopy of Full-Length α-Subunit of Human Potassium Channel Kv7.1. BIOCHEMISTRY (MOSCOW) 2018; 83:562-573. [PMID: 29738690 DOI: 10.1134/s0006297918050097] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Voltage-gated potassium channel Kv7.1 plays an important role in the excitability of cardiac muscle. The α-subunit of Kv7.1 (KCNQ1) is the main structural element of this channel. Tetramerization of KCNQ1 in the membrane results in formation of an ion channel, which comprises a pore and four voltage-sensing domains. Mutations in the human KCNQ1 gene are one of the major causes of inherited arrhythmias, long QT syndrome in particular. The construct encoding full-length human KCNQ1 protein was synthesized in this work, and an expression system in the Pichia pastoris yeast cells was developed. The membrane fraction of the yeast cells containing the recombinant protein (rKCNQ1) was solubilized with CHAPS detergent. To better mimic the lipid environment of the channel, lipid-protein nanodiscs were formed using solubilized membrane fraction and MSP2N2 protein. The rKCNQ1/nanodisc and rKCNQ1/CHAPS samples were purified using the Rho1D4 tag introduced at the C-terminus of the protein. Protein samples were examined using transmission electron microscopy with negative staining. In both cases, homogeneous rKCNQ1 samples were observed based on image analysis. Statistical analysis of the images of individual protein particles solubilized in the detergent revealed the presence of a tetrameric structure confirming intact subunit assembly. A three-dimensional channel structure reconstructed at 2.5-nm resolution represents a compact density with diameter of the membrane part of ~9 nm and height ~11 nm. Analysis of the images of rKCNQ1 in nanodiscs revealed additional electron density corresponding to the lipid bilayer fragment and the MSP2N2 protein. These results indicate that the nanodiscs facilitate protein isolation, purification, and stabilization in solution and can be used for further structural studies of human Kv7.1.
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Affiliation(s)
- Z O Shenkarev
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia.
| | - M G Karlova
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia.,Lomonosov Moscow State University, Faculty of Biology, Moscow, 119991, Russia
| | - D S Kulbatskii
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia.,Lomonosov Moscow State University, Faculty of Biology, Moscow, 119991, Russia
| | - M P Kirpichnikov
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia.,Lomonosov Moscow State University, Faculty of Biology, Moscow, 119991, Russia
| | - E N Lyukmanova
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia.,Lomonosov Moscow State University, Faculty of Biology, Moscow, 119991, Russia
| | - O S Sokolova
- Lomonosov Moscow State University, Faculty of Biology, Moscow, 119991, Russia.
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31
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Klaerke DA, Tejada MDLA, Christensen VG, Lassen M, Pedersen PA, Calloe K. Reconstitution and Electrophysiological Characterization of Ion Channels in Lipid Bilayers. ACTA ACUST UNITED AC 2018; 81:e37. [PMID: 29927074 DOI: 10.1002/cpph.37] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Detergent-solubilized purified ion channels can be reconstituted into lipid bilayers for electrophysiological analysis. Traditionally, ion channels were inserted into vesicles and subsequently fused with planar "black lipid membranes" formed from lipids dissolved in a hydrophobic solvent such as decane. Provided in this article is a step-by-step guide to reconstitute purified ion channel proteins into giant unilamellar vesicles (GUVs). This procedure results in the formation of proteoliposomes that can be used for planar bilayer formation and electrophysiological characterization of single-channel currents. By using preformed GUVs it is possible to omit the membrane solvent. Compared to traditional preparations, the lipid bilayers formed from GUVs provide an environment that more closely resembles the native cell membrane. Also described is an alternate protocol that entails the production of planar lipid bilayers from GUVs onto which proteins in detergent are added. © 2018 by John Wiley & Sons, Inc.
