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Diversification of Potassium Currents in Excitable Cells via Kvβ Proteins. Cells 2022; 11:cells11142230. [PMID: 35883673 PMCID: PMC9317154 DOI: 10.3390/cells11142230] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2022] [Revised: 07/09/2022] [Accepted: 07/12/2022] [Indexed: 12/10/2022] Open
Abstract
Excitable cells of the nervous and cardiovascular systems depend on an assortment of plasmalemmal potassium channels to control diverse cellular functions. Voltage-gated potassium (Kv) channels are central to the feedback control of membrane excitability in these processes due to their activation by depolarized membrane potentials permitting K+ efflux. Accordingly, Kv currents are differentially controlled not only by numerous cellular signaling paradigms that influence channel abundance and shape voltage sensitivity, but also by heteromeric configurations of channel complexes. In this context, we discuss the current knowledge related to how intracellular Kvβ proteins interacting with pore complexes of Shaker-related Kv1 channels may establish a modifiable link between excitability and metabolic state. Past studies in heterologous systems have indicated roles for Kvβ proteins in regulating channel stability, trafficking, subcellular targeting, and gating. More recent works identifying potential in vivo physiologic roles are considered in light of these earlier studies and key gaps in knowledge to be addressed by future research are described.
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2
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Xu Z, Khan S, Schnicker NJ, Baker S. Pentameric assembly of the Kv2.1 tetramerization domain. ACTA CRYSTALLOGRAPHICA SECTION D STRUCTURAL BIOLOGY 2022; 78:792-802. [PMID: 35647925 PMCID: PMC9159280 DOI: 10.1107/s205979832200568x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Accepted: 05/25/2022] [Indexed: 11/25/2022]
Abstract
The selective assembly of Kv subunits into one of four subfamilies of tetrameric, voltage-gated potassium channels is mediated by the T1 tetramerization domain. Here, it was found that unlike the other Kv T1 domains that have been studied to date, the human Kv2.1 T1 domain forms a pentamer, and that zinc binding and electrostatics contribute to the stability of the proteins. The Kv family of voltage-gated potassium channels regulate neuronal excitability. The biophysical characteristics of Kv channels can be matched to the needs of different neurons by forming homotetrameric or heterotetrameric channels within one of four subfamilies. The cytoplasmic tetramerization (T1) domain plays a major role in dictating the compatibility of different Kv subunits. The only Kv subfamily lacking a representative structure of the T1 domain is the Kv2 family. Here, X-ray crystallography was used to solve the structure of the human Kv2.1 T1 domain. The structure is similar to those of other T1 domains, but surprisingly formed a pentamer instead of a tetramer. In solution the Kv2.1 T1 domain also formed a pentamer, as determined by inline SEC–MALS–SAXS and negative-stain electron microscopy. The Kv2.1 T1–T1 interface involves electrostatic interactions, including a salt bridge formed by the negative charges in a previously described CDD motif, and inter-subunit coordination of zinc. It is shown that zinc binding is important for stability. In conclusion, the Kv2.1 T1 domain behaves differently from the other Kv T1 domains, which may reflect the versatility of Kv2.1, which can assemble with the regulatory KvS subunits and scaffold ER–plasma membrane contacts.
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3
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Nilsson M, Lindström SH, Kaneko M, Wang K, Minguez-Viñas T, Angelini M, Steccanella F, Holder D, Ottolia M, Olcese R, Pantazis A. An epilepsy-associated K V1.2 charge-transfer-center mutation impairs K V1.2 and K V1.4 trafficking. Proc Natl Acad Sci U S A 2022; 119:e2113675119. [PMID: 35439054 PMCID: PMC9169947 DOI: 10.1073/pnas.2113675119] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Accepted: 02/25/2022] [Indexed: 12/19/2022] Open
Abstract
We report on a heterozygous KCNA2 variant in a child with epilepsy. KCNA2 encodes KV1.2 subunits, which form homotetrameric potassium channels and participate in heterotetrameric channel complexes with other KV1-family subunits, regulating neuronal excitability. The mutation causes substitution F233S at the KV1.2 charge transfer center of the voltage-sensing domain. Immunocytochemical trafficking assays showed that KV1.2(F233S) subunits are trafficking deficient and reduce the surface expression of wild-type KV1.2 and KV1.4: a dominant-negative phenotype extending beyond KCNA2, likely profoundly perturbing electrical signaling. Yet some KV1.2(F233S) trafficking was rescued by wild-type KV1.2 and KV1.4 subunits, likely in permissible heterotetrameric stoichiometries: electrophysiological studies utilizing applied transcriptomics and concatemer constructs support that up to one or two KV1.2(F233S) subunits can participate in trafficking-capable heterotetramers with wild-type KV1.2 or KV1.4, respectively, and that both early and late events along the biosynthesis and secretion pathway impair trafficking. These studies suggested that F233S causes a depolarizing shift of ∼48 mV on KV1.2 voltage dependence. Optical tracking of the KV1.2(F233S) voltage-sensing domain (rescued by wild-type KV1.2 or KV1.4) revealed that it operates with modestly perturbed voltage dependence and retains pore coupling, evidenced by off-charge immobilization. The equivalent mutation in the Shaker K+ channel (F290S) was reported to modestly affect trafficking and strongly affect function: an ∼80-mV depolarizing shift, disrupted voltage sensor activation and pore coupling. Our work exposes the multigenic, molecular etiology of a variant associated with epilepsy and reveals that charge-transfer-center disruption has different effects in KV1.2 and Shaker, the archetypes for potassium channel structure and function.
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Affiliation(s)
- Michelle Nilsson
- Division of Neurobiology, Department of Biomedical and Clinical Sciences (BKV), Linköping University, 581 83 Linköping, Sweden
| | - Sarah H. Lindström
- Division of Neurobiology, Department of Biomedical and Clinical Sciences (BKV), Linköping University, 581 83 Linköping, Sweden
| | - Maki Kaneko
- Center for Personalized Medicine, Children's Hospital Los Angeles, Los Angeles, CA 90027
- Division of Genomic Medicine, Department of Pathology, Children's Hospital Los Angeles, Los Angeles, CA 90027
| | - Kaiqian Wang
- Division of Neurobiology, Department of Biomedical and Clinical Sciences (BKV), Linköping University, 581 83 Linköping, Sweden
| | - Teresa Minguez-Viñas
- Division of Neurobiology, Department of Biomedical and Clinical Sciences (BKV), Linköping University, 581 83 Linköping, Sweden
| | - Marina Angelini
- Division of Molecular Medicine, Department of Anesthesiology & Perioperative Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA 90095
| | - Federica Steccanella
- Division of Molecular Medicine, Department of Anesthesiology & Perioperative Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA 90095
| | - Deborah Holder
- Comprehensive Epilepsy Program, Children's Hospital Los Angeles, Los Angeles, CA 90027
| | - Michela Ottolia
- Division of Molecular Medicine, Department of Anesthesiology & Perioperative Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA 90095
- UCLA Cardiovascular Theme, David Geffen School of Medicine, University of California, Los Angeles, CA 90095
| | - Riccardo Olcese
- Division of Molecular Medicine, Department of Anesthesiology & Perioperative Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA 90095
- UCLA Cardiovascular Theme, David Geffen School of Medicine, University of California, Los Angeles, CA 90095
- Brain Research Institute, David Geffen School of Medicine, University of California, Los Angeles, CA 90095
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095
| | - Antonios Pantazis
- Division of Neurobiology, Department of Biomedical and Clinical Sciences (BKV), Linköping University, 581 83 Linköping, Sweden
- Wallenberg Center for Molecular Medicine, Linköping University, 581 83 Linköping, Sweden
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4
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Yang S, Wang Y, Wang L, Kamau P, Zhang H, Luo A, Lu X, Lai R. Target switch of centipede toxins for antagonistic switch. SCIENCE ADVANCES 2020; 6:eabb5734. [PMID: 32821839 PMCID: PMC7413724 DOI: 10.1126/sciadv.abb5734] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Accepted: 06/26/2020] [Indexed: 05/02/2023]
Abstract
Animal venoms are powerful, highly evolved chemical weapons for defense and predation. While venoms are used mainly to lethally antagonize heterospecifics (individuals of a different species), nonlethal envenomation of conspecifics (individuals of the same species) is occasionally observed. Both the venom and target specifications underlying these two forms of envenomation are still poorly understood. Here, we show a target-switching mechanism in centipede (Scolopendra subspinipes) venom. On the basis of this mechanism, a major toxin component [Ssm Spooky Toxin (SsTx)] in centipede venom inhibits the Shal channel in conspecifics but not in heterospecifics to cause short-term, recoverable, and nonlethal envenomation. This same toxin causes fatal heterospecific envenomation, for example, by switching its target to the Shaker channels in heterospecifics without inhibiting the Shaker channel of conspecific S. subspinipes individuals. These findings suggest that venom components exhibit intricate coevolution with their targets in both heterospecifics and conspecifics, which enables a single toxin to develop graded intraspecific and interspecific antagonistic interactions.
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Affiliation(s)
- Shilong Yang
- Key Laboratory of Animal Models and Human Disease Mechanisms of Chinese Academy of Sciences/Key Laboratory of bioactive peptides of Yunnan Province, Kunming Institute of Zoology, Kunming, Yunnan 650223, China
- College of Wildlife and Protected Area, Northeast Forestry University, Harbin 150040, China
| | - Yunfei Wang
- College of Wildlife and Protected Area, Northeast Forestry University, Harbin 150040, China
| | - Lu Wang
- State Key Laboratory for Conservation and Utilization of Bio-Resources in Yunnan, Yunnan University, Kunming, Yunnan 650091, China
| | - Peter Kamau
- Key Laboratory of Animal Models and Human Disease Mechanisms of Chinese Academy of Sciences/Key Laboratory of bioactive peptides of Yunnan Province, Kunming Institute of Zoology, Kunming, Yunnan 650223, China
- Kunming College of Life Science, University of Chinese Academy of Sciences, Beijing 100049, China
- Sino-African Joint Research Center, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan 650223, China
| | - Hao Zhang
- Key Laboratory of Animal Models and Human Disease Mechanisms of Chinese Academy of Sciences/Key Laboratory of bioactive peptides of Yunnan Province, Kunming Institute of Zoology, Kunming, Yunnan 650223, China
- Kunming College of Life Science, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Anna Luo
- Key Laboratory of Animal Models and Human Disease Mechanisms of Chinese Academy of Sciences/Key Laboratory of bioactive peptides of Yunnan Province, Kunming Institute of Zoology, Kunming, Yunnan 650223, China
- Kunming College of Life Science, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xiancui Lu
- Key Laboratory of Animal Models and Human Disease Mechanisms of Chinese Academy of Sciences/Key Laboratory of bioactive peptides of Yunnan Province, Kunming Institute of Zoology, Kunming, Yunnan 650223, China
- Kunming College of Life Science, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Ren Lai
- Key Laboratory of Animal Models and Human Disease Mechanisms of Chinese Academy of Sciences/Key Laboratory of bioactive peptides of Yunnan Province, Kunming Institute of Zoology, Kunming, Yunnan 650223, China
- Kunming College of Life Science, University of Chinese Academy of Sciences, Beijing 100049, China
- Sino-African Joint Research Center, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan 650223, China
- KIZ-CUHK Joint Laboratory of Bioresources and Molecular Research in Common Diseases, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan 650223, China
- Center for Biosafety Mega-Science, Chinese Academy of Sciences, Wuhan, Hubei 430071, China
- Institute for Drug Discovery and Development, Chinese Academy of Sciences, Shanghai 201203, China
- Corresponding author.
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Determining the correct stoichiometry of Kv2.1/Kv6.4 heterotetramers, functional in multiple stoichiometrical configurations. Proc Natl Acad Sci U S A 2020; 117:9365-9376. [PMID: 32284408 DOI: 10.1073/pnas.1916166117] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The electrically silent (KvS) members of the voltage-gated potassium (Kv) subfamilies Kv5, Kv6, Kv8, and Kv9 selectively modulate Kv2 subunits by forming heterotetrameric Kv2/KvS channels. Based on the reported 3:1 stoichiometry of Kv2.1/Kv9.3 channels, we tested the hypothesis that Kv2.1/Kv6.4 channels express, in contrast to the assumed 3:1, in a 2:2 stoichiometry. We investigate the Kv2.1/Kv6.4 stoichiometry using single subunit counting and functional characterization of tetrameric concatemers. For selecting the most probable stoichiometry, we introduce a model-selection method that is applicable for any multimeric complex by investigating the stoichiometry of Kv2.1/Kv6.4 channels. Weighted likelihood calculations bring rigor to a powerful technique. Using the weighted-likelihood model-selection method and analysis of electrophysiological data, we show that Kv2.1/Kv6.4 channels express, in contrast to the assumed 3:1, in a 2:2 stoichiometry. Within this stoichiometry, the Kv6.4 subunits have to be positioned alternating with Kv2.1 to express functional channels. The variability in Kv2/KvS assembly increases the diversity of heterotetrameric configurations and extends the regulatory possibilities of KvS by allowing the presence of more than one silent subunit.
