1
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González-González MA, Conde SV, Latorre R, Thébault SC, Pratelli M, Spitzer NC, Verkhratsky A, Tremblay MÈ, Akcora CG, Hernández-Reynoso AG, Ecker M, Coates J, Vincent KL, Ma B. Bioelectronic Medicine: a multidisciplinary roadmap from biophysics to precision therapies. Front Integr Neurosci 2024; 18:1321872. [PMID: 38440417 PMCID: PMC10911101 DOI: 10.3389/fnint.2024.1321872] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Accepted: 01/10/2024] [Indexed: 03/06/2024] Open
Abstract
Bioelectronic Medicine stands as an emerging field that rapidly evolves and offers distinctive clinical benefits, alongside unique challenges. It consists of the modulation of the nervous system by precise delivery of electrical current for the treatment of clinical conditions, such as post-stroke movement recovery or drug-resistant disorders. The unquestionable clinical impact of Bioelectronic Medicine is underscored by the successful translation to humans in the last decades, and the long list of preclinical studies. Given the emergency of accelerating the progress in new neuromodulation treatments (i.e., drug-resistant hypertension, autoimmune and degenerative diseases), collaboration between multiple fields is imperative. This work intends to foster multidisciplinary work and bring together different fields to provide the fundamental basis underlying Bioelectronic Medicine. In this review we will go from the biophysics of the cell membrane, which we consider the inner core of neuromodulation, to patient care. We will discuss the recently discovered mechanism of neurotransmission switching and how it will impact neuromodulation design, and we will provide an update on neuronal and glial basis in health and disease. The advances in biomedical technology have facilitated the collection of large amounts of data, thereby introducing new challenges in data analysis. We will discuss the current approaches and challenges in high throughput data analysis, encompassing big data, networks, artificial intelligence, and internet of things. Emphasis will be placed on understanding the electrochemical properties of neural interfaces, along with the integration of biocompatible and reliable materials and compliance with biomedical regulations for translational applications. Preclinical validation is foundational to the translational process, and we will discuss the critical aspects of such animal studies. Finally, we will focus on the patient point-of-care and challenges in neuromodulation as the ultimate goal of bioelectronic medicine. This review is a call to scientists from different fields to work together with a common endeavor: accelerate the decoding and modulation of the nervous system in a new era of therapeutic possibilities.
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Affiliation(s)
- María Alejandra González-González
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital, Houston, TX, United States
- Department of Pediatric Neurology, Baylor College of Medicine, Houston, TX, United States
| | - Silvia V. Conde
- iNOVA4Health, NOVA Medical School, Faculdade de Ciências Médicas, NOVA University, Lisbon, Portugal
| | - Ramon Latorre
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile
| | - Stéphanie C. Thébault
- Laboratorio de Investigación Traslacional en salud visual (D-13), Instituto de Neurobiología, Universidad Nacional Autónoma de México (UNAM), Querétaro, Mexico
| | - Marta Pratelli
- Neurobiology Department, Kavli Institute for Brain and Mind, UC San Diego, La Jolla, CA, United States
| | - Nicholas C. Spitzer
- Neurobiology Department, Kavli Institute for Brain and Mind, UC San Diego, La Jolla, CA, United States
| | - Alexei Verkhratsky
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom
- Achucarro Centre for Neuroscience, IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
- Department of Forensic Analytical Toxicology, School of Forensic Medicine, China Medical University, Shenyang, China
- International Collaborative Center on Big Science Plan for Purinergic Signaling, Chengdu University of Traditional Chinese Medicine, Chengdu, China
- Department of Stem Cell Biology, State Research Institute Centre for Innovative Medicine, Vilnius, Lithuania
| | - Marie-Ève Tremblay
- Division of Medical Sciences, University of Victoria, Victoria, BC, Canada
- Department of Neurology and Neurosurgery, McGill University, Montreal, QC, Canada
- Department of Molecular Medicine, Université Laval, Québec City, QC, Canada
- Department of Biochemistry and Molecular Biology, The University of British Columbia, Vancouver, BC, Canada
| | - Cuneyt G. Akcora
- Department of Computer Science, University of Central Florida, Orlando, FL, United States
| | | | - Melanie Ecker
- Department of Biomedical Engineering, University of North Texas, Denton, TX, United States
| | | | - Kathleen L. Vincent
- Department of Obstetrics and Gynecology, University of Texas Medical Branch, Galveston, TX, United States
| | - Brandy Ma
- Stanley H. Appel Department of Neurology, Houston Methodist Hospital, Houston, TX, United States
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2
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Catterall WA. Voltage gated sodium and calcium channels: Discovery, structure, function, and Pharmacology. Channels (Austin) 2023; 17:2281714. [PMID: 37983307 PMCID: PMC10761118 DOI: 10.1080/19336950.2023.2281714] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2023] [Accepted: 10/11/2023] [Indexed: 11/22/2023] Open
Abstract
Voltage-gated sodium channels initiate action potentials in nerve and muscle, and voltage-gated calcium channels couple depolarization of the plasma membrane to intracellular events such as secretion, contraction, synaptic transmission, and gene expression. In this Review and Perspective article, I summarize early work that led to identification, purification, functional reconstitution, and determination of the amino acid sequence of the protein subunits of sodium and calcium channels and showed that their pore-forming subunits are closely related. Decades of study by antibody mapping, site-directed mutagenesis, and electrophysiological recording led to detailed two-dimensional structure-function maps of the amino acid residues involved in voltage-dependent activation and inactivation, ion permeation and selectivity, and pharmacological modulation. Most recently, high-resolution three-dimensional structure determination by X-ray crystallography and cryogenic electron microscopy has revealed the structural basis for sodium and calcium channel function and pharmacological modulation at the atomic level. These studies now define the chemical basis for electrical signaling and provide templates for future development of new therapeutic agents for a range of neurological and cardiovascular diseases.
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3
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Khan F, Elgeti M, Grandfield S, Paz A, Naughton FB, Marcoline FV, Althoff T, Ermolova N, Wright EM, Hubbell WL, Grabe M, Abramson J. Membrane potential accelerates sugar uptake by stabilizing the outward facing conformation of the Na/glucose symporter vSGLT. Nat Commun 2023; 14:7511. [PMID: 37980423 PMCID: PMC10657379 DOI: 10.1038/s41467-023-43119-z] [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: 09/08/2022] [Accepted: 10/30/2023] [Indexed: 11/20/2023] Open
Abstract
Sodium-dependent glucose transporters (SGLTs) couple a downhill Na+ ion gradient to actively transport sugars. Here, we investigate the impact of the membrane potential on vSGLT structure and function using sugar uptake assays, double electron-electron resonance (DEER), electrostatic calculations, and kinetic modeling. Negative membrane potentials, as present in all cell types, shift the conformational equilibrium of vSGLT towards an outward-facing conformation, leading to increased sugar transport rates. Electrostatic calculations identify gating charge residues responsible for this conformational shift that when mutated reduce galactose transport and eliminate the response of vSGLT to potential. Based on these findings, we propose a comprehensive framework for sugar transport via vSGLT, where the cellular membrane potential facilitates resetting of the transporter after cargo release. This framework holds significance not only for SGLTs but also for other transporters and channels.
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Affiliation(s)
- Farha Khan
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, 90095, USA
- Department of Structural Biology, Van Andel Institute, Grand Rapids, MI, 49503, USA
| | - Matthias Elgeti
- Stein Eye Institute, University of California, Los Angeles, Los Angeles, CA, 90095, USA.
- Institute for Drug Discovery, Leipzig University Medical School, Leipzig, Germany.
| | - Samuel Grandfield
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, 90095, USA
- Renaissance School of Medicine at Stony Brook University, Stony Brook, NY, 11794, USA
| | - Aviv Paz
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, 90095, USA
- Hauptman-Woodward Medical Research Institute, 700 Ellicott Street, Buffalo, NY, 14203, USA
| | - Fiona B Naughton
- Department of Pharmaceutical Chemistry, Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA, 94158, USA
| | - Frank V Marcoline
- Department of Pharmaceutical Chemistry, Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA, 94158, USA
| | - Thorsten Althoff
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Natalia Ermolova
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Ernest M Wright
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Wayne L Hubbell
- Stein Eye Institute, University of California, Los Angeles, Los Angeles, CA, 90095, USA
- Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, CA, 90095, USA
| | - Michael Grabe
- Department of Pharmaceutical Chemistry, Cardiovascular Research Institute, University of California, San Francisco, San Francisco, CA, 94158, USA.
| | - Jeff Abramson
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, 90095, USA.
