1
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Guo SC, Shen R, Roux B, Dinner AR. Dynamics of activation in the voltage-sensing domain of Ciona intestinalis phosphatase Ci-VSP. Nat Commun 2024; 15:1408. [PMID: 38360718 PMCID: PMC10869754 DOI: 10.1038/s41467-024-45514-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Accepted: 01/25/2024] [Indexed: 02/17/2024] Open
Abstract
The Ciona intestinalis voltage-sensing phosphatase (Ci-VSP) is a membrane protein containing a voltage-sensing domain (VSD) that is homologous to VSDs from voltage-gated ion channels responsible for cellular excitability. Previously published crystal structures of Ci-VSD in putative resting and active conformations suggested a helical-screw voltage sensing mechanism in which the S4 helix translocates and rotates to enable exchange of salt-bridge partners, but the microscopic details of the transition between the resting and active conformations remained unknown. Here, by combining extensive molecular dynamics simulations with a recently developed computational framework based on dynamical operators, we elucidate the microscopic mechanism of the resting-active transition at physiological membrane potential. Sparse regression reveals a small set of coordinates that distinguish intermediates that are hidden from electrophysiological measurements. The intermediates arise from a noncanonical helical-screw mechanism in which translocation, rotation, and side-chain movement of the S4 helix are only loosely coupled. These results provide insights into existing experimental and computational findings on voltage sensing and suggest ways of further probing its mechanism.
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Affiliation(s)
- Spencer C Guo
- Department of Chemistry, The University of Chicago, Chicago, IL, 60637, USA
- James Franck Institute, The University of Chicago, Chicago, IL, 60637, USA
| | - Rong Shen
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, 60637, USA
| | - Benoît Roux
- Department of Chemistry, The University of Chicago, Chicago, IL, 60637, USA.
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL, 60637, USA.
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL, 60637, USA.
| | - Aaron R Dinner
- Department of Chemistry, The University of Chicago, Chicago, IL, 60637, USA.
- James Franck Institute, The University of Chicago, Chicago, IL, 60637, USA.
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL, 60637, USA.
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2
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García-Morales A, Balleza D. Exploring Flexibility and Folding Patterns Throughout Time in Voltage Sensors. J Mol Evol 2023; 91:819-836. [PMID: 37955698 DOI: 10.1007/s00239-023-10140-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2023] [Accepted: 10/27/2023] [Indexed: 11/14/2023]
Abstract
The voltage-sensing domain (VSD) is a module capable of responding to changes in the membrane potential through conformational changes and facilitating electromechanical coupling to open a pore gate, activate proton permeation pathways, or promote enzymatic activity in some membrane-anchored phosphatases. To carry out these functions, this module acts cooperatively through conformational changes. The VSD is formed by four transmembrane segments (S1-S4) but the S4 segment is critical since it carries positively charged residues, mainly Arg or Lys, which require an aqueous environment for its proper function. The discovery of this module in voltage-gated ion channels (VGICs), proton channels (Hv1), and voltage sensor-containing phosphatases (VSPs) has expanded our understanding of the principle of modularity in the voltage-sensing mechanism of these proteins. Here, by sequence comparison and the evaluation of the relationship between sequence composition, intrinsic flexibility, and structural analysis in 14 selected representatives of these three major protein groups, we report five interesting differences in the folding patterns of the VSD both in prokaryotes and eukaryotes. Our main findings indicate that this module is highly conserved throughout the evolutionary scale, however: (1) segments S1 to S3 in eukaryotes are significantly more hydrophobic than those present in prokaryotes; (2) the S4 segment has retained its hydrophilic character; (3) in eukaryotes the extramembranous linkers are significantly larger and more flexible in comparison with those present in prokaryotes; (4) the sensors present in the kHv1 proton channel and the ciVSP phosphatase, both of eukaryotic origin, exhibit relationships of flexibility and folding patterns very close to the typical ones found in prokaryotic voltage sensors; and (5) archaeal channels KvAP and MVP have flexibility profiles which are clearly contrasting in the S3-S4 region, which could explain their divergent activation mechanisms. Finally, to elucidate the obscure origins of this module, we show further evidence for a possible connection between voltage sensors and TolQ proteins.
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Affiliation(s)
- Abigail García-Morales
- Tecnológico Nacional de México, Instituto Tecnológico de Veracruz, Unidad de Investigación y Desarrollo en Alimentos, Calz. Miguel Angel de Quevedo 2779, Col. Formando Hogar, CP. 91897, Veracruz, Ver, Mexico
| | - Daniel Balleza
- Tecnológico Nacional de México, Instituto Tecnológico de Veracruz, Unidad de Investigación y Desarrollo en Alimentos, Calz. Miguel Angel de Quevedo 2779, Col. Formando Hogar, CP. 91897, Veracruz, Ver, Mexico.
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3
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Leuchtag HR. On molecular steps that activate a voltage sensitive ion channel at critical depolarization. Biophys Chem 2023; 301:107078. [PMID: 37544083 DOI: 10.1016/j.bpc.2023.107078] [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: 03/08/2023] [Revised: 06/16/2023] [Accepted: 07/23/2023] [Indexed: 08/08/2023]
Abstract
At high transmembrane electric field, a voltage sensitive ion channel is an insulator; when the field is critically reduced, it becomes a conductor of selected ions. The Channel Activation by Electrostatic Repulsion (CAbER) hypothesis proposes that an ordered polarization field of induced dipoles at the high electric field magnitude of the excitable state is overcome by thermal disorder at a critical depolarization. Increased repulsions between positive charges in the S4 segments cause an allosteric transition in which these segments expand and separate in a chiral proteinquake. The increased space allows the P segments to refold and the ion-semiconducting S5 and S6 segments to relax and expand outward in a breathing mode. Stripped permeant ions enter widened hydrogen bonds in the core helices of these segments. Driven by concentration differences and the electric field, the ions hop along transient pathways across the channel, appearing as fractal, stochastic bursts of single-channel currents. To support order amid thermal fluctuations, an object must be of a minimum size. The critical role of an ion channel's size suggests that the evolution of Metazoa became possible only after its DNA had grown enough to code for proteins larger than the correlation length.
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4
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Chaves G, Ayuyan AG, Cherny VV, Morgan D, Franzen A, Fieber L, Nausch L, Derst C, Mahorivska I, Jardin C, DeCoursey TE, Musset B. Unexpected expansion of the voltage-gated proton channel family. FEBS J 2023; 290:1008-1026. [PMID: 36062330 PMCID: PMC10911540 DOI: 10.1111/febs.16617] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Revised: 08/17/2022] [Accepted: 09/02/2022] [Indexed: 11/27/2022]
Abstract
Voltage-gated ion channels, whose first identified function was to generate action potentials, are divided into subfamilies with numerous members. The family of voltage-gated proton channels (HV ) is tiny. To date, all species found to express HV have exclusively one gene that codes for this unique ion channel. Here we report the discovery and characterization of three proton channel genes in the classical model system of neural plasticity, Aplysia californica. The three channels (AcHV 1, AcHV 2, and AcHV 3) are distributed throughout the whole animal. Patch-clamp analysis confirmed proton selectivity of these channels but they all differed markedly in gating. AcHV 1 gating resembled HV in mammalian cells where it is responsible for proton extrusion and charge compensation. AcHV 2 activates more negatively and conducts extensive inward proton current, properties likely to acidify the cytosol. AcHV 3, which differs from AcHV 1 and AcHV 2 in lacking the first arginine in the S4 helix, exhibits proton selective leak currents and weak voltage dependence. We report the expansion of the proton channel family, demonstrating for the first time the expression of three functionally distinct proton channels in a single species.
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Affiliation(s)
- Gustavo Chaves
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
| | - Artem G Ayuyan
- Department of Physiology & Biophysics, Rush University, Chicago, IL, USA
| | - Vladimir V Cherny
- Department of Physiology & Biophysics, Rush University, Chicago, IL, USA
| | - Deri Morgan
- Department of Radiation Oncology, University of Kansas Medical Center, MO, USA
| | - Arne Franzen
- Institute of Biological Information Processing, Molecular and Cellular Physiology (IBI-1), Jülich, Germany
| | - Lynne Fieber
- Department of Marine Biology and Ecology - Rosenstiel School of Marine and Atmospheric Science, Miami, FL, USA
| | - Lydia Nausch
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
- Department of Agriculture, Food and Nutrition, Institute of Nutrition and Food Supply Management, University of Applied Sciences Weihenstephan-Triesdorf, Freising, Germany
| | - Christian Derst
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
| | - Iryna Mahorivska
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
| | - Christophe Jardin
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
| | - Thomas E DeCoursey
- Department of Physiology & Biophysics, Rush University, Chicago, IL, USA
| | - Boris Musset
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Nuremberg, Germany
- Center of Physiology, Pathophysiology and Biophysics, Paracelsus Medical University, Salzburg, Austria
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5
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Wu X, Zhang L, Hong L. The role of Phe150 in human voltage-gated proton channel. iScience 2022; 25:105420. [PMID: 36388967 PMCID: PMC9646954 DOI: 10.1016/j.isci.2022.105420] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Revised: 08/15/2022] [Accepted: 10/18/2022] [Indexed: 11/06/2022] Open
Abstract
The voltage-gated proton channel Hv1 is a member of voltage-gated ion channels containing voltage-sensing domains (VSDs). The VSDs are made of four membrane-spanning segments (S1 through S4), and their function is to detect changes in membrane potential in the cells. A highly conserved phenylalanine 150 (F150) is located in the S2 segment of human voltage-gated proton channels. We previously discovered that the F150 is a binding site for the open channel blocker 2GBI. Here, we show that the Hv1 VSD voltage-dependent activation requires a hydrophobic group at position F150. We perform double-mutant cycle analysis to probe interactions between F150 and positively charged arginines in the S4 segment of the channel. Our results indicate that F150 interacts with two arginines (R2 and R3) in the S4 segment and catalyzes the transfer of the S4 arginines in the process of voltage-dependent activation. Hydrophobicity of F150 is crucial for human Hv1 channel voltage-dependent activation F150 interacts with R2 to stabilize the closed state of the Hv1 channel When depolarized, R3 moves upward to interact with F150 stabilizing the open state of Hv1 F150 is essential for the transfer of the Hv1 arginines in the process of voltage sensing
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Affiliation(s)
- Xin Wu
- Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA
| | - Lu Zhang
- Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA
| | - Liang Hong
- Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA
- Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, IL 60612, USA
- Corresponding author
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6
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Gualdani R, Gailly P, Yuan JH, Yerna X, Di Stefano G, Truini A, Cruccu G, Dib-Hajj SD, Waxman SG. A TRPM7 mutation linked to familial trigeminal neuralgia: Omega current and hyperexcitability of trigeminal ganglion neurons. Proc Natl Acad Sci U S A 2022; 119:e2119630119. [PMID: 36095216 PMCID: PMC9499596 DOI: 10.1073/pnas.2119630119] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Trigeminal neuralgia (TN) is a unique pain disorder characterized by intense paroxysmal facial pain within areas innervated by the trigeminal nerve. Although most cases of TN are sporadic, familial clusters of TN suggest that genetic factors may contribute to this disorder. Whole-exome sequencing in patients with TN reporting positive family history demonstrated a spectrum of variants of ion channels including TRP channels. Here, we used patch-clamp analysis and Ca2+ and Na+ imaging to assess a rare variant in the TRPM7 channel, p.Ala931Thr, within transmembrane domain 3, identified in a man suffering from unilateral TN. We showed that A931T produced an abnormal inward current carried by Na+ and insensitive to the pore blocker Gd3+. Hypothesizing that replacement of the hydrophobic alanine at position 931 with the more polar threonine destabilizes a hydrophobic ring, near the voltage sensor domain, we performed alanine substitutions of F971 and W972 and obtained results suggesting a role of A931-W972 hydrophobic interaction in S3-S4 hydrophobic cleft stability. Finally, we transfected trigeminal ganglion neurons with A931T channels and observed that expression of this TRPM7 variant lowers current threshold and resting membrane potential, and increases evoked firing activity in TG neurons. Our results support the notion that the TRPM7-A931T mutation located in the S3 segment at the interface with the transmembrane region S4, generates an omega current that carries Na+ influx in physiological conditions. A931T produces hyperexcitability and a sustained Na+ influx in trigeminal ganglion neurons that may underlie pain in this kindred with trigeminal neuralgia.