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Affiliation(s)
- Dan A Klaerke
- Department of Veterinary and Animal Sciences, Section for Anatomy, Biochemistry, and Physiology, University of Copenhagen, Frederiksberg, Denmark
| | - Maria de Los Angeles Tejada
- Department of Veterinary and Animal Sciences, Section for Anatomy, Biochemistry, and Physiology, University of Copenhagen, Frederiksberg, Denmark
| | - Vibeke Grøsfjeld Christensen
- Department of Veterinary and Animal Sciences, Section for Anatomy, Biochemistry, and Physiology, University of Copenhagen, Frederiksberg, Denmark
| | - Mette Lassen
- Department of Veterinary and Animal Sciences, Section for Anatomy, Biochemistry, and Physiology, University of Copenhagen, Frederiksberg, Denmark
| | - Per Amstrup Pedersen
- Department of Biology, Cell Biology and Physiology, University of Copenhagen, Copenhagen, Denmark
| | - Kirstine Calloe
- Department of Veterinary and Animal Sciences, Section for Anatomy, Biochemistry, and Physiology, University of Copenhagen, Frederiksberg, Denmark
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32
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Abstract
Crystallization of dual-topology fluoride (Fluc) channels requires small, soluble crystallization chaperones known as monobodies, which act as primary crystal lattice contacts. Previous structures of Flucs have been solved in the presence of monobodies that inhibit fluoride currents in single-channel electrophysiological recordings. These structures have revealed two-fold symmetric, doubly bound arrangements, with one monobody on each side of the membrane. The combined electrophysiological and structural observations raise the possibility that chaperone binding allosterically closes the channel, altering the structure from its conducting form. To address this, we identify and solve the structure with a different monobody that only partially blocks fluoride currents. The structure of the channel-monobody complex is asymmetric, with monobody bound to one side of the channel only. The channel conformation is nearly identical on the bound and uncomplexed sides, and to all previously solved structures, providing direct structural evidence that monobody binding does not induce local structural changes. Inhibitory crystallization chaperones bind on each side of the membrane Crystal structure of channel with one side free of chaperone binding S8 chaperone-bound channel is competent for fluoride transport Chaperones inhibit channels via a “cork-in-bottle” mechanism of physical occlusion
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33
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Herrera F, Sevrain CM, Jaffrès PA, Couthon H, Grélard A, Dufourc EJ, Chantôme A, Potier-Cartereau M, Vandier C, Bouchet AM. Singular Interaction between an Antimetastatic Agent and the Lipid Bilayer: The Ohmline Case. ACS OMEGA 2017; 2:6361-6370. [PMID: 30023517 PMCID: PMC6045331 DOI: 10.1021/acsomega.7b00936] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Accepted: 09/08/2017] [Indexed: 06/08/2023]
Abstract
SK3 channels are abnormaly expressed in metastatic cells, and Ohmline (OHM), an ether lipid, has been shown to reduce the activity of SK3 channels and the migration capacity of cancer cells. OHM incorporation into the plasma membrane is proposed to dissociate the protein complex formed between SK3 and Orai1, a potassium and a calcium channel, respectively, and would lead to a modification in the lipid environment of both the proteins. Here, we report the synthesis of deuterated OHM that affords the determination, through solid-state NMR, of its entire partitioning into membranes mimicking the SK3 environment. Use of deuterated lipids affords the demonstration of an OHM-induced membrane disordering, which is dose-dependent and increases with increasing amounts of cholesterol (CHOL). Molecular dynamics simulations comfort the disordering action and show that OHM interacts with the carbonyl and phosphate groups of stearoylphosphatidylcholine and sphingomyelin and to a minor extent with CHOL. OHM is thus proposed to remove the CHOL OH moieties away from their main binding sites, forcing a new rearrangement with other lipid groups. Such an interaction takes its origin at the lipid-water interface, but it propagates toward the entire lipid molecules and leads to a cooperative destabilization of the lipid acyl chains, that is, membrane disordering. The consequences of this reorganization of the lipid phases are discussed in the context of the OHM-induced inhibition of SK3 channels.
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Affiliation(s)
- Fernando
E. Herrera
- Physics
Department, Universidad Nacional del Litoral,
Ciudad Universitaria, 3000 Santa Fe, Argentina
| | - Charlotte M. Sevrain
- Université
de Brest, CEMCA, UMR CNRS 6521, IBSAM, 6, Avenue Victor le Gorgeu, 29238 Brest, France
- Network
and Cancer-Canceropole Grand Ouest, (IC-CGO), Maison de la Recherche
en Santé, 63 Quai
Magellan, 44000 Nantes, France
| | - Paul-Alain Jaffrès
- Université
de Brest, CEMCA, UMR CNRS 6521, IBSAM, 6, Avenue Victor le Gorgeu, 29238 Brest, France
- Network
and Cancer-Canceropole Grand Ouest, (IC-CGO), Maison de la Recherche
en Santé, 63 Quai
Magellan, 44000 Nantes, France
| | - Hélène Couthon
- Université
de Brest, CEMCA, UMR CNRS 6521, IBSAM, 6, Avenue Victor le Gorgeu, 29238 Brest, France
- Network
and Cancer-Canceropole Grand Ouest, (IC-CGO), Maison de la Recherche
en Santé, 63 Quai
Magellan, 44000 Nantes, France
| | - Axelle Grélard
- Université
Bordeaux, Institute of Chemistry & Biology of Membranes &
Nanoobjects, UMR5248 CNRS, Allée de Geoffroy St Hilaire Bât B14 Pessac, 33600 Bordeaux, France
| | - Erick J. Dufourc
- Université
Bordeaux, Institute of Chemistry & Biology of Membranes &
Nanoobjects, UMR5248 CNRS, Allée de Geoffroy St Hilaire Bât B14 Pessac, 33600 Bordeaux, France
