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Sampedro-Castañeda M, Baltussen LL, Lopes AT, Qiu Y, Sirvio L, Mihaylov SR, Claxton S, Richardson JC, Lignani G, Ultanir SK. Epilepsy-linked kinase CDKL5 phosphorylates voltage-gated calcium channel Cav2.3, altering inactivation kinetics and neuronal excitability. Nat Commun 2023; 14:7830. [PMID: 38081835 PMCID: PMC10713615 DOI: 10.1038/s41467-023-43475-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2023] [Accepted: 11/09/2023] [Indexed: 12/18/2023] Open
Abstract
Developmental and epileptic encephalopathies (DEEs) are a group of rare childhood disorders characterized by severe epilepsy and cognitive deficits. Numerous DEE genes have been discovered thanks to advances in genomic diagnosis, yet putative molecular links between these disorders are unknown. CDKL5 deficiency disorder (CDD, DEE2), one of the most common genetic epilepsies, is caused by loss-of-function mutations in the brain-enriched kinase CDKL5. To elucidate CDKL5 function, we looked for CDKL5 substrates using a SILAC-based phosphoproteomic screen. We identified the voltage-gated Ca2+ channel Cav2.3 (encoded by CACNA1E) as a physiological target of CDKL5 in mice and humans. Recombinant channel electrophysiology and interdisciplinary characterization of Cav2.3 phosphomutant mice revealed that loss of Cav2.3 phosphorylation leads to channel gain-of-function via slower inactivation and enhanced cholinergic stimulation, resulting in increased neuronal excitability. Our results thus show that CDD is partly a channelopathy. The properties of unphosphorylated Cav2.3 closely resemble those described for CACNA1E gain-of-function mutations causing DEE69, a disorder sharing clinical features with CDD. We show that these two single-gene diseases are mechanistically related and could be ameliorated with Cav2.3 inhibitors.
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Affiliation(s)
| | - Lucas L Baltussen
- Kinases and Brain Development Lab, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
- Laboratory for the Research of Neurodegenerative Diseases (VIB-KU Leuven), Department of Neurosciences, ON5 Herestraat 49, 3000, Leuven, Belgium
| | - André T Lopes
- Kinases and Brain Development Lab, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
| | - Yichen Qiu
- Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, Queen Square House, London, WC1N 3BG, UK
| | - Liina Sirvio
- Kinases and Brain Development Lab, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
| | - Simeon R Mihaylov
- Kinases and Brain Development Lab, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
| | - Suzanne Claxton
- Kinases and Brain Development Lab, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK
| | - Jill C Richardson
- Neuroscience, MSD Research Laboratories, 120 Moorgate, London, EC2M 6UR, UK
| | - Gabriele Lignani
- Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, Queen Square House, London, WC1N 3BG, UK
| | - Sila K Ultanir
- Kinases and Brain Development Lab, The Francis Crick Institute, 1 Midland Road, London, NW1 1AT, UK.
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2
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Coste de Bagneaux P, von Elsner L, Bierhals T, Campiglio M, Johannsen J, Obermair GJ, Hempel M, Flucher BE, Kutsche K. A homozygous missense variant in CACNB4 encoding the auxiliary calcium channel beta4 subunit causes a severe neurodevelopmental disorder and impairs channel and non-channel functions. PLoS Genet 2020; 16:e1008625. [PMID: 32176688 PMCID: PMC7176149 DOI: 10.1371/journal.pgen.1008625] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Revised: 04/22/2020] [Accepted: 01/23/2020] [Indexed: 12/27/2022] Open
Abstract
P/Q-type channels are the principal presynaptic calcium channels in brain functioning in neurotransmitter release. They are composed of the pore-forming CaV2.1 α1 subunit and the auxiliary α2δ-2 and β4 subunits. β4 is encoded by CACNB4, and its multiple splice variants serve isoform-specific functions as channel subunits and transcriptional regulators in the nucleus. In two siblings with intellectual disability, psychomotor retardation, blindness, epilepsy, movement disorder and cerebellar atrophy we identified rare homozygous variants in the genes LTBP1, EMILIN1, CACNB4, MINAR1, DHX38 and MYO15 by whole-exome sequencing. In silico tools, animal model, clinical, and genetic data suggest the p.(Leu126Pro) CACNB4 variant to be likely pathogenic. To investigate the functional consequences of the CACNB4 variant, we introduced the corresponding mutation L125P into rat β4b cDNA. Heterologously expressed wild-type β4b associated with GFP-CaV1.2 and accumulated in presynaptic boutons of cultured hippocampal neurons. In contrast, the β4b-L125P mutant failed to incorporate into calcium channel complexes and to cluster presynaptically. When co-expressed with CaV2.1 in tsA201 cells, β4b and β4b-L125P augmented the calcium current amplitudes, however, β4b-L125P failed to stably complex with α1 subunits. These results indicate that p.Leu125Pro disrupts the stable association of β4b with native calcium channel complexes, whereas membrane incorporation, modulation of current density and activation properties of heterologously expressed channels remained intact. Wildtype β4b was specifically targeted to the nuclei of quiescent excitatory cells. Importantly, the p.Leu125Pro mutation abolished nuclear targeting of β4b in cultured myotubes and hippocampal neurons. While binding of β4b to the known interaction partner PPP2R5D (B56δ) was not affected by the mutation, complex formation between β4b-L125P and the neuronal TRAF2 and NCK interacting kinase (TNIK) seemed to be disturbed. In summary, our data suggest that the homozygous CACNB4 p.(Leu126Pro) variant underlies the severe neurological phenotype in the two siblings, most likely by impairing both channel and non-channel functions of β4b.