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Affiliation(s)
- Roberta Gualdani
- aInstitute of Neuroscience, Université catholique de Louvain, B-1200 Brussels, Belgium
| | - Philippe Gailly
- aInstitute of Neuroscience, Université catholique de Louvain, B-1200 Brussels, Belgium
| | - Jun-Hui Yuan
- bDepartment of Neurology, Yale School of Medicine, New Haven, CT 06520
- cCenter for Neuroscience and Regeneration Research, Veterans Affairs Connecticut Healthcare, West Haven, CT 06515
| | - Xavier Yerna
- aInstitute of Neuroscience, Université catholique de Louvain, B-1200 Brussels, Belgium
| | - Giulia Di Stefano
- dDepartment of Human Neuroscience, Sapienza University, 00185 Rome, Italy
| | - Andrea Truini
- dDepartment of Human Neuroscience, Sapienza University, 00185 Rome, Italy
| | - Giorgio Cruccu
- dDepartment of Human Neuroscience, Sapienza University, 00185 Rome, Italy
| | - Sulayman D. Dib-Hajj
- bDepartment of Neurology, Yale School of Medicine, New Haven, CT 06520
- cCenter for Neuroscience and Regeneration Research, Veterans Affairs Connecticut Healthcare, West Haven, CT 06515
| | - Stephen G. Waxman
- bDepartment of Neurology, Yale School of Medicine, New Haven, CT 06520
- cCenter for Neuroscience and Regeneration Research, Veterans Affairs Connecticut Healthcare, West Haven, CT 06515
- 2To whom correspondence may be addressed.
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7
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Van Theemsche KM, Heymans JG, Popovic NZ, Martinez-Morales E, Snyders DJ, Labro AJ. Offsetting Voltage-Dependent Kv1.5 Channel Opening Through Charged Residue Substitutions on Top of the First Transmembrane Segment. Bioelectricity 2022. [DOI: 10.1089/bioe.2022.0005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Kenny M. Van Theemsche
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, Ghent, Belgium
- Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Joni G. Heymans
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, Ghent, Belgium
| | - Nikola Z. Popovic
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, Ghent, Belgium
| | | | - Dirk J. Snyders
- Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Alain J. Labro
- Department of Basic and Applied Medical Sciences, Faculty of Medicine, Ghent University, Ghent, Belgium
- Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
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8
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Naranjo D. A scenario for the origin of life: Volume regulation by bacteriorhodopsin required extremely voltage sensitive Na‐channels and very selective K‐channels. Bioessays 2022; 44:e2100210. [DOI: 10.1002/bies.202100210] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Revised: 07/20/2022] [Accepted: 07/21/2022] [Indexed: 12/25/2022]
Affiliation(s)
- David Naranjo
- Instituto de Neurociencia, Facultad de Ciencias Universidad de Valparaíso Playa Ancha Valparaíso Chile
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9
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Yang ND, Kanyo R, Zhao L, Li J, Kang PW, Dou AK, White KM, Shi J, Nerbonne JM, Kurata HT, Cui J. Electro-mechanical coupling of KCNQ channels is a target of epilepsy-associated mutations and retigabine. SCIENCE ADVANCES 2022; 8:eabo3625. [PMID: 35857840 PMCID: PMC9299555 DOI: 10.1126/sciadv.abo3625] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/29/2022] [Accepted: 06/07/2022] [Indexed: 06/15/2023]
Abstract
KCNQ2 and KCNQ3 form the M-channels that are important in regulating neuronal excitability. Inherited mutations that alter voltage-dependent gating of M-channels are associated with neonatal epilepsy. In the homolog KCNQ1 channel, two steps of voltage sensor activation lead to two functionally distinct open states, the intermediate-open (IO) and activated-open (AO), which define the gating, physiological, and pharmacological properties of KCNQ1. However, whether the M-channel shares the same mechanism is unclear. Here, we show that KCNQ2 and KCNQ3 feature only a single conductive AO state but with a conserved mechanism for the electro-mechanical (E-M) coupling between voltage sensor activation and pore opening. We identified some epilepsy-linked mutations in KCNQ2 and KCNQ3 that disrupt E-M coupling. The antiepileptic drug retigabine rescued KCNQ3 currents that were abolished by a mutation disrupting E-M coupling, suggesting that modulating the E-M coupling in KCNQ channels presents a potential strategy for antiepileptic therapy.
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Affiliation(s)
- Nien-Du Yang
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, and Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO 63130, USA
| | - Richard Kanyo
- Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
| | - Lu Zhao
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, and Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO 63130, USA
| | - Jingru Li
- Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
| | - Po Wei Kang
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, and Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO 63130, USA
| | - Alex Kelly Dou
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, and Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO 63130, USA
| | - Kelli McFarland White
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, and Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO 63130, USA
| | - Jingyi Shi
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, and Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO 63130, USA
| | - Jeanne M. Nerbonne
- Departments of Developmental Biology and Internal Medicine, Cardiovascular Division, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Harley T. Kurata
- Department of Pharmacology, Alberta Diabetes Institute, University of Alberta, Edmonton, AB, Canada
| | - Jianmin Cui
- Department of Biomedical Engineering, Center for the Investigation of Membrane Excitability Disorders, and Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO 63130, USA
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10
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Abstract
In neurosecretion, allosteric communication between voltage sensors and Ca2+ binding in BK channels is crucially involved in damping excitatory stimuli. Nevertheless, the voltage-sensing mechanism of BK channels is still under debate. Here, based on gating current measurements, we demonstrate that two arginines in the transmembrane segment S4 (R210 and R213) function as the BK gating charges. Significantly, the energy landscape of the gating particles is electrostatically tuned by a network of salt bridges contained in the voltage sensor domain (VSD). Molecular dynamics simulations and proton transport experiments in the hyperpolarization-activated R210H mutant suggest that the electric field drops off within a narrow septum whose boundaries are defined by the gating charges. Unlike Kv channels, the charge movement in BK appears to be limited to a small displacement of the guanidinium moieties of R210 and R213, without significant movement of the S4.
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11
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Sattler C, Benndorf K. Enlightening activation gating in P2X receptors. Purinergic Signal 2022; 18:177-191. [PMID: 35188598 PMCID: PMC9123132 DOI: 10.1007/s11302-022-09850-w] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Accepted: 02/04/2022] [Indexed: 12/20/2022] Open
Abstract
P2X receptors are trimeric nonselective cation channels gated by ATP. They assemble from seven distinct subunit isoforms as either homo- or heteromeric complexes and contain three extracellularly located binding sites for ATP. P2X receptors are expressed in nearly all tissues and are there involved in physiological processes like synaptic transmission, pain, and inflammation. Thus, they are a challenging pharmacological target. The determination of crystal and cryo-EM structures of several isoforms in the last decade in closed, open, and desensitized states has provided a firm basis for interpreting the huge amount of functional and biochemical data. Electrophysiological characterization in conjugation with optical approaches has generated significant insights into structure–function relationships of P2X receptors. This review focuses on novel optical and related approaches to better understand the conformational changes underlying the activation of these receptors.
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Affiliation(s)
- Christian Sattler
- Institut Für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, 07740, Jena, Germany.
| | - Klaus Benndorf
- Institut Für Physiologie II, Universitätsklinikum Jena, Friedrich-Schiller-Universität Jena, 07740, Jena, Germany.
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12
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Su T, Chen ML, Liu LH, Meng H, Tang B, Liu XR, Liao WP. Critical Role of E1623 Residue in S3-S4 Loop of Nav1.1 Channel and Correlation Between Nature of Substitution and Functional Alteration. Front Mol Neurosci 2022; 14:797628. [PMID: 35082603 PMCID: PMC8785683 DOI: 10.3389/fnmol.2021.797628] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Accepted: 12/15/2021] [Indexed: 12/24/2022] Open
Abstract
Objective: An overwhelming majority of the genetic variants associated with genetic disorders are missense. The association between the nature of substitution and the functional alteration, which is critical in determining the pathogenicity of variants, remains largely unknown. With a novel missense variant (E1623A) identified from two epileptic cases, which occurs in the extracellular S3-S4 loop of Nav1.1, we studied functional changes of all latent mutations at residue E1623, aiming to understand the relationship between substitution nature and functional alteration. Methods: Six latent mutants with amino acid substitutions at E1623 were generated, followed by measurements of their electrophysiological alterations. Different computational analyses were used to parameterize the residue alterations. Results: Structural modeling indicated that the E1623 was located in the peripheral region far from the central pore, and contributed to the tight turn of the S3-S4 loop. The E1623 residue exhibited low functional tolerance to the substitutions with the most remarkable loss-of-function found in E1623A, including reduced current density, less steady-state availability of activation and inactivation, and slower recovery from fast inactivation. Correlation analysis between electrophysiological parameters and the parameterized physicochemical properties of different residues suggested that hydrophilicity of side-chain at E1623 might be a crucial contributor for voltage-dependent kinetics. However, none of the established algorithms on the physicochemical variations of residues could well predict changes in the channel conductance property indicated by peak current density. Significance: The results established the important role of the extracellular S3-S4 loop in Nav1.1 channel gating and proposed a possible effect of local conformational loop flexibility on channel conductance and kinetics. Site-specific knowledge of protein will be a fundamental task for future bioinformatics.
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Affiliation(s)
- Tao Su
- Department of Neurology, Institute of Neuroscience, Second Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
- Key Laboratory of Neurogenetics and Channelopathies of the Ministry of Education of China, Guangzhou, China
| | - Meng-Long Chen
- Department of Neurology, Institute of Neuroscience, Second Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
- Key Laboratory of Neurogenetics and Channelopathies of the Ministry of Education of China, Guangzhou, China
| | - Li-Hong Liu
- Department of Neurology, Institute of Neuroscience, Second Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
- Key Laboratory of Neurogenetics and Channelopathies of the Ministry of Education of China, Guangzhou, China
| | - Hen Meng
- Department of Neurology, Institute of Neuroscience, Second Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
- Key Laboratory of Neurogenetics and Channelopathies of the Ministry of Education of China, Guangzhou, China
| | - Bin Tang
- Department of Neurology, Institute of Neuroscience, Second Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
- Key Laboratory of Neurogenetics and Channelopathies of the Ministry of Education of China, Guangzhou, China
| | - Xiao-Rong Liu
- Department of Neurology, Institute of Neuroscience, Second Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
- Key Laboratory of Neurogenetics and Channelopathies of the Ministry of Education of China, Guangzhou, China
| | - Wei-Ping Liao
- Department of Neurology, Institute of Neuroscience, Second Affiliated Hospital of Guangzhou Medical University, Guangzhou, China
- Key Laboratory of Neurogenetics and Channelopathies of the Ministry of Education of China, Guangzhou, China
- *Correspondence: Wei-Ping Liao
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13
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IUPAB 2021 Symposium 13: ion channels and membrane transporters. Biophys Rev 2021; 13:871-873. [DOI: 10.1007/s12551-021-00874-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Accepted: 10/26/2021] [Indexed: 10/19/2022] Open
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14
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Priest MF, Lee EE, Bezanilla F. Tracking the movement of discrete gating charges in a voltage-gated potassium channel. eLife 2021; 10:58148. [PMID: 34779404 PMCID: PMC8635975 DOI: 10.7554/elife.58148] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Accepted: 11/08/2021] [Indexed: 01/18/2023] Open
Abstract
Positively charged amino acids respond to membrane potential changes to drive voltage sensor movement in voltage-gated ion channels, but determining the displacements of voltage sensor gating charges has proven difficult. We optically tracked the movement of the two most extracellular charged residues (R1 and R2) in the Shaker potassium channel voltage sensor using a fluorescent positively charged bimane derivative (qBBr) that is strongly quenched by tryptophan. By individually mutating residues to tryptophan within the putative pathway of gating charges, we observed that the charge motion during activation is a rotation and a tilted translation that differs between R1 and R2. Tryptophan-induced quenching of qBBr also indicates that a crucial residue of the hydrophobic plug is linked to the Cole-Moore shift through its interaction with R1. Finally, we show that this approach extends to additional voltage-sensing membrane proteins using the Ciona intestinalis voltage-sensitive phosphatase (CiVSP).
