1
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Williams ZJ, Payne LB, Wu X, Gourdie RG. New focus on cardiac voltage-gated sodium channel β1 and β1B: Novel targets for treating and understanding arrhythmias? Heart Rhythm 2024:S1547-5271(24)02742-5. [PMID: 38908461 DOI: 10.1016/j.hrthm.2024.06.029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/03/2024] [Revised: 06/09/2024] [Accepted: 06/17/2024] [Indexed: 06/24/2024]
Abstract
Voltage-gated sodium channels (VGSCs) are transmembrane protein complexes that are vital to the generation and propagation of action potentials in nerve and muscle fibers. The canonical VGSC is generally conceived as a heterotrimeric complex formed by 2 classes of membrane-spanning subunit: an α-subunit (pore forming) and 2 β-subunits (non-pore forming). NaV1.5 is the main sodium channel α-subunit of mammalian ventricle, with lower amounts of other α-subunits, including NaV1.6, being present. There are 4 β-subunits (β1-β4) encoded by 4 genes (SCN1B-SCN4B), each of which is expressed in cardiac tissues. Recent studies suggest that in addition to assignments in channel gating and trafficking, products of Scn1b may have novel roles in conduction of action potential in the heart and intracellular signaling. This includes evidence that the β-subunit extracellular amino-terminal domain facilitates adhesive interactions in intercalated discs and that its carboxyl-terminal region is a substrate for a regulated intramembrane proteolysis (RIP) signaling pathway, with a carboxyl-terminal peptide generated by β1 RIP trafficked to the nucleus and altering transcription of various genes, including NaV1.5. In addition to β1, the Scn1b gene encodes for an alternative splice variant, β1B, which contains an identical extracellular adhesion domain to β1 but has a unique carboxyl-terminus. Although β1B is generally understood to be a secreted variant, evidence indicates that when co-expressed with NaV1.5, it is maintained at the cell membrane, suggesting potential unique roles for this understudied protein. In this review, we focus on what is known of the 2 β-subunit variants encoded by Scn1b in heart, with particular focus on recent findings and the questions raised by this new information. We also explore data that indicate β1 and β1B may be attractive targets for novel antiarrhythmic therapeutics.
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Affiliation(s)
- Zachary J Williams
- Fralin Biomedical Research Institute, Virginia Polytechnic University, Roanoke, Virginia
| | - Laura Beth Payne
- Fralin Biomedical Research Institute, Virginia Polytechnic University, Roanoke, Virginia
| | - Xiaobo Wu
- Fralin Biomedical Research Institute, Virginia Polytechnic University, Roanoke, Virginia
| | - Robert G Gourdie
- Fralin Biomedical Research Institute, Virginia Polytechnic University, Roanoke, Virginia; School of Medicine, Virgina Polytechnic University, Roanoke, Virginia; Department of Biomedical Engineering and Mechanics, Virginia Polytechnic University, Blacksburg, Virginia.
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2
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Seneci L, Mikheyev AS. Sodium Channel β Subunits-An Additional Element in Animal Tetrodotoxin Resistance? Int J Mol Sci 2024; 25:1478. [PMID: 38338757 PMCID: PMC10855141 DOI: 10.3390/ijms25031478] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Revised: 12/09/2023] [Accepted: 12/15/2023] [Indexed: 02/12/2024] Open
Abstract
Tetrodotoxin (TTX) is a neurotoxic molecule used by many animals for defense and/or predation, as well as an important biomedical tool. Its ubiquity as a defensive agent has led to repeated independent evolution of tetrodotoxin resistance in animals. TTX binds to voltage-gated sodium channels (VGSC) consisting of α and β subunits. Virtually all studies investigating the mechanisms behind TTX resistance have focused on the α subunit of voltage-gated sodium channels, where tetrodotoxin binds. However, the possibility of β subunits also contributing to tetrodotoxin resistance was never explored, though these subunits act in concert. In this study, we present preliminary evidence suggesting a potential role of β subunits in the evolution of TTX resistance. We gathered mRNA sequences for all β subunit types found in vertebrates across 12 species (three TTX-resistant and nine TTX-sensitive) and tested for signatures of positive selection with a maximum likelihood approach. Our results revealed several sites experiencing positive selection in TTX-resistant taxa, though none were exclusive to those species in subunit β1, which forms a complex with the main physiological target of TTX (VGSC Nav1.4). While experimental data validating these findings would be necessary, this work suggests that deeper investigation into β subunits as potential players in tetrodotoxin resistance may be worthwhile.
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Affiliation(s)
- Lorenzo Seneci
- Adaptive Biotoxicology Lab, School of the Environment, The University of Queensland, St Lucia, QLD 4067, Australia;
| | - Alexander S. Mikheyev
- Evolutionary Genomics Group, Research School of Biology, Australian National University, Canberra, ACT 0200, Australia
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3
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Sanchez-Sandoval AL, Hernández-Plata E, Gomora JC. Voltage-gated sodium channels: from roles and mechanisms in the metastatic cell behavior to clinical potential as therapeutic targets. Front Pharmacol 2023; 14:1206136. [PMID: 37456756 PMCID: PMC10348687 DOI: 10.3389/fphar.2023.1206136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Accepted: 06/21/2023] [Indexed: 07/18/2023] Open
Abstract
During the second half of the last century, the prevalent knowledge recognized the voltage-gated sodium channels (VGSCs) as the proteins responsible for the generation and propagation of action potentials in excitable cells. However, over the last 25 years, new non-canonical roles of VGSCs in cancer hallmarks have been uncovered. Their dysregulated expression and activity have been associated with aggressive features and cancer progression towards metastatic stages, suggesting the potential use of VGSCs as cancer markers and prognostic factors. Recent work has elicited essential information about the signalling pathways modulated by these channels: coupling membrane activity to transcriptional regulation pathways, intracellular and extracellular pH regulation, invadopodia maturation, and proteolytic activity. In a promising scenario, the inhibition of VGSCs with FDA-approved drugs as well as with new synthetic compounds, reduces cancer cell invasion in vitro and cancer progression in vivo. The purpose of this review is to present an update regarding recent advances and ongoing efforts to have a better understanding of molecular and cellular mechanisms on the involvement of both pore-forming α and auxiliary β subunits of VGSCs in the metastatic processes, with the aim at proposing VGSCs as new oncological markers and targets for anticancer treatments.