| | - Aurélie Chantôme
- Network
and Cancer-Canceropole Grand Ouest, (IC-CGO), Maison de la Recherche
en Santé, 63 Quai
Magellan, 44000 Nantes, France
- Université
François Rabelais de Tours, Nutrition, Croissance et Cancer, Inserm UMR1069, 10 Boulevard Tonnellé Bât. Dutrochet, 2ème étage, 37032 Tours, France
| | - Marie Potier-Cartereau
- Network
and Cancer-Canceropole Grand Ouest, (IC-CGO), Maison de la Recherche
en Santé, 63 Quai
Magellan, 44000 Nantes, France
- Université
François Rabelais de Tours, Nutrition, Croissance et Cancer, Inserm UMR1069, 10 Boulevard Tonnellé Bât. Dutrochet, 2ème étage, 37032 Tours, France
| | - Christophe Vandier
- Network
and Cancer-Canceropole Grand Ouest, (IC-CGO), Maison de la Recherche
en Santé, 63 Quai
Magellan, 44000 Nantes, France
- Université
François Rabelais de Tours, Nutrition, Croissance et Cancer, Inserm UMR1069, 10 Boulevard Tonnellé Bât. Dutrochet, 2ème étage, 37032 Tours, France
| | - Ana M. Bouchet
- Network
and Cancer-Canceropole Grand Ouest, (IC-CGO), Maison de la Recherche
en Santé, 63 Quai
Magellan, 44000 Nantes, France
- Université
François Rabelais de Tours, Nutrition, Croissance et Cancer, Inserm UMR1069, 10 Boulevard Tonnellé Bât. Dutrochet, 2ème étage, 37032 Tours, France
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34
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Thoring L, Dondapati SK, Stech M, Wüstenhagen DA, Kubick S. High-yield production of "difficult-to-express" proteins in a continuous exchange cell-free system based on CHO cell lysates. Sci Rep 2017; 7:11710. [PMID: 28916746 PMCID: PMC5601898 DOI: 10.1038/s41598-017-12188-8] [Citation(s) in RCA: 75] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Accepted: 09/06/2017] [Indexed: 11/10/2022] Open
Abstract
Cell-free protein synthesis (CFPS) represents a promising technology for efficient protein production targeting especially so called "difficult-to-express" proteins whose synthesis is challenging in conventional in vivo protein production platforms. Chinese hamster ovary (CHO) cells are one of the most prominent and safety approved cell lines for industrial protein production. In this study we demonstrated the ability to produce high yields of various protein types including membrane proteins and single chain variable fragments (scFv) in a continuous exchange cell-free (CECF) system based on CHO cell lysate that contains endogenous microsomal structures. We showed significant improvement of protein yield compared to batch formatted reactions and proved biological activity of synthesized proteins using various analysis technologies. Optimized CECF reaction conditions led to membrane protein yields up to 980 µg/ml, which is the highest protein yield reached in a microsome containing eukaryotic cell-free system presented so far.
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Affiliation(s)
- Lena Thoring
- Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am Mühlenberg 13, D-14476, Potsdam, Germany
- Institute for Biotechnology, Technical University of Berlin (TUB), Gustav-Meyer-Allee 25, 13355, Berlin, Germany
| | - Srujan K Dondapati
- Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am Mühlenberg 13, D-14476, Potsdam, Germany
| | - Marlitt Stech
- Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am Mühlenberg 13, D-14476, Potsdam, Germany
| | - Doreen A Wüstenhagen
- Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am Mühlenberg 13, D-14476, Potsdam, Germany
| | - Stefan Kubick
- Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am Mühlenberg 13, D-14476, Potsdam, Germany.
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35
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Thoring L, Dondapati SK, Stech M, Wüstenhagen DA, Kubick S. High-yield production of "difficult-to-express" proteins in a continuous exchange cell-free system based on CHO cell lysates. Sci Rep 2017; 7:11710. [PMID: 28916746 DOI: 10.1038/s41598-017-12188-12188] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Accepted: 09/06/2017] [Indexed: 05/28/2023] Open
Abstract
Cell-free protein synthesis (CFPS) represents a promising technology for efficient protein production targeting especially so called "difficult-to-express" proteins whose synthesis is challenging in conventional in vivo protein production platforms. Chinese hamster ovary (CHO) cells are one of the most prominent and safety approved cell lines for industrial protein production. In this study we demonstrated the ability to produce high yields of various protein types including membrane proteins and single chain variable fragments (scFv) in a continuous exchange cell-free (CECF) system based on CHO cell lysate that contains endogenous microsomal structures. We showed significant improvement of protein yield compared to batch formatted reactions and proved biological activity of synthesized proteins using various analysis technologies. Optimized CECF reaction conditions led to membrane protein yields up to 980 µg/ml, which is the highest protein yield reached in a microsome containing eukaryotic cell-free system presented so far.
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Affiliation(s)
- Lena Thoring
- Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am Mühlenberg 13, D-14476, Potsdam, Germany
- Institute for Biotechnology, Technical University of Berlin (TUB), Gustav-Meyer-Allee 25, 13355, Berlin, Germany
| | - Srujan K Dondapati
- Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am Mühlenberg 13, D-14476, Potsdam, Germany
| | - Marlitt Stech
- Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am Mühlenberg 13, D-14476, Potsdam, Germany
| | - Doreen A Wüstenhagen
- Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am Mühlenberg 13, D-14476, Potsdam, Germany
| | - Stefan Kubick
- Fraunhofer Institute for Cell Therapy and Immunology (IZI), Branch Bioanalytics and Bioprocesses (IZI-BB), Am Mühlenberg 13, D-14476, Potsdam, Germany.