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4
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Catacuzzeno L, Conti F, Franciolini F. Fifty years of gating currents and channel gating. J Gen Physiol 2023; 155:e202313380. [PMID: 37410612 PMCID: PMC10324510 DOI: 10.1085/jgp.202313380] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 05/12/2023] [Accepted: 06/02/2023] [Indexed: 07/08/2023] Open
Abstract
We celebrate this year the 50th anniversary of the first electrophysiological recordings of the gating currents from voltage-dependent ion channels done in 1973. This retrospective tries to illustrate the context knowledge on channel gating and the impact gating-current recording had then, and how it continued to clarify concepts, elaborate new ideas, and steer the scientific debate in these 50 years. The notion of gating particles and gating currents was first put forward by Hodgkin and Huxley in 1952 as a necessary assumption for interpreting the voltage dependence of the Na and K conductances of the action potential. 20 years later, gating currents were actually recorded, and over the following decades have represented the most direct means of tracing the movement of the gating charges and gaining insights into the mechanisms of channel gating. Most work in the early years was focused on the gating currents from the Na and K channels as found in the squid giant axon. With channel cloning and expression on heterologous systems, other channels as well as voltage-dependent enzymes were investigated. Other approaches were also introduced (cysteine mutagenesis and labeling, site-directed fluorometry, cryo-EM crystallography, and molecular dynamics [MD] modeling) to provide an integrated and coherent view of voltage-dependent gating in biological macromolecules. The layout of this retrospective reflects the past 50 years of investigations on gating currents, first addressing studies done on Na and K channels and then on other voltage-gated channels and non-channel structures. The review closes with a brief overview of how the gating-charge/voltage-sensor movements are translated into pore opening and the pathologies associated with mutations targeting the structures involved with the gating currents.
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Affiliation(s)
- Luigi Catacuzzeno
- Department of Chemistry Biology and Biotechnology, University of Perugia, Perugia, Italy
| | - Franco Conti
- Department of Physics, University of Genova, Genova, Italy
| | - Fabio Franciolini
- Department of Chemistry Biology and Biotechnology, University of Perugia, Perugia, Italy
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5
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Kostritskii AY, Machtens JP. Domain- and state-specific shape of the electric field tunes voltage sensing in voltage-gated sodium channels. Biophys J 2023; 122:1807-1821. [PMID: 37077046 PMCID: PMC10209041 DOI: 10.1016/j.bpj.2023.04.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2022] [Revised: 03/27/2023] [Accepted: 04/12/2023] [Indexed: 04/21/2023] Open
Abstract
The ability to sense transmembrane voltage underlies most physiological roles of voltage-gated sodium (Nav) channels. Whereas the key role of their voltage-sensing domains (VSDs) in channel activation is well established, the molecular underpinnings of voltage coupling remain incompletely understood. Voltage-dependent energetics of the activation process can be described in terms of the gating charge that is defined by coupling of charged residues to the external electric field. The shape of the electric field within VSDs is therefore crucial for the activation of voltage-gated ion channels. Here, we employed molecular dynamics simulations of cardiac Nav1.5 and bacterial NavAb, together with our recently developed tool g_elpot, to gain insights into the voltage-sensing mechanisms of Nav channels via high-resolution quantification of VSD electrostatics. In contrast to earlier low-resolution studies, we found that the electric field within VSDs of Nav channels has a complex isoform- and domain-specific shape, which prominently depends on the activation state of a VSD. Different VSDs vary not only in the length of the region where the electric field is focused but also differ in their overall electrostatics, with possible implications in the diverse ion selectivity of their gating pores. Due to state-dependent field reshaping, not only translocated basic but also relatively immobile acidic residues contribute significantly to the gating charge. In the case of NavAb, we found that the transition between structurally resolved activated and resting states results in a gating charge of 8e, which is noticeably lower than experimental estimates. Based on the analysis of VSD electrostatics in the two activation states, we propose that the VSD likely adopts a deeper resting state upon hyperpolarization. In conclusion, our results provide an atomic-level description of the gating charge, demonstrate diversity in VSD electrostatics, and reveal the importance of electric-field reshaping for voltage sensing in Nav channels.
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Affiliation(s)
- Andrei Y Kostritskii
- Institute of Biological Information Processing (IBI-1), Molekular- und Zellphysiologie, and JARA-HPC, Forschungszentrum Jülich, Jülich, Germany; Institute of Clinical Pharmacology, RWTH Aachen University, Aachen, Germany.
| | - Jan-Philipp Machtens
- Institute of Biological Information Processing (IBI-1), Molekular- und Zellphysiologie, and JARA-HPC, Forschungszentrum Jülich, Jülich, Germany; Institute of Clinical Pharmacology, RWTH Aachen University, Aachen, Germany.
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6
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The sensor for animal electricity. Proc Natl Acad Sci U S A 2023; 120:e2218703120. [PMID: 36574669 PMCID: PMC9910495 DOI: 10.1073/pnas.2218703120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
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7
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Guidelli R. A historical biophysical dogma vs. an understanding of the structure and function of voltage-gated tetrameric ion channels. A review. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:184046. [PMID: 36096197 DOI: 10.1016/j.bbamem.2022.184046] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Revised: 08/18/2022] [Accepted: 09/06/2022] [Indexed: 06/15/2023]
Abstract
The outstanding work of several eminent biophysicists has allowed the functional features of voltage-gated tetrameric ion channels to be disclosed using ingenious and sophisticated electrophysiological techniques. However, the kinetics and mechanism underlying these functions have been heavily conditioned by an arbitrary interpretation of the groundbreaking results obtained by Hodgkin and Huxley (HH) in their investigation of sodium and potassium currents using the voltage clamp technique. Thus, the heavy parametrization of their results was considered to indicate that any proposed sequence of closed states terminates with a single open state. This 'dogma' of HH parametrization has influenced the formulation of countless mechanistic models, mainly stochastic, requiring a high number of free parameters and of often unspecified conformational states. This note aims to point out the advantages of a deterministic kinetic model that simulates the main features of tetrameric ion channels using only two free parameters by assuming their stepwise opening accompanied by a progressively increasing cation flow. This model exploits the electrostatic attractive interactions stemming from the charge distribution shared by all tetrameric ion channels, providing a close connection between their structure and function. Quite significantly, a stepwise opening of all ligand-gated tetrameric ion channels, such as glutamate receptors (GluRs), with concomitant ion flow, is nowadays generally accepted, not having been influenced by this dogma. This provides a unified picture of both voltage-gated and ligand-gated tetrameric ion channels.
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Affiliation(s)
- Rolando Guidelli
- Department of Chemistry "Ugo Schiff", Florence University, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze, Italy.
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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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Catacuzzeno L, Franciolini F. The 70-year search for the voltage sensing mechanism of ion channels. J Physiol 2022; 600:3227-3247. [PMID: 35665931 PMCID: PMC9545881 DOI: 10.1113/jp282780] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2022] [Accepted: 04/25/2022] [Indexed: 01/10/2023] Open
Abstract
This retrospective on the voltage‐sensing mechanisms and gating models of ion channels begins in 1952 with the charged gating particles postulated by Hodgkin and Huxley, viewed as charges moving across the membrane and controlling its permeability to Na+ and K+ ions. Hodgkin and Huxley postulated that their movement should generate small and fast capacitive currents, which were recorded 20 years later as gating currents. In the early 1980s, several voltage‐dependent channels were cloned and found to share a common architecture: four homologous domains or subunits, each displaying six transmembrane α‐helical segments, with the fourth segment (S4) displaying four to seven positive charges invariably separated by two non‐charged residues. This immediately suggested that this segment was serving as the voltage sensor of the channel (the molecular counterpart of the charged gating particle postulated by Hodgkin and Huxley) and led to the development of the sliding helix model. Twenty years later, the X‐ray crystallographic structures of many voltage‐dependent channels allowed investigation of their gating by molecular dynamics. Further understanding of how channels gate will benefit greatly from the acquisition of high‐resolution structures of each of their relevant functional or structural states. This will allow the application of molecular dynamics and other approaches. It will also be key to investigate the energetics of channel gating, permitting an understanding of the physical and molecular determinants of gating. The use of multiscale hierarchical approaches might finally prove to be a rewarding strategy to overcome the limits of the various single approaches to the study of channel gating.
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Affiliation(s)
- Luigi Catacuzzeno
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Italy
| | - Fabio Franciolini
- Department of Chemistry, Biology and Biotechnology, University of Perugia, Italy
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10
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Wisedchaisri G, Gamal El-Din TM. Druggability of Voltage-Gated Sodium Channels-Exploring Old and New Drug Receptor Sites. Front Pharmacol 2022; 13:858348. [PMID: 35370700 PMCID: PMC8968173 DOI: 10.3389/fphar.2022.858348] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Accepted: 03/01/2022] [Indexed: 01/12/2023] Open
Abstract
Voltage-gated ion channels are important drug targets because they play crucial physiological roles in both excitable and non-excitable cells. About 15% of clinical drugs used for treating human diseases target ion channels. However, most of these drugs do not provide sufficient specificity to a single subtype of the channels and their off-target side effects can be serious and sometimes fatal. Recent advancements in imaging techniques have enabled us for the first time to visualize unique and hidden parts of voltage-gated sodium channels in different structural conformations, and to develop drugs that further target a selected functional state in each channel subtype with the potential for high precision and low toxicity. In this review we describe the druggability of voltage-gated sodium channels in distinct functional states, which could potentially be used to selectively target the channels. We review classical drug receptors in the channels that have recently been structurally characterized by cryo-electron microscopy with natural neurotoxins and clinical drugs. We further examine recent drug discoveries for voltage-gated sodium channels and discuss opportunities to use distinct, state-dependent receptor sites in the voltage sensors as unique drug targets. Finally, we explore potential new receptor sites that are currently unknown for sodium channels but may be valuable for future drug discovery. The advancement presented here will help pave the way for drug development that selectively targets voltage-gated sodium channels.