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Affiliation(s)
- Ana Laura Sanchez-Sandoval
- Departamento de Neuropatología Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
- Medicina Genómica, Hospital General de México “Dr Eduardo Liceaga”, Mexico City, Mexico
| | - Everardo Hernández-Plata
- Consejo Nacional de Humanidades, Ciencias y Tecnologías and Instituto Nacional de Medicina Genómica, Mexico City, Mexico
| | - Juan Carlos Gomora
- Departamento de Neuropatología Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico City, Mexico
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4
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Angsutararux P, Zhu W, Voelker TL, Silva JR. Molecular Pathology of Sodium Channel Beta-Subunit Variants. Front Pharmacol 2021; 12:761275. [PMID: 34867379 PMCID: PMC8640220 DOI: 10.3389/fphar.2021.761275] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Accepted: 10/28/2021] [Indexed: 12/19/2022] Open
Abstract
The voltage-gated Na+ channel regulates the initiation and propagation of the action potential in excitable cells. The major cardiac isoform NaV1.5, encoded by SCN5A, comprises a monomer with four homologous repeats (I-IV) that each contain a voltage sensing domain (VSD) and pore domain. In native myocytes, NaV1.5 forms a macromolecular complex with NaVβ subunits and other regulatory proteins within the myocyte membrane to maintain normal cardiac function. Disturbance of the NaV complex may manifest as deadly cardiac arrhythmias. Although SCN5A has long been identified as a gene associated with familial atrial fibrillation (AF) and Brugada Syndrome (BrS), other genetic contributors remain poorly understood. Emerging evidence suggests that mutations in the non-covalently interacting NaVβ1 and NaVβ3 are linked to both AF and BrS. Here, we investigated the molecular pathologies of 8 variants in NaVβ1 and NaVβ3. Our results reveal that NaVβ1 and NaVβ3 variants contribute to AF and BrS disease phenotypes by modulating both NaV1.5 expression and gating properties. Most AF-linked variants in the NaVβ1 subunit do not alter the gating kinetics of the sodium channel, but rather modify the channel expression. In contrast, AF-related NaVβ3 variants directly affect channel gating, altering voltage-dependent activation and the time course of recovery from inactivation via the modulation of VSD activation.
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Affiliation(s)
- Paweorn Angsutararux
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States
| | - Wandi Zhu
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States.,Department of Medicine, Brigham and Women's Hospital, Boston, MA, United States
| | - Taylor L Voelker
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States
| | - Jonathan R Silva
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States
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5
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Kwon JW, Jeon YK, Kim J, Kim SJ, Kim SJ. Intramolecular Disulfide Bonds for Biogenesis of CALHM1 Ion Channel Are Dispensable for Voltage-Dependent Activation. Mol Cells 2021; 44:758-769. [PMID: 34711692 PMCID: PMC8560582 DOI: 10.14348/molcells.2021.0131] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Revised: 08/19/2021] [Accepted: 09/06/2021] [Indexed: 11/27/2022] Open
Abstract
Calcium homeostasis modulator 1 (CALHM1) is a membrane protein with four transmembrane helices that form an octameric ion channel with voltage-dependent activation. There are four conserved cysteine (Cys) residues in the extracellular domain that form two intramolecular disulfide bonds. We investigated the roles of C42-C127 and C44-C161 in human CALHM1 channel biogenesis and the ionic current (ICALHM1). Replacing Cys with Ser or Ala abolished the membrane trafficking as well as ICALHM1. Immunoblotting analysis revealed dithiothreitol-sensitive multimeric CALHM1, which was markedly reduced in C44S and C161S, but preserved in C42S and C127S. The mixed expression of C42S and wild-type did not show a dominant-negative effect. While the heteromeric assembly of CALHM1 and CALHM3 formed active ion channels, the co-expression of C42S and CALHM3 did not produce functional channels. Despite the critical structural role of the extracellular cysteine residues, a treatment with the membrane-impermeable reducing agent tris(2-carboxyethyl) phosphine (TCEP, 2 mM) did not affect ICALHM1 for up to 30 min. Interestingly, incubation with TCEP (2 mM) for 2-6 h reduced both ICALHM1 and the surface expression of CALHM1 in a time-dependent manner. We propose that the intramolecular disulfide bonds are essential for folding, oligomerization, trafficking and maintenance of CALHM1 in the plasma membrane, but dispensable for the voltage-dependent activation once expressed on the plasma membrane.