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Affiliation(s)
- Michael F Priest
- Committee on Neurobiology and Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, United States
| | - Elizabeth El Lee
- Committee on Neurobiology and Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, United States
| | - Francisco Bezanilla
- Committee on Neurobiology and Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, United States.,Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, United States
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15
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Sokolov VS, Cherny VV, Ayuyan AG, DeCoursey TE. Analysis of an electrostatic mechanism for ΔpH dependent gating of the voltage-gated proton channel, H V1, supports a contribution of protons to gating charge. BIOCHIMICA ET BIOPHYSICA ACTA. BIOENERGETICS 2021; 1862:148480. [PMID: 34363792 PMCID: PMC8432343 DOI: 10.1016/j.bbabio.2021.148480] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Revised: 07/23/2021] [Accepted: 08/02/2021] [Indexed: 11/23/2022]
Abstract
Voltage-gated proton channels (HV1) resemble the voltage-sensing domain of other voltage-gated ion channels, but differ in containing the conduction pathway. Essential to the functions of HV1 channels in many cells and species is a unique feature called ΔpH dependent gating. The pH on both sides of the membrane strictly regulates the voltage range of channel opening, generally resulting in exclusively outward proton current. Two types of mechanisms could produce ΔpH dependent gating. The "countercharge" mechanism proposes that protons destabilize salt bridges between amino acids in the protein that stabilize specific gating configurations (closed or open). An "electrostatic" mechanism proposes that protons bound to the channel alter the electrical field sensed by the protein. Obligatory proton binding within the membrane electrical field would contribute to measured gating charge. Estimations on the basis of the electrostatic model explain ΔpH dependent gating, but quantitative modeling requires calculations of the electric field inside the protein which, in turn, requires knowledge of its structure. We conclude that both mechanisms operate and contribute to ΔpH dependent gating of HV1.
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Affiliation(s)
- Valerij S Sokolov
- Frumkin Institute of Physical Chemistry and Electrochemistry of Russian Academy of Sciences, Moscow 119071, Russia
| | - Vladimir V Cherny
- Department of Physiology & Biophysics, Rush University, Chicago, IL 60612, USA
| | - Artem G Ayuyan
- Department of Physiology & Biophysics, Rush University, Chicago, IL 60612, USA
| | - Thomas E DeCoursey
- Department of Physiology & Biophysics, Rush University, Chicago, IL 60612, USA.
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16
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Catacuzzeno L, Franciolini F, Bezanilla F, Eisenberg RS. Gating current noise produced by Brownian models of a voltage sensor. Biophys J 2021; 120:3983-4001. [PMID: 34411574 DOI: 10.1016/j.bpj.2021.08.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Revised: 06/07/2021] [Accepted: 08/11/2021] [Indexed: 11/19/2022] Open
Abstract
The activation of voltage-dependent ion channels is associated with the movement of gating charges, which give rise to gating currents. Although gating currents from a single channel are too small to be detected, analysis of the fluctuations of macroscopic gating currents from a population of channels allows a good guess of their magnitude. The analysis of experimental gating current fluctuations, when interpreted in terms of a rate model of channel activation and assuming sufficiently high bandwidth, is in accordance with the presence of a main step along the activation pathway carrying a charge of 2.3-2.4 e0. To give a physical interpretation to these results and to relate them to the known atomic structure of the voltage sensor domain, we used a Brownian model of voltage-dependent gating based on atomic detail structure, that follows the laws of electrodynamics. The model predicts gating currents and gating current fluctuations essentially similar to those experimentally observed. The detailed study of the model output, also performed by making several simplifications aimed at understanding the basic dependencies of the gating current fluctuations, suggests that in real channels the voltage sensor moves along a sequence of intermediate states separated by relatively low (<5 kT) energy barriers. As a consequence, crossings of successive gating charges through the gating pore become very frequent, and the corresponding current shots are often seen to overlap because of the relatively high filtering. Notably, this limited bandwidth effect is at the origin of the relatively high single-step charge experimentally detected.
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Affiliation(s)
- Luigi Catacuzzeno
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy.
| | - Fabio Franciolini
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy
| | - Francisco Bezanilla
- Department of Biochemistry and Molecular Biology, University of Chicago, Gordon Center for Integrative Sciences, Chicago, Illinois
| | - Robert S Eisenberg
- Department of Physiology and Biophysics, Rush University, Chicago, Illinois; Department of Applied Mathematics, Illinois Institute of Technology, Chicago, Illinois
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17
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Structural Pharmacology of Voltage-Gated Sodium Channels. J Mol Biol 2021; 433:166967. [PMID: 33794261 DOI: 10.1016/j.jmb.2021.166967] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Revised: 03/22/2021] [Accepted: 03/22/2021] [Indexed: 12/19/2022]
Abstract
Voltage-gated sodium (NaV) channels initiate and propagate action potentials in excitable tissues to mediate key physiological processes including heart contraction and nervous system function. Accordingly, NaV channels are major targets for drugs, toxins and disease-causing mutations. Recent breakthroughs in cryo-electron microscopy have led to the visualization of human NaV1.1, NaV1.2, NaV1.4, NaV1.5 and NaV1.7 channel subtypes at high-resolution. These landmark studies have greatly advanced our structural understanding of channel architecture, ion selectivity, voltage-sensing, electromechanical coupling, fast inactivation, and the molecular basis underlying NaV channelopathies. NaV channel structures have also been increasingly determined in complex with toxin and small molecule modulators that target either the pore module or voltage sensor domains. These structural studies have provided new insights into the mechanisms of pharmacological action and opportunities for subtype-selective NaV channel drug design. This review will highlight the structural pharmacology of human NaV channels as well as the potential use of engineered and chimeric channels in future drug discovery efforts.
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18
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Bassetto CA, Carvalho-de-Souza JL, Bezanilla F. Molecular basis for functional connectivity between the voltage sensor and the selectivity filter gate in Shaker K + channels. eLife 2021; 10:63077. [PMID: 33620313 PMCID: PMC7943188 DOI: 10.7554/elife.63077] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Accepted: 02/22/2021] [Indexed: 01/18/2023] Open
Abstract
In Shaker K+ channels, the S4-S5 linker couples the voltage sensor (VSD) and pore domain (PD). Another coupling mechanism is revealed using two W434F-containing channels: L361R:W434F and L366H:W434F. In L361R:W434F, W434F affects the L361R VSD seen as a shallower charge-voltage (Q-V) curve that crosses the conductance-voltage (G-V) curve. In L366H:W434F, L366H relieves the W434F effect converting a non-conductive channel in a conductive one. We report a chain of residues connecting the VSD (S4) to the selectivity filter (SF) in the PD of an adjacent subunit as the molecular basis for voltage sensor selectivity filter gate (VS-SF) coupling. Single alanine substitutions in this region (L409A, S411A, S412A, or F433A) are enough to disrupt the VS-SF coupling, shown by the absence of Q-V and G-V crossing in L361R:W434F mutant and by the lack of ionic conduction in the L366H:W434F mutant. This residue chain defines a new coupling between the VSD and the PD in voltage-gated channels.
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Affiliation(s)
- Carlos Az Bassetto
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, United States
| | - João Luis Carvalho-de-Souza
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, United States.,Department of Anesthesiology, University of Arizona, Tucson, United States
| | - Francisco Bezanilla
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, United States.,Institute for Biophysical Dynamics, The University of Chicago, Chicago, United States.,Centro Interdisciplinario de Neurociencias, Facultad de Ciencias, Universidad de Valparaiso, Valparaiso, Chile
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19
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Eisenberg RS. Maxwell Equations without a Polarization Field, Using a Paradigm from Biophysics. ENTROPY (BASEL, SWITZERLAND) 2021; 23:172. [PMID: 33573137 PMCID: PMC7912333 DOI: 10.3390/e23020172] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/13/2020] [Revised: 01/26/2021] [Accepted: 01/26/2021] [Indexed: 01/17/2023]
Abstract
When forces are applied to matter, the distribution of mass changes. Similarly, when an electric field is applied to matter with charge, the distribution of charge changes. The change in the distribution of charge (when a local electric field is applied) might in general be called the induced charge. When the change in charge is simply related to the applied local electric field, the polarization field P is widely used to describe the induced charge. This approach does not allow electrical measurements (in themselves) to determine the structure of the polarization fields. Many polarization fields will produce the same electrical forces because only the divergence of polarization enters Maxwell's first equation, relating charge and electric forces and field. The curl of any function can be added to a polarization field P without changing the electric field at all. The divergence of the curl is always zero. Additional information is needed to specify the curl and thus the structure of the P field. When the structure of charge changes substantially with the local electric field, the induced charge is a nonlinear and time dependent function of the field and P is not a useful framework to describe either the electrical or structural basis-induced charge. In the nonlinear, time dependent case, models must describe the charge distribution and how it varies as the field changes. One class of models has been used widely in biophysics to describe field dependent charge, i.e., the phenomenon of nonlinear time dependent induced charge, called 'gating current' in the biophysical literature. The operational definition of gating current has worked well in biophysics for fifty years, where it has been found to makes neurons respond sensitively to voltage. Theoretical estimates of polarization computed with this definition fit experimental data. I propose that the operational definition of gating current be used to define voltage and time dependent induced charge, although other definitions may be needed as well, for example if the induced charge is fundamentally current dependent. Gating currents involve substantial changes in structure and so need to be computed from a combination of electrodynamics and mechanics because everything charged interacts with everything charged as well as most things mechanical. It may be useful to separate the classical polarization field as a component of the total induced charge, as it is in biophysics. When nothing is known about polarization, it is necessary to use an approximate representation of polarization with a dielectric constant that is a single real positive number. This approximation allows important results in some cases, e.g., design of integrated circuits in silicon semiconductors, but can be seriously misleading in other cases, e.g., ionic solutions.
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Affiliation(s)
- Robert S. Eisenberg
- Department of Applied Mathematics, Illinois Institute of Technology, Chicago, IL 60616, USA; ; Tel.: +1-708-932-2597
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, IL 60612, USA
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20
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Catacuzzeno L, Sforna L, Franciolini F, Eisenberg RS. Multiscale modeling shows that dielectric differences make NaV channels faster than KV channels. J Gen Physiol 2021; 153:211724. [PMID: 33502441 PMCID: PMC7845922 DOI: 10.1085/jgp.202012706] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Revised: 11/22/2020] [Accepted: 12/18/2020] [Indexed: 12/31/2022] Open
Abstract
The generation of action potentials in excitable cells requires different activation kinetics of voltage-gated Na (NaV) and K (KV) channels. NaV channels activate much faster and allow the initial Na+ influx that generates the depolarizing phase and propagates the signal. Recent experimental results suggest that the molecular basis for this kinetic difference is an amino acid side chain located in the gating pore of the voltage sensor domain, which is a highly conserved isoleucine in KV channels but an equally highly conserved threonine in NaV channels. Mutagenesis suggests that the hydrophobicity of this side chain in Shaker KV channels regulates the energetic barrier that gating charges cross as they move through the gating pore and control the rate of channel opening. We use a multiscale modeling approach to test this hypothesis. We use high-resolution molecular dynamics to study the effect of the mutation on polarization charge within the gating pore. We then incorporate these results in a lower-resolution model of voltage gating to predict the effect of the mutation on the movement of gating charges. The predictions of our hierarchical model are fully consistent with the tested hypothesis, thus suggesting that the faster activation kinetics of NaV channels comes from a stronger dielectric polarization by threonine (NaV channel) produced as the first gating charge enters the gating pore compared with isoleucine (KV channel).