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6
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Finol-Urdaneta RK, Belovanovic A, Micic-Vicovac M, Kinsella GK, McArthur JR, Al-Sabi A. Marine Toxins Targeting Kv1 Channels: Pharmacological Tools and Therapeutic Scaffolds. Mar Drugs 2020; 18:E173. [PMID: 32245015 PMCID: PMC7143316 DOI: 10.3390/md18030173] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Revised: 03/15/2020] [Accepted: 03/16/2020] [Indexed: 12/11/2022] Open
Abstract
Toxins from marine animals provide molecular tools for the study of many ion channels, including mammalian voltage-gated potassium channels of the Kv1 family. Selectivity profiling and molecular investigation of these toxins have contributed to the development of novel drug leads with therapeutic potential for the treatment of ion channel-related diseases or channelopathies. Here, we review specific peptide and small-molecule marine toxins modulating Kv1 channels and thus cover recent findings of bioactives found in the venoms of marine Gastropod (cone snails), Cnidarian (sea anemones), and small compounds from cyanobacteria. Furthermore, we discuss pivotal advancements at exploiting the interaction of κM-conotoxin RIIIJ and heteromeric Kv1.1/1.2 channels as prevalent neuronal Kv complex. RIIIJ's exquisite Kv1 subtype selectivity underpins a novel and facile functional classification of large-diameter dorsal root ganglion neurons. The vast potential of marine toxins warrants further collaborative efforts and high-throughput approaches aimed at the discovery and profiling of Kv1-targeted bioactives, which will greatly accelerate the development of a thorough molecular toolbox and much-needed therapeutics.
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Affiliation(s)
- Rocio K. Finol-Urdaneta
- Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW 2522, Australia;
- Electrophysiology Facility for Cell Phenotyping and Drug Discovery, Wollongong, NSW 2522, Australia
| | - Aleksandra Belovanovic
- College of Engineering and Technology, American University of the Middle East, Kuwait; (A.B.); (M.M.-V.)
| | - Milica Micic-Vicovac
- College of Engineering and Technology, American University of the Middle East, Kuwait; (A.B.); (M.M.-V.)
| | - Gemma K. Kinsella
- School of Food Science and Environmental Health, College of Sciences and Health, Technological University Dublin, D07 ADY7 Dublin, Ireland;
| | - Jeffrey R. McArthur
- Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW 2522, Australia;
| | - Ahmed Al-Sabi
- College of Engineering and Technology, American University of the Middle East, Kuwait; (A.B.); (M.M.-V.)
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7
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Bar C, Barcia G, Jennesson M, Le Guyader G, Schneider A, Mignot C, Lesca G, Breuillard D, Montomoli M, Keren B, Doummar D, Billette de Villemeur T, Afenjar A, Marey I, Gerard M, Isnard H, Poisson A, Dupont S, Berquin P, Meyer P, Genevieve D, De Saint Martin A, El Chehadeh S, Chelly J, Guët A, Scalais E, Dorison N, Myers CT, Mefford HC, Howell KB, Marini C, Freeman JL, Nica A, Terrone G, Sekhara T, Lebre A, Odent S, Sadleir LG, Munnich A, Guerrini R, Scheffer IE, Kabashi E, Nabbout R. Expanding the genetic and phenotypic relevance of
KCNB1
variants in developmental and epileptic encephalopathies: 27 new patients and overview of the literature. Hum Mutat 2019; 41:69-80. [DOI: 10.1002/humu.23915] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 08/28/2019] [Accepted: 09/09/2019] [Indexed: 12/28/2022]
Affiliation(s)
- Claire Bar
- Department of Pediatric Neurology, Reference Centre for Rare EpilepsiesHôpital Necker‐Enfants MaladesParis France
- Imagine institute, laboratory of Translational Research for Neurological Disorders, INSERM UMR 1163Imagine InstituteParis France
- Université Paris Descartes‐Sorbonne Paris CitéParis France
| | - Giulia Barcia
- Imagine institute, laboratory of Translational Research for Neurological Disorders, INSERM UMR 1163Imagine InstituteParis France
- Université Paris Descartes‐Sorbonne Paris CitéParis France
- Department of genetics, Necker Enfants Malades hospitalAssistance Publique‐Hôpitaux de ParisParis France
| | | | - Gwenaël Le Guyader
- Department of geneticsUniversity hospital PoitiersPoitiers Cedex France
- EA3808‐NEUVACOD Unité Neurovasculaire et Troubles Cognitifs, Pôle Biologie SantéUniversité de PoitiersPoitiers France
| | - Amy Schneider
- Department of Medicine, Epilepsy Research Centre, Austin HealthThe University of MelbourneHeidelberg Victoria Australia
| | - Cyril Mignot
- Institut du Cerveau et de la Moelle épinière, INSERM, U 1127, CNRS UMR 7225Sorbonne Universités UPMC Univ Paris 06 UMR S 1127 Paris France
- Département de Génétique et de Cytogénétique, Centre de Reference Déficience Intellectuelle de Causes Rares, APHP, Hôpital Pitié‐SalpêtrièreGRC UPMC (Déficience Intellectuelle et Autisme)Paris France
| | - Gaetan Lesca
- Department of geneticsHospices Civils de LyonLyon France
- Neurosciences centre of Lyon, INSERM U1028, UMR CNRS 5292Université Claude Bernard Lyon 1Bron Cedex France
| | - Delphine Breuillard
- Department of Pediatric Neurology, Reference Centre for Rare EpilepsiesHôpital Necker‐Enfants MaladesParis France
| | - Martino Montomoli
- Pediatric Neurology, Neurogenetics and Neurobiology Unit and Laboratories, Department of Neuroscience, A Meyer Children's HospitalUniversity of FlorenceFlorence Italy
| | - Boris Keren
- Département de Génétique et de Cytogénétique, Centre de Reference Déficience Intellectuelle de Causes Rares, APHP, Hôpital Pitié‐SalpêtrièreGRC UPMC (Déficience Intellectuelle et Autisme)Paris France
| | - Diane Doummar
- Department of Pediatric Neurology, Hôpital Armand TrousseauAP‐HPParis France
| | | | - Alexandra Afenjar
- Département de Génétique et Embryologie Médicale, Pathologies Congénitales du Cervelet‐LeucoDystrophies, Centre de Référence déficiences intellectuelles de causes rares, AP‐HP, Hôpital Armand Trousseau, GRC n°19Sorbonne UniversitéParis France
| | - Isabelle Marey
- Département de Génétique et de Cytogénétique, Centre de Reference Déficience Intellectuelle de Causes Rares, APHP, Hôpital Pitié‐SalpêtrièreGRC UPMC (Déficience Intellectuelle et Autisme)Paris France
| | | | | | - Alice Poisson
- Reference Center for Diagnosis and Management of Genetic Psychiatric Disorders, Centre Hospitalier le Vinatier and EDR‐Psy TeamCentre National de la Recherche Scientifique & Lyon 1 Claude Bernard UniversityVilleurbanne France
| | - Sophie Dupont
- Institut du Cerveau et de la Moelle épinière, INSERM, U 1127, CNRS UMR 7225Sorbonne Universités UPMC Univ Paris 06 UMR S 1127 Paris France
- Epileptology and Rehabilitation department, GH Pitie‐Salpêtrière‐Charles FoixAP‐HPParis France
| | - Patrick Berquin
- Department of pediatric neurology Amiens‐Picardie university hospitalUniversité de Picardie Jules VerneAmiens France
| | - Pierre Meyer
- Department of pediatric neurologyMontpellier university hospitalMontpellier France
- PhyMedExp, U1046 INSERMUMR9214 CNRSMontpellier France
| | - David Genevieve
- Service de génétique clinique et du Département de Génétique Médicale, Maladies Rares et Médecine Personnalisée, Centre de référence maladies rares anomalies du développementCHU MontpellierMontpellier France
| | - Anne De Saint Martin
- Department of Pediatric NeurologyStrasbourg University HospitalStrasbourg France
| | - Salima El Chehadeh
- Department of genetics, Hôpital de HautepierreHôpitaux Universitaires de StrasbourgStrasbourg France
| | - Jamel Chelly
- Department of genetics, Hôpital de HautepierreHôpitaux Universitaires de StrasbourgStrasbourg France
| | - Agnès Guët
- Department of PediatricLouis‐Mourier HospitalColombes France
| | - Emmanuel Scalais
- Department of Pediatric Neurology, Centre Hospitalier de LuxembourgLuxembourg CityLuxembourg City Luxembourg
| | - Nathalie Dorison
- Department of pediatric NeurosurgeryRothschild Foundation HospitalParis France
| | - Candace T. Myers
- Department of PediatricsUniversity of WashingtonSeattle Washington
| | - Heather C. Mefford
- Department of Pediatrics, Division of Genetic MedicineUniversity of WashingtonSeattle Washington
| | - Katherine B. Howell
- Departments of Neurology and Paediatrics, Royal Children's HospitalUniversity of MelbourneMelbourne Victoria Australia
- Murdoch Children's Research InstituteMelbourne Victoria Australia
| | - Carla Marini
- Pediatric Neurology, Neurogenetics and Neurobiology Unit and Laboratories, Department of Neuroscience, A Meyer Children's HospitalUniversity of FlorenceFlorence Italy
| | - Jeremy L. Freeman
- Departments of Neurology and Paediatrics, Royal Children's HospitalUniversity of MelbourneMelbourne Victoria Australia
- Murdoch Children's Research InstituteMelbourne Victoria Australia
| | - Anca Nica
- Department of Neurology, Center for Clinical Research (CIC 1414)Rennes University HospitalRennes France
| | - Gaetano Terrone
- Department of Translational Medical Sciences, Section of Pediatrics‐Child Neurology UnitFederico II UniversityNaples Italy
| | - Tayeb Sekhara
- Department of Pediatric NeurologyC.H.I.R.E.CBrussels Belgium
| | - Anne‐Sophie Lebre
- Department of genetics, Maison Blanche hospitalUniversity hospital, ReimsReims France
| | - Sylvie Odent
- Reference Centre for Rare Developmental AbnormalitiesCLAD‐Ouest, CHU RennesRennes France
- Institute of genetics and developmentCNRS UMR 6290, Rennes universityRennes France
| | - Lynette G. Sadleir
- Department of Paediatrics and Child HealthUniversity of OtagoWellington New Zealand
| | - Arnold Munnich
- Université Paris Descartes‐Sorbonne Paris CitéParis France
- Department of genetics, Necker Enfants Malades hospitalAssistance Publique‐Hôpitaux de ParisParis France
| | - Renzo Guerrini
- Pediatric Neurology, Neurogenetics and Neurobiology Unit and Laboratories, Department of Neuroscience, A Meyer Children's HospitalUniversity of FlorenceFlorence Italy
| | - Ingrid E. Scheffer
- Department of Medicine, Epilepsy Research Centre, Austin HealthThe University of MelbourneHeidelberg Victoria Australia
- Departments of Neurology and Paediatrics, Royal Children's HospitalUniversity of MelbourneMelbourne Victoria Australia
- The Florey Institute of Neurosciences and Mental HealthHeidelberg Victoria Australia
| | - Edor Kabashi
- Imagine institute, laboratory of Translational Research for Neurological Disorders, INSERM UMR 1163Imagine InstituteParis France
- Université Paris Descartes‐Sorbonne Paris CitéParis France
| | - Rima Nabbout
- Department of Pediatric Neurology, Reference Centre for Rare EpilepsiesHôpital Necker‐Enfants MaladesParis France
- Imagine institute, laboratory of Translational Research for Neurological Disorders, INSERM UMR 1163Imagine InstituteParis France
- Université Paris Descartes‐Sorbonne Paris CitéParis France
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8
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Guidolin D, Marcoli M, Tortorella C, Maura G, Agnati LF. Receptor-Receptor Interactions as a Widespread Phenomenon: Novel Targets for Drug Development? Front Endocrinol (Lausanne) 2019; 10:53. [PMID: 30833931 PMCID: PMC6387912 DOI: 10.3389/fendo.2019.00053] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/24/2018] [Accepted: 01/21/2019] [Indexed: 12/19/2022] Open
Abstract
The discovery of receptor-receptor interactions (RRI) has expanded our understanding of the role that G protein-coupled receptors (GPCRs) play in intercellular communication. The finding that GPCRs can operate as receptor complexes, and not only as monomers, suggests that several different incoming signals could already be integrated at the plasma membrane level via direct allosteric interactions between the protomers that form the complex. Most research in this field has focused on neuronal populations and has led to the identification of a large number of RRI. However, RRI have been seen to occur not only in neurons but also in astrocytes and, outside the central nervous system, in cells of the cardiovascular and endocrine systems and in cancer cells. Furthermore, RRI involving the formation of macromolecular complexes are not limited to GPCRs, being also observed in other families of receptors. Thus, RRI appear as a widespread phenomenon and oligomerization as a common mechanism for receptor function and regulation. The discovery of these macromolecular assemblies may well have a major impact on pharmacology. Indeed, the formation of receptor complexes significantly broadens the spectrum of mechanisms available to receptors for recognition and signaling, which may be implemented through modulation of the binding sites of the adjacent protomers and of their signal transduction features. In this context, the possible appearance of novel allosteric sites in the receptor complex structure may be of particular relevance. Thus, the existence of RRI offers the possibility of new therapeutic approaches, and novel pharmacological strategies for disease treatment have already been proposed. Several challenges, however, remain. These include the accurate characterization of the role that the receptor complexes identified so far play in pathological conditions and the development of ligands specific to given receptor complexes, in order to efficiently exploit the pharmacological properties of these complexes.