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Affiliation(s)
| | - Leonie von Elsner
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Tatjana Bierhals
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Marta Campiglio
- Department of Physiology and Medical Physics, Medical University Innsbruck, Innsbruck, Austria
| | - Jessika Johannsen
- Childrens Hospital, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Gerald J. Obermair
- Department of Physiology and Medical Physics, Medical University Innsbruck, Innsbruck, Austria
- Division Physiology, Karl Landsteiner University of Health Sciences, Krems, Austria
| | - Maja Hempel
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Bernhard E. Flucher
- Department of Physiology and Medical Physics, Medical University Innsbruck, Innsbruck, Austria
| | - Kerstin Kutsche
- Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
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McCarthy AE, Yoshioka C, Mansoor SE. Full-Length P2X 7 Structures Reveal How Palmitoylation Prevents Channel Desensitization. Cell 2019; 179:659-670.e13. [PMID: 31587896 DOI: 10.1016/j.cell.2019.09.017] [Citation(s) in RCA: 153] [Impact Index Per Article: 30.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Revised: 07/30/2019] [Accepted: 09/13/2019] [Indexed: 12/24/2022]
Abstract
P2X receptors are trimeric, non-selective cation channels activated by extracellular ATP. The P2X7 receptor subtype is a pharmacological target because of involvement in apoptotic, inflammatory, and tumor progression pathways. It is the most structurally and functionally distinct P2X subtype, containing a unique cytoplasmic domain critical for the receptor to initiate apoptosis and not undergo desensitization. However, lack of structural information about the cytoplasmic domain has hindered understanding of the molecular mechanisms underlying these processes. We report cryoelectron microscopy structures of full-length rat P2X7 receptor in apo and ATP-bound states. These structures reveal how one cytoplasmic element, the C-cys anchor, prevents desensitization by anchoring the pore-lining helix to the membrane with palmitoyl groups. They show a second cytoplasmic element with a unique fold, the cytoplasmic ballast, which unexpectedly contains a zinc ion complex and a guanosine nucleotide binding site. Our structures provide first insights into the architecture and function of a P2X receptor cytoplasmic domain.
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Affiliation(s)
- Alanna E McCarthy
- Vollum Institute, Oregon Health and Science University, Portland, OR 97239, USA; Knight Cardiovascular Institute, Oregon Health and Science University, Portland, OR 97239, USA
| | - Craig Yoshioka
- Department of Biomedical Engineering, Oregon Health and Science University, Portland, OR 97201, USA
| | - Steven E Mansoor
- Vollum Institute, Oregon Health and Science University, Portland, OR 97239, USA; Knight Cardiovascular Institute, Oregon Health and Science University, Portland, OR 97239, USA.