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Affiliation(s)
- Goragot Wisedchaisri
- Department of Pharmacology, University of Washington, Seattle, WA, United States
| | - Tamer M Gamal El-Din
- Department of Pharmacology, University of Washington, Seattle, WA, United States
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11
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Gamal El-Din TM, Lenaeus MJ. Fenestropathy of Voltage-Gated Sodium Channels. Front Pharmacol 2022; 13:842645. [PMID: 35222049 PMCID: PMC8873592 DOI: 10.3389/fphar.2022.842645] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Accepted: 01/25/2022] [Indexed: 11/17/2022] Open
Abstract
Voltage-gated sodium channels (Nav) are responsible for the initiation and propagation of action potentials in excitable cells. From pain to heartbeat, these integral membrane proteins are the ignition stations for every sensation and action in human bodies. They are large (>200 kDa, 24 transmembrane helices) multi-domain proteins that couple changes in membrane voltage to the gating cycle of the sodium-selective pore. Nav mutations lead to a multitude of diseases - including chronic pain, cardiac arrhythmia, muscle illnesses, and seizure disorders - and a wide variety of currently used therapeutics block Nav. Despite this, the mechanisms of action of Nav blocking drugs are only modestly understood at this time and many questions remain to be answered regarding their state- and voltage-dependence, as well as the role of the hydrophobic membrane access pathways, or fenestrations, in drug ingress or egress. Nav fenestrations, which are pathways that connect the plasma membrane to the central cavity in the pore domain, were discovered through functional studies more than 40 years ago and once thought to be simple pathways. A variety of recent genetic, structural, and pharmacological data, however, shows that these fenestrations are actually key functional regions of Nav that modulate drug binding, lipid binding, and influence gating behaviors. We discovered that some of the disease mutations that cause arrhythmias alter amino acid residues that line the fenestrations of Nav1.5. This indicates that fenestrations may play a critical role in channel’s gating, and that individual genetic variation may also influence drug access through the fenestrations for resting/inactivated state block. In this review, we will discuss the channelopathies associated with these fenestrations, which we collectively name “Fenestropathy,” and how changes in the fenestrations associated with the opening of the intracellular gate could modulate the state-dependent ingress and egress of drugs binding in the central cavity of voltage gated sodium channels.
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Affiliation(s)
- Tamer M. Gamal El-Din
- Department of Pharmacology, University of Washington, Seattle, WA, United States
- *Correspondence: Tamer M. Gamal El-Din, ; Michael J. Lenaeus,
| | - Michael J. Lenaeus
- Department of Pharmacology, University of Washington, Seattle, WA, United States
- Division of General Internal Medicine, Department of Medicine, University of Washington, Seattle, WA, United States
- *Correspondence: Tamer M. Gamal El-Din, ; Michael J. Lenaeus,
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12
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Guidelli R. The common features of tetrameric ion channels and the role of electrostatic interactions. Electrochem commun 2020. [DOI: 10.1016/j.elecom.2020.106866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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13
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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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14
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Zhang XC, Li H. Interplay between the electrostatic membrane potential and conformational changes in membrane proteins. Protein Sci 2019; 28:502-512. [PMID: 30549351 DOI: 10.1002/pro.3563] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2018] [Revised: 12/12/2018] [Accepted: 12/13/2018] [Indexed: 12/16/2022]
Abstract
Transmembrane electrostatic membrane potential is a major energy source of the cell. Importantly, it determines the structure as well as function of charge-carrying membrane proteins. Here, we discuss the relationship between membrane potential and membrane proteins, in particular whether the conformation of these proteins is integrally connected to the membrane potential. Together, these concepts provide a framework for rationalizing the types of conformational changes that have been observed in membrane proteins and for better understanding the electrostatic effects of the membrane potential on both reversible as well as unidirectional dynamic processes of membrane proteins.
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Affiliation(s)
- Xuejun C Zhang
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Hang Li
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
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15
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Modeling squid axon Na + channel by a nucleation and growth kinetic mechanism. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1861:100-109. [PMID: 30463693 DOI: 10.1016/j.bbamem.2018.08.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Revised: 08/02/2018] [Accepted: 08/19/2018] [Indexed: 11/21/2022]
Abstract
A kinetic model accounting for all salient features of the Na+ channel of the squid giant axon is provided. The model furnishes explanations for the Cole-Moore-like effect, the rising phase of the ON gating current and the slow 'intermediate component' of its decaying phase, as well as the gating charge immobilization. Experimental ON ionic currents are semi-quantitatively simulated by the use of only three free parameters, upon assuming that the Na+ channel opening proceeds along with the stepwise aggregation of its four domains, while they are moving their gating charge outward under depolarizing conditions. The inactivation phase of the ON ionic current is interpreted by a progressive electrostatic attraction between the positively charged 'hinged lid' containing the hydrophobic IFM triad and its receptor inside the channel pore, as the stepwise outward movement of the S4 segments of the Na+ channel progressively increases the negative charge attracting the triad to its receptor. The Na+ channel closing is assumed to proceed by repolarization-induced disaggregation of its domains, accompanied by inward movement of their gating charge. The phenomenon of 'gating charge immobilization' can be explained by assuming that gradual structural changes of the receptor over the time course of depolarization strengthen the interaction between the IFM triad and its receptor, causing a slow release of the gating charge during the subsequent repolarization.
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16
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Abstract
Ion channels are essential for cellular signaling. Voltage-gated ion channels (VGICs) are the largest and most extensively studied superfamily of ion channels. They possess modular structural features such as voltage-sensing domains that encircle and form mechanical connections with the pore-forming domains. Such features are intimately related to their function in sensing and responding to changes in the membrane potential. In the present work, we discuss the thermodynamic mechanisms of the VGIC superfamily, including the two-state gating mechanism, sliding-rocking mechanism of the voltage sensor, subunit cooperation, lipid-infiltration mechanism of inactivation, and the relationship with their structural features.
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17
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Gamal El-Din TM, Lenaeus MJ, Catterall WA. Structural and Functional Analysis of Sodium Channels Viewed from an Evolutionary Perspective. Handb Exp Pharmacol 2018; 246:53-72. [PMID: 29043505 DOI: 10.1007/164_2017_61] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Voltage-gated sodium channels initiate and propagate action potentials in excitable cells. They respond to membrane depolarization through opening, followed by fast inactivation that terminates the sodium current. This ON-OFF behavior of voltage-gated sodium channels underlays the coding of information and its transmission from one location in the nervous system to another. In this review, we explore and compare structural and functional data from prokaryotic and eukaryotic channels to infer the effects of evolution on sodium channel structure and function.
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Affiliation(s)
- Tamer M Gamal El-Din
- Department of Pharmacology, University of Washington, Seattle, WA, 98195-7280, USA.
| | - Michael J Lenaeus
- Department of Pharmacology, University of Washington, Seattle, WA, 98195-7280, USA
| | - William A Catterall
- Department of Pharmacology, University of Washington, Seattle, WA, 98195-7280, USA
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18
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Gating-induced large aqueous volumetric remodeling and aspartate tolerance in the voltage sensor domain of Shaker K + channels. Proc Natl Acad Sci U S A 2018; 115:8203-8208. [PMID: 30038023 DOI: 10.1073/pnas.1806578115] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Neurons encode electrical signals with critically tuned voltage-gated ion channels and enzymes. Dedicated voltage sensor domains (VSDs) in these membrane proteins activate coordinately with an unresolved structural change. Such change conveys the transmembrane translocation of four positively charged arginine side chains, the voltage-sensing residues (VSRs; R1-R4). Countercharges and lipid phosphohead groups likely stabilize these VSRs within the low-dielectric core of the protein. However, the role of hydration, a sign-independent charge stabilizer, remains unclear. We replaced all VSRs and their neighboring residues with negatively charged aspartates in a voltage-gated potassium channel. The ensuing mild functional effects indicate that hydration is also important in VSR stabilization. The voltage dependency of the VSR aspartate variants approached the expected arithmetic summation of charges at VSR positions, as if negative and positive side chains faced similar pathways. In contrast, aspartates introduced between R2 and R3 did not affect voltage dependence as if the side chains moved outside the electric field or together with it, undergoing a large displacement and volumetric remodeling. Accordingly, VSR performed osmotic work at both internal and external aqueous interfaces. Individual VSR contributions to volumetric works approached arithmetical additivity but were largely dissimilar. While R1 and R4 displaced small volumes, R2 and R3 volumetric works were massive and vectorially opposed, favoring large aqueous remodeling during VSD activation. These diverse volumetric works are, at least for R2 and R3, not compatible with VSR translocation across a unique stationary charge transfer center. Instead, VSRs may follow separated pathways across a fluctuating low-dielectric septum.