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Affiliation(s)
- Diego Guidolin
- Department of Neuroscience, University of Padova, Padova, Italy
- *Correspondence: Diego Guidolin
| | - Manuela Marcoli
- Department of Pharmacy and Center of Excellence for Biomedical Research, University of Genova, Genoa, Italy
| | | | - Guido Maura
- Department of Pharmacy and Center of Excellence for Biomedical Research, University of Genova, Genoa, Italy
| | - Luigi F. Agnati
- Department of Biomedical Sciences, University of Modena and Reggio Emilia, Modena, Italy
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
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9
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Pisupati A, Mickolajczyk KJ, Horton W, van Rossum DB, Anishkin A, Chintapalli SV, Li X, Chu-Luo J, Busey G, Hancock WO, Jegla T. The S6 gate in regulatory Kv6 subunits restricts heteromeric K + channel stoichiometry. J Gen Physiol 2018; 150:1702-1721. [PMID: 30322883 PMCID: PMC6279357 DOI: 10.1085/jgp.201812121] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Revised: 07/03/2018] [Accepted: 09/26/2018] [Indexed: 11/24/2022] Open
Abstract
Atypical substitutions in the S6 activation gate sequence distinguish “regulatory” Kv subunits, which cannot homotetramerize due to T1 self-incompatibility. Pisupati et al. show that such substitutions in Kv6 work together with self-incompatibility to restrict Kv2:Kv6 heteromeric stoichiometry to 3:1. The Shaker-like family of voltage-gated K+ channels comprises four functionally independent gene subfamilies, Shaker (Kv1), Shab (Kv2), Shaw (Kv3), and Shal (Kv4), each of which regulates distinct aspects of neuronal excitability. Subfamily-specific assembly of tetrameric channels is mediated by the N-terminal T1 domain and segregates Kv1–4, allowing multiple channel types to function independently in the same cell. Typical Shaker-like Kv subunits can form functional channels as homotetramers, but a group of mammalian Kv2-related genes (Kv5.1, Kv6s, Kv8s, and Kv9s) encodes subunits that have a “silent” or “regulatory” phenotype characterized by T1 self-incompatibility. These channels are unable to form homotetramers, but instead heteromerize with Kv2.1 or Kv2.2 to diversify the functional properties of these delayed rectifiers. While T1 self-incompatibility predicts that these heterotetramers could contain up to two regulatory (R) subunits, experiments show a predominance of 3:1R stoichiometry in which heteromeric channels contain a single regulatory subunit. Substitution of the self-compatible Kv2.1 T1 domain into the regulatory subunit Kv6.4 does not alter the stoichiometry of Kv2.1:Kv6.4 heteromers. Here, to identify other channel structures that might be responsible for favoring the 3:1R stoichiometry, we compare the sequences of mammalian regulatory subunits to independently evolved regulatory subunits from cnidarians. The most widespread feature of regulatory subunits is the presence of atypical substitutions in the highly conserved consensus sequence of the intracellular S6 activation gate of the pore. We show that two amino acid substitutions in the S6 gate of the regulatory subunit Kv6.4 restrict the functional stoichiometry of Kv2.1:Kv6.4 to 3:1R by limiting the formation and function of 2:2R heteromers. We propose a two-step model for the evolution of the asymmetric 3:1R stoichiometry, which begins with evolution of self-incompatibility to establish the regulatory phenotype, followed by drift of the activation gate consensus sequence under relaxed selection to limit stoichiometry to 3:1R.
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Affiliation(s)
- Aditya Pisupati
- Department of Biology, Pennsylvania State University, University Park, PA.,Medical Scientist Training Program, College of Medicine, Pennsylvania State University, Hershey, PA
| | - Keith J Mickolajczyk
- Department of Biomedical Engineering, Pennsylvania State University, University Park, PA
| | - William Horton
- Department of Animal Science, Pennsylvania State University, University Park, PA
| | - Damian B van Rossum
- The Jake Gittlen Laboratories for Cancer Research, College of Medicine, Pennsylvania State University, Hershey, PA.,Division of Experimental Pathology, Department of Pathology, College of Medicine, Pennsylvania State University, Hershey, PA
| | - Andriy Anishkin
- Department of Biology, University of Maryland, College Park, MD
| | - Sree V Chintapalli
- Arkansas Children's Nutrition Center and Department of Pediatrics, University of Arkansas for Medical Sciences, Little Rock, AR
| | - Xiaofan Li
- Department of Biology, Pennsylvania State University, University Park, PA
| | - Jose Chu-Luo
- Department of Biology, Pennsylvania State University, University Park, PA
| | - Gregory Busey
- Department of Biology, Pennsylvania State University, University Park, PA
| | - William O Hancock
- Department of Biomedical Engineering, Pennsylvania State University, University Park, PA
| | - Timothy Jegla
- Department of Biology, Pennsylvania State University, University Park, PA .,Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, PA
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10
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Kaczmarek LK, Zhang Y. Kv3 Channels: Enablers of Rapid Firing, Neurotransmitter Release, and Neuronal Endurance. Physiol Rev 2017; 97:1431-1468. [PMID: 28904001 PMCID: PMC6151494 DOI: 10.1152/physrev.00002.2017] [Citation(s) in RCA: 103] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Revised: 04/24/2017] [Accepted: 05/05/2017] [Indexed: 12/11/2022] Open
Abstract
The intrinsic electrical characteristics of different types of neurons are shaped by the K+ channels they express. From among the more than 70 different K+ channel genes expressed in neurons, Kv3 family voltage-dependent K+ channels are uniquely associated with the ability of certain neurons to fire action potentials and to release neurotransmitter at high rates of up to 1,000 Hz. In general, the four Kv3 channels Kv3.1-Kv3.4 share the property of activating and deactivating rapidly at potentials more positive than other channels. Each Kv3 channel gene can generate multiple protein isoforms, which contribute to the high-frequency firing of neurons such as auditory brain stem neurons, fast-spiking GABAergic interneurons, and Purkinje cells of the cerebellum, and to regulation of neurotransmitter release at the terminals of many neurons. The different Kv3 channels have unique expression patterns and biophysical properties and are regulated in different ways by protein kinases. In this review, we cover the function, localization, and modulation of Kv3 channels and describe how levels and properties of the channels are altered by changes in ongoing neuronal activity. We also cover how the protein-protein interaction of these channels with other proteins affects neuronal functions, and how mutations or abnormal regulation of Kv3 channels are associated with neurological disorders such as ataxias, epilepsies, schizophrenia, and Alzheimer's disease.
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Affiliation(s)
- Leonard K Kaczmarek
- Departments of Pharmacology and of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
| | - Yalan Zhang
- Departments of Pharmacology and of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut
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11
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Abbott GW. β Subunits Functionally Differentiate Human Kv4.3 Potassium Channel Splice Variants. Front Physiol 2017; 8:66. [PMID: 28228734 PMCID: PMC5296356 DOI: 10.3389/fphys.2017.00066] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 01/24/2017] [Indexed: 11/22/2022] Open
Abstract
The human ventricular cardiomyocyte transient outward K+ current (Ito) mediates the initial phase of myocyte repolarization and its disruption is implicated in Brugada Syndrome and heart failure (HF). Human cardiac Ito is generated primarily by two Kv4.3 splice variants (Kv4.3L and Kv4.3S, diverging only by a C-terminal, S6-proximal, 19-residue stretch unique to Kv4.3L), which are differentially remodeled in HF, but considered functionally alike at baseline. Kv4.3 is regulated in human heart by β subunits including KChIP2b and KCNEs, but their effects were previously assumed to be Kv4.3 isoform-independent. Here, this assumption was tested experimentally using two-electrode voltage-clamp analysis of human subunits co-expressed in Xenopus laevis oocytes. Unexpectedly, Kv4.3L-KChIP2b channels exhibited up to 8-fold lower current augmentation, 40% slower inactivation, and 5 mV-shifted steady-state inactivation compared to Kv4.3S-KChIP2b. A synthetic peptide mimicking the 19-residue stretch diminished these differences, reinforcing the importance of this segment in mediating Kv4.3 regulation by KChIP2b. KCNE subunits induced further functional divergence, including a 7-fold increase in Kv4.3S-KCNE4-KChIP2b current compared to Kv4.3L-KCNE4-KChIP2b. The discovery of β-subunit-dependent functional divergence in human Kv4.3 splice variants suggests a C-terminal signaling hub is crucial to governing β-subunit effects upon Kv4.3, and demonstrates the potential significance of differential Kv4.3 gene-splicing and β subunit expression in myocyte physiology and pathobiology.
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Affiliation(s)
- Geoffrey W Abbott
- Bioelectricity Laboratory, Department of Pharmacology and Department of Physiology and Biophysics, School of Medicine, University of California, Irvine Irvine, CA, USA
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12
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Cotranslational association of mRNA encoding subunits of heteromeric ion channels. Proc Natl Acad Sci U S A 2016; 113:4859-64. [PMID: 27078096 DOI: 10.1073/pnas.1521577113] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Oligomers of homomeric voltage-gated potassium channels associate early in biogenesis as the nascent proteins emerge from the polysome. Less is known about how proteins emerging from different polysomes associate to form hetero-oligomeric channels. Here, we report that alternate mRNA transcripts encoding human ether-à-go-go-related gene (hERG) 1a and 1b subunits, which assemble to produce ion channels mediating cardiac repolarization, are physically associated during translation. We show that shRNA specifically targeting either hERG 1a or 1b transcripts reduced levels of both transcripts, but only when they were coexpressed heterologously. Both transcripts could be copurified with an Ab against the nascent hERG 1a N terminus. This interaction occurred even when translation of 1b was prevented, indicating the transcripts associate independent of their encoded proteins. The association was also demonstrated in cardiomyocytes, where levels of both hERG transcripts were reduced by either 1a or 1b shRNA, but native KCNE1 and ryanodine receptor 2 (RYR2) transcripts were unaffected. Changes in protein levels and membrane currents mirrored changes in transcript levels, indicating the targeted transcripts were undergoing translation. The physical association of transcripts encoding different subunits provides the spatial proximity required for nascent proteins to interact during biogenesis, and may represent a general mechanism facilitating assembly of heteromeric protein complexes involved in a range of biological processes.