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Affiliation(s)
- Luigi Catacuzzeno
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy
| | - Luigi Sforna
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy
| | - Fabio Franciolini
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy
| | - Robert S Eisenberg
- Department of Physiology and Biophysics, Rush University, Chicago, IL.,Department of Applied Mathematics, Illinois Institute of Technology, Chicago, IL
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21
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Unravelling the intricate cooperativity of subunit gating in P2X2 ion channels. Sci Rep 2020; 10:21751. [PMID: 33303878 PMCID: PMC7729398 DOI: 10.1038/s41598-020-78672-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Accepted: 11/25/2020] [Indexed: 01/23/2023] Open
Abstract
Ionotropic purinergic (P2X) receptors are trimeric channels that are activated by the binding of ATP. They are involved in multiple physiological functions, including synaptic transmission, pain and inflammation. The mechanism of activation is still elusive. Here we kinetically unraveled and quantified subunit activation in P2X2 receptors by an extensive global fit approach with four complex and intimately coupled kinetic schemes to currents obtained from wild type and mutated receptors using ATP and its fluorescent derivative 2-[DY-547P1]-AET-ATP (fATP). We show that the steep concentration-activation relationship in wild type channels is caused by a subunit flip reaction with strong positive cooperativity, overbalancing a pronounced negative cooperativity for the three ATP binding steps, that the net probability fluxes in the model generate a marked hysteresis in the activation-deactivation cycle, and that the predicted fATP binding matches the binding measured by fluorescence. Our results shed light into the intricate activation process of P2X channels.
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22
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Groome JR, Bayless-Edwards L. Roles for Countercharge in the Voltage Sensor Domain of Ion Channels. Front Pharmacol 2020; 11:160. [PMID: 32180723 PMCID: PMC7059764 DOI: 10.3389/fphar.2020.00160] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Accepted: 02/07/2020] [Indexed: 12/19/2022] Open
Abstract
Voltage-gated ion channels share a common structure typified by peripheral, voltage sensor domains. Their S4 segments respond to alteration in membrane potential with translocation coupled to ion permeation through a central pore domain. The mechanisms of gating in these channels have been intensely studied using pioneering methods such as measurement of charge displacement across a membrane, sequencing of genes coding for voltage-gated ion channels, and the development of all-atom molecular dynamics simulations using structural information from prokaryotic and eukaryotic channel proteins. One aspect of this work has been the description of the role of conserved negative countercharges in S1, S2, and S3 transmembrane segments to promote sequential salt-bridge formation with positively charged residues in S4 segments. These interactions facilitate S4 translocation through the lipid bilayer. In this review, we describe functional and computational work investigating the role of these countercharges in S4 translocation, voltage sensor domain hydration, and in diseases resulting from countercharge mutations.
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Affiliation(s)
- James R. Groome
- Department of Biological Sciences, Idaho State University, Pocatello, ID, United States
| | - Landon Bayless-Edwards
- Department of Biological Sciences, Idaho State University, Pocatello, ID, United States
- Oregon Health and Sciences University School of Medicine, Portland, OR, United States
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23
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Catacuzzeno L, Sforna L, Franciolini F. Voltage-dependent gating in K channels: experimental results and quantitative models. Pflugers Arch 2019; 472:27-47. [PMID: 31863286 DOI: 10.1007/s00424-019-02336-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Revised: 11/27/2019] [Accepted: 11/28/2019] [Indexed: 12/18/2022]
Abstract
Voltage-dependent K channels open and close in response to voltage changes across the cell membrane. This voltage dependence was postulated to depend on the presence of charged particles moving through the membrane in response to voltage changes. Recording of gating currents originating from the movement of these particles fully confirmed this hypothesis, and gave substantial experimental clues useful for the detailed understanding of the process. In the absence of structural information, the voltage-dependent gating was initially investigated using discrete Markov models, an approach only capable of providing a kinetic and thermodynamic comprehension of the process. The elucidation of the crystal structure of the first voltage-dependent channel brought in a dramatic change of pace in the understanding of channel gating, and in modeling the underlying processes. It was now possible to construct quantitative models using molecular dynamics, where all the interactions of each individual atom with the surroundings were taken into account, and its motion predicted by Newton's laws. Unfortunately, this modeling is computationally very demanding, and in spite of the advances in simulation procedures and computer technology, it is still limited in its predictive ability. To overcome these limitations, several groups have developed more macroscopic voltage gating models. Their approaches understandably require a number of approximations, which must however be physically well justified. One of these models, based on the description of the voltage sensor as a Brownian particle, that we have recently developed, is able to simultaneously describe the behavior of a single voltage sensor and to predict the macroscopic gating current originating from a population of sensors. The basics of this model are here described, and a typical application using the Kv1.2/2.1 chimera channel structure is also presented.
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Affiliation(s)
- Luigi Catacuzzeno
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Elce di Sotto 8, 06123, Perugia, Italy.
| | - Luigi Sforna
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Elce di Sotto 8, 06123, Perugia, Italy
| | - Fabio Franciolini
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Elce di Sotto 8, 06123, Perugia, Italy.
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24
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Romero-Romero S, Martínez-Delgado G, Balleza D. Voltage vs. Ligand II: Structural insights of the intrinsic flexibility in cyclic nucleotide-gated channels. Channels (Austin) 2019; 13:382-399. [PMID: 31552786 PMCID: PMC6768053 DOI: 10.1080/19336950.2019.1666456] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2019] [Revised: 08/30/2019] [Accepted: 09/03/2019] [Indexed: 12/23/2022] Open
Abstract
In the preceding article, we present a flexibility analysis of the voltage-gated ion channel (VGIC) superfamily. In this study, we describe in detail the flexibility profile of the voltage-sensor domain (VSD) and the pore domain (PD) concerning the evolution of 6TM ion channels. In particular, we highlight the role of flexibility in the emergence of CNG channels and describe a significant level of sequence similarity between the archetypical VSD and the TolQ proteins. A highly flexible S4-like segment exhibiting Lys instead Arg for these membrane proteins is reported. Sequence analysis indicates that, in addition to this S4-like segment, TolQ proteins also show similarity with specific motifs in S2 and S3 from typical V-sensors. Notably, S3 flexibility profiles from typical VSDs and S3-like in TolQ proteins are also similar. Interestingly, TolQ from early divergent prokaryotes are comparatively more flexible than those in modern counterparts or true V-sensors. Regarding the PD, we also found that 2TM K+-channels in early prokaryotes are considerably more flexible than the ones in modern microbes, and such flexibility is comparable to the one present in CNG channels. Voltage dependence is mainly exhibited in prokaryotic CNG channels whose VSD is rigid whereas the eukaryotic CNG channels are considerably more flexible and poorly V-dependent. The implication of the flexibility present in CNG channels, their sensitivity to cyclic nucleotides and the cation selectivity are discussed. Finally, we generated a structural model of the putative cyclic nucleotide-modulated ion channel, which we coined here as AqK, from the thermophilic bacteria Aquifex aeolicus, one of the earliest diverging prokaryotes known. Overall, our analysis suggests that V-sensors in CNG-like channels were essentially rigid in early prokaryotes but raises the possibility that this module was probably part of a very flexible stator protein of the bacterial flagellum motor complex.
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Affiliation(s)
- Sergio Romero-Romero
- Facultad de Medicina, Departamento de Bioquímica, Universidad Nacional Autónoma de México, 04510 Mexico City, Mexico. Current address: Department of Biochemistry, University of Bayreuth, Bayreuth, Germany
| | - Gustavo Martínez-Delgado
- Laboratorio de Genómica de Enfermedades Cardiovasculares, Instituto Nacional de Medicina Genómica, Mexico City, Mexico
| | - Daniel Balleza
- Departamento de Química ICET, Universidad Autónoma de Guadalajara, Zapopan, Jalisco, Mexico
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25
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Balleza D, Rosas ME, Romero-Romero S. Voltage vs. Ligand I: Structural basis of the intrinsic flexibility of S3 segment and its significance in ion channel activation. Channels (Austin) 2019; 13:455-476. [PMID: 31647368 PMCID: PMC6833973 DOI: 10.1080/19336950.2019.1674242] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
We systematically predict the internal flexibility of the S3 segment, one of the most mobile elements in the voltage-sensor domain. By analyzing the primary amino acid sequences of V-sensor containing proteins, including Hv1, TPC channels and the voltage-sensing phosphatases, we established correlations between the local flexibility and modes of activation for different members of the VGIC superfamily. Taking advantage of the structural information available, we also assessed structural aspects to understand the role played by the flexibility of S3 during the gating of the pore. We found that S3 flexibility is mainly determined by two specific regions: (1) a short NxxD motif in the N-half portion of the helix (S3a), and (2) a short sequence at the beginning of the so-called paddle motif where the segment has a kink that, in some cases, divide S3 into two distinct helices (S3a and S3b). A good correlation between the flexibility of S3 and the reported sensitivity to temperature and mechanical stretch was found. Thus, if the channel exhibits high sensitivity to heat or membrane stretch, local S3 flexibility is low. On the other hand, high flexibility of S3 is preferentially associated to channels showing poor heat and mechanical sensitivities. In contrast, we did not find any apparent correlation between S3 flexibility and voltage or ligand dependence. Overall, our results provide valuable insights into the dynamics of channel-gating and its modulation.
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Affiliation(s)
- Daniel Balleza
- Departamento de Química ICET, Universidad Autónoma de Guadalajara , Zapopan Jalisco , Mexico
| | - Mario E Rosas
- Departamento de Química ICET, Universidad Autónoma de Guadalajara , Zapopan Jalisco , Mexico
| | - Sergio Romero-Romero
- Facultad de Medicina, Departamento de Bioquímica, Universidad Nacional Autónoma de México, 04510 Mexico City, Mexico. Current address: Department of Biochemistry, University of Bayreuth , Bayreuth , Germany
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26
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Bassetto CAZ, Carvalho-de-Souza JL, Bezanilla F. Metal Bridge in S4 Segment Supports Helix Transition in Shaker Channel. Biophys J 2019; 118:922-933. [PMID: 31635788 DOI: 10.1016/j.bpj.2019.08.035] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Revised: 08/22/2019] [Accepted: 08/29/2019] [Indexed: 02/05/2023] Open
Abstract
Voltage-gated ion channels play important roles in physiological processes, especially in excitable cells, in which they shape the action potential. In S4-based voltage sensors voltage-gated channels, a common feature is shared; the transmembrane segment 4 (S4) contains positively charged residues intercalated by hydrophobic residues. Although several advances have been made in understating how S4 moves through a hydrophobic plug upon voltage changes, the possible helix transition from α- to 310-helix in S4 during the activation process is still unresolved. Here, we have mutated several hydrophobic residues from I360 to F370 in the S4 segment into histidine, in i, i + 3 and i, i + 6 or i, i + 4 and i, i + 7 pairs, to favor 310- or α-helical conformations, respectively. We have taken advantage of the ability of His to coordinate Zn2+ to promote metal ion bridges, and we have found that the histidine introduced at position 366 (L366H) can interact with the introduced histidine at position 370 (stabilizing that portion of the S4 segment in α-helical conformation). In the presence of 20 μM of Zn2+, the activation currents of L366H:F370H channels were slowed down by a factor of 3.5, and the voltage dependence is shifted by 10 mV toward depolarized potentials with no change on the deactivation time constant. Our data supports that by stabilizing a region of the S4 segment in α-helical conformation, a closed (resting or intermediate) state is stabilized rather than destabilizing the open (active) state. Taken together, our data indicates that S4 undergoes α-helical conformation to a short-lived different secondary structure transiently before reaching the active state in the activation process.
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Affiliation(s)
- Carlos A Z Bassetto
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois
| | | | - Francisco Bezanilla
- Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois; Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois; Centro Interdisciplinario de Neurociencias, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile.