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Affiliation(s)
- Jae Won Kwon
- Department of Physiology, Seoul National University College of Medicine, Seoul 03080, Korea
- Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Korea
| | - Young Keul Jeon
- Department of Physiology, Seoul National University College of Medicine, Seoul 03080, Korea
- Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Korea
| | - Jinsung Kim
- Department of Physiology, Seoul National University College of Medicine, Seoul 03080, Korea
- Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Korea
| | - Sang Jeong Kim
- Department of Physiology, Seoul National University College of Medicine, Seoul 03080, Korea
- Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Korea
| | - Sung Joon Kim
- Department of Physiology, Seoul National University College of Medicine, Seoul 03080, Korea
- Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Korea
- Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul 03080, Korea
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6
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Mehboob R, Kurdi M, Ahmad M, Gilani SA, Khalid S, Nasief H, Mirdad A, Malibary H, Hakamy S, Hassan A, Alaifan M, Bamaga A, Shahzad SA. Comprehensive Analysis of Genes Associated With Sudden Infant Death Syndrome. Front Pediatr 2021; 9:742225. [PMID: 34722422 PMCID: PMC8555024 DOI: 10.3389/fped.2021.742225] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Accepted: 09/13/2021] [Indexed: 12/15/2022] Open
Abstract
Background: Sudden infant death syndrome (SIDS) is a tragic incident which remains a mystery even after post-mortem investigation and thorough researches. Methods: This comprehensive review is based on the genes reported in the molecular autopsy studies conducted on SIDS so far. A total of 20 original studies and 7 case reports were identified and included in this analysis. The genes identified in children or adults were not included. Most of the genes reported in these studies belonged to cardiac channel and cardiomyopathy. Cardiac channel genes in SIDS were scrutinized for further analysis. Results: After screening and removing the duplicates, 42 unique genes were extracted. When the location of these genes was assessed, it was observed that most of these belonged to Chromosomes 11, 1 and 3 in sequential manner. The pathway analysis shows that these genes are involved in the regulation of heart rate, action potential, cardiac muscle cell contraction and heart contraction. The protein-protein interaction network was also very big and highly interactive. SCN5A, CAV3, ALG10B, AKAP9 and many more were mainly found in these cases and were regulated by many transcription factors such as MYOG C2C1 and CBX3 HCT11. Micro RNA, "hsa-miR-133a-3p" was found to be prevalent in the targeted genes. Conclusions: Molecular and computational approaches are a step forward toward exploration of these sad demises. It is so far a new arena but seems promising to dig out the genetic cause of SIDS in the years to come.
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Affiliation(s)
- Riffat Mehboob
- Research Unit, Faculty of Allied Health Sciences, The University of Lahore, Lahore, Pakistan.,Lahore Medical Research Center, LLP, Lahore, Pakistan
| | - Maher Kurdi
- Department of Pathology, Faculty of Medicine in Rabigh, King Abdulaziz University, Jeddah, Saudi Arabia
| | - Mursleen Ahmad
- Department of Medicine, Sahiwal Medical College, Sahiwal, Pakistan
| | - Syed Amir Gilani
- Research Unit, Faculty of Allied Health Sciences, The University of Lahore, Lahore, Pakistan
| | - Sidra Khalid
- Lahore Medical Research Center, LLP, Lahore, Pakistan
| | - Hisham Nasief
- Department of Obstetric and Gynecology, Faculty of Medicine, King Abdulaziz University and Hospital, Jeddah, Saudi Arabia
| | - Abeer Mirdad
- Pediatric Department, East Jeddah Hospital, Jeddah, Saudi Arabia
| | - Husam Malibary
- Department of Internal Medicine, Faculty of Medicine, King Abdul Aziz University, Jeddah, Saudi Arabia
| | - Sahar Hakamy
- Center of Excellence in Genomic Research, King Abdulaziz University, Jeddah, Saudi Arabia
| | - Amber Hassan
- Research Unit, Faculty of Allied Health Sciences, The University of Lahore, Lahore, Pakistan
| | - Meshari Alaifan
- Department of Paediatrics, Faculty of Medicine, King Abdulaziz University, Jeddah, Saudi Arabia
| | - Ahmed Bamaga
- Paediatric Department, King Faisal Specialist Hospital and Research Center, Jeddah, Saudi Arabia.,Neurology and Pediatric Department, Faculty of Medicine, King Abdulaziz University Hospital, King Abdulaziz University, Jeddah, Saudi Arabia
| | - Syed Adnan Shahzad
- Faculty of Medicine and University Hospital of Cologne, Institute of Virology, University of Cologne, Cologne, Germany
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7
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Chemometric Models of Differential Amino Acids at the Na vα and Na vβ Interface of Mammalian Sodium Channel Isoforms. Molecules 2020; 25:molecules25153551. [PMID: 32756517 PMCID: PMC7435598 DOI: 10.3390/molecules25153551] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Revised: 07/21/2020] [Accepted: 07/22/2020] [Indexed: 12/19/2022] Open
Abstract
(1) Background: voltage-gated sodium channels (Navs) are integral membrane proteins that allow the sodium ion flux into the excitable cells and initiate the action potential. They comprise an α (Navα) subunit that forms the channel pore and are coupled to one or more auxiliary β (Navβ) subunits that modulate the gating to a variable extent. (2) Methods: after performing homology in silico modeling for all nine isoforms (Nav1.1α to Nav1.9α), the Navα and Navβ protein-protein interaction (PPI) was analyzed chemometrically based on the primary and secondary structures as well as topological or spatial mapping. (3) Results: our findings reveal a unique isoform-specific correspondence between certain segments of the extracellular loops of the Navα subunits. Precisely, loop S5 in domain I forms part of the PPI and assists Navβ1 or Navβ3 on all nine mammalian isoforms. The implied molecular movements resemble macroscopic springs, all of which explains published voltage sensor effects on sodium channel fast inactivation in gating. (4) Conclusions: currently, the specific functions exerted by the Navβ1 or Navβ3 subunits on the modulation of Navα gating remain unknown. Our work determined functional interaction in the extracellular domains on theoretical grounds and we propose a schematic model of the gating mechanism of fast channel sodium current inactivation by educated guessing.
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8
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Salvage SC, Huang CLH, Jackson AP. Cell-Adhesion Properties of β-Subunits in the Regulation of Cardiomyocyte Sodium Channels. Biomolecules 2020; 10:biom10070989. [PMID: 32630316 PMCID: PMC7407995 DOI: 10.3390/biom10070989] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2020] [Revised: 06/25/2020] [Accepted: 06/27/2020] [Indexed: 12/17/2022] Open
Abstract
Voltage-gated sodium (Nav) channels drive the rising phase of the action potential, essential for electrical signalling in nerves and muscles. The Nav channel α-subunit contains the ion-selective pore. In the cardiomyocyte, Nav1.5 is the main Nav channel α-subunit isoform, with a smaller expression of neuronal Nav channels. Four distinct regulatory β-subunits (β1–4) bind to the Nav channel α-subunits. Previous work has emphasised the β-subunits as direct Nav channel gating modulators. However, there is now increasing appreciation of additional roles played by these subunits. In this review, we focus on β-subunits as homophilic and heterophilic cell-adhesion molecules and the implications for cardiomyocyte function. Based on recent cryogenic electron microscopy (cryo-EM) data, we suggest that the β-subunits interact with Nav1.5 in a different way from their binding to other Nav channel isoforms. We believe this feature may facilitate trans-cell-adhesion between β1-associated Nav1.5 subunits on the intercalated disc and promote ephaptic conduction between cardiomyocytes.