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13
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Regnier G, Bocksteins E, Van de Vijver G, Snyders DJ, van Bogaert PP. The contribution of Kv2.2-mediated currents decreases during the postnatal development of mouse dorsal root ganglion neurons. Physiol Rep 2016; 4:4/6/e12731. [PMID: 27033450 PMCID: PMC4814888 DOI: 10.14814/phy2.12731] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Accepted: 02/12/2016] [Indexed: 11/24/2022] Open
Abstract
Delayed rectifier voltage-gated K(+)(Kv) channels play an important role in the regulation of the electrophysiological properties of neurons. In mouse dorsal root ganglion (DRG) neurons, a large fraction of the delayed rectifier current is carried by both homotetrameric Kv2 channels and heterotetrameric channels consisting of Kv2 and silent Kv (KvS) subunits (i.e., Kv5-Kv6 and Kv8-Kv9). However, little is known about the contribution of Kv2-mediated currents during the postnatal development ofDRGneurons. Here, we report that the Stromatoxin-1 (ScTx)-sensitive fraction of the total outward K(+)current (IK) from mouseDRGneurons gradually decreased (~13%,P < 0.05) during the first month of postnatal development. Because ScTx inhibits both Kv2.1- and Kv2.2-mediated currents, this gradual decrease may reflect a decrease in currents containing either subunit. However, the fraction of Kv2.1 antibody-sensitive current that only reflects the Kv2.1-mediated currents remained constant during that same period. These results suggested that the fractional contribution of Kv2.2-mediated currents relative toIKdecreased with postnatal age. SemiquantitativeRT-PCRanalysis indicated that this decrease can be attributed to developmental changes in Kv2.2 expression as themRNAlevels of the Kv2.2 subunit decreased gradually between 1 and 4 weeks of age. In addition, we observed age-dependent fluctuations in themRNAlevels of the Kv6.3, Kv8.1, Kv9.1, and Kv9.3 subunits. These results support an important role of both Kv2 and KvS subunits in the postnatal maturation ofDRGneurons.
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Affiliation(s)
- Glenn Regnier
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Antwerpen, Belgium
| | - Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Antwerpen, Belgium
| | - Gerda Van de Vijver
- Laboratory for Cardiovascular Research, Institute Born-Bunge University of Antwerp, CDE, Antwerpen, Belgium
| | - Dirk J Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, CDE, Antwerpen, Belgium
| | - Pierre-Paul van Bogaert
- Laboratory for Cardiovascular Research, Institute Born-Bunge University of Antwerp, CDE, Antwerpen, Belgium
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14
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Mixing and matching TREK/TRAAK subunits generate heterodimeric K2P channels with unique properties. Proc Natl Acad Sci U S A 2016; 113:4200-5. [PMID: 27035965 DOI: 10.1073/pnas.1522748113] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The tandem of pore domain in a weak inwardly rectifying K(+) channel (Twik)-related acid-arachidonic activated K(+) channel (TRAAK) and Twik-related K(+) channels (TREK) 1 and TREK2 are active as homodimers gated by stretch, fatty acids, pH, and G protein-coupled receptors. These two-pore domain potassium (K2P) channels are broadly expressed in the nervous system where they control excitability. TREK/TRAAK KO mice display altered phenotypes related to nociception, neuroprotection afforded by polyunsaturated fatty acids, learning and memory, mood control, and sensitivity to general anesthetics. These channels have emerged as promising targets for the development of new classes of anesthetics, analgesics, antidepressants, neuroprotective agents, and drugs against addiction. Here, we show that the TREK1, TREK2, and TRAAK subunits assemble and form active heterodimeric channels with electrophysiological, regulatory, and pharmacological properties different from those of homodimeric channels. Heteromerization occurs between all TREK variants produced by alternative splicing and alternative translation initiation. These results unveil a previously unexpected diversity of K2P channels that will be challenging to analyze in vivo, but which opens new perspectives for the development of clinically relevant drugs.
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15
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Bocksteins E. Kv5, Kv6, Kv8, and Kv9 subunits: No simple silent bystanders. J Gen Physiol 2016; 147:105-25. [PMID: 26755771 PMCID: PMC4727947 DOI: 10.1085/jgp.201511507] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Accepted: 12/11/2015] [Indexed: 12/19/2022] Open
Abstract
Members of the electrically silent voltage-gated K(+) (Kv) subfamilies (Kv5, Kv6, Kv8, and Kv9, collectively identified as electrically silent voltage-gated K(+) channel [KvS] subunits) do not form functional homotetrameric channels but assemble with Kv2 subunits into heterotetrameric Kv2/KvS channels with unique biophysical properties. Unlike the ubiquitously expressed Kv2 subunits, KvS subunits show a more restricted expression. This raises the possibility that Kv2/KvS heterotetramers have tissue-specific functions, making them potential targets for the development of novel therapeutic strategies. Here, I provide an overview of the expression of KvS subunits in different tissues and discuss their proposed role in various physiological and pathophysiological processes. This overview demonstrates the importance of KvS subunits and Kv2/KvS heterotetramers in vivo and the importance of considering KvS subunits and Kv2/KvS heterotetramers in the development of novel treatments.
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Affiliation(s)
- Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology, and Pharmacology, Department for Biomedical Sciences, University of Antwerp, 2610 Antwerp, Belgium
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16
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Major diversification of voltage-gated K+ channels occurred in ancestral parahoxozoans. Proc Natl Acad Sci U S A 2015; 112:E1010-9. [PMID: 25691740 DOI: 10.1073/pnas.1422941112] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
We examined the origins and functional evolution of the Shaker and KCNQ families of voltage-gated K(+) channels to better understand how neuronal excitability evolved. In bilaterians, the Shaker family consists of four functionally distinct gene families (Shaker, Shab, Shal, and Shaw) that share a subunit structure consisting of a voltage-gated K(+) channel motif coupled to a cytoplasmic domain that mediates subfamily-exclusive assembly (T1). We traced the origin of this unique Shaker subunit structure to a common ancestor of ctenophores and parahoxozoans (cnidarians, bilaterians, and placozoans). Thus, the Shaker family is metazoan specific but is likely to have evolved in a basal metazoan. Phylogenetic analysis suggested that the Shaker subfamily could predate the divergence of ctenophores and parahoxozoans, but that the Shab, Shal, and Shaw subfamilies are parahoxozoan specific. In support of this, putative ctenophore Shaker subfamily channel subunits coassembled with cnidarian and mouse Shaker subunits, but not with cnidarian Shab, Shal, or Shaw subunits. The KCNQ family, which has a distinct subunit structure, also appears solely within the parahoxozoan lineage. Functional analysis indicated that the characteristic properties of Shaker, Shab, Shal, Shaw, and KCNQ currents evolved before the divergence of cnidarians and bilaterians. These results show that a major diversification of voltage-gated K(+) channels occurred in ancestral parahoxozoans and imply that many fundamental mechanisms for the regulation of action potential propagation evolved at this time. Our results further suggest that there are likely to be substantial differences in the regulation of neuronal excitability between ctenophores and parahoxozoans.
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17
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Moran Y, Barzilai MG, Liebeskind BJ, Zakon HH. Evolution of voltage-gated ion channels at the emergence of Metazoa. J Exp Biol 2015; 218:515-25. [DOI: 10.1242/jeb.110270] [Citation(s) in RCA: 85] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Voltage-gated ion channels are large transmembrane proteins that enable the passage of ions through their pore across the cell membrane. These channels belong to one superfamily and carry pivotal roles such as the propagation of neuronal and muscular action potentials and the promotion of neurotransmitter secretion in synapses. In this review, we describe in detail the current state of knowledge regarding the evolution of these channels with a special emphasis on the metazoan lineage. We highlight the contribution of the genomic revolution to the understanding of ion channel evolution and for revealing that these channels appeared long before the appearance of the first animal. We also explain how the elucidation of channel selectivity properties and function in non-bilaterian animals such as cnidarians (sea anemones, corals, jellyfish and hydroids) can contribute to the study of channel evolution. Finally, we point to open questions and future directions in this field of research.
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Affiliation(s)
- Yehu Moran
- Department of Ecology, Evolution and Behavior, Alexander Silberman Institute of Life Sciences, Faculty of Science, Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Maya Gur Barzilai
- Department of Molecular Biology and Ecology of Plants, George S. Wise Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 69978, Israel
| | - Benjamin J. Liebeskind
- Department of Integrative Biology and Center for Computational Biology and Bioinformatics, University of Texas, Austin, TX 78712, USA
| | - Harold H. Zakon
- Department of Integrative Biology and Center for Computational Biology and Bioinformatics, University of Texas, Austin, TX 78712, USA
- Department of Neuroscience, University of Texas at Austin, TX 78712, USA
- Josephine Bay Paul Center for Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, MA 02543, USA
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18
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Bocksteins E, Mayeur E, Van Tilborg A, Regnier G, Timmermans JP, Snyders DJ. The subfamily-specific interaction between Kv2.1 and Kv6.4 subunits is determined by interactions between the N- and C-termini. PLoS One 2014; 9:e98960. [PMID: 24901643 PMCID: PMC4047056 DOI: 10.1371/journal.pone.0098960] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Accepted: 05/08/2014] [Indexed: 12/14/2022] Open
Abstract
The "silent" voltage-gated potassium (KvS) channel subunit Kv6.4 does not form electrically functional homotetramers at the plasma membrane but assembles with Kv2.1 subunits, generating functional Kv2.1/Kv6.4 heterotetramers. The N-terminal T1 domain determines the subfamily-specific assembly of Kv1-4 subunits by preventing interactions between subunits that belong to different subfamilies. For Kv6.4, yeast-two-hybrid experiments showed an interaction of the Kv6.4 N-terminus with the Kv2.1 N-terminus, but unexpectedly also with the Kv3.1 N-terminus. We confirmed this interaction by Fluorescence Resonance Energy Transfer (FRET) and co-immunoprecipitation (co-IP) using N-terminal Kv3.1 and Kv6.4 fragments. However, full-length Kv3.1 and Kv6.4 subunits do not form heterotetramers at the plasma membrane. Therefore, additional interactions between the Kv6.4 and Kv2.1 subunits should be important in the Kv2.1/Kv6.4 subfamily-specificity. Using FRET and co-IP approaches with N- and C-terminal fragments we observed that the Kv6.4 C-terminus physically interacts with the Kv2.1 N-terminus but not with the Kv3.1 N-terminus. The N-terminal amino acid sequence CDD which is conserved between Kv2 and KvS subunits appeared to be a key determinant since charge reversals with arginine substitutions abolished the interaction between the N-terminus of Kv2.1 and the C-terminus of both Kv2.1 and Kv6.4. In addition, the Kv6.4(CKv3.1) chimera in which the C-terminus of Kv6.4 was replaced by the corresponding domain of Kv3.1, disrupted the assembly with Kv2.1. These results indicate that the subfamily-specific Kv2.1/Kv6.4 heterotetramerization is determined by interactions between Kv2.1 and Kv6.4 that involve both the N- and C-termini in which the conserved N-terminal CDD sequence plays a key role.
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Affiliation(s)
- Elke Bocksteins
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Evy Mayeur
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Abbi Van Tilborg
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Glenn Regnier
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
| | - Jean-Pierre Timmermans
- Laboratory of Cell Biology and Histology, Department of Veterinary Sciences, University of Antwerp, Antwerp, Belgium
| | - Dirk J. Snyders
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp, Antwerp, Belgium
- * E-mail:
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19
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Barry J, Gu C. Coupling mechanical forces to electrical signaling: molecular motors and the intracellular transport of ion channels. Neuroscientist 2013; 19:145-59. [PMID: 22910031 PMCID: PMC3625366 DOI: 10.1177/1073858412456088] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Proper localization of various ion channels is fundamental to neuronal functions, including postsynaptic potential plasticity, dendritic integration, action potential initiation and propagation, and neurotransmitter release. Microtubule-based forward transport mediated by kinesin motors plays a key role in placing ion channel proteins to correct subcellular compartments. PDZ- and coiled-coil-domain proteins function as adaptor proteins linking ionotropic glutamate and GABA receptors to various kinesin motors, respectively. Recent studies show that several voltage-gated ion channel/transporter proteins directly bind to kinesins during forward transport. Three major regulatory mechanisms underlying intracellular transport of ion channels are also revealed. These studies contribute to understanding how mechanical forces are coupled to electrical signaling and illuminating pathogenic mechanisms in neurodegenerative diseases.
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Affiliation(s)
- Joshua Barry
- The Molecular, Cellular and Developmental Biology Graduate Program, The Ohio State University, Columbus, OH, USA
| | - Chen Gu
- The Molecular, Cellular and Developmental Biology Graduate Program, The Ohio State University, Columbus, OH, USA
- Department of Neuroscience, The Ohio State University, Columbus, OH, USA
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20
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Barry J, Xu M, Gu Y, Dangel AW, Jukkola P, Shrestha C, Gu C. Activation of conventional kinesin motors in clusters by Shaw voltage-gated K+ channels. J Cell Sci 2013; 126:2027-41. [PMID: 23487040 DOI: 10.1242/jcs.122234] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The conventional kinesin motor transports many different cargos to specific locations in neurons. How cargos regulate motor function remains unclear. Here we focus on KIF5, the heavy chain of conventional kinesin, and report that the Kv3 (Shaw) voltage-gated K(+) channel, the only known tetrameric KIF5-binding protein, clusters and activates KIF5 motors during axonal transport. Endogenous KIF5 often forms clusters along axons, suggesting a potential role of KIF5-binding proteins. Our biochemical assays reveal that the high-affinity multimeric binding between the Kv3.1 T1 domain and KIF5B requires three basic residues in the KIF5B tail. Kv3.1 T1 competes with the motor domain and microtubules, but not with kinesin light chain 1 (KLC1), for binding to the KIF5B tail. Live-cell imaging assays show that four KIF5-binding proteins, Kv3.1, KLC1 and two synaptic proteins SNAP25 and VAMP2, differ in how they regulate KIF5B distribution. Only Kv3.1 markedly increases the frequency and number of KIF5B-YFP anterograde puncta. Deletion of Kv3.1 channels reduces KIF5 clusters in mouse cerebellar neurons. Therefore, clustering and activation of KIF5 motors by Kv3 regulate the motor number in carrier vesicles containing the channel proteins, contributing not only to the specificity of Kv3 channel transport, but also to the cargo-mediated regulation of motor function.