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36
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Grigolon S, Franz S, Marsili M. Identifying relevant positions in proteins by Critical Variable Selection. MOLECULAR BIOSYSTEMS 2017; 12:2147-58. [PMID: 26974515 DOI: 10.1039/c6mb00047a] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Evolution in its course has found a variety of solutions to the same optimisation problem. The advent of high-throughput genomic sequencing has made available extensive data from which, in principle, one can infer the underlying structure on which biological functions rely. In this paper, we present a new method aimed at the extraction of sites encoding structural and functional properties from a set of protein primary sequences, namely a multiple sequence alignment. The method, called critical variable selection, is based on the idea that subsets of relevant sites correspond to subsequences that occur with a particularly broad frequency distribution in the dataset. By applying this algorithm to in silico sequences, to the response regulator receiver and to the voltage sensor domain of ion channels, we show that this procedure recovers not only the information encoded in single site statistics and pairwise correlations but also captures dependencies going beyond pairwise correlations. The method proposed here is complementary to statistical coupling analysis, in that the most relevant sites predicted by the two methods differ markedly. We find robust and consistent results for datasets as small as few hundred sequences that reveal a hidden hierarchy of sites that are consistent with the present knowledge on biologically relevant sites and evolutionary dynamics. This suggests that critical variable selection is capable of identifying a core of sites encoding functional and structural information in a multiple sequence alignment.
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Affiliation(s)
- Silvia Grigolon
- The Francis Crick Institute, Lincoln's Inn Fields Laboratory, 44, Lincoln's Inn Fields, London WC2A 3LY, UK.
| | - Silvio Franz
- LPTMS - Laboratoire de Physique Théorique et Modèles Statistiques, UMR CNRS 8626, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay, France.
| | - Matteo Marsili
- Abdus Salam International Center of Theoretical Physics, Strada Costiera 11, 34151 Trieste, Italy.
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37
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Venom-derived peptide inhibitors of voltage-gated potassium channels. Neuropharmacology 2017; 127:124-138. [PMID: 28689025 DOI: 10.1016/j.neuropharm.2017.07.002] [Citation(s) in RCA: 58] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Revised: 07/02/2017] [Accepted: 07/04/2017] [Indexed: 12/11/2022]
Abstract
Voltage-gated potassium channels play a key role in human physiology and pathology. Reflecting their importance, numerous channelopathies have been characterised that arise from mutations in these channels or from autoimmune attack on the channels. Voltage-gated potassium channels are also the target of a broad range of peptide toxins from venomous organisms, including sea anemones, scorpions, spiders, snakes and cone snails; many of these peptides bind to the channels with high potency and selectivity. In this review we describe the various classes of peptide toxins that block these channels and illustrate the broad range of three-dimensional structures that support channel blockade. The therapeutic opportunities afforded by these peptides are also highlighted. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'
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38
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Buono RA, Leier A, Paez-Valencia J, Pennington J, Goodman K, Miller N, Ahlquist P, Marquez-Lago TT, Otegui MS. ESCRT-mediated vesicle concatenation in plant endosomes. J Cell Biol 2017; 216:2167-2177. [PMID: 28592443 PMCID: PMC5496621 DOI: 10.1083/jcb.201612040] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Revised: 04/06/2017] [Accepted: 05/01/2017] [Indexed: 11/23/2022] Open
Abstract
ESCRT proteins play essential functions by remodeling cellular membranes. Buono et al. report on a novel ESCRT-dependent mechanism in plant endosomes that leads to sequential concatenation of vesicle buds by temporally uncoupling membrane constriction from membrane fission. During this process, ESCRT-III proteins remain inside endosomes after intralumenal vesicle release. Ubiquitinated plasma membrane proteins (cargo) are delivered to endosomes and sorted by endosomal sorting complex required for transport (ESCRT) machinery into endosome intralumenal vesicles (ILVs) for degradation. In contrast to the current model that postulates that ILVs form individually from inward budding of the endosomal limiting membrane, plant ILVs form as networks of concatenated vesicle buds by a novel vesiculation mechanism. We ran computational simulations based on experimentally derived diffusion coefficients of an ESCRT cargo protein and electron tomograms of Arabidopsis thaliana endosomes to measure cargo escape from budding ILVs. We found that 50% of the ESCRT cargo would escape from a single budding profile in 5–20 ms and from three concatenated ILVs in 80–200 ms. These short cargo escape times predict the need for strong diffusion barriers in ILVs. Consistent with a potential role as a diffusion barrier, we find that the ESCRT-III protein SNF7 remains associated with ILVs and is delivered to the vacuole for degradation.