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19
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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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20
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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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21
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Abstract
Voltage-gated sodium (Na+) channels are expressed in virtually all electrically excitable tissues and are essential for muscle contraction and the conduction of impulses within the peripheral and central nervous systems. Genetic disorders that disrupt the function of these channels produce an array of Na+ channelopathies resulting in neuronal impairment, chronic pain, neuromuscular pathologies, and cardiac arrhythmias. Because of their importance to the conduction of electrical signals, Na+ channels are the target of a wide variety of local anesthetic, antiarrhythmic, anticonvulsant, and antidepressant drugs. The voltage-gated family of Na+ channels is composed of α-subunits that encode for the voltage sensor domains and the Na+-selective permeation pore. In vivo, Na+ channel α-subunits are associated with one or more accessory β-subunits (β1-β4) that regulate gating properties, trafficking, and cell-surface expression of the channels. The permeation pore of Na+ channels is divided in two parts: the outer mouth of the pore is the site of the ion selectivity filter, while the inner cytoplasmic pore serves as the channel activation gate. The cytoplasmic lining of the permeation pore is formed by the S6 segments that include highly conserved aromatic amino acids important for drug binding. These residues are believed to undergo voltage-dependent conformational changes that alter drug binding as the channels cycle through the closed, open, and inactivated states. The purpose of this chapter is to broadly review the mechanisms of Na+ channel gating and the models used to describe drug binding and Na+ channel inhibition.
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Affiliation(s)
- M E O'Leary
- Cooper Medical School of Rowan University, Camden, NJ, USA
| | - M Chahine
- CERVO Brain Research Center, Institut universitaire en santé mentale de Québec, Quebec City, QC, Canada.
- Department of Medicine, Université Laval, Quebec City, QC, Canada.
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22
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Sun RN, Gong H. Simulating the Activation of Voltage Sensing Domain for a Voltage-Gated Sodium Channel Using Polarizable Force Field. J Phys Chem Lett 2017; 8:901-908. [PMID: 28171721 DOI: 10.1021/acs.jpclett.7b00023] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Voltage-gated sodium (NaV) channels play vital roles in the signal transduction of excitable cells. Upon activation of a NaV channel, the change of transmembrane voltage triggers conformational change of the voltage sensing domain, which then elicits opening of the pore domain and thus allows an influx of Na+ ions. Description of this process with atomistic details is in urgent demand. In this work, we simulated the partial activation process of the voltage sensing domain of a prokaryotic NaV channel using a polarizable force field. We not only observed the conformational change of the voltage sensing domain from resting to preactive state, but also rigorously estimated the free energy profile along the identified reaction pathway. Comparison with the control simulation using an additive force field indicates that voltage-gating thermodynamics of NaV channels may be inaccurately described without considering the electrostatic polarization effect.
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Affiliation(s)
- Rui-Ning Sun
- MOE Key Laboratory of Bioinformatics, School of Life Sciences, Tsinghua University , Beijing 100084, China
| | - Haipeng Gong
- MOE Key Laboratory of Bioinformatics, School of Life Sciences, Tsinghua University , Beijing 100084, China
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23
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Cryo-EM structure of the open high-conductance Ca 2+-activated K + channel. Nature 2016; 541:46-51. [PMID: 27974795 DOI: 10.1038/nature20608] [Citation(s) in RCA: 172] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Accepted: 11/03/2016] [Indexed: 12/12/2022]
Abstract
The Ca2+-activated K+ channel, Slo1, has an unusually large conductance and contains a voltage sensor and multiple chemical sensors. Dual activation by membrane voltage and Ca2+ renders Slo1 central to processes that couple electrical signalling to Ca2+-mediated events such as muscle contraction and neuronal excitability. Here we present the cryo-electron microscopy structure of a full-length Slo1 channel from Aplysia californica in the presence of Ca2+ and Mg2+ at a resolution of 3.5 Å. The channel adopts an open conformation. Its voltage-sensor domain adopts a non-domain-swapped attachment to the pore and contacts the cytoplasmic Ca2+-binding domain from a neighbouring subunit. Unique structural features of the Slo1 voltage sensor suggest that it undergoes different conformational changes than other known voltage sensors. The structure reveals the molecular details of three distinct divalent cation-binding sites identified through electrophysiological studies of mutant Slo1 channels.
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24
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Congruent pattern of accessibility identifies minimal pore gate in a non-symmetric voltage-gated sodium channel. Nat Commun 2016; 7:11608. [PMID: 27186888 PMCID: PMC4873679 DOI: 10.1038/ncomms11608] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Accepted: 04/13/2016] [Indexed: 01/03/2023] Open
Abstract
Opening and closing of the central ion-conducting pore in voltage-dependent ion channels is gated by changes in membrane potential. Although a gate residue in the eukaryotic voltage-gated sodium channel has been identified, the minimal molecular determinants of this gate region remain unknown. Here, by measuring the closed- and open-state reactivity of MTSET to substituted cysteines in all the pore-lining helices, we show that the state-dependent accessibility is delineated by four hydrophobic residues at homologous positions in each domain. Introduced cysteines above these sites do not react with intracellular MTSET while the channels are closed and yet are rapidly modified while the channels are open. These findings, in conjunction with state-dependent metal cross-bridging, support the notion that the gate residues in each of the four S6 segments of the eukaryotic sodium channel form an occlusion for ions in the closed state and are splayed open on activation. Gating of the central pore in voltage-dependent ion channels is mediated by changes in membrane potential. Here, the authors use substituted cysteine accessibility and metal cross-bridging to identify gate residues that form a physical occlusion when closed in a eukaryotic voltage-gated sodium channel.
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25
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Abstract
Voltage-gated potassium channels or Kv's are membrane proteins with fundamental physiological roles. They are composed of 2 main functional protein domains, the pore domain, which regulates ion permeation, and the voltage-sensing domain, which is in charge of sensing voltage and undergoing a conformational change that is later transduced into pore opening. The voltage-sensing domain or VSD is a highly conserved structural motif found in all voltage-gated ion channels and can also exist as an independent feature, giving rise to voltage sensitive enzymes and also sustaining proton fluxes in proton-permeable channels. In spite of the structural conservation of VSDs in potassium channels, there are several differences in the details of VSD function found across variants of Kvs. These differences are mainly reflected in variations in the electrostatic energy needed to open different potassium channels. In turn, the differences in detailed VSD functioning among voltage-gated potassium channels might have physiological consequences that have not been explored and which might reflect evolutionary adaptations to the different roles played by Kv channels in cell physiology.
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Affiliation(s)
- León D Islas
- a Departamento de Fisiología, Facultad de Medicina ; National Autonomous University of Mexico (UNAM), Ciudad Universitaria , México City , México
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26
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Affiliation(s)
- William A Catterall
- Department of Pharmacology, University of Washington, Seattle, Washington 98195-7280.
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27
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Matson DJ, Hamamoto DT, Bregman H, Cooke M, DiMauro EF, Huang L, Johnson D, Li X, McDermott J, Morgan C, Wilenkin B, Malmberg AB, McDonough SI, Simone DA. Inhibition of Inactive States of Tetrodotoxin-Sensitive Sodium Channels Reduces Spontaneous Firing of C-Fiber Nociceptors and Produces Analgesia in Formalin and Complete Freund's Adjuvant Models of Pain. PLoS One 2015; 10:e0138140. [PMID: 26379236 PMCID: PMC4575030 DOI: 10.1371/journal.pone.0138140] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2015] [Accepted: 08/25/2015] [Indexed: 11/18/2022] Open
Abstract
While genetic evidence shows that the Nav1.7 voltage-gated sodium ion channel is a key regulator of pain, it is unclear exactly how Nav1.7 governs neuronal firing and what biophysical, physiological, and distribution properties of a pharmacological Nav1.7 inhibitor are required to produce analgesia. Here we characterize a series of aminotriazine inhibitors of Nav1.7 in vitro and in rodent models of pain and test the effects of the previously reported "compound 52" aminotriazine inhibitor on the spiking properties of nociceptors in vivo. Multiple aminotriazines, including some with low terminal brain to plasma concentration ratios, showed analgesic efficacy in the formalin model of pain. Effective concentrations were consistent with the in vitro potency as measured on partially-inactivated Nav1.7 but were far below concentrations required to inhibit non-inactivated Nav1.7. Compound 52 also reversed thermal hyperalgesia in the complete Freund's adjuvant (CFA) model of pain. To study neuronal mechanisms, electrophysiological recordings were made in vivo from single nociceptive fibers from the rat tibial nerve one day after CFA injection. Compound 52 reduced the spontaneous firing of C-fiber nociceptors from approximately 0.7 Hz to 0.2 Hz and decreased the number of action potentials evoked by suprathreshold tactile and heat stimuli. It did not, however, appreciably alter the C-fiber thresholds for response to tactile or thermal stimuli. Surprisingly, compound 52 did not affect spontaneous activity or evoked responses of Aδ-fiber nociceptors. Results suggest that inhibition of inactivated states of TTX-S channels, mostly likely Nav1.7, in the peripheral nervous system produces analgesia by regulating the spontaneous discharge of C-fiber nociceptors.