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Arteaga-Tlecuitl R, Sanchez-Sandoval AL, Ramirez-Cordero BE, Rosendo-Pineda MJ, Vaca L, Gomora JC. Increase of Ca V3 channel activity induced by HVA β1b-subunit is not mediated by a physical interaction. BMC Res Notes 2018; 11:810. [PMID: 30428904 PMCID: PMC6236959 DOI: 10.1186/s13104-018-3917-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2018] [Accepted: 11/09/2018] [Indexed: 01/13/2023] Open
Abstract
Objective Low voltage-activated (LVA) calcium channels are crucial for regulating oscillatory behavior in several types of neurons and other excitable cells. LVA channels dysfunction has been implicated in epilepsy, neuropathic pain, cancer, among other diseases. Unlike for High Voltage-Activated (HVA) channels, voltage-dependence and kinetics of currents carried by recombinant LVA, i.e., CaV3 channels, are quite similar to those observed in native currents. Therefore, whether these channels are regulated by HVA auxiliary subunits, remain controversial. Here, we used the α1-subunits of CaV3.1, CaV3.2, and CaV3.3 channels, together with HVA auxiliary β-subunits to perform electrophysiological, confocal microscopy and immunoprecipitation experiments, in order to further explore this possibility. Results Functional expression of CaV3 channels is up-regulated by all four β-subunits, although most consistent effects were observed with the β1b-subunit. The biophysical properties of CaV3 channels were not modified by any β-subunit. Furthermore, although β1b-subunits increased colocalization of GFP-tagged CaV3 channels and the plasma membrane of HEK-293 cells, western blots analysis revealed the absence of physical interaction between CaV3.3 and β1b-subunits as no co-immunoprecipitation was observed. These results provide solid evidence that the up-regulation of LVA channels in the presence of HVA-β1b subunit is not mediated by a high affinity interaction between both proteins. Electronic supplementary material The online version of this article (10.1186/s13104-018-3917-1) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Rogelio Arteaga-Tlecuitl
- Departamento de Neuropatología Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico
| | - Ana Laura Sanchez-Sandoval
- Departamento de Neuropatología Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico
| | - Belen Ernestina Ramirez-Cordero
- Departamento de Neuropatología Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico
| | - Margarita Jacaranda Rosendo-Pineda
- Departamento de Biología Celular y del Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico
| | - Luis Vaca
- Departamento de Biología Celular y del Desarrollo, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico
| | - Juan Carlos Gomora
- Departamento de Neuropatología Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510, Mexico City, Mexico.
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5
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Mukherjee A, Wang Z, Kinlough CL, Poland PA, Marciszyn AL, Montalbetti N, Carattino MD, Butterworth MB, Kleyman TR, Hughey RP. Specific Palmitoyltransferases Associate with and Activate the Epithelial Sodium Channel. J Biol Chem 2017; 292:4152-4163. [PMID: 28154191 DOI: 10.1074/jbc.m117.776146] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Indexed: 11/06/2022] Open
Abstract
The epithelial sodium channel (ENaC) has an important role in regulating extracellular fluid volume and blood pressure, as well as airway surface liquid volume and mucociliary clearance. ENaC is a trimer of three homologous subunits (α, β, and γ). We previously reported that cytoplasmic residues on the β (βCys-43 and βCys-557) and γ (γCys-33 and γCys-41) subunits are palmitoylated. Mutation of Cys that blocked ENaC palmitoylation also reduced channel open probability. Furthermore, γ subunit palmitoylation had a dominant role over β subunit palmitoylation in regulating ENaC. To determine which palmitoyltransferases (termed DHHCs) regulate the channel, mouse ENaCs were co-expressed in Xenopus oocytes with each of the 23 mouse DHHCs. ENaC activity was significantly increased by DHHCs 1, 2, 3, 7, and 14. ENaC activation by DHHCs was lost when γ subunit palmitoylation sites were mutated, whereas DHHCs 1, 2, and 14 still activated ENaC lacking β subunit palmitoylation sites. β subunit palmitoylation was increased by ENaC co-expression with DHHC 7. Both wild type ENaC and channels lacking β and γ palmitoylation sites co-immunoprecipitated with the five activating DHHCs, suggesting that ENaC forms a complex with multiple DHHCs. RT-PCR revealed that transcripts for the five activating DHHCs were present in cultured mCCDcl1 cells, and DHHC 3 was expressed in aquaporin 2-positive principal cells of mouse aldosterone-sensitive distal nephron where ENaC is localized. Treatment of polarized mCCDcl1 cells with a general inhibitor of palmitoylation reduced ENaC-mediated Na+ currents within minutes. Our results indicate that specific DHHCs have a role in regulating ENaC.