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Affiliation(s)
- Rafael Andrade Buono
- Department of Botany, University of Wisconsin-Madison, Madison, WI.,R.M. Bock Laboratories of Cell and Molecular Biology, University of Wisconsin-Madison, Madison, WI
| | - André Leier
- Informatics Institute, School of Medicine, University of Alabama at Birmingham, Birmingham, AL.,Department of Genetics, School of Medicine, University of Alabama at Birmingham, Birmingham, AL
| | - Julio Paez-Valencia
- Department of Botany, University of Wisconsin-Madison, Madison, WI.,R.M. Bock Laboratories of Cell and Molecular Biology, University of Wisconsin-Madison, Madison, WI
| | | | - Kaija Goodman
- Department of Botany, University of Wisconsin-Madison, Madison, WI.,R.M. Bock Laboratories of Cell and Molecular Biology, University of Wisconsin-Madison, Madison, WI
| | - Nathan Miller
- Department of Botany, University of Wisconsin-Madison, Madison, WI
| | - Paul Ahlquist
- Institute for Molecular Virology, University of Wisconsin-Madison, Madison, WI.,Departments of Oncology, University of Wisconsin-Madison, Madison, WI.,Department of Plant Pathology, University of Wisconsin-Madison, Madison, WI.,Howard Hughes Medical Institute, Chevy Chase, MD.,Morgridge Institute for Research, Madison, WI
| | - Tatiana T Marquez-Lago
- Informatics Institute, School of Medicine, University of Alabama at Birmingham, Birmingham, AL.,Department of Genetics, School of Medicine, University of Alabama at Birmingham, Birmingham, AL
| | - Marisa S Otegui
- Department of Botany, University of Wisconsin-Madison, Madison, WI .,R.M. Bock Laboratories of Cell and Molecular Biology, University of Wisconsin-Madison, Madison, WI.,Department of Genetics, University of Wisconsin-Madison, Madison, WI
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39
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Qi H, Tang W, Bai L, Gao L. Structure and positioning of three transmembrane segments from Slc11a1 in SDS micelles. Chem Res Chin Univ 2017. [DOI: 10.1007/s40242-017-6288-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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40
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Hegle AP, Frank CA, Berndt A, Klose M, Allan DW, Accili EA. The Ih Channel Gene Promotes Synaptic Transmission and Coordinated Movement in Drosophila melanogaster. Front Mol Neurosci 2017; 10:41. [PMID: 28286469 PMCID: PMC5323408 DOI: 10.3389/fnmol.2017.00041] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2016] [Accepted: 02/06/2017] [Indexed: 11/13/2022] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-gated “HCN” channels, which underlie the hyperpolarization-activated current (Ih), have been proposed to play diverse roles in neurons. The presynaptic HCN channel is thought to both promote and inhibit neurotransmitter release from synapses, depending upon its interactions with other presynaptic ion channels. In larvae of Drosophila melanogaster, inhibition of the presynaptic HCN channel by the drug ZD7288 reduces the enhancement of neurotransmitter release at motor terminals by serotonin but this drug has no effect on basal neurotransmitter release, implying that the channel does not contribute to firing under basal conditions. Here, we show that genetic disruption of the sole HCN gene (Ih) reduces the amplitude of the evoked response at the neuromuscular junction (NMJ) of third instar larvae by decreasing the number of released vesicles. The anatomy of the (NMJ) is not notably affected by disruption of the Ih gene. We propose that the presynaptic HCN channel is active under basal conditions and promotes neurotransmission at larval motor terminals. Finally, we demonstrate that Ih partial loss-of-function mutant adult flies have impaired locomotion, and, thus, we hypothesize that the presynaptic HCN channel at the (NMJ) may contribute to coordinated movement.
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Affiliation(s)
- Andrew P Hegle
- Department of Cellular and Physiological Sciences, The University of British Columbia Vancouver, BC, Canada
| | - C Andrew Frank
- Department of Anatomy and Cell Biology, The University of Iowa Iowa City, IA, USA
| | - Anthony Berndt
- Department of Cellular and Physiological Sciences, The University of British Columbia Vancouver, BC, Canada
| | - Markus Klose
- Department of Cellular and Physiological Sciences, The University of British Columbia Vancouver, BC, Canada
| | - Douglas W Allan
- Department of Cellular and Physiological Sciences, The University of British Columbia Vancouver, BC, Canada
| | - Eric A Accili
- Department of Cellular and Physiological Sciences, The University of British Columbia Vancouver, BC, Canada
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Paramonov AS, Lyukmanova EN, Myshkin MY, Shulepko MA, Kulbatskii DS, Petrosian NS, Chugunov AO, Dolgikh DA, Kirpichnikov MP, Arseniev AS, Shenkarev ZO. NMR investigation of the isolated second voltage-sensing domain of human Nav1.4 channel. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:493-506. [PMID: 28065835 DOI: 10.1016/j.bbamem.2017.01.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Revised: 12/06/2016] [Accepted: 01/04/2017] [Indexed: 10/20/2022]
Abstract
Voltage-gated Na+ channels are essential for the functioning of cardiovascular, muscular, and nervous systems. The α-subunit of eukaryotic Na+ channel consists of ~2000 amino acid residues and encloses 24 transmembrane (TM) helices, which form five membrane domains: four voltage-sensing (VSD) and one pore domain. The structural complexity significantly impedes recombinant production and structural studies of full-sized Na+ channels. Modular organization of voltage-gated channels gives an idea for studying of the isolated second VSD of human skeletal muscle Nav1.4 channel (VSD-II). Several variants of VSD-II (~150a.a., four TM helices) with different N- and C-termini were produced by cell-free expression. Screening of membrane mimetics revealed low stability of VSD-II samples in media containing phospholipids (bicelles, nanodiscs) associated with the aggregation of electrically neutral domain molecules. The almost complete resonance assignment of 13C,15N-labeled VSD-II was obtained in LPPG micelles. The secondary structure of VSD-II showed similarity with the structures of bacterial Na+ channels. The fragment of S4 TM helix between the first and second conserved Arg residues probably adopts 310-helical conformation. Water accessibility of S3 helix, observed by the Mn2+ titration, pointed to the formation of water-filled crevices in the micelle embedded VSD-II. 15N relaxation data revealed characteristic pattern of μs-ms time scale motions in the VSD-II regions sharing expected interhelical contacts. VSD-II demonstrated enhanced mobility at ps-ns time scale as compared to isolated VSDs of K+ channels. These results validate structural studies of isolated VSDs of Na+ channels and show possible pitfalls in application of this 'divide and conquer' approach.