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Affiliation(s)
- David J. Matson
- Department of Neuroscience, Amgen Inc., Cambridge, Massachusetts, United States of America
| | - Darryl T. Hamamoto
- Department of Diagnostics and Biological Sciences, University of Minnesota School of Dentistry, Minneapolis, Minnesota, United States of America
| | - Howard Bregman
- Department of Medicinal Chemistry, Amgen Inc., Cambridge, Massachusetts, United States of America
| | - Melanie Cooke
- Department of Pharmaceutics Research & Development, Amgen Inc., Cambridge, Massachusetts, United States of America
| | - Erin F. DiMauro
- Department of Medicinal Chemistry, Amgen Inc., Cambridge, Massachusetts, United States of America
| | - Liyue Huang
- Department of Pharmacokinetics & Drug Metabolism, Amgen Inc., Cambridge, Massachusetts, United States of America
| | - Danielle Johnson
- Department of Neuroscience, Amgen Inc., Cambridge, Massachusetts, United States of America
| | - Xingwen Li
- Department of Pharmacokinetics & Drug Metabolism, Amgen Inc., Cambridge, Massachusetts, United States of America
| | - Jeff McDermott
- Department of Neuroscience, Amgen Inc., Cambridge, Massachusetts, United States of America
| | - Carrie Morgan
- Department of Pharmaceutics Research & Development, Amgen Inc., Cambridge, Massachusetts, United States of America
| | - Ben Wilenkin
- Department of Neuroscience, Amgen Inc., Cambridge, Massachusetts, United States of America
| | - Annika B. Malmberg
- Department of Neuroscience, Amgen Inc., Cambridge, Massachusetts, United States of America
| | - Stefan I. McDonough
- Department of Neuroscience, Amgen Inc., Cambridge, Massachusetts, United States of America
| | - Donald A. Simone
- Department of Diagnostics and Biological Sciences, University of Minnesota School of Dentistry, Minneapolis, Minnesota, United States of America
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28
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Gamal El-Din TM, Scheuer T, Catterall WA. Tracking S4 movement by gating pore currents in the bacterial sodium channel NaChBac. ACTA ACUST UNITED AC 2015; 144:147-57. [PMID: 25070432 PMCID: PMC4113903 DOI: 10.1085/jgp.201411210] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Comparison of the kinetics and voltage dependence of gating pore current conducted by S4 gating charge mutants supports the sliding-helix model of voltage sensor function and elucidates the pathogenic mechanisms underlying periodic paralysis syndromes. Voltage-gated sodium channels mediate the initiation and propagation of action potentials in excitable cells. Transmembrane segment S4 of voltage-gated sodium channels resides in a gating pore where it senses the membrane potential and controls channel gating. Substitution of individual S4 arginine gating charges (R1–R3) with smaller amino acids allows ionic currents to flow through the mutant gating pore, and these gating pore currents are pathogenic in some skeletal muscle periodic paralysis syndromes. The voltage dependence of gating pore currents provides information about the transmembrane position of the gating charges as S4 moves in response to membrane potential. Here we studied gating pore current in mutants of the homotetrameric bacterial sodium channel NaChBac in which individual arginine gating charges were replaced by cysteine. Gating pore current was observed for each mutant channel, but with different voltage-dependent properties. Mutating the first (R1C) or second (R2C) arginine to cysteine resulted in gating pore current at hyperpolarized membrane potentials, where the channels are in resting states, but not at depolarized potentials, where the channels are activated. Conversely, the R3C gating pore is closed at hyperpolarized membrane potentials and opens with channel activation. Negative conditioning pulses revealed time-dependent deactivation of the R3C gating pore at the most hyperpolarized potentials. Our results show sequential voltage dependence of activation of gating pore current from R1 to R3 and support stepwise outward movement of the substituted cysteines through the narrow portion of the gating pore that is sealed by the arginine side chains in the wild-type channel. This pattern of voltage dependence of gating pore current is consistent with a sliding movement of the S4 helix through the gating pore. Through comparison with high-resolution models of the voltage sensor of bacterial sodium channels, these results shed light on the structural basis for pathogenic gating pore currents in periodic paralysis syndromes.
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Affiliation(s)
| | - Todd Scheuer
- Department of Pharmacology, University of Washington, Seattle, WA 98195
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29
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Ishida IG, Rangel-Yescas GE, Carrasco-Zanini J, Islas LD. Voltage-dependent gating and gating charge measurements in the Kv1.2 potassium channel. ACTA ACUST UNITED AC 2015; 145:345-58. [PMID: 25779871 PMCID: PMC4380214 DOI: 10.1085/jgp.201411300] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Kv1.2’s gating charge is less than Shaker’s, and the specific contributions of charged S4 residues differ, suggesting that the electric field distribution in the Kv1.2 voltage-sensing domain is different than Shaker’s. Much has been learned about the voltage sensors of ion channels since the x-ray structure of the mammalian voltage-gated potassium channel Kv1.2 was published in 2005. High resolution structural data of a Kv channel enabled the structural interpretation of numerous electrophysiological findings collected in various ion channels, most notably Shaker, and permitted the development of meticulous computational simulations of the activation mechanism. The fundamental premise for the structural interpretation of functional measurements from Shaker is that this channel and Kv1.2 have the same characteristics, such that correlation of data from both channels would be a trivial task. We tested these assumptions by measuring Kv1.2 voltage-dependent gating and charge per channel. We found that the Kv1.2 gating charge is near 10 elementary charges (eo), ∼25% less than the well-established 13–14 eo in Shaker. Next, we neutralized positive residues in the Kv1.2 S4 transmembrane segment to investigate the cause of the reduction of the gating charge and found that, whereas replacing R1 with glutamine decreased voltage sensitivity to ∼50% of the wild-type channel value, mutation of the subsequent arginines had a much smaller effect. These data are in marked contrast to the effects of charge neutralization in Shaker, where removal of the first four basic residues reduces the gating charge by roughly the same amount. In light of these differences, we propose that the voltage-sensing domains (VSDs) of Kv1.2 and Shaker might undergo the same physical movement, but the septum that separates the aqueous crevices in the VSD of Kv1.2 might be thicker than Shaker’s, accounting for the smaller Kv1.2 gating charge.
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Affiliation(s)
- Itzel G Ishida
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, Distrito Federal 04510, México
| | - Gisela E Rangel-Yescas
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, Distrito Federal 04510, México
| | - Julia Carrasco-Zanini
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, Distrito Federal 04510, México
| | - León D Islas
- Departamento de Fisiología, Facultad de Medicina, Universidad Nacional Autónoma de México, Distrito Federal 04510, México
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30
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Raddatz N, Castillo JP, Gonzalez C, Alvarez O, Latorre R. Temperature and voltage coupling to channel opening in transient receptor potential melastatin 8 (TRPM8). J Biol Chem 2014; 289:35438-54. [PMID: 25352597 DOI: 10.1074/jbc.m114.612713] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Expressed in somatosensory neurons of the dorsal root and trigeminal ganglion, the transient receptor potential melastatin 8 (TRPM8) channel is a Ca(2+)-permeable cation channel activated by cold, voltage, phosphatidylinositol 4,5-bisphosphate, and menthol. Although TRPM8 channel gating has been characterized at the single channel and macroscopic current levels, there is currently no consensus regarding the extent to which temperature and voltage sensors couple to the conduction gate. In this study, we extended the range of voltages where TRPM8-induced ionic currents were measured and made careful measurements of the maximum open probability the channel can attain at different temperatures by means of fluctuation analysis. The first direct measurements of TRPM8 channel temperature-driven conformational rearrangements provided here suggest that temperature alone is able to open the channel and that the opening reaction is voltage-independent. Voltage is a partial activator of TRPM8 channels, because absolute open probability values measured with fully activated voltage sensors are less than 1, and they decrease as temperature rises. By unveiling the fast temperature-dependent deactivation process, we show that TRPM8 channel deactivation is well described by a double exponential time course. The fast and slow deactivation processes are temperature-dependent with enthalpy changes of 27.2 and 30.8 kcal mol(-1). The overall Q10 for the closing reaction is about 33. A three-tiered allosteric model containing four voltage sensors and four temperature sensors can account for the complex deactivation kinetics and coupling between voltage and temperature sensor activation and channel opening.