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27
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De La Rosa V, Ramsey IS. Gating Currents in the Hv1 Proton Channel. Biophys J 2019; 114:2844-2854. [PMID: 29925021 DOI: 10.1016/j.bpj.2018.04.049] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2018] [Revised: 04/19/2018] [Accepted: 04/30/2018] [Indexed: 11/25/2022] Open
Abstract
The Hv1 proton channel shares striking structural homology with fourth transmembrane helical segment-type voltage-sensor (VS) domains but manifests distinctive functional properties, including a proton-selective "aqueous" conductance and allosteric control of voltage-dependent gating by changes in the transmembrane pH gradient. The mechanisms responsible for Hv1's functional properties remain poorly understood, in part because methods for measuring gating currents that directly report VS activation have not yet been described. Here, we describe an approach that allows robust and reproducible measurement of gating-associated charge movements in Hv1. Gating currents reveal that VS activation and proton-selective aqueous conductance opening are thermodynamically distinct steps in the Hv1 activation pathway and show that pH changes directly alter VS activation. The availability of an assay for gating currents in Hv1 may aid future efforts to elucidate the molecular mechanisms of gating cooperativity, pH-dependent modulation, and H+ selectivity in a model VS domain protein.
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Affiliation(s)
- Victor De La Rosa
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, Virginia
| | - Ian Scott Ramsey
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, Virginia.
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Hydrophobic gasket mutation produces gating pore currents in closed human voltage-gated proton channels. Proc Natl Acad Sci U S A 2019; 116:18951-18961. [PMID: 31462498 PMCID: PMC6754559 DOI: 10.1073/pnas.1905462116] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
A large family of membrane proteins, voltage-gated ion channels, regulate a vast array of physiological functions in essentially all life forms. How these molecules sense membrane potential and respond by creating ionic conduction is incompletely understood. The voltage sensors of these channels contain a “hydrophobic gasket,” a ring of hydrophobic amino acids near the center of the membrane, separating internal and external aqueous solutions. Although voltage-gated proton channels, HV1, resemble voltage-sensing domains of other channels, they differ fundamentally. On depolarization, HV1 conducts protons, whereas other voltage sensors open a physically distinct pore. We identify Val109, Phe150, Val177, and Val178 as the hHV1 hydrophobic gasket. Replacement with less hydrophobic amino acids accelerated channel opening and caused proton-selective leak through closed channels. The hydrophobic gasket (HG), a ring of hydrophobic amino acids in the voltage-sensing domain of most voltage-gated ion channels, forms a constriction between internal and external aqueous vestibules. Cationic Arg or Lys side chains lining the S4 helix move through this “gating pore” when the channel opens. S4 movement may occur during gating of the human voltage-gated proton channel, hHV1, but proton current flows through the same pore in open channels. Here, we replaced putative HG residues with less hydrophobic residues or acidic Asp. Substitution of individuals, pairs, or all 3 HG positions did not impair proton selectivity. Evidently, the HG does not act as a secondary selectivity filter. However, 2 unexpected functions of the HG in HV1 were discovered. Mutating HG residues independently accelerated channel opening and compromised the closed state. Mutants exhibited open–closed gating, but strikingly, at negative voltages where “normal” gating produces a nonconducting closed state, the channel leaked protons. Closed-channel proton current was smaller than open-channel current and was inhibited by 10 μM Zn2+. Extreme hyperpolarization produced a deeper closed state through a weakly voltage-dependent transition. We functionally identify the HG as Val109, Phe150, Val177, and Val178, which play a critical and exclusive role in preventing H+ influx through closed channels. Molecular dynamics simulations revealed enhanced mobility of Arg208 in mutants exhibiting H+ leak. Mutation of HG residues produces gating pore currents reminiscent of several channelopathies.
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29
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Costé de Bagneaux P, Campiglio M, Benedetti B, Tuluc P, Flucher BE. Role of putative voltage-sensor countercharge D4 in regulating gating properties of Ca V1.2 and Ca V1.3 calcium channels. Channels (Austin) 2019; 12:249-261. [PMID: 30001160 PMCID: PMC6161609 DOI: 10.1080/19336950.2018.1482183] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Voltage-dependent calcium channels (CaV) activate over a wide range of membrane potentials, and the voltage-dependence of activation of specific channel isoforms is exquisitely tuned to their diverse functions in excitable cells. Alternative splicing further adds to the stunning diversity of gating properties. For example, developmentally regulated insertion of an alternatively spliced exon 29 in the fourth voltage-sensing domain (VSD IV) of CaV1.1 right-shifts voltage-dependence of activation by 30 mV and decreases the current amplitude several-fold. Previously we demonstrated that this regulation of gating properties depends on interactions between positive gating charges (R1, R2) and a negative countercharge (D4) in VSD IV of CaV1.1. Here we investigated whether this molecular mechanism plays a similar role in the VSD IV of CaV1.3 and in VSDs II and IV of CaV1.2 by introducing charge-neutralizing mutations (D4N or E4Q) in the corresponding positions of CaV1.3 and in two splice variants of CaV1.2. In both channels the D4N (VSD IV) mutation resulted in a ̴5 mV right-shift of the voltage-dependence of activation and in a reduction of current density to about half of that in controls. However in CaV1.2 the effects were independent of alternative splicing, indicating that the two modulatory processes operate by distinct mechanisms. Together with our previous findings these results suggest that molecular interactions engaging D4 in VSD IV contribute to voltage-sensing in all examined CaV1 channels, however its striking role in regulating the gating properties by alternative splicing appears to be a unique property of the skeletal muscle CaV1.1 channel.
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Affiliation(s)
- Pierre Costé de Bagneaux
- a Department of Physiology and Medical Physics , Medical University of Innsbruck , Innsbruck , Austria
| | - Marta Campiglio
- a Department of Physiology and Medical Physics , Medical University of Innsbruck , Innsbruck , Austria
| | - Bruno Benedetti
- b Institute of Experimental Neuroregeneration Spinal Cord Injury and Tissue Regeneration Center Salzburg (SCI-TReCS) , Paracelsus Medical University , Salzburg , Austria
| | - Petronel Tuluc
- c Department of Pharmacology and Toxicology , University of Innsbruck , Innsbruck , Austria
| | - Bernhard E Flucher
- a Department of Physiology and Medical Physics , Medical University of Innsbruck , Innsbruck , Austria
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30
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Horng TL, Eisenberg RS, Liu C, Bezanilla F. Continuum Gating Current Models Computed with Consistent Interactions. Biophys J 2018; 116:270-282. [PMID: 30612713 PMCID: PMC6350011 DOI: 10.1016/j.bpj.2018.11.3140] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Revised: 11/14/2018] [Accepted: 11/28/2018] [Indexed: 01/01/2023] Open
Abstract
The action potential of nerve and muscle is produced by voltage-sensitive channels that include a specialized device to sense voltage. The voltage sensor depends on the movement of charges in the changing electric field as suggested by Hodgkin and Huxley. Gating currents of the voltage sensor are now known to depend on the movements of positively charged arginines through the hydrophobic plug of a voltage sensor domain. Transient movements of these permanently charged arginines, caused by the change of transmembrane potential V, further drag the S4 segment and induce opening/closing of the ion conduction pore by moving the S4-S5 linker. This moving permanent charge induces capacitive current flow everywhere. Everything interacts with everything else in the voltage sensor and protein, and so it must also happen in its mathematical model. A Poisson-Nernst-Planck (PNP)-steric model of arginines and a mechanical model for the S4 segment are combined using energy variational methods in which all densities and movements of charge satisfy conservation laws, which are expressed as partial differential equations in space and time. The model computes gating current flowing in the baths produced by arginines moving in the voltage sensor. The model also captures the capacitive pile up of ions in the vestibules that link the bulk solution to the hydrophobic plug. Our model reproduces the signature properties of gating current: 1) equality of ON and OFF charge Q in integrals of gating current, 2) saturating voltage dependence in the Q(charge)-voltage curve, and 3) many (but not all) details of the shape of gating current as a function of voltage. Our results agree qualitatively with experiments and can be improved by adding more details of the structure and its correlated movements. The proposed continuum model is a promising tool to explore the dynamics and mechanism of the voltage sensor.
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Affiliation(s)
- Tzyy-Leng Horng
- Department of Applied Mathematics, Feng Chia University, Taichung, Taiwan
| | - Robert S Eisenberg
- Department of Applied Mathematics, Illinois Institute of Technology, Chicago, Illinois; Department of Physiology and Biophysics, Rush University, Chicago, Illinois
| | - Chun Liu
- Department of Applied Mathematics, Illinois Institute of Technology, Chicago, Illinois
| | - Francisco Bezanilla
- Department of Biochemistry and Molecular Biology and Institute for Biophysical Dynamics, University of Chicago, Chicago, Illinois; Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile.
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31
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Fernandes JRC, Bleicher L, Beirão PSL. Closed- and open-state models of human skeletal muscle sodium channel. Biochem Biophys Res Commun 2018; 506:826-832. [PMID: 30389137 DOI: 10.1016/j.bbrc.2018.10.110] [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: 10/10/2018] [Accepted: 10/17/2018] [Indexed: 10/28/2022]
Abstract
Voltage-gated sodium channels play important roles in human physiology. However, their complexity hinders the understanding of their physiology and pathology at atomic level. We took advantage of the structural reports of similar channels obtained by cryo-EM (EeNav1.4, and NavPaS), and constructed models of human Nav1.4 channels at closed and open states. The open-state model is very similar to the recently published cryo-EM structure of hNav1.4. The comparison of both models shows shifts of the voltage sensors (VS) of DIII and DIV. The activated position of VS-DII in the closed model was demonstrated by Ts1 docking, thereby confirming the requirement that VS-DI, VS-DII and VS-DIII must be activated for the channel to open. The interactions observed with VS-DIII suggest a stepwise, yet fast, transition from resting to activated state. These models provide structural insights on the closed-open transition of the channel.
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Affiliation(s)
- João R C Fernandes
- Department of Biochemistry and Immunology - ICB, Universidade Federal de Minas Gerais - UFMG, Av. Antonio Carlos, 6627, 31270-901, Belo Horizonte, MG, Brazil
| | - Lucas Bleicher
- Department of Biochemistry and Immunology - ICB, Universidade Federal de Minas Gerais - UFMG, Av. Antonio Carlos, 6627, 31270-901, Belo Horizonte, MG, Brazil
| | - Paulo S L Beirão
- Department of Biochemistry and Immunology - ICB, Universidade Federal de Minas Gerais - UFMG, Av. Antonio Carlos, 6627, 31270-901, Belo Horizonte, MG, Brazil.
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32
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Kasimova MA, Lindahl E, Delemotte L. Determining the molecular basis of voltage sensitivity in membrane proteins. J Gen Physiol 2018; 150:1444-1458. [PMID: 30150239 PMCID: PMC6168238 DOI: 10.1085/jgp.201812086] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 08/07/2018] [Indexed: 12/31/2022] Open
Abstract
The identification of voltage-sensing elements in membrane proteins is challenging due to the diversity of voltage-sensing mechanisms. Kasimova et al. present a computational approach to predict the elements involved in voltage sensing, which they validate using voltage-gated ion channels. Voltage-sensitive membrane proteins are united by their ability to transform changes in membrane potential into mechanical work. They are responsible for a spectrum of physiological processes in living organisms, including electrical signaling and cell-cycle progression. Although the mechanism of voltage-sensing has been well characterized for some membrane proteins, including voltage-gated ion channels, even the location of the voltage-sensing elements remains unknown for others. Moreover, the detection of these elements by using experimental techniques is challenging because of the diversity of membrane proteins. Here, we provide a computational approach to predict voltage-sensing elements in any membrane protein, independent of its structure or function. It relies on an estimation of the propensity of a protein to respond to changes in membrane potential. We first show that this property correlates well with voltage sensitivity by applying our approach to a set of voltage-sensitive and voltage-insensitive membrane proteins. We further show that it correctly identifies authentic voltage-sensitive residues in the voltage-sensor domain of voltage-gated ion channels. Finally, we investigate six membrane proteins for which the voltage-sensing elements have not yet been characterized and identify residues and ions that might be involved in the response to voltage. The suggested approach is fast and simple and enables a characterization of voltage sensitivity that goes beyond mere identification of charges. We anticipate that its application before mutagenesis experiments will significantly reduce the number of potential voltage-sensitive elements to be tested.