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Affiliation(s)
- Samantha C. Salvage
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK;
- Correspondence: (S.C.S.); (A.P.J.); Tel.: +44-1223-765950 (S.C.S.); +44-1223-765951 (A.P.J.)
| | - Christopher L.-H. Huang
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK;
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3EG, UK
| | - Antony P. Jackson
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK;
- Correspondence: (S.C.S.); (A.P.J.); Tel.: +44-1223-765950 (S.C.S.); +44-1223-765951 (A.P.J.)
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9
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Salvage SC, Rees JS, McStea A, Hirsch M, Wang L, Tynan CJ, Reed MW, Irons JR, Butler R, Thompson AJ, Martin-Fernandez ML, Huang CL, Jackson AP. Supramolecular clustering of the cardiac sodium channel Nav1.5 in HEK293F cells, with and without the auxiliary β3-subunit. FASEB J 2020; 34:3537-3553. [PMID: 31950564 PMCID: PMC7079131 DOI: 10.1096/fj.201701473rr] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2017] [Revised: 09/30/2019] [Accepted: 10/08/2019] [Indexed: 01/24/2023]
Abstract
Voltage-gated sodium channels comprise an ion-selective α-subunit and one or more associated β-subunits. The β3-subunit (encoded by the SCN3B gene) is an important physiological regulator of the heart-specific sodium channel, Nav1.5. We have previously shown that when expressed alone in HEK293F cells, the full-length β3-subunit forms trimers in the plasma membrane. We extend this result with biochemical assays and use the proximity ligation assay (PLA) to identify oligomeric β3-subunits, not just at the plasma membrane, but throughout the secretory pathway. We then investigate the corresponding clustering properties of the α-subunit and the effects upon these of the β3-subunits. The oligomeric status of the Nav1.5 α-subunit in vivo, with or without the β3-subunit, has not been previously investigated. Using super-resolution fluorescence imaging, we show that under conditions typically used in electrophysiological studies, the Nav1.5 α-subunit assembles on the plasma membrane of HEK293F cells into spatially localized clusters rather than individual and randomly dispersed molecules. Quantitative analysis indicates that the β3-subunit is not required for this clustering but β3 does significantly change the distribution of cluster sizes and nearest-neighbor distances between Nav1.5 α-subunits. However, when assayed by PLA, the β3-subunit increases the number of PLA-positive signals generated by anti-(Nav1.5 α-subunit) antibodies, mainly at the plasma membrane. Since PLA can be sensitive to the orientation of proteins within a cluster, we suggest that the β3-subunit introduces a significant change in the relative alignment of individual Nav1.5 α-subunits, but the clustering itself depends on other factors. We also show that these structural and higher-order changes induced by the β3-subunit do not alter the degree of electrophysiological gating cooperativity between Nav1.5 α-subunits. Our data provide new insights into the role of the β3-subunit and the supramolecular organization of sodium channels, in an important model cell system that is widely used to study Nav channel behavior.
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Affiliation(s)
| | | | - Alexandra McStea
- Central Laser FacilityResearch Complex at HarwellScience and Technology Facilities CouncilRutherford Appleton LaboratoryOxfordUK
| | - Michael Hirsch
- Central Laser FacilityResearch Complex at HarwellScience and Technology Facilities CouncilRutherford Appleton LaboratoryOxfordUK
| | - Lin Wang
- Central Laser FacilityResearch Complex at HarwellScience and Technology Facilities CouncilRutherford Appleton LaboratoryOxfordUK
| | - Christopher J. Tynan
- Central Laser FacilityResearch Complex at HarwellScience and Technology Facilities CouncilRutherford Appleton LaboratoryOxfordUK
| | - Matthew W. Reed
- Department of Nuclear PhysicsResearch School of Physics and EngineeringAustralian National UniversityCanberrraACTAustralia
| | | | - Richard Butler
- Wellcome Trust/Cancer Research UK Gurdon InstituteUniversity of CambridgeCambridgeUK
| | | | - Marisa L. Martin-Fernandez
- Central Laser FacilityResearch Complex at HarwellScience and Technology Facilities CouncilRutherford Appleton LaboratoryOxfordUK
| | - Christopher L.‐H. Huang
- Deparment of BiochemistryUniversity of CambridgeCambridgeUK
- Department of Physiology, Development and NeuroscienceUniversity of CambridgeCambridgeUK
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10
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Salvage SC, Zhu W, Habib ZF, Hwang SS, Irons JR, Huang CLH, Silva JR, Jackson AP. Gating control of the cardiac sodium channel Nav1.5 by its β3-subunit involves distinct roles for a transmembrane glutamic acid and the extracellular domain. J Biol Chem 2019; 294:19752-19763. [PMID: 31659116 PMCID: PMC6926464 DOI: 10.1074/jbc.ra119.010283] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Revised: 10/24/2019] [Indexed: 11/06/2022] Open
Abstract
The auxiliary β3-subunit is an important functional regulator of the cardiac sodium channel Nav1.5, and some β3 mutations predispose individuals to cardiac arrhythmias. The β3-subunit uses its transmembrane α-helix and extracellular domain to bind to Nav1.5. Here, we investigated the role of an unusually located and highly conserved glutamic acid (Glu-176) within the β3 transmembrane region and its potential for functionally synergizing with the β3 extracellular domain (ECD). We substituted Glu-176 with lysine (E176K) in the WT β3-subunit and in a β3-subunit lacking the ECD. Patch-clamp experiments indicated that the E176K substitution does not affect the previously observed β3-dependent depolarizing shift of V½ of steady-state inactivation but does attenuate the accelerated recovery from inactivation conferred by the WT β3-subunit. Removal of the β3-ECD abrogated both the depolarizing shift of steady-state inactivation and the accelerated recovery, irrespective of the presence or absence of the Glu-176 residue. We found that steady-state inactivation and recovery from inactivation involve movements of the S4 helices within the DIII and DIV voltage sensors in response to membrane potential changes. Voltage-clamp fluorometry revealed that the E176K substitution alters DIII voltage sensor dynamics without affecting DIV. In contrast, removal of the ECD significantly altered the dynamics of both DIII and DIV. These results imply distinct roles for the β3-Glu-176 residue and the β3-ECD in regulating the conformational changes of the voltage sensors that determine channel inactivation and recovery from inactivation.