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Affiliation(s)
- Natalia Raddatz
- From the Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103 and
| | - Juan P Castillo
- From the Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103 and
| | - Carlos Gonzalez
- From the Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103 and
| | - Osvaldo Alvarez
- From the Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103 and the Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Santiago 7800003, Chile
| | - Ramon Latorre
- From the Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2366103 and
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31
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Mi W, Rybalchenko V, Cannon SC. Disrupted coupling of gating charge displacement to Na+ current activation for DIIS4 mutations in hypokalemic periodic paralysis. ACTA ACUST UNITED AC 2014; 144:137-45. [PMID: 25024265 PMCID: PMC4113897 DOI: 10.1085/jgp.201411199] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Missense mutations at arginine residues in the S4 voltage-sensor domains of NaV1.4 are an established cause of hypokalemic periodic paralysis, an inherited disorder of skeletal muscle involving recurrent episodes of weakness in conjunction with low serum K(+). Expression studies in oocytes have revealed anomalous, hyperpolarization-activated gating pore currents in mutant channels. This aberrant gating pore conductance creates a small inward current at the resting potential that is thought to contribute to susceptibility to depolarization in low K(+) during attacks of weakness. A critical component of this hypothesis is the magnitude of the gating pore conductance relative to other conductances that are active at the resting potential in mammalian muscle: large enough to favor episodes of paradoxical depolarization in low K(+), yet not so large as to permanently depolarize the fiber. To improve the estimate of the specific conductance for the gating pore in affected muscle, we sequentially measured Na(+) current through the channel pore, gating pore current, and gating charge displacement in oocytes expressing R669H, R672G, or wild-type NaV1.4 channels. The relative conductance of the gating pore to that of the pore domain pathway for Na(+) was 0.03%, which implies a specific conductance in muscle from heterozygous patients of ∼ 10 µS/cm(2) or 1% of the total resting conductance. Unexpectedly, our data also revealed a substantial decoupling between gating charge displacement and peak Na(+) current for both R669H and R672G mutant channels. This decoupling predicts a reduced Na(+) current density in affected muscle, consistent with the observations that the maximal dV/dt and peak amplitude of the action potential are reduced in fibers from patients with R672G and in a knock-in mouse model of R669H. The defective coupling between gating charge displacement and channel activation identifies a previously unappreciated mechanism that contributes to the reduced excitability of affected fibers seen with these mutations and possibly with other R/X mutations of S4 of NaV, CaV, and KV channels associated with human disease.
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Affiliation(s)
- Wentao Mi
- Department of Neurology and Neurotherapeutics, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Volodymyr Rybalchenko
- Department of Neurology and Neurotherapeutics, University of Texas Southwestern Medical Center, Dallas, TX 75390
| | - Stephen C Cannon
- Department of Neurology and Neurotherapeutics, University of Texas Southwestern Medical Center, Dallas, TX 75390
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KCNE1 divides the voltage sensor movement in KCNQ1/KCNE1 channels into two steps. Nat Commun 2014; 5:3750. [PMID: 24769622 PMCID: PMC4019390 DOI: 10.1038/ncomms4750] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2013] [Accepted: 03/28/2014] [Indexed: 11/09/2022] Open
Abstract
The functional properties of KCNQ1 channels are highly dependent on associated KCNE β subunits. Mutations in KCNQ1 or KCNE subunits can cause congenital channelopathies, such as deafness, cardiac arrhythmias, and epilepsy. The mechanism by which KCNE1 beta subunits slow the kinetics of KCNQ1 channels is a matter of current controversy. Here we show that KCNQ1/KCNE1 channel activation occurs in two steps: first, mutually independent voltage sensor movements in the four KCNQ1 subunits generate the main gating charge movement and underlie the initial delay in the activation time course of KCNQ1/KCNE1 currents. Second, a slower and concerted conformational change of all four voltage sensors and the gate, which opens the KCNQ1/KCNE1 channel. Our data show that KCNE1 divides the voltage sensor movement into two steps with widely different voltage dependences and kinetics. The two voltage sensor steps in KCNQ1/KCNE1 channels can be pharmacologically isolated and further separated by a disease-causing mutation.
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Abstract
The paralytic agent (+)-saxitoxin (STX), most commonly associated with oceanic red tides and shellfish poisoning, is a potent inhibitor of electrical conduction in cells. Its nefarious effects result from inhibition of voltage-gated sodium channels (Na(V)s), the obligatory proteins responsible for the initiation and propagation of action potentials. In the annals of ion channel research, the identification and characterization of Na(V)s trace to the availability of STX and an allied guanidinium derivative, tetrodotoxin. The mystique of STX is expressed in both its function and form, as this uniquely compact dication boasts more heteroatoms than carbon centers. This Review highlights both the chemistry and chemical biology of this fascinating natural product, and offers a perspective as to how molecular design and synthesis may be used to explore Na(V) structure and function.
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Affiliation(s)
- Arun P Thottumkara
- Department of Chemistry, Stanford University, Stanford, CA 94305-5080 (USA)
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Goldschen-Ohm MP, Chanda B. Probing gating mechanisms of sodium channels using pore blockers. Handb Exp Pharmacol 2014; 221:183-201. [PMID: 24737237 DOI: 10.1007/978-3-642-41588-3_9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Several classes of small molecules and peptides bind at the central pore of voltage-gated sodium channels either from the extracellular or intracellular side of the membrane and block ion conduction through the pore. Biophysical studies that shed light on the chemical nature, accessibility, and kinetics of binding of these naturally occurring and synthetic compounds reveal a wealth of information about how these channels gate. Here, we discuss insights into the structural underpinnings of gating of the channel pore and its coupling to the voltage sensors obtained from pore blockers including site 1 neurotoxins and local anesthetics.
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36
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Chowdhury S, Chanda B. Perspectives on: conformational coupling in ion channels: thermodynamics of electromechanical coupling in voltage-gated ion channels. ACTA ACUST UNITED AC 2013. [PMID: 23183697 PMCID: PMC3514737 DOI: 10.1085/jgp.201210840] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Sandipan Chowdhury
- Graduate Program in Biophysics, University of Wisconsin, Madison, WI 53706, USA
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37
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DeCoursey TE. Voltage-gated proton channels: molecular biology, physiology, and pathophysiology of the H(V) family. Physiol Rev 2013; 93:599-652. [PMID: 23589829 PMCID: PMC3677779 DOI: 10.1152/physrev.00011.2012] [Citation(s) in RCA: 178] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Voltage-gated proton channels (H(V)) are unique, in part because the ion they conduct is unique. H(V) channels are perfectly selective for protons and have a very small unitary conductance, both arguably manifestations of the extremely low H(+) concentration in physiological solutions. They open with membrane depolarization, but their voltage dependence is strongly regulated by the pH gradient across the membrane (ΔpH), with the result that in most species they normally conduct only outward current. The H(V) channel protein is strikingly similar to the voltage-sensing domain (VSD, the first four membrane-spanning segments) of voltage-gated K(+) and Na(+) channels. In higher species, H(V) channels exist as dimers in which each protomer has its own conduction pathway, yet gating is cooperative. H(V) channels are phylogenetically diverse, distributed from humans to unicellular marine life, and perhaps even plants. Correspondingly, H(V) functions vary widely as well, from promoting calcification in coccolithophores and triggering bioluminescent flashes in dinoflagellates to facilitating killing bacteria, airway pH regulation, basophil histamine release, sperm maturation, and B lymphocyte responses in humans. Recent evidence that hH(V)1 may exacerbate breast cancer metastasis and cerebral damage from ischemic stroke highlights the rapidly expanding recognition of the clinical importance of hH(V)1.
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Affiliation(s)
- Thomas E DeCoursey
- Dept. of Molecular Biophysics and Physiology, Rush University Medical Center HOS-036, 1750 West Harrison, Chicago, IL 60612, USA.
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38
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Wu BM, Wang XH, Zhao B, Bian EB, Yan H, Cheng H, Lv XW, Xiong ZG, Li J. Electrophysiology properties of voltage-gated potassium channels in rat peritoneal macrophages. Int J Clin Exp Med 2013; 6:166-173. [PMID: 23573347 PMCID: PMC3609692] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2013] [Accepted: 02/23/2013] [Indexed: 06/02/2023]
Abstract
Ion channels are important for the functions of excitable and non-excitable cells. Using the whole-cell patch clamp technique, we analyzed the electrophysiological and pharmacological properties of voltage-gated potassium channels in primary rat peritoneal macrophages. With intracellular solution contained K(+) as the main charge carrier, all cells showed outward currents in response to membrane depolarization. The currents can be inhibited by TEA (10 mM), a non-selective blocker for voltage-gated K(+) channels, and attenuated when intracellular K(+) was substituted with Cs(+). Changing holding potential from -80 to -30 mV or -10 mV also inhibited the outward currents. In contrast, increasing the concentration of ATP in the intracellular solution decreased the amplitude of the outward currents. Thus, rat peritoneal macrophages express several types of functional voltage-gated K(+) channels.
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Affiliation(s)
- Bao-Ming Wu
- School of Pharmacy, Anhui Medical UniversityHeifei, 230032, Anhui Province, China
| | - Xiao-Hua Wang
- School of Pharmacy, Anhui Medical UniversityHeifei, 230032, Anhui Province, China
| | - Bin Zhao
- School of Pharmacy, Anhui Medical UniversityHeifei, 230032, Anhui Province, China
- Deputy ChiefTong Guan Shan, Tongling city ,244000, Anhui Province, China
| | - Er-Bao Bian
- School of Pharmacy, Anhui Medical UniversityHeifei, 230032, Anhui Province, China
| | - Huang Yan
- School of Pharmacy, Anhui Medical UniversityHeifei, 230032, Anhui Province, China
| | - Huang Cheng
- School of Pharmacy, Anhui Medical UniversityHeifei, 230032, Anhui Province, China
| | - Xiong-Wen Lv
- School of Pharmacy, Anhui Medical UniversityHeifei, 230032, Anhui Province, China
| | - Zhi-Gang Xiong
- School of Pharmacy, Anhui Medical UniversityHeifei, 230032, Anhui Province, China
- Neuroscience Institute, Morehouse School of MedicineAtlanta, GA 30310, USA
| | - Jun Li
- School of Pharmacy, Anhui Medical UniversityHeifei, 230032, Anhui Province, China
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Gonzalez C, Rebolledo S, Perez ME, Larsson HP. Molecular mechanism of voltage sensing in voltage-gated proton channels. ACTA ACUST UNITED AC 2013; 141:275-85. [PMID: 23401575 PMCID: PMC3581690 DOI: 10.1085/jgp.201210857] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Voltage-gated proton (Hv) channels play an essential role in phagocytic cells by generating a hyperpolarizing proton current that electrically compensates for the depolarizing current generated by the NADPH oxidase during the respiratory burst, thereby ensuring a sustained production of reactive oxygen species by the NADPH oxidase in phagocytes to neutralize engulfed bacteria. Despite the importance of the voltage-dependent Hv current, it is at present unclear which residues in Hv channels are responsible for the voltage activation. Here we show that individual neutralizations of three charged residues in the fourth transmembrane domain, S4, all reduce the voltage dependence of activation. In addition, we show that the middle S4 charged residue moves from a position accessible from the cytosolic solution to a position accessible from the extracellular solution, suggesting that this residue moves across most of the membrane electric field during voltage activation of Hv channels. Our results show for the first time that the charge movement of these three S4 charges accounts for almost all of the measured gating charge in Hv channels.