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Affiliation(s)
- Marina A Kasimova
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Erik Lindahl
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Stockholm, Sweden.,Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Stockholm, Sweden
| | - Lucie Delemotte
- Department of Applied Physics, Science for Life Laboratory, KTH Royal Institute of Technology, Stockholm, Sweden
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33
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Abstract
A voltage change across a membrane protein moves charges or dipoles producing a gating current that is an electrical expression of a conformational change. Many membrane proteins sense the voltage across the membrane where they are inserted, and their function is affected by voltage changes. The voltage sensor consists of charges or dipoles that move in response to changes in the electric field, and their movement produces an electric current that has been called gating current. In the case of voltage-gated ion channels, the kinetic and steady-state properties of the gating charges provide information of conformational changes between closed states that are not visible when observing ionic currents only. In this Journal of General Physiology Milestone, the basic principles of voltage sensing and gating currents are presented, followed by a historical description of the recording of gating currents. The results of gating current recordings are then discussed in the context of structural changes in voltage-dependent membrane proteins and how these studies have provided new insights on gating mechanisms.
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Affiliation(s)
- Francisco Bezanilla
- Department of Biochemistry and Molecular Biology, Institute for Biophysical Dynamics, University of Chicago, Chicago, IL
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34
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De La Rosa V, Bennett AL, Ramsey IS. Coupling between an electrostatic network and the Zn 2+ binding site modulates Hv1 activation. J Gen Physiol 2018; 150:863-881. [PMID: 29743298 PMCID: PMC5987874 DOI: 10.1085/jgp.201711822] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Revised: 02/15/2018] [Accepted: 04/05/2018] [Indexed: 01/20/2023] Open
Abstract
The voltage sensor (VS) domain in Hv1 proton channels mediates a voltage-dependent and H+-selective "aqueous" conductance (GAQ) that is potently modulated by extracellular Zn2+ Although two conserved His residues are required for Zn2+ effects on GAQ gating, the atomic structure of the Zn2+ coordination site and mechanism by which extracellular Zn2+ stabilizes a closed-state conformation remain unknown. Here we use His mutagenesis to identify residues that increase Zn2+ potency and are therefore likely to participate in first solvation shell interactions with Zn2+ Experimental Zn2+-mapping data were then used to constrain the structure of a new resting-state Hv1 model (Hv1 F). Molecular dynamics (MD) simulations show how protein and water atoms directly contribute to octahedral Zn2+ coordination spheres in Zn2+-bound and -unbound Hv1 F models. During MD simulations, we observed correlated movements of Zn2+-interacting side chains and residues in a highly conserved intracellular Coulombic network (ICN) that contains highly conserved Arg "gating charges" in S4 as well as acidic "counter-charges" in S2 and S3 and is known to control VS activation, suggesting that occupancy of the extracellular Zn2+ site is conformationally coupled to reorganization of the ICN. To test this hypothesis, we neutralized an ICN Glu residue (E153) and show that in addition to shifting GAQ activation to more negative voltages, E153A also decreases Zn2+ potency. We speculate that extracellular gating-modifier toxins and other ligands may use a generally similar long-range conformational coupling mechanism to modulate VS activation in related ion channel proteins.
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Affiliation(s)
- Victor De La Rosa
- Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Medical College of Virginia Campus, Richmond, VA
| | - Ashley L Bennett
- Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Medical College of Virginia Campus, Richmond, VA
| | - Ian Scott Ramsey
- Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Medical College of Virginia Campus, Richmond, VA
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35
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Vinayagam D, Mager T, Apelbaum A, Bothe A, Merino F, Hofnagel O, Gatsogiannis C, Raunser S. Electron cryo-microscopy structure of the canonical TRPC4 ion channel. eLife 2018; 7:e36615. [PMID: 29717981 PMCID: PMC5951680 DOI: 10.7554/elife.36615] [Citation(s) in RCA: 69] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Accepted: 04/30/2018] [Indexed: 12/31/2022] Open
Abstract
Canonical transient receptor channels (TRPC) are non-selective cation channels. They are involved in receptor-operated Ca2+ signaling and have been proposed to act as store-operated channels (SOC). Their malfunction is related to cardiomyopathies and their modulation by small molecules has been shown to be effective against renal cancer cells. The molecular mechanism underlying the complex activation and regulation is poorly understood. Here, we report the electron cryo-microscopy structure of zebrafish TRPC4 in its unliganded (apo), closed state at an overall resolution of 3.6 Å. The structure reveals the molecular architecture of the cation conducting pore, including the selectivity filter and lower gate. The cytoplasmic domain contains two key hubs that have been shown to interact with modulating proteins. Structural comparisons with other TRP channels give novel insights into the general architecture and domain organization of this superfamily of channels and help to understand their function and pharmacology.
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Affiliation(s)
| | - Thomas Mager
- Department of Biophysical ChemistryMax Planck Institute of BiophysicsFrankfurt am MainGermany
| | - Amir Apelbaum
- Department of Structural BiochemistryMax Planck Institute of Molecular PhysiologyDortmundGermany
| | - Arne Bothe
- Department of Structural BiochemistryMax Planck Institute of Molecular PhysiologyDortmundGermany
| | - Felipe Merino
- Department of Structural BiochemistryMax Planck Institute of Molecular PhysiologyDortmundGermany
| | - Oliver Hofnagel
- Department of Structural BiochemistryMax Planck Institute of Molecular PhysiologyDortmundGermany
| | - Christos Gatsogiannis
- Department of Structural BiochemistryMax Planck Institute of Molecular PhysiologyDortmundGermany
| | - Stefan Raunser
- Department of Structural BiochemistryMax Planck Institute of Molecular PhysiologyDortmundGermany
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36
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Held K, Gruss F, Aloi VD, Janssens A, Ulens C, Voets T, Vriens J. Mutations in the voltage-sensing domain affect the alternative ion permeation pathway in the TRPM3 channel. J Physiol 2018; 596:2413-2432. [PMID: 29604058 PMCID: PMC6002228 DOI: 10.1113/jp274124] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Accepted: 03/19/2018] [Indexed: 01/23/2023] Open
Abstract
Key points Mutagenesis at positively charged amino acids (arginines and lysines) (R1–R4) in the voltage‐sensor domain (transmembrane segment (S) 4) of voltage‐gated Na+, K+ and Ca2+ channels can lead to an alternative ion permeation pathway distinct from the central pore. Recently, a non‐canonical ion permeation pathway was described in TRPM3, a member of the transient receptor potential (TRP) superfamily. The non‐canonical pore exists in the native TRPM3 channel and can be activated by co‐stimulation of the endogenous agonist pregnenolone sulphate and the antifungal drug clotrimazole or by stimulation of the synthetic agonist CIM0216. Alignment of the voltage sensor of Shaker K+ channels with the entire TRPM3 sequence revealed the highest degree of similarity in the putative S4 region of TRPM3, and suggested that only one single gating charge arginine (R2) in the putative S4 region is conserved. Mutagenesis studies in the voltage‐sensing domain of TRPM3 revealed several residues in the voltage sensor (S4) as well as in S1 and S3 that are crucial for the occurrence of the non‐canonical inward currents. In conclusion, this study provides evidence for the involvement of the voltage‐sensing domain of TRPM3 in the formation of an alternative ion permeation pathway.
Abstract Transient receptor potential (TRP) channels are cationic channels involved in a broad array of functions, including homeostasis, motility and sensory functions. TRP channel subunits consist of six transmembrane segments (S1–S6), and form tetrameric channels with a central pore formed by the region encompassing S5 and S6. Recently, evidence was provided for the existence of an alternative ion permeation pathway in TRPM3, which allows large inward currents upon hyperpolarization independently of the central pore. However, very little knowledge is available concerning the localization of this alternative pathway in the native TRPM3 channel protein. Guided by sequence homology with Shaker K+ channels, in which mutations in S4 can create an analogous ‘omega’ pore, we performed site‐directed mutagenesis studies and patch clamp experiments to identify amino acid residues involved in the formation of the non‐canonical pore in TRPM3. Based on our results, we pinpoint four residues in S4 (W982, R985, D988 and G991) as crucial determinants of the properties of the alternative ion permeation pathway. Mutagenesis at positively charged amino acids (arginines and lysines) (R1–R4) in the voltage‐sensor domain (transmembrane segment (S) 4) of voltage‐gated Na+, K+ and Ca2+ channels can lead to an alternative ion permeation pathway distinct from the central pore. Recently, a non‐canonical ion permeation pathway was described in TRPM3, a member of the transient receptor potential (TRP) superfamily. The non‐canonical pore exists in the native TRPM3 channel and can be activated by co‐stimulation of the endogenous agonist pregnenolone sulphate and the antifungal drug clotrimazole or by stimulation of the synthetic agonist CIM0216. Alignment of the voltage sensor of Shaker K+ channels with the entire TRPM3 sequence revealed the highest degree of similarity in the putative S4 region of TRPM3, and suggested that only one single gating charge arginine (R2) in the putative S4 region is conserved. Mutagenesis studies in the voltage‐sensing domain of TRPM3 revealed several residues in the voltage sensor (S4) as well as in S1 and S3 that are crucial for the occurrence of the non‐canonical inward currents. In conclusion, this study provides evidence for the involvement of the voltage‐sensing domain of TRPM3 in the formation of an alternative ion permeation pathway.
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Affiliation(s)
- Katharina Held
- Laboratory of Experimental Gynecology and G-PURE, KU Leuven, Department of Development and Regeneration, Herestraat 49 box 611, B-3000, Leuven, Belgium.,Laboratory of Ion Channel Research and TRP Research Platform Leuven (TRPLe), KU Leuven, Department of Cellular and Molecular Medicine, Herestraat 49 box 802, B-3000, Leuven, Belgium.,VIB Center for Brain & Disease Research, B-3000, Leuven, Belgium
| | - Fabian Gruss
- Laboratory of Structural Neurobiology and TRP Research Platform Leuven (TRPLe), KU Leuven, Department of Cellular and Molecular Medicine, Herestraat 49 box 601, B-3000, Leuven, Belgium
| | - Vincenzo Davide Aloi
- Laboratory of Experimental Gynecology and G-PURE, KU Leuven, Department of Development and Regeneration, Herestraat 49 box 611, B-3000, Leuven, Belgium.,Laboratory of Ion Channel Research and TRP Research Platform Leuven (TRPLe), KU Leuven, Department of Cellular and Molecular Medicine, Herestraat 49 box 802, B-3000, Leuven, Belgium.,VIB Center for Brain & Disease Research, B-3000, Leuven, Belgium
| | - Annelies Janssens
- Laboratory of Ion Channel Research and TRP Research Platform Leuven (TRPLe), KU Leuven, Department of Cellular and Molecular Medicine, Herestraat 49 box 802, B-3000, Leuven, Belgium.,VIB Center for Brain & Disease Research, B-3000, Leuven, Belgium
| | - Chris Ulens
- Laboratory of Structural Neurobiology and TRP Research Platform Leuven (TRPLe), KU Leuven, Department of Cellular and Molecular Medicine, Herestraat 49 box 601, B-3000, Leuven, Belgium
| | - Thomas Voets
- Laboratory of Ion Channel Research and TRP Research Platform Leuven (TRPLe), KU Leuven, Department of Cellular and Molecular Medicine, Herestraat 49 box 802, B-3000, Leuven, Belgium.,VIB Center for Brain & Disease Research, B-3000, Leuven, Belgium
| | - Joris Vriens
- Laboratory of Experimental Gynecology and G-PURE, KU Leuven, Department of Development and Regeneration, Herestraat 49 box 611, B-3000, Leuven, Belgium
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37
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DeCoursey TE. Voltage and pH sensing by the voltage-gated proton channel, H V1. J R Soc Interface 2018; 15:20180108. [PMID: 29643227 PMCID: PMC5938591 DOI: 10.1098/rsif.2018.0108] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Accepted: 03/19/2018] [Indexed: 12/15/2022] Open
Abstract
Voltage-gated proton channels are unique ion channels, membrane proteins that allow protons but no other ions to cross cell membranes. They are found in diverse species, from unicellular marine life to humans. In all cells, their function requires that they open and conduct current only under certain conditions, typically when the electrochemical gradient for protons is outwards. Consequently, these proteins behave like rectifiers, conducting protons out of cells. Their activity has electrical consequences and also changes the pH on both sides of the membrane. Here we summarize what is known about the way these proteins sense the membrane potential and the pH inside and outside the cell. Currently, it is hypothesized that membrane potential is sensed by permanently charged arginines (with very high pKa) within the protein, which results in parts of the protein moving to produce a conduction pathway. The mechanism of pH sensing appears to involve titratable side chains of particular amino acids. For this purpose their pKa needs to be within the operational pH range. We propose a 'counter-charge' model for pH sensing in which electrostatic interactions within the protein are selectively disrupted by protonation of internally or externally accessible groups.