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Affiliation(s)
- Samantha C Salvage
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom
| | - Wandi Zhu
- Department of Biomedical Engineering, Washington University, St. Louis, Missouri 63130-489
| | - Zaki F Habib
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom.,Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3EG, United Kingdom
| | - Soyon S Hwang
- Department of Biomedical Engineering, Washington University, St. Louis, Missouri 63130-489
| | - Jennifer R Irons
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom
| | - Christopher L H Huang
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom .,Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3EG, United Kingdom
| | - Jonathan R Silva
- Department of Biomedical Engineering, Washington University, St. Louis, Missouri 63130-489
| | - Antony P Jackson
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom
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11
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Sanchez-Sandoval AL, Gomora JC. Contribution of voltage-gated sodium channel β-subunits to cervical cancer cells metastatic behavior. Cancer Cell Int 2019; 19:35. [PMID: 30814913 PMCID: PMC6377746 DOI: 10.1186/s12935-019-0757-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Accepted: 02/12/2019] [Indexed: 01/23/2023] Open
Abstract
Background Voltage-gated sodium (NaV) channels are heteromeric proteins consisting of a single pore forming α-subunit associated with one or two auxiliary β-subunits. These channels are classically known for being responsible of action potential generation and propagation in excitable cells; but lately they have been reported as widely expressed and regulated in several human cancer types. We have previously demonstrated the overexpression of NaV1.6 channel in cervical cancer (CeCa) biopsies and primary cultures, and its contribution to cell migration and invasiveness. Here, we investigated the expression of NaV channels β-subunits (NaVβs) in the CeCa cell lines HeLa, SiHa and CaSki, and determined their contribution to cell proliferation, migration and invasiveness. Methods We assessed the expression of NaVβs in CeCa cell lines by performing RT-PCR and western blotting experiments. We also evaluated CeCa cell lines proliferation, migration, and invasion by in vitro assays, both in basal conditions and after inducing changes in NaVβs levels by transfecting specific cDNAs or siRNAs. The potential role of NaVβs in modulating the expression of NaV α-subunits in the plasma membrane of CeCa cells was examined by the patch-clamp whole-cell technique. Furthermore, we investigated the role of NaVβ1 on cell cycle in SiHa cells by flow cytometry. Results We found that the four NaVβs are expressed in the three CeCa cell lines, even in the absence of functional NaV α-subunit expression in the plasma membrane. Functional in vitro assays showed differential roles for NaVβ1 and NaVβ4, the latter as a cell invasiveness repressor and the former as a migration abolisher in CeCa cells. In silico analysis of NaVβ4 expression in cervical tissues corroborated the downregulation of this protein expression in CeCa vs normal cervix, supporting the evidence of NaVβ4’s role as a cell invasiveness repressor. Conclusions Our results contribute to the recent conception about NaVβs as multifunctional proteins involved in cell processes like ion channel regulation, cell adhesion and motility, and even in metastatic cell behaviors. These non-canonical functions of NaVβs are independent of the presence of functional NaV α-subunits in the plasma membrane and might represent a new therapeutic target for the treatment of cervical cancer. Electronic supplementary material The online version of this article (10.1186/s12935-019-0757-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Ana Laura Sanchez-Sandoval
- Departamento de Neuropatología Molecular, División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510 Mexico City, Mexico
| | - Juan Carlos Gomora
- Departamento de Neuropatología Molecular, División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510 Mexico City, Mexico
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12
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Edokobi N, Isom LL. Voltage-Gated Sodium Channel β1/β1B Subunits Regulate Cardiac Physiology and Pathophysiology. Front Physiol 2018; 9:351. [PMID: 29740331 PMCID: PMC5924814 DOI: 10.3389/fphys.2018.00351] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2018] [Accepted: 03/20/2018] [Indexed: 12/19/2022] Open
Abstract
Cardiac myocyte contraction is initiated by a set of intricately orchestrated electrical impulses, collectively known as action potentials (APs). Voltage-gated sodium channels (NaVs) are responsible for the upstroke and propagation of APs in excitable cells, including cardiomyocytes. NaVs consist of a single, pore-forming α subunit and two different β subunits. The β subunits are multifunctional cell adhesion molecules and channel modulators that have cell type and subcellular domain specific functional effects. Variants in SCN1B, the gene encoding the Nav-β1 and -β1B subunits, are linked to atrial and ventricular arrhythmias, e.g., Brugada syndrome, as well as to the early infantile epileptic encephalopathy Dravet syndrome, all of which put patients at risk for sudden death. Evidence over the past two decades has demonstrated that Nav-β1/β1B subunits play critical roles in cardiac myocyte physiology, in which they regulate tetrodotoxin-resistant and -sensitive sodium currents, potassium currents, and calcium handling, and that Nav-β1/β1B subunit dysfunction generates substrates for arrhythmias. This review will highlight the role of Nav-β1/β1B subunits in cardiac physiology and pathophysiology.