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Affiliation(s)
- Carlos Gonzalez
- Department of Physiology and Biophysics, University of Miami, Miami, FL 33136, USA. carlos.gonzalezl@uv
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40
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Smith SM, DeCoursey TE. Consequences of dimerization of the voltage-gated proton channel. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2013; 117:335-60. [PMID: 23663974 PMCID: PMC3963466 DOI: 10.1016/b978-0-12-386931-9.00012-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/19/2024]
Abstract
The human voltage-gated proton channel, hHV1, appears to exist mainly as a dimer. Teleologically, this is puzzling because each protomer retains the main properties that characterize this protein: proton conduction that is regulated by conformational (channel opening and closing) changes that occur in response to both voltage and pH. The HV1 dimer is mainly linked by C-terminal coiled-coil interactions. Several types of mutations produce monomeric constructs that open approximately five times faster than the wild-type dimeric channel but with weaker voltage dependence. Intriguingly, the quintessential function of the HV1 dimer, opening to allow H(+) conduction, occurs cooperatively. Both protomers undergo a conformational change, but both must undergo this transition before either can conduct. The teleological purpose of dimerization may be to steepen the voltage dependence of channel opening, at least in phagocytes. In other cells, the purpose is not understood. Finally, several single-celled species have HV that are likely monomeric.
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Affiliation(s)
- Susan M.E. Smith
- Department of Pathology and Laboratory Medicine, Emory School of Medicine, Atlanta GA 30322 USA
| | - Thomas E. DeCoursey
- Department of Molecular Biophysics and Physiology, Rush University, Chicago IL 60612 USA
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41
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Nguyen NV, Gruslova A, Kosiba WA, Wang B. Combined single-channel and macroscopic recording techniques to analyze gating mechanisms of the large conductance Ca2+ and voltage activated (BK) potassium channel. Methods Mol Biol 2013; 998:133-47. [PMID: 23529426 DOI: 10.1007/978-1-62703-351-0_10] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Ion channels are integral membrane proteins that regulate membrane potentials and signaling of cells in response to various stimuli. The patch-clamp technique enables the study of single channels or a population of channels. The macroscopic recording approaches are powerful in revealing population-averaged behaviors of channels both under basal conditions and in response to various stimuli, modulators and drugs. On their own, however, these approaches can be insufficient for determinations of channel gating mechanisms as they do not accurately report channel open probabilities below 10(-2) to 10(-3). This obstacle can be overcome with the use of single-channel recording techniques. Single-channel recording techniques can be applied to one or a few channels to estimate P o over a larger range than macroscopic recordings. The combination of heterologous overexpression of ion channels with macroscopic and single-channel recordings can be applied to hundreds of channels to estimate P o between 1 and 10(-8). Here, we describe practical approaches of single-channel recordings that our laboratory utilizes. We also provide examples where the combined macroscopic and single channel approach can be employed to study gating mechanisms of the BK type, large conductance, Ca(2+) and voltage activated potassium channel in a mammalian expression system. The techniques presented should be generally applicable to the studies of ion channels in heterologous expression systems.
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Affiliation(s)
- Nguyen V Nguyen
- Department of Radiology, University of Miami School of Medicine, Miami, FL, USA
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42
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Ryu S, Yellen G. Charge movement in gating-locked HCN channels reveals weak coupling of voltage sensors and gate. J Gen Physiol 2012; 140:469-79. [PMID: 23071265 PMCID: PMC3483112 DOI: 10.1085/jgp.201210850] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2012] [Accepted: 09/18/2012] [Indexed: 01/13/2023] Open
Abstract
HCN (hyperpolarization-activated cyclic nucleotide gated) pacemaker channels have an architecture similar to that of voltage-gated K(+) channels, but they open with the opposite voltage dependence. HCN channels use essentially the same positively charged voltage sensors and intracellular activation gates as K(+) channels, but apparently these two components are coupled differently. In this study, we examine the energetics of coupling between the voltage sensor and the pore by using cysteine mutant channels for which low concentrations of Cd(2+) ions freeze the open-closed gating machinery but still allow the sensors to move. We were able to lock mutant channels either into open or into closed states by the application of Cd(2+) and measure the effect on voltage sensor movement. Cd(2+) did not immobilize the gating charge, as expected for strict coupling, but rather it produced shifts in the voltage dependence of voltage sensor charge movement, consistent with its effect of confining transitions to either closed or open states. From the magnitude of the Cd(2+)-induced shifts, we estimate that each voltage sensor produces a roughly three- to sevenfold effect on the open-closed equilibrium, corresponding to a coupling energy of ∼1.3-2 kT per sensor. Such coupling is not only opposite in sign to the coupling in K(+) channels, but also much weaker.
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Affiliation(s)
- Sujung Ryu
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA
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43
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Gonzalez C, Contreras GF, Peyser A, Larsson P, Neely A, Latorre R. Voltage sensor of ion channels and enzymes. Biophys Rev 2012; 4:1-15. [PMID: 28509999 PMCID: PMC5425699 DOI: 10.1007/s12551-011-0061-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2011] [Accepted: 11/17/2011] [Indexed: 10/14/2022] Open
Abstract
Placed in the cell membrane (a two-dimensional environment), ion channels and enzymes are able to sense voltage. How these proteins are able to detect the difference in the voltage across membranes has attracted much attention, and at times, heated debate during the last few years. Sodium, Ca2+ and K+ voltage-dependent channels have a conserved positively charged transmembrane (S4) segment that moves in response to changes in membrane voltage. In voltage-dependent channels, S4 forms part of a domain that crystallizes as a well-defined structure consisting of the first four transmembrane (S1-S4) segments of the channel-forming protein, which is defined as the voltage sensor domain (VSD). The VSD is tied to a pore domain and VSD movements are allosterically coupled to the pore opening to various degrees, depending on the type of channel. How many charges are moved during channel activation, how much they move, and which are the molecular determinants that mediate the electromechanical coupling between the VSD and the pore domains are some of the questions that we discuss here. The VSD can function, however, as a bona fide proton channel itself, and, furthermore, the VSD can also be a functional part of a voltage-dependent phosphatase.
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Affiliation(s)
- Carlos Gonzalez
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Pasaje Harrington 287, Valparaíso, 2360103, Chile
| | - Gustavo F Contreras
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Pasaje Harrington 287, Valparaíso, 2360103, Chile
| | - Alexander Peyser
- Department of Physiology and Biophysics, University of Miami, Miami, FL, USA
| | - Peter Larsson
- Department of Physiology and Biophysics, University of Miami, Miami, FL, USA
| | - Alan Neely
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Pasaje Harrington 287, Valparaíso, 2360103, Chile
| | - Ramón Latorre
- Centro Interdisciplinario de Neurociencia de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Pasaje Harrington 287, Valparaíso, 2360103, Chile.
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Chowdhury S, Chanda B. Estimating the voltage-dependent free energy change of ion channels using the median voltage for activation. ACTA ACUST UNITED AC 2011; 139:3-17. [PMID: 22155736 PMCID: PMC3250103 DOI: 10.1085/jgp.201110722] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Voltage-gated ion channels are crucial for electrical activity and chemical signaling in a variety of cell types. Structure-activity studies involving electrophysiological characterization of mutants are widely used and allow us to quickly realize the energetic effects of a mutation by measuring macroscopic currents and fitting the observed voltage dependence of conductance to a Boltzmann equation. However, such an approach is somewhat limiting, principally because of the inherent assumption that the channel activation is a two-state process. In this analysis, we show that the area delineated by the gating charge displacement curve and its ordinate axis is related to the free energy of activation of a voltage-gated ion channel. We derive a parameter, the median voltage of charge transfer (Vm), which is proportional to this area, and prove that the chemical component of free energy change of a system can be obtained from the knowledge of Vm and the maximum number of charges transferred. Our method is not constrained by the number or connectivity of intermediate states and is applicable to instances in which the observed responses show a multiphasic behavior. We consider various models of ion channel gating with voltage-dependent steps, latent charge movement, inactivation, etc. and discuss the applicability of this approach in each case. Notably, our method estimates a net free energy change of approximately −14 kcal/mol associated with the full-scale activation of the Shaker potassium channel, in contrast to −2 to −3 kcal/mol estimated from a single Boltzmann fit. Our estimate of the net free energy change in the system is consistent with those derived from detailed kinetic models (Zagotta et al. 1994. J. Gen. Physiol. doi:10.1085/jgp.103.2.321). The median voltage method can reliably quantify the magnitude of free energy change associated with activation of a voltage-dependent system from macroscopic equilibrium measurements. This will be particularly useful in scanning mutagenesis experiments.