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Affiliation(s)
- Thomas E DeCoursey
- Department of Physiology & Biophysics, Rush University, 1750 West Harrison, Chicago, IL 60612, USA
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38
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Monteleone S, Lieb A, Pinggera A, Negro G, Fuchs JE, Hofer F, Striessnig J, Tuluc P, Liedl KR. Mechanisms Responsible for ω-Pore Currents in Ca v Calcium Channel Voltage-Sensing Domains. Biophys J 2017; 113:1485-1495. [PMID: 28978442 PMCID: PMC5627182 DOI: 10.1016/j.bpj.2017.08.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2017] [Revised: 06/28/2017] [Accepted: 08/07/2017] [Indexed: 12/27/2022] Open
Abstract
Mutations of positively charged amino acids in the S4 transmembrane segment of a voltage-gated ion channel form ion-conducting pathways through the voltage-sensing domain, named ω-current. Here, we used structure modeling and MD simulations to predict pathogenic ω-currents in CaV1.1 and CaV1.3 Ca2+ channels bearing several S4 charge mutations. Our modeling predicts that mutations of CaV1.1-R1 (R528H/G, R897S) or CaV1.1-R2 (R900S, R1239H) linked to hypokalemic periodic paralysis type 1 and of CaV1.3-R3 (R990H) identified in aldosterone-producing adenomas conducts ω-currents in resting state, but not during voltage-sensing domain activation. The mechanism responsible for the ω-current and its amplitude depend on the number of charges in S4, the position of the mutated S4 charge and countercharges, and the nature of the replacing amino acid. Functional characterization validates the modeling prediction showing that CaV1.3-R990H channels conduct ω-currents at hyperpolarizing potentials, but not upon membrane depolarization compared with wild-type channels.
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Affiliation(s)
- Stefania Monteleone
- Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innsbruck, Austria
| | - Andreas Lieb
- Department of Pharmacology and Toxicology, Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria; Institute of Neurology, University College London, London, United Kingdom
| | - Alexandra Pinggera
- Department of Pharmacology and Toxicology, Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria; Neurobiology Division, MRC Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - Giulia Negro
- Department of Pharmacology and Toxicology, Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria
| | - Julian E Fuchs
- Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innsbruck, Austria
| | - Florian Hofer
- Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innsbruck, Austria
| | - Jörg Striessnig
- Department of Pharmacology and Toxicology, Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria
| | - Petronel Tuluc
- Department of Pharmacology and Toxicology, Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria.
| | - Klaus R Liedl
- Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innsbruck, Austria.
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39
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DeCoursey TE, Morgan D, Musset B, Cherny VV. Insights into the structure and function of HV1 from a meta-analysis of mutation studies. J Gen Physiol 2017; 148:97-118. [PMID: 27481712 PMCID: PMC4969798 DOI: 10.1085/jgp.201611619] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Accepted: 06/30/2016] [Indexed: 01/26/2023] Open
Abstract
The voltage-gated proton channel (HV1) is a widely distributed, proton-specific ion channel with unique properties. Since 2006, when genes for HV1 were identified, a vast array of mutations have been generated and characterized. Accessing this potentially useful resource is hindered, however, by the sheer number of mutations and interspecies differences in amino acid numbering. This review organizes all existing information in a logical manner to allow swift identification of studies that have characterized any particular mutation. Although much can be gained from this meta-analysis, important questions about the inner workings of HV1 await future revelation.
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Affiliation(s)
- Thomas E DeCoursey
- Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612
| | - Deri Morgan
- Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612
| | - Boris Musset
- Institut für Physiologie, PMU Klinikum Nürnberg, 90419 Nürnberg, Germany
| | - Vladimir V Cherny
- Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL 60612
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40
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Bennett AL, Ramsey IS. CrossTalk opposing view: proton transfer in Hv1 utilizes a water wire, and does not require transient protonation of a conserved aspartate in the S1 transmembrane helix. J Physiol 2017; 595:6797-6799. [PMID: 29023730 DOI: 10.1113/jp274553] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Affiliation(s)
- Ashley L Bennett
- Virginia Commonwealth University School of Medicine, Richmond, VA, USA
| | - Ian Scott Ramsey
- Virginia Commonwealth University School of Medicine, Richmond, VA, USA
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41
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Electron current recordings in living cells. Biophys Chem 2017; 229:57-61. [DOI: 10.1016/j.bpc.2017.05.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2017] [Revised: 05/16/2017] [Accepted: 05/16/2017] [Indexed: 11/22/2022]
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42
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Rodriguez JD, Haq S, Bachvaroff T, Nowak KF, Nowak SJ, Morgan D, Cherny VV, Sapp MM, Bernstein S, Bolt A, DeCoursey TE, Place AR, Smith SME. Identification of a vacuolar proton channel that triggers the bioluminescent flash in dinoflagellates. PLoS One 2017; 12:e0171594. [PMID: 28178296 PMCID: PMC5298346 DOI: 10.1371/journal.pone.0171594] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Accepted: 01/23/2017] [Indexed: 11/19/2022] Open
Abstract
In 1972, J. Woodland Hastings and colleagues predicted the existence of a proton selective channel (HV1) that opens in response to depolarizing voltage across the vacuole membrane of bioluminescent dinoflagellates and conducts protons into specialized luminescence compartments (scintillons), thereby causing a pH drop that triggers light emission. HV1 channels were subsequently identified and demonstrated to have important functions in a multitude of eukaryotic cells. Here we report a predicted protein from Lingulodinium polyedrum that displays hallmark properties of bona fide HV1, including time-dependent opening with depolarization, perfect proton selectivity, and characteristic ΔpH dependent gating. Western blotting and fluorescence confocal microscopy of isolated L. polyedrum scintillons immunostained with antibody to LpHV1 confirm LpHV1's predicted organellar location. Proteomics analysis demonstrates that isolated scintillon preparations contain peptides that map to LpHV1. Finally, Zn2+ inhibits both LpHV1 proton current and the acid-induced flash in isolated scintillons. These results implicate LpHV1 as the voltage gated proton channel that triggers bioluminescence in L. polyedrum, confirming Hastings' hypothesis. The same channel likely mediates the action potential that communicates the signal along the tonoplast to the scintillon.
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Affiliation(s)
- Juan D. Rodriguez
- Department of Molecular and Cellular Biology, Kennesaw State University, Kennesaw, Georgia, United States of America
| | - Saddef Haq
- Institute of Marine and Environmental Technology, University of Maryland Center for Environmental Science, Baltimore, Maryland, United States of America
| | - Tsvetan Bachvaroff
- Institute of Marine and Environmental Technology, University of Maryland Center for Environmental Science, Baltimore, Maryland, United States of America
| | - Kristine F. Nowak
- Department of Molecular and Cellular Biology, Kennesaw State University, Kennesaw, Georgia, United States of America
| | - Scott J. Nowak
- Department of Molecular and Cellular Biology, Kennesaw State University, Kennesaw, Georgia, United States of America
| | - Deri Morgan
- Department of Molecular Biophysics and Physiology, Rush University, Chicago, Illinois, United States of America
| | - Vladimir V. Cherny
- Department of Molecular Biophysics and Physiology, Rush University, Chicago, Illinois, United States of America
| | - Maredith M. Sapp
- Department of Molecular and Cellular Biology, Kennesaw State University, Kennesaw, Georgia, United States of America
| | - Steven Bernstein
- Department of Molecular and Cellular Biology, Kennesaw State University, Kennesaw, Georgia, United States of America
| | - Andrew Bolt
- Department of Molecular and Cellular Biology, Kennesaw State University, Kennesaw, Georgia, United States of America
| | - Thomas E. DeCoursey
- Department of Molecular Biophysics and Physiology, Rush University, Chicago, Illinois, United States of America
| | - Allen R. Place
- Institute of Marine and Environmental Technology, University of Maryland Center for Environmental Science, Baltimore, Maryland, United States of America
| | - Susan M. E. Smith
- Department of Molecular and Cellular Biology, Kennesaw State University, Kennesaw, Georgia, United States of America
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43
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Grandi E, Sanguinetti MC, Bartos DC, Bers DM, Chen-Izu Y, Chiamvimonvat N, Colecraft HM, Delisle BP, Heijman J, Navedo MF, Noskov S, Proenza C, Vandenberg JI, Yarov-Yarovoy V. Potassium channels in the heart: structure, function and regulation. J Physiol 2016; 595:2209-2228. [PMID: 27861921 DOI: 10.1113/jp272864] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2016] [Accepted: 07/18/2016] [Indexed: 12/22/2022] Open
Abstract
This paper is the outcome of the fourth UC Davis Systems Approach to Understanding Cardiac Excitation-Contraction Coupling and Arrhythmias Symposium, a biannual event that aims to bring together leading experts in subfields of cardiovascular biomedicine to focus on topics of importance to the field. The theme of the 2016 symposium was 'K+ Channels and Regulation'. Experts in the field contributed their experimental and mathematical modelling perspectives and discussed emerging questions, controversies and challenges on the topic of cardiac K+ channels. This paper summarizes the topics of formal presentations and informal discussions from the symposium on the structural basis of voltage-gated K+ channel function, as well as the mechanisms involved in regulation of K+ channel gating, expression and membrane localization. Given the critical role for K+ channels in determining the rate of cardiac repolarization, it is hardly surprising that essentially every aspect of K+ channel function is exquisitely regulated in cardiac myocytes. This regulation is complex and highly interrelated to other aspects of myocardial function. K+ channel regulatory mechanisms alter, and are altered by, physiological challenges, pathophysiological conditions, and pharmacological agents. An accompanying paper focuses on the integrative role of K+ channels in cardiac electrophysiology, i.e. how K+ currents shape the cardiac action potential, and how their dysfunction can lead to arrhythmias, and discusses K+ channel-based therapeutics. A fundamental understanding of K+ channel regulatory mechanisms and disease processes is fundamental to reveal new targets for human therapy.