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Affiliation(s)
- Joshua Barry
- Molecular, Cellular and Developmental Biology Graduate Program, The Ohio State University, Columbus, OH 43210, USA
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21
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Gu Y, Barry J, Gu C. Kv3 channel assembly, trafficking and activity are regulated by zinc through different binding sites. J Physiol 2013; 591:2491-507. [PMID: 23420657 DOI: 10.1113/jphysiol.2013.251983] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Zinc, a divalent heavy metal ion and an essential mineral for life, regulates synaptic transmission and neuronal excitability via ion channels. However, its binding sites and regulatory mechanisms are poorly understood. Here, we report that Kv3 channel assembly, localization and activity are regulated by zinc through different binding sites. Local perfusion of zinc reversibly reduced spiking frequency of cultured neurons most likely by suppressing Kv3 channels. Indeed, zinc inhibited Kv3.1 channel activity and slowed activation kinetics, independent of its site in the N-terminal T1 domain. Biochemical assays surprisingly identified a novel zinc-binding site in the Kv3.1 C-terminus, critical for channel activity and axonal targeting, but not for the zinc inhibition. Finally, mutagenesis revealed an important role of the junction between the first transmembrane (TM) segment and the first extracellular loop in sensing zinc. Its mutant enabled fast spiking with relative resistance to the zinc inhibition. Therefore, our studies provide novel mechanistic insights into the multifaceted regulation of Kv3 channel activity and localization by divalent heavy metal ions.
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Affiliation(s)
- Yuanzheng Gu
- 182 Rightmire Hall, 1060 Carmack Road, The Ohio State University, Columbus, OH 43210, USA.
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22
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Social networking among voltage-activated potassium channels. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2013; 117:269-302. [PMID: 23663972 DOI: 10.1016/b978-0-12-386931-9.00010-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Voltage-activated potassium channels (Kv channels) are ubiquitously expressed proteins that subserve a wide range of cellular functions. From their birth in the endoplasmic reticulum, Kv channels assemble from multiple subunits in complex ways that determine where they live in the cell, their biophysical characteristics, and their role in enabling different kinds of cells to respond to specific environmental signals to generate appropriate functional responses. This chapter describes the types of protein-protein interactions among pore-forming channel subunits and their auxiliary protein partners, as well as posttranslational protein modifications that occur in various cell types. This complex oligomerization of channel subunits establishes precise cell type-specific Kv channel localization and function, which in turn drives a diverse range of cellular signal transduction mechanisms uniquely suited to the physiological contexts in which they are found.
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Zhang A, Sun C, Zhang L, Lv Y, Xue X, Li G, Cui C, Yan GX. L539 fs/47, a truncated mutation of human ether-a-go-go-related gene (hERG), decreases hERG ion channel currents in HEK 293 cells. Clin Exp Pharmacol Physiol 2012; 40:28-36. [DOI: 10.1111/1440-1681.12028] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Revised: 10/12/2012] [Accepted: 11/04/2012] [Indexed: 01/09/2023]
Affiliation(s)
| | - Chaofeng Sun
- Department of Cardiovascular Medicine; MOE; Ion Channel Disease Laboratory; MOE Key Laboratory of Environment and Genes Related to Diseases, The First Affiliated Hospital of Xi'an Jiaotong University; Xi'an; Shaanxi; China
| | - Li Zhang
- Main Line Health Heart Center; Lankenau Institute for Medical Research; Wynnewood; Pennsylvania; USA
| | - Ying Lv
- Department of Cardiovascular Medicine; MOE; Ion Channel Disease Laboratory; MOE Key Laboratory of Environment and Genes Related to Diseases, The First Affiliated Hospital of Xi'an Jiaotong University; Xi'an; Shaanxi; China
| | - Xiaolin Xue
- Department of Cardiovascular Medicine; MOE; Ion Channel Disease Laboratory; MOE Key Laboratory of Environment and Genes Related to Diseases, The First Affiliated Hospital of Xi'an Jiaotong University; Xi'an; Shaanxi; China
| | - Guoliang Li
- Department of Cardiovascular Medicine; MOE; Ion Channel Disease Laboratory; MOE Key Laboratory of Environment and Genes Related to Diseases, The First Affiliated Hospital of Xi'an Jiaotong University; Xi'an; Shaanxi; China
| | - Changcong Cui
- Department of Cardiovascular Medicine; MOE; Ion Channel Disease Laboratory; MOE Key Laboratory of Environment and Genes Related to Diseases, The First Affiliated Hospital of Xi'an Jiaotong University; Xi'an; Shaanxi; China
| | - Gan-Xin Yan
- Main Line Health Heart Center; Lankenau Institute for Medical Research; Wynnewood; Pennsylvania; USA
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Jegla T, Marlow HQ, Chen B, Simmons DK, Jacobo SM, Martindale MQ. Expanded functional diversity of shaker K(+) channels in cnidarians is driven by gene expansion. PLoS One 2012; 7:e51366. [PMID: 23251506 PMCID: PMC3519636 DOI: 10.1371/journal.pone.0051366] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2012] [Accepted: 10/29/2012] [Indexed: 12/27/2022] Open
Abstract
The genome of the cnidarian Nematostella vectensis (starlet sea anemone) provides a molecular genetic view into the first nervous systems, which appeared in a late common ancestor of cnidarians and bilaterians. Nematostella has a surprisingly large and diverse set of neuronal signaling genes including paralogs of most neuronal signaling molecules found in higher metazoans. Several ion channel gene families are highly expanded in the sea anemone, including three subfamilies of the Shaker K+ channel gene family: Shaker (Kv1), Shaw (Kv3) and Shal (Kv4). In order to better understand the physiological significance of these voltage-gated K+ channel expansions, we analyzed the function of 18 members of the 20 gene Shaker subfamily in Nematostella. Six of the Nematostella Shaker genes express functional homotetrameric K+ channels in vitro. These include functional orthologs of bilaterian Shakers and channels with an unusually high threshold for voltage activation. We identified 11 Nematostella Shaker genes with a distinct “silent” or “regulatory” phenotype; these encode subunits that function only in heteromeric channels and serve to further diversify Nematostella Shaker channel gating properties. Subunits with the regulatory phenotype have not previously been found in the Shaker subfamily, but have evolved independently in the Shab (Kv2) family in vertebrates and the Shal family in a cnidarian. Phylogenetic analysis indicates that regulatory subunits were present in ancestral cnidarians, but have continued to diversity at a high rate after the split between anthozoans and hydrozoans. Comparison of Shaker family gene complements from diverse metazoan species reveals frequent, large scale duplication has produced highly unique sets of Shaker channels in the major metazoan lineages.
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Affiliation(s)
- Timothy Jegla
- Department of Biology and Huck Institute of Life Sciences, Eberly College of Science, Penn State University, University Park, PA, USA.
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25
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Kanda VA, Abbott GW. KCNE Regulation of K(+) Channel Trafficking - a Sisyphean Task? Front Physiol 2012; 3:231. [PMID: 22754540 PMCID: PMC3385356 DOI: 10.3389/fphys.2012.00231] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2012] [Accepted: 06/08/2012] [Indexed: 11/16/2022] Open
Abstract
Voltage-gated potassium (Kv) channels shape the action potentials of excitable cells and regulate membrane potential and ion homeostasis in excitable and non-excitable cells. With 40 known members in the human genome and a variety of homomeric and heteromeric pore-forming α subunit interactions, post-translational modifications, cellular locations, and expression patterns, the functional repertoire of the Kv α subunit family is monumental. This versatility is amplified by a host of interacting proteins, including the single membrane-spanning KCNE ancillary subunits. Here, examining both the secretory and the endocytic pathways, we review recent findings illustrating the surprising virtuosity of the KCNE proteins in orchestrating not just the function, but also the composition, diaspora and retrieval of channels formed by their Kv α subunit partners.
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Affiliation(s)
- Vikram A Kanda
- Department of Biology, Manhattan College Riverdale, New York, NY, USA
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26
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Bocksteins E, Snyders DJ. Electrically Silent Kv Subunits: Their Molecular and Functional Characteristics. Physiology (Bethesda) 2012; 27:73-84. [DOI: 10.1152/physiol.00023.2011] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Electrically silent voltage-gated potassium (KvS) α-subunits do not form homotetramers but heterotetramerize with Kv2 subunits, generating functional Kv2/KvS channel complexes in which the KvS subunits modulate the Kv2 current. This poses intriguing questions into the molecular mechanisms by which these KvS subunits cannot form functional homotetramers, why they only interact with Kv2 subunits, and how they modulate the Kv2 current.
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Affiliation(s)
- Elke Bocksteins
- Department of Biomedical Sciences, Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerpen, Belgium
| | - Dirk J. Snyders
- Department of Biomedical Sciences, Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, Antwerpen, Belgium
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27
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Barros F, Domínguez P, de la Peña P. Cytoplasmic domains and voltage-dependent potassium channel gating. Front Pharmacol 2012; 3:49. [PMID: 22470342 PMCID: PMC3311039 DOI: 10.3389/fphar.2012.00049] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Accepted: 03/05/2012] [Indexed: 12/20/2022] Open
Abstract
The basic architecture of the voltage-dependent K+ channels (Kv channels) corresponds to a transmembrane protein core in which the permeation pore, the voltage-sensing components and the gating machinery (cytoplasmic facing gate and sensor–gate coupler) reside. Usually, large protein tails are attached to this core, hanging toward the inside of the cell. These cytoplasmic regions are essential for normal channel function and, due to their accessibility to the cytoplasmic environment, constitute obvious targets for cell-physiological control of channel behavior. Here we review the present knowledge about the molecular organization of these intracellular channel regions and their role in both setting and controlling Kv voltage-dependent gating properties. This includes the influence that they exert on Kv rapid/N-type inactivation and on activation/deactivation gating of Shaker-like and eag-type Kv channels. Some illustrative examples about the relevance of these cytoplasmic domains determining the possibilities for modulation of Kv channel gating by cellular components are also considered.
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Affiliation(s)
- Francisco Barros
- Departamento de Bioquímica y Biología Molecular, Universidad de Oviedo Oviedo, Asturias, Spain
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28
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Abstract
KCNE2, originally designated MinK-related peptide 1 (MiRP1), belongs to a five-strong family of potassium channel ancillary (β) subunits that, despite the diminutive size of the family and its members, has loomed large in the field of ion channel physiology. KCNE2 dictates K (+) channel gating, conductance, α subunit composition, trafficking and pharmacology, and also modifies functional properties of monovalent cation-nonselective HCN channels. The Kcne2 (-/-) mouse exhibits cardiac arrhythmia and hypertrophy, achlorhydria, gastric neoplasia, hypothyroidism, alopecia, stunted growth and choroid plexus epithelial dysfunction, illustrating the breadth and depth of the influence of KCNE2, mutations which are also associated with human cardiac arrhythmias. Here, the modus operandi and physiological roles of this potent regulator of membrane excitability and ion secretion are reviewed with particular emphasis on the ability of KCNE2 to shape the electrophysiological landscape of both excitable and non-excitable cells.
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Affiliation(s)
- Geoffrey W Abbott
- Departments of Pharmacology and Physiology and Biophysics, University of California, Irvine, Irvine, CA, USA.