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Affiliation(s)
- Sandipan Chowdhury
- Graduate Program in Biophysics, University of Wisconsin-Madison, Madison, WI 53706, USA
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45
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46
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Sokolov S, Scheuer T, Catterall WA. Ion permeation and block of the gating pore in the voltage sensor of NaV1.4 channels with hypokalemic periodic paralysis mutations. ACTA ACUST UNITED AC 2010; 136:225-36. [PMID: 20660662 PMCID: PMC2912069 DOI: 10.1085/jgp.201010414] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Hypokalemic periodic paralysis and normokalemic periodic paralysis are caused by mutations of the gating charge–carrying arginine residues in skeletal muscle NaV1.4 channels, which induce gating pore current through the mutant voltage sensor domains. Inward sodium currents through the gating pore of mutant R666G are only ∼1% of central pore current, but substitution of guanidine for sodium in the extracellular solution increases their size by 13- ± 2-fold. Ethylguanidine is permeant through the R666G gating pore at physiological membrane potentials but blocks the gating pore at hyperpolarized potentials. Guanidine is also highly permeant through the proton-selective gating pore formed by the mutant R666H. Gating pore current conducted by the R666G mutant is blocked by divalent cations such as Ba2+ and Zn2+ in a voltage-dependent manner. The affinity for voltage-dependent block of gating pore current by Ba2+ and Zn2+ is increased at more negative holding potentials. The apparent dissociation constant (Kd) values for Zn2+ block for test pulses to −160 mV are 650 ± 150 µM, 360 ± 70 µM, and 95.6 ± 11 µM at holding potentials of 0 mV, −80 mV, and −120 mV, respectively. Gating pore current is blocked by trivalent cations, but in a nearly voltage-independent manner, with an apparent Kd for Gd3+ of 238 ± 14 µM at −80 mV. To test whether these periodic paralyses might be treated by blocking gating pore current, we screened several aromatic and aliphatic guanidine derivatives and found that 1-(2,4-xylyl)guanidinium can block gating pore current in the millimolar concentration range without affecting normal NaV1.4 channel function. Together, our results demonstrate unique permeability of guanidine through NaV1.4 gating pores, define voltage-dependent and voltage-independent block by divalent and trivalent cations, respectively, and provide initial support for the concept that guanidine-based gating pore blockers could be therapeutically useful.
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Affiliation(s)
- Stanislav Sokolov
- Department of Pharmacology, University of Washington, Seattle, WA 98195, USA
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47
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Reduced voltage sensitivity in a K+-channel voltage sensor by electric field remodeling. Proc Natl Acad Sci U S A 2010; 107:5178-83. [PMID: 20194763 DOI: 10.1073/pnas.1000963107] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Propagation of the nerve impulse relies on the extreme voltage sensitivity of Na(+) and K(+) channels. The transmembrane movement of four arginine residues, located at the fourth transmembrane segment (S4), in each of their four voltage-sensing domains is mostly responsible for the translocation of 12 to 13 e(o) across the transmembrane electric field. Inserting additional positively charged residues between the voltage-sensing arginines in S4 would, in principle, increase voltage sensitivity. Here we show that either positively or negatively charged residues added between the two most external sensing arginines of S4 decreased voltage sensitivity of a Shaker voltage-gated K(+)-channel by up to approximately 50%. The replacement of Val363 with a charged residue displaced inwardly the external boundaries of the electric field by at least 6 A, leaving the most external arginine of S4 constitutively exposed to the extracellular space and permanently excluded from the electric field. Both the physical trajectory of S4 and its electromechanical coupling to open the pore gate seemed unchanged. We propose that the separation between the first two sensing charges at resting is comparable to the thickness of the low dielectric transmembrane barrier they must cross. Thus, at most a single sensing arginine side chain could be found within the field. The conserved hydrophobic nature of the residues located between the voltage-sensing arginines in S4 may shape the electric field geometry for optimal voltage sensitivity in voltage-gated ion channels.
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48
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Tombola F, Ulbrich MH, Kohout SC, Isacoff EY. The opening of the two pores of the Hv1 voltage-gated proton channel is tuned by cooperativity. Nat Struct Mol Biol 2009; 17:44-50. [PMID: 20023640 PMCID: PMC2925041 DOI: 10.1038/nsmb.1738] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2009] [Accepted: 10/26/2009] [Indexed: 01/25/2023]
Abstract
In voltage-gated sodium, potassium, and calcium channels the functions of ion conduction and voltage sensing are performed by two distinct structural units: the pore domain and the voltage-sensing domain (VSD). In the Hv1 voltage-gated proton channel, the VSD has the remarkable property of performing both functions. Hv1 was recently found to dimerize and to form channels made of two pores. However, the channels were also found to function when dimerization was prevented, raising a question about the functional role of dimerization. Here we show that the two subunits of the Hv1 dimer influence one another during gating, with positive cooperativity shaping the response to voltage of the two pores. We also find that the two voltage sensors undergo conformational changes that precede pore opening and that these conformational changes are allosterically coupled between the two subunits. Our results point to a major role of dimerization in the modulation of Hv1 activity.
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Affiliation(s)
- Francesco Tombola
- Department of Physiology and Biophysics, University of California, Irvine, California, USA
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49
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Sequential formation of ion pairs during activation of a sodium channel voltage sensor. Proc Natl Acad Sci U S A 2009; 106:22498-503. [PMID: 20007787 DOI: 10.1073/pnas.0912307106] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Electrical signaling in biology depends upon a unique electromechanical transduction process mediated by the S4 segments of voltage-gated ion channels. These transmembrane segments are driven outward by the force of the electric field on positively charged amino acid residues termed "gating charges," which are positioned at three-residue intervals in the S4 transmembrane segment, and this movement is coupled to opening of the pore. Here, we use the disulfide-locking method to demonstrate sequential ion pair formation between the fourth gating charge in the S4 segment (R4) and two acidic residues in the S2 segment during activation. R4 interacts first with E70 at the intracellular end of the S2 segment and then with D60 near the extracellular end. Analysis with the Rosetta Membrane method reveals the 3-D structures of the gating pore as these ion pairs are formed sequentially to catalyze the S4 transmembrane movement required for voltage-dependent activation. Our results directly demonstrate sequential ion pair formation that is an essential feature of the sliding helix model of voltage sensor function but is not compatible with the other widely discussed gating models.
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50
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Ma Z, Kong J, Kallen RG. Studies of alpha-helicity and intersegmental interactions in voltage-gated Na+ channels: S2D4. PLoS One 2009; 4:e7674. [PMID: 19881885 PMCID: PMC2766034 DOI: 10.1371/journal.pone.0007674] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2009] [Accepted: 04/14/2009] [Indexed: 11/25/2022] Open
Abstract
Much data, including crystallographic, support structural models of sodium and potassium channels consisting of S1–S4 transmembrane segments (the “voltage-sensing domain”) clustered around a central pore-forming region (S5–S6 segments and the intervening loop). Voltage gated sodium channels have four non-identical domains which differentiates them from the homotetrameric potassium channels that form the basis for current structural models. Since potassium and sodium channels also exhibit many different functional characteristics and the fourth domain (D4) of sodium channels differs in function from other domains (D1–D3), we have explored its structure in order to determine whether segments in D4 of sodium channels differ significantly from that determined for potassium channels. We have probed the secondary and tertiary structure and the role of the individual amino acid residues of the S2D4) of Nav1.4 by employing cysteine-scanning mutagenesis (with tryptophan and glutamine substituted for native cysteine). A Fourier transform power spectrum of perturbations in free energy of steady-state inactivation gating (using midpoint potentials and slopes of Boltzmann equation fits of channel availability, h∞-V plots) indicates a substantial amount of α-helical structure in S2D4 (peak at 106°, α-Periodicity Index (α-PI) of 3.10), This conclusion is supported by α-PI values of 3.28 and 2.84 for the perturbations in rate constants of entry into (β) and exit from (α) fast inactivation at 0 mV for mutant channels relative to WT channels assuming a simple two-state model for transition from the open to inactivated state. The results of cysteine substitution at the two most sensitive sites of the S2D4 α-helix (N1382 and E1392C) support the existence of electrostatic network interactions between S2 and other transmembrane segments within Nav1.4D4 similar to but not identical to those proposed for K+ channels.
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Affiliation(s)
- Zhongming Ma
- Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Jun Kong
- Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Roland G. Kallen
- Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
- Mahoney Institute for Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, United States of America
- * E-mail:
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