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Affiliation(s)
- A S Paramonov
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya str., 16/10, Moscow 117997, Russia; Lomonosov Moscow State University, Moscow 119991, Russia
| | - E N Lyukmanova
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya str., 16/10, Moscow 117997, Russia; Lomonosov Moscow State University, Moscow 119991, Russia
| | - M Yu Myshkin
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya str., 16/10, Moscow 117997, Russia; Moscow Institute of Physics and Technology (State University), Institutskiy Pereulok 9, Dolgoprudny, Moscow Region 141700, Russia
| | - M A Shulepko
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya str., 16/10, Moscow 117997, Russia; Lomonosov Moscow State University, Moscow 119991, Russia
| | - D S Kulbatskii
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya str., 16/10, Moscow 117997, Russia; Lomonosov Moscow State University, Moscow 119991, Russia
| | - N S Petrosian
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya str., 16/10, Moscow 117997, Russia; Moscow Institute of Physics and Technology (State University), Institutskiy Pereulok 9, Dolgoprudny, Moscow Region 141700, Russia
| | - A O Chugunov
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya str., 16/10, Moscow 117997, Russia
| | - D A Dolgikh
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya str., 16/10, Moscow 117997, Russia; Lomonosov Moscow State University, Moscow 119991, Russia
| | - M P Kirpichnikov
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya str., 16/10, Moscow 117997, Russia; Lomonosov Moscow State University, Moscow 119991, Russia
| | - A S Arseniev
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya str., 16/10, Moscow 117997, Russia; Moscow Institute of Physics and Technology (State University), Institutskiy Pereulok 9, Dolgoprudny, Moscow Region 141700, Russia
| | - Z O Shenkarev
- Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Miklukho-Maklaya str., 16/10, Moscow 117997, Russia; Moscow Institute of Physics and Technology (State University), Institutskiy Pereulok 9, Dolgoprudny, Moscow Region 141700, Russia.
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The "Sticky Patch" Model of Crystallization and Modification of Proteins for Enhanced Crystallizability. Methods Mol Biol 2017; 1607:77-115. [PMID: 28573570 DOI: 10.1007/978-1-4939-7000-1_4] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Crystallization of macromolecules has long been perceived as a stochastic process, which cannot be predicted or controlled. This is consistent with another popular notion that the interactions of molecules within the crystal, i.e., crystal contacts, are essentially random and devoid of specific physicochemical features. In contrast, functionally relevant surfaces, such as oligomerization interfaces and specific protein-protein interaction sites, are under evolutionary pressures so their amino acid composition, structure, and topology are distinct. However, current theoretical and experimental studies are significantly changing our understanding of the nature of crystallization. The increasingly popular "sticky patch" model, derived from soft matter physics, describes crystallization as a process driven by interactions between select, specific surface patches, with properties thermodynamically favorable for cohesive interactions. Independent support for this model comes from various sources including structural studies and bioinformatics. Proteins that are recalcitrant to crystallization can be modified for enhanced crystallizability through chemical or mutational modification of their surface to effectively engineer "sticky patches" which would drive crystallization. Here, we discuss the current state of knowledge of the relationship between the microscopic properties of the target macromolecule and its crystallizability, focusing on the "sticky patch" model. We discuss state-of-the-art in silico methods that evaluate the propensity of a given target protein to form crystals based on these relationships, with the objective to design variants with modified molecular surface properties and enhanced crystallization propensity. We illustrate this discussion with specific cases where these approaches allowed to generate crystals suitable for structural analysis.
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Disulfide mapping the voltage-sensing mechanism of a voltage-dependent potassium channel. Sci Rep 2016; 6:37303. [PMID: 27853286 PMCID: PMC5112519 DOI: 10.1038/srep37303] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2016] [Accepted: 10/27/2016] [Indexed: 11/08/2022] Open
Abstract
Voltage-dependent potassium (Kv) channels allow for the selective permeability of potassium ions in a membrane potential dependent manner, playing crucial roles in neurotransmission and muscle contraction. Kv channel is a tetramer, in which each subunit possesses a voltage-sensing domain (VSD) and a pore domain (PD). Although several lines of evidence indicated that membrane depolarization is sensed as the movement of helix S4 of the VSD, the detailed voltage-sensing mechanism remained elusive, due to the difficulty of structural analyses at resting potential. In this study, we conducted a comprehensive disulfide locking analysis of the VSD using 36 double Cys mutants, in order to identify the proximal residue pairs of the VSD in the presence or absence of a membrane potential. An intramolecular SS-bond was formed between 6 Cys pairs under both polarized and depolarized environment, and one pair only under depolarized environment. The multiple conformations captured by the SS-bond can be divided by two states, up and down, where S4 lies on the extracellular and intracellular sides of the membrane, respectively, with axial rotation of 180°. The transition between these two states is caused by the S4 translocation of 12 Å, enabling allosteric regulation of the gating at the PD.