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29
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Kanda VA, Lewis A, Xu X, Abbott GW. KCNE1 and KCNE2 provide a checkpoint governing voltage-gated potassium channel α-subunit composition. Biophys J 2011; 101:1364-75. [PMID: 21943417 DOI: 10.1016/j.bpj.2011.08.014] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2011] [Revised: 07/25/2011] [Accepted: 08/05/2011] [Indexed: 11/28/2022] Open
Abstract
Voltage-gated potassium (Kv) currents generated by N-type α-subunit homotetramers inactivate rapidly because an N-terminal ball domain blocks the channel pore after activation. Hence, the inactivation rate of heterotetrameric channels comprising both N-type and non-N-type (delayed rectifier) α-subunits depends upon the number of N-type α-subunits in the complex. As Kv channel inactivation and inactivation recovery rates regulate cellular excitability, the composition and expression of these heterotetrameric complexes are expected to be tightly regulated. In a companion article, we showed that the single transmembrane segment ancillary (β) subunits KCNE1 and KCNE2 suppress currents generated by homomeric Kv1.4, Kv3.3, and Kv3.4 channels, by trapping them early in the secretory pathway. Here, we show that this trapping is prevented by coassembly of the N-type α-subunits with intra-subfamily delayed rectifier α-subunits. Extra-subfamily delayed rectifier α-subunits, regardless of their capacity to interact with KCNE1 and KCNE2, cannot rescue Kv1.4 or Kv3.4 surface expression unless engineered to interact with them using N-terminal A and B domain swapping. The KCNE1/2-enforced checkpoint ensures N-type α-subunits only reach the cell surface as part of intra-subfamily mixed-α complexes, thereby governing channel composition, inactivation rate, and-by extension-cellular excitability.
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Affiliation(s)
- Vikram A Kanda
- Department of Pharmacology, Weill Medical College of Cornell University, New York, New York, USA
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30
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Wissinger B, Schaich S, Baumann B, Bonin M, Jägle H, Friedburg C, Varsányi B, Hoyng CB, Dollfus H, Heckenlively JR, Rosenberg T, Rudolph G, Kellner U, Salati R, Plomp A, De Baere E, Andrassi-Darida M, Sauer A, Wolf C, Zobor D, Bernd A, Leroy BP, Enyedi P, Cremers FP, Lorenz B, Zrenner E, Kohl S. Large deletions of theKCNV2gene are common in patients with cone dystrophy with supernormal rod response. Hum Mutat 2011; 32:1398-406. [DOI: 10.1002/humu.21580] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2010] [Accepted: 07/11/2011] [Indexed: 11/11/2022]
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31
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Cooper EC. Made for "anchorin": Kv7.2/7.3 (KCNQ2/KCNQ3) channels and the modulation of neuronal excitability in vertebrate axons. Semin Cell Dev Biol 2011; 22:185-92. [PMID: 20940059 PMCID: PMC3070838 DOI: 10.1016/j.semcdb.2010.10.001] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2010] [Revised: 09/30/2010] [Accepted: 10/01/2010] [Indexed: 12/13/2022]
Abstract
Kv7.2 and Kv7.3 (encoded by KCNQ2 and KCNQ3) are homologous subunits forming a widely expressed neuronal voltage-gated K(+) (Kv) channel. Hypomorphic mutations in either KCNQ2 or KCNQ3 cause a highly penetrant, though transient, human phenotype-epilepsy during the first months of life. Some KCNQ2 mutations also cause involuntary muscle rippling, or myokymia, which is indicative of motoneuron axon hyperexcitability. Kv7.2 and Kv7.3 are concentrated at axonal initial segments (AISs), and at nodes of Ranvier in the central and peripheral nervous system. Kv7.2 and Kv7.3 share a novel ∼80 residue C-terminal domain bearing an "anchor" motif, which interacts with ankyrin-G and is required for channel AIS (and likely, nodal) localization. This domain includes the sequence IAEGES/TDTD, which is analogous (not homologous) to the ankyrin-G interaction motif of voltage-gated Na(+) (Na(V)) channels. The KCNQ subfamily is evolutionarily ancient, with two genes (KCNQ1 and KCNQ5) persisting as orthologues in extant bilaterian animals from worm to man. However, KCNQ2 and KCNQ3 arose much more recently, in the interval between the divergence of extant jawless and jawed vertebrates. This is precisely the interval during which myelin and saltatory conduction evolved. The natural selection for KCNQ2 and KCNQ3 appears to hinge on these subunits' unique ability to be coordinately localized with Na(V) channels by ankyrin-G, and the resulting enhancement in the reliability of neuronal excitability.
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Affiliation(s)
- Edward C Cooper
- Neurology and Neuroscience, Baylor College of Medicine, Houston, TX 77030, United States.
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32
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Kinesin I transports tetramerized Kv3 channels through the axon initial segment via direct binding. J Neurosci 2010; 30:15987-6001. [PMID: 21106837 DOI: 10.1523/jneurosci.3565-10.2010] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Precise targeting of various voltage-gated ion channels to proper membrane domains is crucial for their distinct roles in neuronal excitability and synaptic transmission. How each channel protein is transported within the cytoplasm is poorly understood. Here, we report that KIF5/kinesin I transports Kv3.1 voltage-gated K(+) (Kv) channels through the axon initial segment (AIS) via direct binding. First, we have identified a novel interaction between Kv3.1 and KIF5, confirmed by immunoprecipitation from mouse brain lysates and by pull-down assays with exogenously expressed proteins. The interaction is mediated by a direct binding between the Kv3.1 N-terminal T1 domain and a conserved region in KIF5 tail domains, in which proper T1 tetramerization is crucial. Overexpression of this region of KIF5B markedly reduces axonal levels of Kv3.1bHA. In mature hippocampal neurons, endogenous Kv3.1b and KIF5 colocalize. Suppressing the endogenous KIF5B level by RNA interference significantly reduces the Kv3.1b axonal level. Furthermore, mutating the Zn(2+)-binding site within T1 markedly decreases channel axonal targeting and forward trafficking, likely through disrupting T1 tetramerization and hence eliminating the binding to KIF5 tail. The mutation also alters channel activity. Interestingly, coexpression of the YFP (yellow fluorescent protein)-tagged KIF5B assists dendritic Kv3.1a and even mutants with a faulty axonal targeting motif to penetrate the AIS. Finally, fluorescently tagged Kv3.1 channels colocalize and comove with KIF5B along axons revealed by two-color time-lapse imaging. Our findings suggest that the binding to KIF5 ensures properly assembled and functioning Kv3.1 channels to be transported into axons.
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33
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Liang P, Chen H, Cui Y, Lei L, Wang K. Functional rescue of Kv4.3 channel tetramerization mutants by KChIP4a. Biophys J 2010; 98:2867-76. [PMID: 20550899 DOI: 10.1016/j.bpj.2010.03.044] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2009] [Revised: 03/12/2010] [Accepted: 03/15/2010] [Indexed: 11/16/2022] Open
Abstract
KChIP4a shows a high homology with other members of the family of Kv channel-interacting proteins (KChIPs) in the conserved C-terminal core region, but exhibits a unique modulation of Kv4 channel gating and surface expression. Unlike KChIP1, the KChIP4 splice variant KChIP4a has been shown to inhibit surface expression and function as a suppressor of channel inactivation of Kv4. In this study, we sought to determine whether the multitasking KChIP4a modulates Kv4 function in a clamping fashion similar to that shown by KChIP1. Injection of Kv4.3 T1 zinc mutants into Xenopus oocytes resulted in the nonfunctional expression of Kv4.3 channels. Coexpression of Kv4.3 zinc mutants with WT KChIP4a gave rise to the functional expression of Kv4.3 current. Oocyte surface labeling results confirm the correlation between functional rescue and enhanced surface expression of zinc mutant proteins. Chimeric mutations that replace the Kv4.3 N-terminus with N-terminal KChIP4a or N-terminal deletion of KChIP4a further demonstrate that the functional rescue of Kv4.3 channel tetramerization mutants depends on the KChIP4a core region, but not its N-terminus. Structure-guided mutation of two critical residues of core KChIP4a attenuated functional rescue and tetrameric assembly. Moreover, size exclusion chromatography combined with fast protein liquid chromatography showed that KChIP4a can drive zinc mutant monomers to assemble as tetramers. Taken together, our results show that KChIP4a can rescue the function of tetramerization-defective Kv4 monomers. Therefore, we propose that core KChIP4a functions to promote tetrameric assembly and enhance surface expression of Kv4 channels by a clamping action, whereas its N-terminus inhibits surface expression of Kv4 by a mechanism that remains elusive.
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Affiliation(s)
- Ping Liang
- Department of Neurobiology, Neuroscience Research Institute, Peking University Health Science Center, Beijing, China
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34
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Lebaudy A, Pascaud F, Véry AA, Alcon C, Dreyer I, Thibaud JB, Lacombe B. Preferential KAT1-KAT2 heteromerization determines inward K+ current properties in Arabidopsis guard cells. J Biol Chem 2009; 285:6265-74. [PMID: 20040603 DOI: 10.1074/jbc.m109.068445] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Guard cells adjust their volume by changing their ion content due to intense fluxes that, for K(+), are believed to flow through inward or outward Shaker channels. Because Shaker channels can be homo- or heterotetramers and Arabidopsis guard cells express at least five genes encoding inward Shaker subunits, including the two major ones, KAT1 and KAT2, the molecular identity of inward Shaker channels operating therein is not yet completely elucidated. Here, we first addressed the properties of KAT1-KAT2 heteromers by expressing KAT1-KAT2 tandems in Xenopus oocytes. Then, computer analyses of the data suggested that coexpression of free KAT1 and KAT2 subunits resulted mainly in heteromeric channels made of two subunits of each type due to some preferential association of KAT1-KAT2 heterodimers at the first step of channel assembly. This was further supported by the analysis of KAT2 effect on KAT1 targeting in tobacco cells. Finally, patch-clamp recordings of native inward channels in wild-type and mutant genotypes strongly suggested that this preferential heteromerization occurs in planta and that Arabidopsis guard cell inward Shaker channels are mainly heteromers of KAT1 and KAT2 subunits.
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Affiliation(s)
- Anne Lebaudy
- Biochimie et Physiologie Moléculaire des Plantes, CNRS UMR 5004, Institut National de la Recherche Agronomique U386, Montpellier SupAgro, Université Montpellier II, Place Viala, 34060 Montpellier Cedex, France
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35
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Burg ED, Platoshyn O, Tsigelny IF, Lozano-Ruiz B, Rana BK, Yuan JXJ. Tetramerization domain mutations in KCNA5 affect channel kinetics and cause abnormal trafficking patterns. Am J Physiol Cell Physiol 2009; 298:C496-509. [PMID: 20018952 DOI: 10.1152/ajpcell.00464.2009] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The activity of voltage-gated K(+) (K(V)) channels plays an important role in regulating pulmonary artery smooth muscle cell (PASMC) contraction, proliferation, and apoptosis. The highly conserved NH(2)-terminal tetramerization domain (T1) of K(V) channels is important for proper channel assembly, association with regulatory K(V) beta-subunits, and localization of the channel to the plasma membrane. We recently reported two nonsynonymous mutations (G182R and E211D) in the KCNA5 gene of patients with idiopathic pulmonary arterial hypertension, which localize to the T1 domain of KCNA5. To study the electrophysiological properties and expression patterns of the mutants compared with the wild-type (WT) channel in vitro, we transfected HEK-293 cells with WT KCNA5, G182R, E211D, or the double mutant G182R/E211D channel. The mutants form functional channels; however, whole cell current kinetic differences between WT and mutant channels exist. Steady-state inactivation curves of the G182R and G182R/E211D channels reveal accelerated inactivation; the mutant channels inactivated at more hyperpolarized potentials compared with the WT channel. Channel protein expression was also decreased by the mutations. Compared with the WT channel, which was present in its mature glycosylated form, the mutant channels are present in greater proportion in their immature form in HEK-293 cells. Furthermore, G182R protein level is greatly reduced in COS-1 cells compared with WT. Immunostaining data support the hypothesis that, while WT protein localizes to the plasma membrane, mutant protein is mainly retained in intracellular packets. Overall, these data support a role for the T1 domain in channel kinetics as well as in KCNA5 channel subcellular localization.
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Affiliation(s)
- Elyssa D Burg
- Dept. of Medicine, Univ. of California, San Diego, 9500 Gilman Dr., MC 0725, La Jolla, CA 92093-0725, USA
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36
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Age-dependent axonal expression of potassium channel proteins during development in mouse hippocampus. Histochem Cell Biol 2009; 133:301-12. [DOI: 10.1007/s00418-009-0668-z] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/24/2009] [Indexed: 10/20/2022]
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37
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Yuchi Z, Pau VPT, Lu BX, Junop M, Yang DSC. An engineered right-handed coiled coil domain imparts extreme thermostability to the KcsA channel. FEBS J 2009; 276:6236-46. [PMID: 19780836 DOI: 10.1111/j.1742-4658.2009.07327.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
KcsA, a potassium channel from Streptomyces lividans, was the first ion channel to have its transmembrane domain structure determined by crystallography. Previously we have shown that its C-terminal cytoplasmic domain is crucial for the thermostability and the expression of the channel. Expression was almost abolished in its absence, but could be rescued by the presence of an artificial left-handed coiled coil tetramerization domain GCN4. In this study, we noticed that the handedness of GCN4 is not the same as the bundle crossing of KcsA. Therefore, a compatible right-handed coiled coil structure was identified from the Protein Data Bank and used to replace the C-terminal domain of KcsA. The hybrid channel exhibited a higher expression level than the wild-type and is extremely thermostable. Surprisingly, this stable hybrid channel is equally active as the wild-type channel in conducting potassium ions through a lipid bilayer at an acidic pH. We suggest that a similar engineering strategy could be applied to other ion channels for both functional and structural studies.