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Affiliation(s)
| | - Lori L. Isom
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI, United States
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13
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Hull JM, Isom LL. Voltage-gated sodium channel β subunits: The power outside the pore in brain development and disease. Neuropharmacology 2017; 132:43-57. [PMID: 28927993 DOI: 10.1016/j.neuropharm.2017.09.018] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2017] [Revised: 07/19/2017] [Accepted: 09/11/2017] [Indexed: 12/19/2022]
Abstract
Voltage gated sodium channels (VGSCs) were first identified in terms of their role in the upstroke of the action potential. The underlying proteins were later identified as saxitoxin and scorpion toxin receptors consisting of α and β subunits. We now know that VGSCs are heterotrimeric complexes consisting of a single pore forming α subunit joined by two β subunits; a noncovalently linked β1 or β3 and a covalently linked β2 or β4 subunit. VGSC α subunits contain all the machinery necessary for channel cell surface expression, ion conduction, voltage sensing, gating, and inactivation, in one central, polytopic, transmembrane protein. VGSC β subunits are more than simple accessories to α subunits. In the more than two decades since the original cloning of β1, our knowledge of their roles in physiology and pathophysiology has expanded immensely. VGSC β subunits are multifunctional. They confer unique gating mechanisms, regulate cellular excitability, affect brain development, confer distinct channel pharmacology, and have functions that are independent of the α subunits. The vast array of functions of these proteins stems from their special station in the channelome: being the only known constituents that are cell adhesion and intra/extracellular signaling molecules in addition to being part of channel complexes. This functional trifecta and how it goes awry demonstrates the power outside the pore in ion channel signaling complexes, broadening the term channelopathy beyond defects in ion conduction. This article is part of the Special Issue entitled 'Channelopathies.'
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Affiliation(s)
- Jacob M Hull
- Neuroscience Program and Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI 48109, United States
| | - Lori L Isom
- Neuroscience Program and Department of Pharmacology, University of Michigan Medical School, Ann Arbor, MI 48109, United States.
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14
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Zhu W, Voelker TL, Varga Z, Schubert AR, Nerbonne JM, Silva JR. Mechanisms of noncovalent β subunit regulation of Na V channel gating. J Gen Physiol 2017; 149:813-831. [PMID: 28720590 PMCID: PMC5560778 DOI: 10.1085/jgp.201711802] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Accepted: 06/26/2017] [Indexed: 11/20/2022] Open
Abstract
Voltage-gated NaV channels are modulated by two different noncovalent accessory subunits: β1 and β3. Zhu et al. present data showing that β1 and β3 cause distinct effects on channel gating because they interact with NaV channels at different locations. β3 regulates the voltage sensor in domain III, whereas β1 regulates the one in domain IV. Voltage-gated Na+ (NaV) channels comprise a macromolecular complex whose components tailor channel function. Key components are the non-covalently bound β1 and β3 subunits that regulate channel gating, expression, and pharmacology. Here, we probe the molecular basis of this regulation by applying voltage clamp fluorometry to measure how the β subunits affect the conformational dynamics of the cardiac NaV channel (NaV1.5) voltage-sensing domains (VSDs). The pore-forming NaV1.5 α subunit contains four domains (DI–DIV), each with a VSD. Our results show that β1 regulates NaV1.5 by modulating the DIV-VSD, whereas β3 alters channel kinetics mainly through DIII-VSD interaction. Introduction of a quenching tryptophan into the extracellular region of the β3 transmembrane segment inverted the DIII-VSD fluorescence. Additionally, a fluorophore tethered to β3 at the same position produced voltage-dependent fluorescence dynamics strongly resembling those of the DIII-VSD. Together, these results provide compelling evidence that β3 binds proximally to the DIII-VSD. Molecular-level differences in β1 and β3 interaction with the α subunit lead to distinct activation and inactivation recovery kinetics, significantly affecting NaV channel regulation of cell excitability.
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Affiliation(s)
- Wandi Zhu
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
| | - Taylor L Voelker
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
| | - Zoltan Varga
- MTA-DE-NAP B Ion Channel Structure-Function Research Group, RCMM, University of Debrecen, Debrecen, Hungary
| | - Angela R Schubert
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
| | - Jeanne M Nerbonne
- Department of Developmental Biology, Washington University in St. Louis, St. Louis, MO.,Department of Internal Medicine, Washington University in St. Louis, St. Louis, MO
| | - Jonathan R Silva
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO
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15
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Characterization of specific allosteric effects of the Na+ channel β1 subunit on the Nav1.4 isoform. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2016; 46:485-494. [DOI: 10.1007/s00249-016-1193-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 11/23/2016] [Accepted: 11/30/2016] [Indexed: 11/26/2022]
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16
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Patel F, Brackenbury WJ. Dual roles of voltage-gated sodium channels in development and cancer. THE INTERNATIONAL JOURNAL OF DEVELOPMENTAL BIOLOGY 2016; 59:357-66. [PMID: 26009234 DOI: 10.1387/ijdb.150171wb] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Voltage-gated Na(+) channels (VGSCs) are heteromeric protein complexes containing pore-forming α subunits together with non-pore-forming β subunits. There are nine α subunits, Nav1.1-Nav1.9, and four β subunits, β1-β4. The β subunits are multifunctional, modulating channel activity, cell surface expression, and are members of the immunoglobulin superfamily of cell adhesion molecules. VGSCs are classically responsible for action potential initiation and conduction in electrically excitable cells, including neurons and muscle cells. In addition, through the β1 subunit, VGSCs regulate neurite outgrowth and pathfinding in the developing central nervous system. Reciprocal signalling through Nav1.6 and β1 collectively regulates Na(+) current, electrical excitability and neurite outgrowth in cerebellar granule neurons. Thus, α and β subunits may have diverse interacting roles dependent on cell/tissue type. VGSCs are also expressed in non-excitable cells, including cells derived from a number of types of cancer. In cancer cells, VGSC α and β subunits regulate cellular morphology, migration, invasion and metastasis. VGSC expression associates with poor prognosis in several studies. It is hypothesised that VGSCs are up-regulated in metastatic tumours, favouring an invasive phenotype. Thus, VGSCs may have utility as prognostic markers, and/or as novel therapeutic targets for reducing/preventing metastatic disease burden. VGSCs appear to regulate a number of key cellular processes, both during normal postnatal development of the CNS and during cancer metastasis, by a combination of conducting (i.e. via Na(+) current) and non-conducting mechanisms.