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Taylor KC, Sanders CR. Regulation of KCNQ/Kv7 family voltage-gated K + channels by lipids. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1859:586-597. [PMID: 27818172 DOI: 10.1016/j.bbamem.2016.10.023] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Revised: 10/24/2016] [Accepted: 10/31/2016] [Indexed: 12/19/2022]
Abstract
Many years of studies have established that lipids can impact membrane protein structure and function through bulk membrane effects, by direct but transient annular interactions with the bilayer-exposed surface of protein transmembrane domains, and by specific binding to protein sites. Here, we focus on how phosphatidylinositol 4,5-bisphosphate (PIP2) and polyunsaturated fatty acids (PUFAs) impact ion channel function and how the structural details of the interactions of these lipids with ion channels are beginning to emerge. We focus on the Kv7 (KCNQ) subfamily of voltage-gated K+ channels, which are regulated by both PIP2 and PUFAs and play a variety of important roles in human health and disease. This article is part of a Special Issue entitled: Lipid order/lipid defects and lipid-control of protein activity edited by Dirk Schneider.
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Affiliation(s)
- Keenan C Taylor
- Department of Biochemistry, Vanderbilt University, Nashville, TN, USA; Center for Structural Biology, Vanderbilt University, Nashville, TN, USA
| | - Charles R Sanders
- Department of Biochemistry, Vanderbilt University, Nashville, TN, USA; Center for Structural Biology, Vanderbilt University, Nashville, TN, USA; Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, USA.
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The topogenic function of S4 promotes membrane insertion of the voltage-sensor domain in the KvAP channel. Biochem J 2016; 473:4361-4372. [PMID: 27694387 DOI: 10.1042/bcj20160746] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2016] [Revised: 09/20/2016] [Accepted: 09/30/2016] [Indexed: 11/17/2022]
Abstract
Voltage-dependent K+ (KV) channels control K+ permeability in response to shifts in the membrane potential. Voltage sensing in KV channels is mediated by the positively charged transmembrane domain S4. The best-characterized KV channel, KvAP, lacks the distinct hydrophilic region corresponding to the S3-S4 extracellular loop that is found in other K+ channels. In the present study, we evaluated the topogenic properties of the transmembrane regions within the voltage-sensing domain in KvAP. S3 had low membrane insertion activity, whereas S4 possessed a unique type-I signal anchor (SA-I) function, which enabled it to insert into the membrane by itself. S4 was also found to function as a stop-transfer signal for retention in the membrane. The length and structural nature of the extracellular S3-S4 loop affected the membrane insertion of S3 and S4, suggesting that S3 membrane insertion was dependent on S4. Replacement of charged residues within the transmembrane regions with residues of opposite charge revealed that Asp72 in S2 and Glu93 in S3 contributed to membrane insertion of S3 and S4, and increased the stability of S4 in the membrane. These results indicate that the SA-I function of S4, unique among K+ channels studied to date, promotes the insertion of S3 into the membrane, and that the charged residues essential for voltage sensing contribute to the membrane-insertion of the voltage sensor domain in KvAP.
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Lau CHY, King GF, Mobli M. Molecular basis of the interaction between gating modifier spider toxins and the voltage sensor of voltage-gated ion channels. Sci Rep 2016; 6:34333. [PMID: 27677715 PMCID: PMC5039624 DOI: 10.1038/srep34333] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2016] [Accepted: 09/12/2016] [Indexed: 01/02/2023] Open
Abstract
Voltage-sensor domains (VSDs) are modular transmembrane domains of voltage-gated ion channels that respond to changes in membrane potential by undergoing conformational changes that are coupled to gating of the ion-conducting pore. Most spider-venom peptides function as gating modifiers by binding to the VSDs of voltage-gated channels and trapping them in a closed or open state. To understand the molecular basis underlying this mode of action, we used nuclear magnetic resonance to delineate the atomic details of the interaction between the VSD of the voltage-gated potassium channel KvAP and the spider-venom peptide VSTx1. Our data reveal that the toxin interacts with residues in an aqueous cleft formed between the extracellular S1-S2 and S3-S4 loops of the VSD whilst maintaining lipid interactions in the gaps formed between the S1-S4 and S2-S3 helices. The resulting network of interactions increases the energetic barrier to the conformational changes required for channel gating, and we propose that this is the mechanism by which gating modifier toxins inhibit voltage-gated ion channels.