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Affiliation(s)
- Zhiguang Yuchi
- Department of Biochemistry and Biomedical Sciences, Faculty of Health Sciences, McMaster University, Hamilton, Canada
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38
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Bocksteins E, Labro AJ, Mayeur E, Bruyns T, Timmermans JP, Adriaensen D, Snyders DJ. Conserved negative charges in the N-terminal tetramerization domain mediate efficient assembly of Kv2.1 and Kv2.1/Kv6.4 channels. J Biol Chem 2009; 284:31625-34. [PMID: 19717558 DOI: 10.1074/jbc.m109.039479] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Voltage-gated potassium (Kv) channels are transmembrane tetramers of individual alpha-subunits. Eight different Shaker-related Kv subfamilies have been identified in which the tetramerization domain T1, located on the intracellular N terminus, facilitates and controls the assembly of both homo- and heterotetrameric channels. Only the Kv2 alpha-subunits are able to form heterotetramers with members of the silent Kv subfamilies (Kv5, Kv6, Kv8, and Kv9). The T1 domain contains two subdomains, A and B box, which presumably determine subfamily specificity by preventing incompatible subunits to assemble. In contrast, little is known about the involvement of the A/B linker sequence. Both Kv2 and silent Kv subfamilies contain a fully conserved and negatively charged sequence (CDD) in this linker that is lacking in the other subfamilies. Neutralizing these aspartates in Kv2.1 by mutating them to alanines did not affect the gating properties, but reduced the current density moderately. However, charge reversal arginine substitutions strongly reduced the current density of these homotetrameric mutant Kv2.1 channels and immunocytochemistry confirmed the reduced expression at the plasma membrane. Förster resonance energy transfer measurements using confocal microscopy showed that the latter was not due to impaired trafficking, but to a failure to assemble the tetramer. This was further confirmed with co-immunoprecipitation experiments. The corresponding arginine substitution in Kv6.4 prevented its heterotetrameric interaction with Kv2.1. These results indicate that these aspartates (especially the first one) in the A/B box linker of the T1 domain are required for efficient assembly of both homotetrameric Kv2.1 and heterotetrameric Kv2.1/silent Kv6.4 channels.
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Affiliation(s)
- Elke Bocksteins
- Department of Biomedical Sciences, Laboratory for Molecular Biophysics, Physiology and Pharmacology, University of Antwerp, CDE, Universiteitsplein 1, 2610 Antwerp, Belgium
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39
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Tertiary interactions within the ribosomal exit tunnel. Nat Struct Mol Biol 2009; 16:405-11. [PMID: 19270700 PMCID: PMC2670549 DOI: 10.1038/nsmb.1571] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2008] [Accepted: 01/30/2009] [Indexed: 11/21/2022]
Abstract
Although tertiary folding of whole protein domains is prohibited by the cramped dimensions of the ribosomal tunnel, dynamic tertiary interactions may permit folding of small elementary units within the tunnel. To probe this possibility, we used a β-hairpin as well as an α-helical hairpin from the cytosolic N-terminus of a voltage-gated potassium channel and determined a probability of folding for each at defined locations inside and outside the tunnel. Minimalist tertiary structures can form near the exit port of the tunnel, a region that provides an entropic window for initial exploration of local peptide conformations. Tertiary subdomains of the nascent peptide fold sequentially, but not independently, during translation. These studies offer an approach for diagnosing the molecular basis for folding defects that lead to protein malfunction and provide insight into the role of the ribosome during early potassium channel biogenesis.
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Mederos Y Schnitzler M, Rinné S, Skrobek L, Renigunta V, Schlichthörl G, Derst C, Gudermann T, Daut J, Preisig-Müller R. Mutation of histidine 105 in the T1 domain of the potassium channel Kv2.1 disrupts heteromerization with Kv6.3 and Kv6.4. J Biol Chem 2008; 284:4695-704. [PMID: 19074135 DOI: 10.1074/jbc.m808786200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The voltage-activated K(+) channel subunit Kv2.1 can form heterotetramers with members of the Kv6 subfamily, generating channels with biophysical properties different from homomeric Kv2.1 channels. The N-terminal tetramerization domain (T1) has been shown previously to play a role in Kv channel assembly, but the mechanisms controlling specific heteromeric assembly are still unclear. In Kv6.x channels the histidine residue of the zinc ion-coordinating C3H1 motif of Kv2.1 is replaced by arginine or valine. Using a yeast two-hybrid assay, we found that substitution of the corresponding histidine 105 in Kv2.1 by valine (H105V) or arginine (H105R) disrupted the interaction of the T1 domain of Kv2.1 with the T1 domains of both Kv6.3 and Kv6.4, whereas interaction of the T1 domain of Kv2.1 with itself was unaffected by this mutation. Using fluorescence resonance energy transfer (FRET), interaction could be detected between the subunits Kv2.1/Kv2.1, Kv2.1/Kv6.3, and Kv2.1/Kv6.4. Reduced FRET signals were obtained after co-expression of Kv2.1(H105V) or Kv2.1(H105R) with Kv6.3 or Kv6.4. Wild-type Kv2.1 but not Kv2.1(H105V) could be co-immunoprecipitated with Kv6.4. Co-expression of dominant-negative mutants of Kv6.3 reduced the current produced Kv2.1, but not of Kv2.1(H105R) mutants. Co-expression of Kv6.3 or Kv6.4 with wt Kv2.1 but not with Kv2.1(H105V) or Kv2.1(H105R) changed the voltage dependence of activation of the channels. Our results suggest that His-105 in the T1 domain of Kv2.1 is required for functional heteromerization with members of the Kv6 subfamily. We conclude from our findings that Kv2.1 and Kv6.x subunits have complementary T1 domains that control selective heteromerization.
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Ionic channel function in action potential generation: current perspective. Mol Neurobiol 2008; 35:129-50. [PMID: 17917103 DOI: 10.1007/s12035-007-8001-0] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2006] [Revised: 11/30/1999] [Accepted: 11/10/2006] [Indexed: 10/23/2022]
Abstract
Over 50 years ago, Hodgkin and Huxley laid down the foundations of our current understanding of ionic channels. An impressive progress has been made during the following years that culminated in the revelation of the details of potassium channel structure. Nevertheless, even today, we cannot separate well currents recorded in central mammalian neurons. Many modern concepts about the function of sodium and potassium currents are based on experiments performed in nonmammalian cells. The recent recognition of the fast delayed rectifier current indicates that we need to reevaluate the biophysical role of sodium and potassium currents. This review will consider high quality voltage clamp data obtained from the soma of central mammalian neurons in the view of our current knowledge about proteins forming ionic channels. Fast sodium currents and three types of outward potassium currents, the delayed rectifier, the subthreshold A-type, and the D-type potassium currents, are discussed here. An updated current classification with biophysical role of each current subtype is provided. This review shows that details of kinetics of both sodium and outward potassium currents differ significantly from the classical descriptions and these differences may be of functional significance.
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Covarrubias M, Bhattacharji A, De Santiago-Castillo JA, Dougherty K, Kaulin YA, Na-Phuket TR, Wang G. The neuronal Kv4 channel complex. Neurochem Res 2008; 33:1558-67. [PMID: 18357523 DOI: 10.1007/s11064-008-9650-8] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2007] [Accepted: 03/04/2008] [Indexed: 01/31/2023]
Abstract
Kv4 channel complexes mediate the neuronal somatodendritic A-type K(+) current (I(SA)), which plays pivotal roles in dendritic signal integration. These complexes are composed of pore-forming voltage-gated alpha-subunits (Shal/Kv4) and at least two classes of auxiliary beta-subunits: KChIPs (K(+)-Channel-Interacting-Proteins) and DPLPs (Dipeptidyl-Peptidase-Like-Proteins). Here, we review our investigations of Kv4 gating mechanisms and functional remodeling by specific auxiliary beta-subunits. Namely, we have concluded that: (1) the Kv4 channel complex employs novel alternative mechanisms of closed-state inactivation; (2) the intracellular Zn(2+) site in the T1 domain undergoes a conformational change tightly coupled to voltage-dependent gating and is targeted by nitrosative modulation; and (3) discrete and specific interactions mediate the effects of KChIPs and DPLPs on activation, inactivation and permeation of Kv4 channels. These studies are shedding new light on the molecular bases of I(SA) function and regulation.
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Affiliation(s)
- Manuel Covarrubias
- Department of Pathology, Anatomy and Cell Biology, Jefferson Medical College of Thomas Jefferson University, 1020 Locust Street, JAH 245, Philadelphia, PA 19107, USA.
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Potapova IA, Cohen IS, Doronin SV. Voltage-gated ion channel Kv4.3 is associated with Rap guanine nucleotide exchange factors and regulates angiotensin receptor type 1 signaling to small G-protein Rap. FEBS J 2007; 274:4375-84. [PMID: 17725712 DOI: 10.1111/j.1742-4658.2007.05966.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The voltage-gated potassium channel Kv4.3 was coexpressed with its beta-subunit Kv channel-interacting protein 2 and the angiotensin type 1 receptor in HEK-293 cells. Proteomic analysis of proteins coimmunoprecipitated with Kv4.3 revealed that Kv4.3 is associated with Rap guanine nucleotide exchange factors MR-GEF and EPAC-1. Previously, we demonstrated that Kv4.3 interacts with the angiotensin type 1 receptor in HE293 cells and cardiac myocytes. On the basis of this, we investigated the angiotensin type 1 receptor signaling to small G-proteins Ras and Rap-1 in the presence and absence of the Kv4.3-Kv channel-interacting protein 2 macromolecular complex. Ras activation was not significantly affected by coexpression of Kv4.3 and Kv channel-interacting protein 2. Ras exhibited a rapid activation-inactivation pattern with maximum activity at 2.5 min after addition of angiotensin II. In contrast, activation of Rap-1 was affected dramatically by coexpression of Kv4.3 and Kv channel-interacting protein 2 with the angiotensin type 1 receptor. In the absence of Kv4.3 and Kv channel-interacting protein 2, stimulation of the angiotensin type 1 receptor resulted in steady activation of Rap-1 that reached a plateau 25 min after addition of angiotensin II. In the presence of Kv4.3 and Kv channel-interacting protein 2, Rap-1 reaches a maximum activity 2.5 min after addition of angiotensin II and then deactivates rapidly, demonstrating a pattern of activation similar to that of Ras. Our findings show that Kv4.3 regulates angiotensin type 1 receptor signaling to the small G-protein Rap-1.
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Affiliation(s)
- Irina A Potapova
- Department of Physiology and Biophysics, Institute of Molecular Cardiology, State University of New York at Stony Brook, Stony Brook, NY 11794, USA
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Sokolov MV, Shamotienko O, Dhochartaigh SN, Sack JT, Dolly JO. Concatemers of brain Kv1 channel alpha subunits that give similar K+ currents yield pharmacologically distinguishable heteromers. Neuropharmacology 2007; 53:272-82. [PMID: 17637465 DOI: 10.1016/j.neuropharm.2007.05.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2007] [Revised: 04/16/2007] [Accepted: 05/15/2007] [Indexed: 01/06/2023]
Abstract
At least five subtypes of voltage-gated (Kv1) channels occur in neurons as tetrameric combinations of different alpha subunits. Their involvement in controlling cell excitability and synaptic transmission make them potential targets for neurotherapeutics. As a prerequisite for this, we established herein how the characteristics of hetero-oligomeric K(+) channels can be influenced by alpha subunit composition. Since the three most prevalent Kv1 subunits in brain are Kv1.2, 1.1 and 1.6, new Kv1.6-1.2 and Kv1.1-1.2 concatenated constructs in pIRES-EGFP were stably expressed in HEK cells and the biophysical plus pharmacological properties of their K(+) currents determined relative to those for the requisite homo-tetramers. These heteromers yielded delayed-rectifier type K(+) currents whose activation, deactivation and inactivation parameters are fairly similar although substituting Kv1.1 with Kv1.6 led to a small negative shift in the conductance-voltage relationship, a direction unexpected from the characteristics of the parental homo-tetramers. Changes resulting from swapping Kv1.6 for Kv1.1 in the concatemers were clearly discerned with two pharmacological agents, as measured by inhibition of the K(+) currents and Rb(+) efflux. alphaDendrotoxin and 4-aminopyridine gave a similar blockade of both hetero-tetramers, as expected. Most important for pharmacological dissection of channel subtypes, dendrotoxin(k) and tetraethylammonium readily distinguished the susceptible Kv1.1-1.2 containing oligomers from the resistant Kv1.6-1.2 channels. Moreover, the discriminating ability of dendrotoxin(k) was further confirmed by its far greater ability to displace (125)I-labelled alphadendrotoxin binding to Kv1.1-1.2 than Kv1.6-1.2 channels. Thus, due to the profiles of these two channel subtypes being found to differ, it seems that only multimers corresponding to those present in the nervous system provide meaningful targets for drug development.