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17
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Winters JJ, Isom LL. Developmental and Regulatory Functions of Na(+) Channel Non-pore-forming β Subunits. CURRENT TOPICS IN MEMBRANES 2016; 78:315-51. [PMID: 27586289 DOI: 10.1016/bs.ctm.2016.07.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Voltage-gated Na(+) channels (VGSCs) isolated from mammalian neurons are heterotrimeric complexes containing one pore-forming α subunit and two non-pore-forming β subunits. In excitable cells, VGSCs are responsible for the initiation of action potentials. VGSC β subunits are type I topology glycoproteins, containing an extracellular amino-terminal immunoglobulin (Ig) domain with homology to many neural cell adhesion molecules (CAMs), a single transmembrane segment, and an intracellular carboxyl-terminal domain. VGSC β subunits are encoded by a gene family that is distinct from the α subunits. While α subunits are expressed in prokaryotes, β subunit orthologs did not arise until after the emergence of vertebrates. β subunits regulate the cell surface expression, subcellular localization, and gating properties of their associated α subunits. In addition, like many other Ig-CAMs, β subunits are involved in cell migration, neurite outgrowth, and axon pathfinding and may function in these roles in the absence of associated α subunits. In sum, these multifunctional proteins are critical for both channel regulation and central nervous system development.
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Affiliation(s)
- J J Winters
- University of Michigan Neuroscience Program, Ann Arbor, MI, United States
| | - L L Isom
- University of Michigan Neuroscience Program, Ann Arbor, MI, United States; University of Michigan Medical School, Ann Arbor, MI, United States
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18
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Abstract
Voltage-gated sodium channels (VGSCs), composed of a pore-forming α subunit and up to two associated β subunits, are critical for the initiation of the action potential (AP) in excitable tissues. Building on the monumental discovery and description of sodium current in 1952, intrepid researchers described the voltage-dependent gating mechanism, selectivity of the channel, and general structure of the VGSC channel. Recently, crystal structures of bacterial VGSC α subunits have confirmed many of these studies and provided new insights into VGSC function. VGSC β subunits, first cloned in 1992, modulate sodium current but also have nonconducting roles as cell-adhesion molecules and function in neurite outgrowth and neuronal pathfinding. Mutations in VGSC α and β genes are associated with diseases caused by dysfunction of excitable tissues such as epilepsy. Because of the multigenic and drug-resistant nature of some of these diseases, induced pluripotent stem cells and other novel approaches are being used to screen for new drugs and further understand how mutations in VGSC genes contribute to pathophysiology.
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19
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Abstract
Voltage-gated sodium channels (VGSCs) are responsible for the initiation and propagation of action potentials in excitable cells. VGSCs in mammalian brain are heterotrimeric complexes of α and β subunits. Although β subunits were originally termed auxiliary, we now know that they are multifunctional signaling molecules that play roles in both excitable and nonexcitable cell types and with or without the pore-forming α subunit present. β subunits function in VGSC and potassium channel modulation, cell adhesion, and gene regulation, with particularly important roles in brain development. Mutations in the genes encoding β subunits are linked to a number of diseases, including epilepsy, sudden death syndromes like SUDEP and SIDS, and cardiac arrhythmia. Although VGSC β subunit-specific drugs have not yet been developed, this protein family is an emerging therapeutic target.
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Affiliation(s)
- Heather A O'Malley
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan 48109;
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20
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Namadurai S, Yereddi NR, Cusdin FS, Huang CLH, Chirgadze DY, Jackson AP. A new look at sodium channel β subunits. Open Biol 2015; 5:140192. [PMID: 25567098 PMCID: PMC4313373 DOI: 10.1098/rsob.140192] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Voltage-gated sodium (Nav) channels are intrinsic plasma membrane proteins that initiate the action potential in electrically excitable cells. They are a major focus of research in neurobiology, structural biology, membrane biology and pharmacology. Mutations in Nav channels are implicated in a wide variety of inherited pathologies, including cardiac conduction diseases, myotonic conditions, epilepsy and chronic pain syndromes. Drugs active against Nav channels are used as local anaesthetics, anti-arrhythmics, analgesics and anti-convulsants. The Nav channels are composed of a pore-forming α subunit and associated β subunits. The β subunits are members of the immunoglobulin (Ig) domain family of cell-adhesion molecules. They modulate multiple aspects of Nav channel behaviour and play critical roles in controlling neuronal excitability. The recently published atomic resolution structures of the human β3 and β4 subunit Ig domains open a new chapter in the study of these molecules. In particular, the discovery that β3 subunits form trimers suggests that Nav channel oligomerization may contribute to the functional properties of some β subunits.