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Affiliation(s)
- Carus H Y Lau
- Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD 4072, Australia
| | - Glenn F King
- Institute for Molecular Bioscience, The University of Queensland, St. Lucia, QLD 4072, Australia
| | - Mehdi Mobli
- Centre for Advanced Imaging, The University of Queensland, St. Lucia, QLD 4072, Australia
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48
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Nomura Y, Sato Y, Suno R, Horita S, Iwata S, Nomura N. The intervening removable affinity tag (iRAT) production system facilitates Fv antibody fragment-mediated crystallography. Protein Sci 2016; 25:2268-2276. [PMID: 27595817 DOI: 10.1002/pro.3035] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2016] [Revised: 09/01/2016] [Accepted: 09/01/2016] [Indexed: 01/20/2023]
Abstract
Fv antibody fragments have been used as co-crystallization partners in structural biology, particularly in membrane protein crystallography. However, there are inherent technical issues associated with the large-scale production of soluble, functional Fv fragments through conventional methods in various expression systems. To circumvent these problems, we developed a new method, in which a single synthetic polyprotein consisting of a variable light (VL ) domain, an intervening removable affinity tag (iRAT), and a variable heavy (VH ) domain is expressed by a Gram-positive bacterial secretion system. This method ensures stoichiometric expression of VL and VH from the monocistronic construct followed by proper folding and assembly of the two variable domains. The iRAT segment can be removed by a site-specific protease during the purification process to yield tag-free Fv fragments suitable for crystallization trials. In vitro refolding step is not required to obtain correctly folded Fv fragments. As a proof of concept, we tested the iRAT-based production of multiple Fv fragments, including a crystallization chaperone for a mammalian membrane protein as well as FDA-approved therapeutic antibodies. The resulting Fv fragments were functionally active and crystallized in complex with the target proteins. The iRAT system is a reliable, rapid and broadly applicable means of producing milligram quantities of Fv fragments for structural and biochemical studies.
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Affiliation(s)
- Yayoi Nomura
- Department of Cell Biology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan.,Japan Science and Technology Agency, Research Acceleration Program, Membrane Protein Crystallography Project, Yoshida-Konoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan
| | - Yumi Sato
- Department of Cell Biology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan.,Japan Science and Technology Agency, Research Acceleration Program, Membrane Protein Crystallography Project, Yoshida-Konoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan
| | - Ryoji Suno
- Department of Cell Biology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan
| | - Shoichiro Horita
- Department of Cell Biology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan
| | - So Iwata
- Department of Cell Biology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan.,Japan Science and Technology Agency, Research Acceleration Program, Membrane Protein Crystallography Project, Yoshida-Konoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan.,RIKEN SPring-8 Center, Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5148, Japan
| | - Norimichi Nomura
- Department of Cell Biology, Graduate School of Medicine, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan.,Japan Science and Technology Agency, Research Acceleration Program, Membrane Protein Crystallography Project, Yoshida-Konoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan
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Cyclic Purine and Pyrimidine Nucleotides Bind to the HCN2 Ion Channel and Variably Promote C-Terminal Domain Interactions and Opening. Structure 2016; 24:1629-1642. [PMID: 27568927 DOI: 10.1016/j.str.2016.06.024] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2016] [Revised: 06/22/2016] [Accepted: 06/23/2016] [Indexed: 11/21/2022]
Abstract
Cyclic AMP is thought to facilitate the opening of the HCN2 channel by binding to a C-terminal domain and promoting or inhibiting interactions between subunits. Here, we correlated the ability of cyclic nucleotides to promote interactions of isolated HCN2 C-terminal domains in solution with their ability to facilitate channel opening. Cyclic IMP, a cyclic purine nucleotide, and cCMP, a cyclic pyrimidine nucleotide, bind to a C-terminal domain containing the cyclic nucleotide-binding domain but, in contrast to other cyclic nucleotides examined, fail to promote its oligomerization, and produce only modest facilitation of opening of the full-length channel. Comparisons between ligand bound structures identify a region between the sixth and seventh β strands and the distal C helix as important for facilitation and tight binding. We propose that promotion of interactions between the C-terminal domains by a given ligand contribute to its ability to facilitate opening of the full-length channel.
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Kayalvizhi N, Rameshkumar N, Gunasekaran P. Cloning and characterization of mersacidin like bacteriocin from Bacillus licheniformis MKU3 in Escherichia coli. Journal of Food Science and Technology 2016; 53:2298-306. [PMID: 27407196 DOI: 10.1007/s13197-016-2195-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Revised: 06/26/2014] [Accepted: 07/31/2014] [Indexed: 11/25/2022]
Abstract
A putative gene encoding mersacidin like lantibiotic bacteriocin (lanA) was identified in Bacillus licheniformis genome. The lanA open reading frame codes for 74 amino acids with calculated isoelectric point of 6.7 and molecular mass of 8.2 kDa. The lanA gene was amplified from B. licheniformis MKU3, cloned in pQE30 vector and overexpressed in Escherichia coli M15. The recombinant peptide was purified to homogeneity using Ni-NTA chromatography and the SDS-PAGE analysis of the purified peptide revealed it to be a monomer with molecular mass of ~8.5 kDa. The purified bacteriocin showed wide spectrum activity against gram-positive pathogens. The peptide was found to be stable under in wide range of pH, temperature tolerant and resistant to the proteolytic enzymes. The stable nature of the bacteriocin to high temperature and resistant to various chemicals it also exhibited antimicrobial activity against food-borne pathogens make this bacteriocin as potent attractive antimicrobial agent in food products.
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Affiliation(s)
| | - Neelamegam Rameshkumar
- Department of Environmental Biotechnology, Bharathidasan University, Tiruchirappalli, 620 024 Tamil Nadu India
| | - Paramasamy Gunasekaran
- Department of Genetics, School of Biological Sciences, Madurai Kamaraj University, Madurai, 625 021 Tamil Nadu India
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