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Affiliation(s)
- Maxim V Sokolov
- International Centre for Neurotherapeutics, Dublin City University, Glasnevin, Dublin 9, Ireland
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Phartiyal P, Jones EMC, Robertson GA. Heteromeric assembly of human ether-à-go-go-related gene (hERG) 1a/1b channels occurs cotranslationally via N-terminal interactions. J Biol Chem 2007; 282:9874-9882. [PMID: 17272276 DOI: 10.1074/jbc.m610875200] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Alternate transcripts of the human ether-à-go-go-related gene (hERG1) encode two subunits, hERG 1a and 1b, which form potassium channels regulating cardiac repolarization, neuronal firing frequency, and neoplastic cell growth. The 1a and 1b subunits are identical except for their unique, cytoplasmic N termini, and they readily co-assemble in heterologous and native systems. We tested the hypothesis that interactions of nascent N termini promote heteromeric assembly of 1a and 1b subunits. We found that 1a and 1b N-terminal fragments bind in a direct and dose-dependent manner. hERG1 hetero-oligomerization occurs in the endoplasmic reticulum where co-expression of N-terminal fragments with hERG1 subunits disrupted oligomerization and core glycosylation. The disruption of core glycosylation, a cotranslational event, allows us to pinpoint these N-terminal interactions to the earliest steps in biogenesis. Thus, N-terminal interactions mediate hERG 1a/1b assembly, a process whose perturbation may represent a new mechanism for disease.
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Affiliation(s)
- Pallavi Phartiyal
- Department of Physiology, University of Wisconsin, Madison, Wisconsin 53711; Cellular and Molecular Biology Program, University of Wisconsin, Madison, Wisconsin 53711
| | - Eugenia M C Jones
- Department of Physiology, University of Wisconsin, Madison, Wisconsin 53711
| | - Gail A Robertson
- Department of Physiology, University of Wisconsin, Madison, Wisconsin 53711.
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Xicluna J, Lacombe B, Dreyer I, Alcon C, Jeanguenin L, Sentenac H, Thibaud JB, Chérel I. Increased functional diversity of plant K+ channels by preferential heteromerization of the shaker-like subunits AKT2 and KAT2. J Biol Chem 2007; 282:486-94. [PMID: 17085433 DOI: 10.1074/jbc.m607607200] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Assembly of plant Shaker subunits as heterotetramers, increasing channel functional diversity, has been reported. Here we focus on a new interaction, between AKT2 and KAT2 subunits. The assembly as AKT2/KAT2 heterotetramers is demonstrated by (i) a strong signal in two-hybrid tests with intracytoplasmic C-terminal regions, (ii) the effect of KAT2 on AKT2 subunit targeting in tobacco cells, (iii) the complete inhibition of AKT2 currents by co-expression with a dominant-negative KAT2 subunit in Xenopus oocytes, and reciprocally, and (iv) the appearance, upon co-expression of wild-type AKT2 and KAT2 subunits, of new channel functional properties that cannot be explained by the co-existence of two kinds of homotetrameric channels. In particular, the instantaneous current, characteristic of AKT2, displayed new functional features when compared with those of AKT2 homotetramers: activation by external acidification (instead of inhibition) and weak inhibition by calcium. Single channel current measurements in oocytes co-expressing AKT2 and KAT2 revealed a strong preference for incorporation of subunits into heteromultimers and a diversity of individual channels. In planta, these new channels, which may undergo specific regulations, are likely to be formed in guard cells and in the phloem, where they could participate in the control of membrane potential and potassium fluxes.
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Affiliation(s)
- Jérôme Xicluna
- Laboratoire de Biochimie et Physiologie Moléculaire des Plantes, UMR 5004 Agro-Montpellier/Centre National de la Recherche Scientifique/Institut National de la Recherche Agronomique/Université Montpellier II, Place Viala, 34060 Montpellier Cedex 1, France
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Wang G, Covarrubias M. Voltage-dependent gating rearrangements in the intracellular T1-T1 interface of a K+ channel. ACTA ACUST UNITED AC 2006; 127:391-400. [PMID: 16533897 PMCID: PMC2151515 DOI: 10.1085/jgp.200509442] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
The intracellular tetramerization domain (T1) of most eukaryotic voltage-gated potassium channels (Kv channels) exists as a “hanging gondola” below the transmembrane regions that directly control activation gating via the electromechanical coupling between the S4 voltage sensor and the main S6 gate. However, much less is known about the putative contribution of the T1 domain to Kv channel gating. This possibility is mechanistically intriguing because the T1–S1 linker connects the T1 domain to the voltage-sensing domain. Previously, we demonstrated that thiol-specific reagents inhibit Kv4.1 channels by reacting in a state-dependent manner with native Zn2+ site thiolate groups in the T1–T1 interface; therefore, we concluded that the T1–T1 interface is functionally active and not protected by Zn2+ (Wang, G., M. Shahidullah, C.A. Rocha, C. Strang, P.J. Pfaffinger, and M. Covarrubias. 2005. J. Gen. Physiol. 126:55–69). Here, we co-expressed Kv4.1 channels and auxiliary subunits (KChIP-1 and DPPX-S) to investigate the state and voltage dependence of the accessibility of MTSET to the three interfacial cysteines in the T1 domain. The results showed that the average MTSET modification rate constant (kMTSET) is dramatically enhanced in the activated state relative to the resting and inactivated states (∼260- and ∼47-fold, respectively). Crucially, under three separate conditions that produce distinct activation profiles, kMTSET is steeply voltage dependent in a manner that is precisely correlated with the peak conductance–voltage relations. These observations strongly suggest that Kv4 channel gating is tightly coupled to voltage-dependent accessibility changes of native T1 cysteines in the intersubunit Zn2+ site. Furthermore, cross-linking of cysteine pairs across the T1–T1 interface induced substantial inhibition of the channel, which supports the functionally dynamic role of T1 in channel gating. Therefore, we conclude that the complex voltage-dependent gating rearrangements of eukaryotic Kv channels are not limited to the membrane-spanning core but must include the intracellular T1–T1 interface. Oxidative stress in excitable tissues may perturb this interface to modulate Kv4 channel function.
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Affiliation(s)
- Guangyu Wang
- Department of Pathology, Anatomy, and Cell Biology, Jefferson Medical College of Thomas Jefferson University, Philadelphia, PA 19107, USA
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Gordon E, Roepke TK, Abbott GW. Endogenous KCNE subunits govern Kv2.1 K+ channel activation kinetics in Xenopus oocyte studies. Biophys J 2005; 90:1223-31. [PMID: 16326911 PMCID: PMC1367273 DOI: 10.1529/biophysj.105.072504] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Kv2.1 is a voltage-gated potassium (Kv) channel that generates delayed rectifier currents in mammalian heart and brain. The biophysical properties of Kv2.1 and other ion channels have been characterized by functional expression in heterologous systems, and most commonly in Xenopus laevis oocytes. A number of previous oocyte-based studies of mammalian potassium channels have revealed expression-level-dependent changes in channel properties, leading to the suggestion that endogenous oocyte factors regulate channel gating. Here, we show that endogenous oocyte potassium channel KCNE ancillary subunits xMinK and xMiRP2 slow the activation of oocyte-expressed mammalian Kv2.1 channels two-to-fourfold. This produces a sigmoidal relationship between Kv2.1 current density and activation rate in oocyte-based two-electrode voltage clamp studies. The effect of endogenous xMiRP2 and xMinK on Kv2.1 activation is diluted at high Kv2.1 expression levels, or by RNAi knockdown of either endogenous subunit. RNAi knockdown of both xMiRP2 and xMinK eliminates the correlation between Kv2.1 expression level and activation kinetics. The data demonstrate a molecular basis for expression-level-dependent changes in Kv channel gating observed in heterologous expression studies.
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Affiliation(s)
- Earl Gordon
- Greenberg Division of Cardiology, Department of Medicine, Cornell University, Weill Medical College, New York 10021, USA
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Shin JB, Adams D, Paukert M, Siba M, Sidi S, Levin M, Gillespie PG, Gründer S. Xenopus TRPN1 (NOMPC) localizes to microtubule-based cilia in epithelial cells, including inner-ear hair cells. Proc Natl Acad Sci U S A 2005; 102:12572-7. [PMID: 16116094 PMCID: PMC1194908 DOI: 10.1073/pnas.0502403102] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In vertebrates, the senses of hearing and balance depend on hair cells, which transduce sounds with their hair bundles, containing actin-based stereocilia and microtubule-based kinocilia. A longstanding question in auditory science is the identity of the mechanically sensitive transduction channel of hair cells, thought to be localized at the tips of their stereocilia. Experiments in zebrafish implicated the transient receptor potential (TRP) channel NOMPC (drTRPN1) in this role; TRPN1 is absent from the genomes of higher vertebrates, however, and has not been localized in hair cells. Another candidate for the transduction channel, TRPA1, apparently is required for transduction in mammalian and nonmammalian vertebrates. This discrepancy raises the question of the relative contribution of TRPN1 and TRPA1 to transduction in nonmammalian vertebrates. To address this question, we cloned the TRPN1 ortholog from the amphibian Xenopus laevis, generated an antibody against the protein, and determined the protein's cellular and subcellular localization. We found that TRPN1 is prominently located in lateral-line hair cells, auditory hair cells, and ciliated epidermal cells of developing Xenopus embryos. In ciliated epidermal cells TRPN1 staining was enriched at the tips and bases of the cilia. In saccular hair cells, TRPN1 was located prominently in the kinocilial bulb, a component of the mechanosensory hair bundles. Moreover, we observed redistribution of TRPN1 upon treatment of hair cells with calcium chelators, which disrupts the transduction apparatus. This result suggests that although TRPN1 is unlikely to be the transduction channel of stereocilia, it plays an essential role, functionally related to transduction, in the kinocilium.
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Affiliation(s)
- Jung-Bum Shin
- Oregon Hearing Research Center and Vollum Institute, Portland, OR 97239, USA
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Ottschytsch N, Raes AL, Timmermans JP, Snyders DJ. Domain analysis of Kv6.3, an electrically silent channel. J Physiol 2005; 568:737-47. [PMID: 16096342 PMCID: PMC1464172 DOI: 10.1113/jphysiol.2005.090142] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The subunit Kv6.3 encodes a voltage-gated potassium channel belonging to the group of electrically silent Kv subunits, i.e. subunits that do not form functional homotetrameric channels. The lack of current, caused by retention in the endoplasmic reticulum (ER), was overcome by coexpression with Kv2.1. To investigate whether a specific section of Kv6.3 was responsible for ER retention, we constructed chimeric subunits between Kv6.3 and Kv2.1, and analysed their subcellular localization and functionality. The results demonstrate that the ER retention of Kv6.3 is not caused by the N-terminal A and B box (NAB) domain nor the intracellular N- or C-termini, but rather by the S1-S6 core protein. Introduction of individual transmembrane segments of Kv6.3 in Kv2.1 was tolerated, with the exception of S6. Indeed, introduction of the S6 domain of Kv6.3 in Kv2.1 was enough to cause ER retention, which was due to the C-terminal section of S6. The S4 segment of Kv6.3 could act as a voltage sensor in the Kv2.1 context, albeit with a major hyperpolarizing shift in the voltage dependence of activation and inactivation, apparently caused by the presence of a tyrosine in Kv6.3 instead of a conserved arginine. This study suggests that the silent behaviour of Kv6.3 is largely caused by the C-terminal part of its sixth transmembrane domain that causes ER retention of the subunit.
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Affiliation(s)
- Natacha Ottschytsch
- Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp (CDE), Universiteitsplein 1, T4.21, 2610 Antwerp, Belgium
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