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Affiliation(s)
- Sivakumar Namadurai
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | - Nikitha R Yereddi
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | - Fiona S Cusdin
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | | | - Dimitri Y Chirgadze
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
| | - Antony P Jackson
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK
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21
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Namadurai S, Balasuriya D, Rajappa R, Wiemhöfer M, Stott K, Klingauf J, Edwardson JM, Chirgadze DY, Jackson AP. Crystal structure and molecular imaging of the Nav channel β3 subunit indicates a trimeric assembly. J Biol Chem 2014; 289:10797-10811. [PMID: 24567321 PMCID: PMC4036194 DOI: 10.1074/jbc.m113.527994] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The vertebrate sodium (Nav) channel is composed of an ion-conducting α subunit and associated β subunits. Here, we report the crystal structure of the human β3 subunit immunoglobulin (Ig) domain, a functionally important component of Nav channels in neurons and cardiomyocytes. Surprisingly, we found that the β3 subunit Ig domain assembles as a trimer in the crystal asymmetric unit. Analytical ultracentrifugation confirmed the presence of Ig domain monomers, dimers, and trimers in free solution, and atomic force microscopy imaging also detected full-length β3 subunit monomers, dimers, and trimers. Mutation of a cysteine residue critical for maintaining the trimer interface destabilized both dimers and trimers. Using fluorescence photoactivated localization microscopy, we detected full-length β3 subunit trimers on the plasma membrane of transfected HEK293 cells. We further show that β3 subunits can bind to more than one site on the Nav 1.5 α subunit and induce the formation of α subunit oligomers, including trimers. Our results suggest a new and unexpected role for the β3 subunits in Nav channel cross-linking and provide new structural insights into some pathological Nav channel mutations.
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Affiliation(s)
- Sivakumar Namadurai
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, United Kingdom
| | - Dilshan Balasuriya
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom
| | - Rajit Rajappa
- Institute of Medical Physics and Biophysics, University of Münster, Robert-Koch Strasse, 31 48149 Münster, Germany
| | - Martin Wiemhöfer
- Institute of Medical Physics and Biophysics, University of Münster, Robert-Koch Strasse, 31 48149 Münster, Germany
| | - Katherine Stott
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, United Kingdom
| | - Jurgen Klingauf
- Institute of Medical Physics and Biophysics, University of Münster, Robert-Koch Strasse, 31 48149 Münster, Germany
| | - J Michael Edwardson
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom
| | - Dimitri Y Chirgadze
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, United Kingdom.
| | - Antony P Jackson
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, United Kingdom.
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22
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Calhoun JD, Isom LL. The role of non-pore-forming β subunits in physiology and pathophysiology of voltage-gated sodium channels. Handb Exp Pharmacol 2014; 221:51-89. [PMID: 24737232 DOI: 10.1007/978-3-642-41588-3_4] [Citation(s) in RCA: 76] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Voltage-gated sodium channel β1 and β2 subunits were discovered as auxiliary proteins that co-purify with pore-forming α subunits in brain. The other family members, β1B, β3, and β4, were identified by homology and shown to modulate sodium current in heterologous systems. Work over the past 2 decades, however, has provided strong evidence that these proteins are not simply ancillary ion channel subunits, but are multifunctional signaling proteins in their own right, playing both conducting (channel modulatory) and nonconducting roles in cell signaling. Here, we discuss evidence that sodium channel β subunits not only regulate sodium channel function and localization but also modulate voltage-gated potassium channels. In their nonconducting roles, VGSC β subunits function as immunoglobulin superfamily cell adhesion molecules that modulate brain development by influencing cell proliferation and migration, axon outgrowth, axonal fasciculation, and neuronal pathfinding. Mutations in genes encoding β subunits are linked to paroxysmal diseases including epilepsy, cardiac arrhythmia, and sudden infant death syndrome. Finally, β subunits may be targets for the future development of novel therapeutics.
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Affiliation(s)
- Jeffrey D Calhoun
- Department of Pharmacology, University of Michigan, Ann Arbor, MI, 48109-5632, USA
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Identification of Navβ1 residues involved in the modulation of the sodium channel Nav1.4. PLoS One 2013; 8:e81995. [PMID: 24358138 PMCID: PMC3864903 DOI: 10.1371/journal.pone.0081995] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Accepted: 10/20/2013] [Indexed: 12/19/2022] Open
Abstract
Voltage-gated sodium channels (VGSCs) are heteromeric protein complexes that initiate action potentials in excitable cells. The voltage-gated sodium channel accessory subunit, Navβ1, allosterically modulates the α subunit pore structure upon binding. To date, the molecular determinants of the interface remain unknown. We made use of sequence, knowledge and structure-based methods to identify residues critical to the association of the α and β1 Nav1.4 subunits. The Navβ1 point mutant C43A disrupted the modulation of voltage dependence of activation and inactivation and delayed the peak current decay, the recovery from inactivation, and induced a use-dependent decay upon depolarisation at 1 Hz. The Navβ1 mutant R89A selectively delayed channel inactivation and recovery from inactivation and had no effect on voltage dependence or repetitive depolarisations. Navβ1 mutants Y32A and G33M selectively modified the half voltage of inactivation without altering the kinetics. Despite low sequence identity, highly conserved structural elements were identified. Our models were consistent with published data and may help relate pathologies associated with VGSCs to the Navβ1 subunit.
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Crystallographic insights into sodium-channel modulation by the β4 subunit. Proc Natl Acad Sci U S A 2013; 110:E5016-24. [PMID: 24297919 DOI: 10.1073/pnas.1314557110] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Voltage-gated sodium (Nav) channels are embedded in a multicomponent membrane signaling complex that plays a crucial role in cellular excitability. Although the mechanism remains unclear, β-subunits modify Nav channel function and cause debilitating disorders when mutated. While investigating whether β-subunits also influence ligand interactions, we found that β4 dramatically alters toxin binding to Nav1.2. To explore these observations further, we solved the crystal structure of the extracellular β4 domain and identified (58)Cys as an exposed residue that, when mutated, eliminates the influence of β4 on toxin pharmacology. Moreover, our results suggest the presence of a docking site that is maintained by a cysteine bridge buried within the hydrophobic core of β4. Disrupting this bridge by introducing a β1 mutation implicated in epilepsy repositions the (58)Cys-containing loop and disrupts β4 modulation of Nav1.2. Overall, the principles emerging from this work (i) help explain tissue-dependent variations in Nav channel pharmacology; (ii) enable the mechanistic interpretation of β-subunit-related disorders; and (iii) provide insights in designing molecules capable of correcting aberrant β-subunit behavior.
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