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Affiliation(s)
- Eleonora Grandi
- Department of Pharmacology, University of California, Davis, Davis, CA, 95616, USA
| | - Michael C Sanguinetti
- Department of Internal Medicine, University of Utah, Nora Eccles Harrison Cardiovascular Research and Training Institute, Salt Lake City, UT, 84112, USA
| | - Daniel C Bartos
- Department of Pharmacology, University of California, Davis, Davis, CA, 95616, USA
| | - Donald M Bers
- Department of Pharmacology, University of California, Davis, Davis, CA, 95616, USA
| | - Ye Chen-Izu
- Department of Pharmacology, University of California, Davis, Davis, CA, 95616, USA.,Department of Internal Medicine, Division of Cardiology, University of California, Davis, CA, 95616, USA
| | - Nipavan Chiamvimonvat
- Department of Internal Medicine, Division of Cardiology, University of California, Davis, CA, 95616, USA
| | - Henry M Colecraft
- Department of Physiology and Cellular Biophysics, Columbia University, New York, NY, 10032, USA
| | - Brian P Delisle
- Department of Physiology, University of Kentucky, Lexington, KY, 40536, USA
| | - Jordi Heijman
- Department of Cardiology, Cardiovascular Research Institute Maastricht, Faculty of Health, Medicine, and Life Sciences, Maastricht University, Maastricht, The Netherlands
| | - Manuel F Navedo
- Department of Pharmacology, University of California, Davis, Davis, CA, 95616, USA
| | - Sergei Noskov
- Centre for Molecular Simulation, Department of Biological Sciences, University of Calgary, Calgary, AB, T2N 1N4, Canada
| | - Catherine Proenza
- Department of Physiology and Biophysics, University of Colorado - Anschutz Medical Campus, Denver, CO, 80045, USA
| | - Jamie I Vandenberg
- Victor Chang Cardiac Research Institute, Darlinghurst, NSW, 2010, Australia
| | - Vladimir Yarov-Yarovoy
- Department of Physiology and Membrane Biology, University of California, Davis, CA, 95616, USA
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44
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Pathak MM, Tran T, Hong L, Joós B, Morris CE, Tombola F. The Hv1 proton channel responds to mechanical stimuli. J Gen Physiol 2016; 148:405-418. [PMID: 27799320 PMCID: PMC5089936 DOI: 10.1085/jgp.201611672] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Accepted: 09/22/2016] [Indexed: 12/21/2022] Open
Abstract
The voltage-gated proton channel, Hv1, is expressed in tissues throughout the body and plays important roles in pH homeostasis and regulation of NADPH oxidase. Hv1 operates in membrane compartments that experience strong mechanical forces under physiological or pathological conditions. In microglia, for example, Hv1 activity is potentiated by cell swelling and causes an increase in brain damage after stroke. The channel complex consists of two proton-permeable voltage-sensing domains (VSDs) linked by a cytoplasmic coiled-coil domain. Here, we report that these VSDs directly respond to mechanical stimuli. We find that membrane stretch facilitates Hv1 channel opening by increasing the rate of activation and shifting the steady-state activation curve to less depolarized potentials. In the presence of a transmembrane pH gradient, membrane stretch alone opens the channel without the need for strong depolarizations. The effect of membrane stretch persists for several minutes after the mechanical stimulus is turned off, suggesting that the channel switches to a "facilitated" mode in which opening occurs more readily and then slowly reverts to the normal mode observed in the absence of membrane stretch. Conductance simulations with a six-state model recapitulate all the features of the channel's response to mechanical stimulation. Hv1 mechanosensitivity thus provides a mechanistic link between channel activation in microglia and brain damage after stroke.
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Affiliation(s)
- Medha M Pathak
- Department of Physiology and Biophysics, University of California, Irvine, CA 92697
| | - Truc Tran
- Department of Physiology and Biophysics, University of California, Irvine, CA 92697
| | - Liang Hong
- Department of Physiology and Biophysics, University of California, Irvine, CA 92697
| | - Béla Joós
- Department of Physics, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
| | | | - Francesco Tombola
- Department of Physiology and Biophysics, University of California, Irvine, CA 92697
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45
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Cui J. Voltage-Dependent Gating: Novel Insights from KCNQ1 Channels. Biophys J 2016; 110:14-25. [PMID: 26745405 DOI: 10.1016/j.bpj.2015.11.023] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Revised: 11/16/2015] [Accepted: 11/17/2015] [Indexed: 11/26/2022] Open
Abstract
Gating of voltage-dependent cation channels involves three general molecular processes: voltage sensor activation, sensor-pore coupling, and pore opening. KCNQ1 is a voltage-gated potassium (Kv) channel whose distinctive properties have provided novel insights on fundamental principles of voltage-dependent gating. 1) Similar to other Kv channels, KCNQ1 voltage sensor activation undergoes two resolvable steps; but, unique to KCNQ1, the pore opens at both the intermediate and activated state of voltage sensor activation. The voltage sensor-pore coupling differs in the intermediate-open and the activated-open states, resulting in changes of open pore properties during voltage sensor activation. 2) The voltage sensor-pore coupling and pore opening require the membrane lipid PIP2 and intracellular ATP, respectively, as cofactors, thus voltage-dependent gating is dependent on multiple stimuli, including the binding of intracellular signaling molecules. These mechanisms underlie the extraordinary KCNE1 subunit modification of the KCNQ1 channel and have significant physiological implications.
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Affiliation(s)
- Jianmin Cui
- Department of Biomedical Engineering, Cardiac Bioelectricity and Arrhythmia Center and Center for the Investigation of Membrane Excitability Disorders, Washington University, St. Louis, Missouri.
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46
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Randolph AL, Mokrab Y, Bennett AL, Sansom MS, Ramsey IS. Proton currents constrain structural models of voltage sensor activation. eLife 2016; 5. [PMID: 27572256 PMCID: PMC5065317 DOI: 10.7554/elife.18017] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Accepted: 08/29/2016] [Indexed: 11/13/2022] Open
Abstract
The Hv1 proton channel is evidently unique among voltage sensor domain proteins in mediating an intrinsic 'aqueous' H+ conductance (GAQ). Mutation of a highly conserved 'gating charge' residue in the S4 helix (R1H) confers a resting-state H+ 'shuttle' conductance (GSH) in VGCs and Ci VSP, and we now report that R1H is sufficient to reconstitute GSH in Hv1 without abrogating GAQ. Second-site mutations in S3 (D185A/H) and S4 (N4R) experimentally separate GSH and GAQ gating, which report thermodynamically distinct initial and final steps, respectively, in the Hv1 activation pathway. The effects of Hv1 mutations on GSH and GAQ are used to constrain the positions of key side chains in resting- and activated-state VS model structures, providing new insights into the structural basis of VS activation and H+ transfer mechanisms in Hv1.
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Affiliation(s)
- Aaron L Randolph
- Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, United States.,Medical College of Virginia Campus, Virginia Commonwealth University School of Medicine, Richmond, United States
| | - Younes Mokrab
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Ashley L Bennett
- Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, United States.,Medical College of Virginia Campus, Virginia Commonwealth University School of Medicine, Richmond, United States
| | - Mark Sp Sansom
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Ian Scott Ramsey
- Department of Physiology and Biophysics, Virginia Commonwealth University School of Medicine, Richmond, United States.,Medical College of Virginia Campus, Virginia Commonwealth University School of Medicine, Richmond, United States
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47
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Armstrong CT, Mason PE, Anderson JLR, Dempsey CE. Arginine side chain interactions and the role of arginine as a gating charge carrier in voltage sensitive ion channels. Sci Rep 2016; 6:21759. [PMID: 26899474 PMCID: PMC4761985 DOI: 10.1038/srep21759] [Citation(s) in RCA: 93] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Accepted: 01/28/2016] [Indexed: 01/18/2023] Open
Abstract
Gating charges in voltage-sensing domains (VSD) of voltage-sensitive ion channels and enzymes are carried on arginine side chains rather than lysine. This arginine preference may result from the unique hydration properties of the side chain guanidinium group which facilitates its movement through a hydrophobic plug that seals the center of the VSD, as suggested by molecular dynamics simulations. To test for side chain interactions implicit in this model we inspected interactions of the side chains of arginine and lysine with each of the 19 non-glycine amino acids in proteins in the protein data bank. The arginine guanidinium interacts with non-polar aromatic and aliphatic side chains above and below the guanidinium plane while hydrogen bonding with polar side chains is restricted to in-plane positions. In contrast, non-polar side chains interact largely with the aliphatic part of the lysine side chain. The hydration properties of arginine and lysine are strongly reflected in their respective interactions with non-polar and polar side chains as observed in protein structures and in molecular dynamics simulations, and likely underlie the preference for arginine as a mobile charge carrier in VSD.
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Affiliation(s)
| | - Philip E Mason
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, 16610 Prague 6, Czech Republic
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48
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Allosteric substrate switching in a voltage-sensing lipid phosphatase. Nat Chem Biol 2016; 12:261-7. [PMID: 26878552 PMCID: PMC4798927 DOI: 10.1038/nchembio.2022] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Accepted: 12/31/2015] [Indexed: 11/29/2022]
Abstract
Allostery provides a critical control over enzyme activity, biasing the catalytic site between inactive and active states. We find the Ciona intestinalis voltage-sensing phosphatase (Ci-VSP), which modifies phosphoinositide signaling lipids (PIPs), to have not one but two sequential active states with distinct substrate specificities, whose occupancy is allosterically controlled by sequential conformations of the voltage sensing domain (VSD). Using fast FRET reporters of PIPs to monitor enzyme activity and voltage clamp fluorometry to monitor conformational changes in the VSD, we find that Ci-VSP switches from inactive to a PIP3-preferring active state when the VSD undergoes an initial voltage sensing motion and then into a second PIP2-preferring active state when the VSD activates fully. This novel 2-step allosteric control over a dual specificity enzyme enables voltage to shape PIP concentrations in time, and provides a mechanism for the complex modulation of PIP-regulated ion channels, transporters, cell motility and endo/exocytosis.
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49
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Kim I, Warshel A. A Microscopic Capacitor Model of Voltage Coupling in Membrane Proteins: Gating Charge Fluctuations in Ci-VSD. J Phys Chem B 2016; 120:418-32. [PMID: 26716721 DOI: 10.1021/acs.jpcb.5b10956] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The voltage sensitivity of membrane proteins is reflected in the response of the voltage sensing domains (VSDs) to the changes in membrane potential. This response is implicated in the displacement of positively charged residues, associated with the conformational changes of VSDs. The displaced charges generate nonlinear (i.e., voltage-dependent) capacitance current called the gating current (and its corresponding gating charge), which is a key experimental quantity that characterizes voltage activation in VSMP. However, the relevant theoretical/computational approaches, aimed to correlate the structural information on VSMP to electrophysiological measurements, have been rather limited, posing a broad challenge in computer simulations of VSMP. Concomitant with the development of our coarse-graining (CG) model of voltage coupling, we apply our theoretical framework for the treatments of voltage effects in membrane proteins to modeling the VSMP activation, taking the VSDs (Ci-VSD) derived from the Ciona intestinalis voltage sensitive phosphatase (Ci-VSP) as a model system. Our CG model reproduces the observed gating charge of Ci-VSD activation in several different perspectives. In particular, a new closed-form expression of the gating charge is evaluated in both nonequilibrium and equilibrium ways, while considering the fluctuation-dissipation relation that connects a nonequilibrium measurement of the gating charge to an equilibrium measurement of charge fluctuations (i.e., the voltage-independent linear component of membrane capacitance). In turn, the expression uncovers a novel link that connects an equilibrium measurement of the voltage-independent linear capacitance to a nonequilibrium measurement of the voltage-dependent nonlinear capacitance (whose integral over voltage is equal to the gating charge). In addition, our CG model yields capacitor-like voltage dependent free energy parabolas, resulting in the free energy difference and the free energy barrier for the Ci-VSD activation at "zero" (depolarization) membrane potential. Significantly, the resultant voltage dependent energetics enables a direct evaluation of capacitance-voltage relationship (C-V curve) as well as charge-voltage relationship (Q-V curve) that is in a good agreement with the observed measurement of Ci-VSD voltage activation. Importantly, an extension of our kinetic/thermodynamic model of voltage dependent activation in VSMP allows for novel derivations of voltage-dependent rate constants, whose parameters are expressed by the intrinsic properties of VSMP. These novel closed-form expressions offer a physicochemical foundation for the semiempirical Eyring-type voltage dependent rate equations that have been the cornerstone for the phenomenological (kinetic) descriptions of gating and membrane currents in the mechanistic study of ion channels and transporters. Our extended theoretical framework developed in the present study has potential implications on the roles played by gating charge fluctuations for the spike generations in nerve cells within the framework of the Hodgkin-Huxley-type model.
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Affiliation(s)
- Ilsoo Kim
- Department of Chemistry, University of Southern California , SGM 418, 3620 McClintock Avenue, Los Angeles, California 90089, United States
| | - Arieh Warshel
- Department of Chemistry, University of Southern California , SGM 418, 3620 McClintock Avenue, Los Angeles, California 90089, United States
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50
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Held K, Voets T, Vriens J. Signature and Pathophysiology of Non-canonical Pores in Voltage-Dependent Cation Channels. Rev Physiol Biochem Pharmacol 2016; 170:67-99. [DOI: 10.1007/112_2015_5003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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