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Affiliation(s)
| | | | | | | | | | | | | | | | - Thomas R Kleyman
- From the Departments of Medicine, .,Cell Biology, and.,Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
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Benmocha Guggenheimer A, Almagor L, Tsemakhovich V, Tripathy DR, Hirsch JA, Dascal N. Interactions between N and C termini of α1C subunit regulate inactivation of CaV1.2 L-type Ca(2+) channel. Channels (Austin) 2016; 10:55-68. [PMID: 26577286 DOI: 10.1080/19336950.2015.1108499] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
The modulation and regulation of voltage-gated Ca(2+) channels is affected by the pore-forming segments, the cytosolic parts of the channel, and interacting intracellular proteins. In this study we demonstrate a direct physical interaction between the N terminus (NT) and C terminus (CT) of the main subunit of the L-type Ca(2+) channel CaV1.2, α1C, and explore the importance of this interaction for the regulation of the channel. We used biochemistry to measure the strength of the interaction and to map the location of the interaction sites, and electrophysiology to investigate the functional impact of the interaction. We show that the full-length NT (amino acids 1-154) and the proximal (close to the plasma membrane) part of the CT, pCT (amino acids 1508-1669) interact with sub-micromolar to low-micromolar affinity. Calmodulin (CaM) is not essential for the binding. The results further suggest that the NT-CT interaction regulates the channel's inactivation, and that Ca(2+), presumably through binding to calmodulin (CaM), reduces the strength of NT-CT interaction. We propose a molecular mechanism in which NT and CT of the channel serve as levers whose movements regulate inactivation by promoting changes in the transmembrane core of the channel via S1 (NT) or S6 (pCT) segments of domains I and IV, accordingly, and not as a kind of pore blocker. We hypothesize that Ca(2+)-CaM-induced changes in NT-CT interaction may, in part, underlie the acceleration of CaV1.2 inactivation induced by Ca(2+) entry into the cell.
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Affiliation(s)
- Adva Benmocha Guggenheimer
- a Department of Physiology and Pharmacology ; Sackler School of Medicine; Sagol School of Neuroscience ; Tel Aviv , Israel
| | - Lior Almagor
- b Department of Biochemistry & Molecular Biology ; Institute of Structural Biology, George S Weiss Faculty of Life Sciences; Sagol School of Neuroscience; Tel Aviv University ; Tel Aviv , Israel.,c Present address: Department of Structural Biology , Stanford University, School of Medicine ; Stanford , CA USA
| | - Vladimir Tsemakhovich
- a Department of Physiology and Pharmacology ; Sackler School of Medicine; Sagol School of Neuroscience ; Tel Aviv , Israel
| | - Debi Ranjan Tripathy
- b Department of Biochemistry & Molecular Biology ; Institute of Structural Biology, George S Weiss Faculty of Life Sciences; Sagol School of Neuroscience; Tel Aviv University ; Tel Aviv , Israel
| | - Joel A Hirsch
- b Department of Biochemistry & Molecular Biology ; Institute of Structural Biology, George S Weiss Faculty of Life Sciences; Sagol School of Neuroscience; Tel Aviv University ; Tel Aviv , Israel
| | - Nathan Dascal
- a Department of Physiology and Pharmacology ; Sackler School of Medicine; Sagol School of Neuroscience ; Tel Aviv , Israel
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7
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Proft J, Weiss N. G protein regulation of neuronal calcium channels: back to the future. Mol Pharmacol 2014; 87:890-906. [PMID: 25549669 DOI: 10.1124/mol.114.096008] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2014] [Accepted: 12/30/2014] [Indexed: 11/22/2022] Open
Abstract
Neuronal voltage-gated calcium channels have evolved as one of the most important players for calcium entry into presynaptic endings responsible for the release of neurotransmitters. In turn, and to fine-tune synaptic activity and neuronal communication, numerous neurotransmitters exert a potent negative feedback over the calcium signal provided by G protein-coupled receptors. This regulation pathway of physiologic importance is also extensively exploited for therapeutic purposes, for instance in the treatment of neuropathic pain by morphine and other μ-opioid receptor agonists. However, despite more than three decades of intensive research, important questions remain unsolved regarding the molecular and cellular mechanisms of direct G protein inhibition of voltage-gated calcium channels. In this study, we revisit this particular regulation and explore new considerations.
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Affiliation(s)
- Juliane Proft
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Norbert Weiss
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic
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8
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Shipston MJ. Ion channel regulation by protein S-acylation. J Gen Physiol 2014; 143:659-78. [PMID: 24821965 PMCID: PMC4035745 DOI: 10.1085/jgp.201411176] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2014] [Accepted: 04/18/2014] [Indexed: 01/09/2023] Open
Abstract
Protein S-acylation, the reversible covalent fatty-acid modification of cysteine residues, has emerged as a dynamic posttranslational modification (PTM) that controls the diversity, life cycle, and physiological function of numerous ligand- and voltage-gated ion channels. S-acylation is enzymatically mediated by a diverse family of acyltransferases (zDHHCs) and is reversed by acylthioesterases. However, for most ion channels, the dynamics and subcellular localization at which S-acylation and deacylation cycles occur are not known. S-acylation can control the two fundamental determinants of ion channel function: (1) the number of channels resident in a membrane and (2) the activity of the channel at the membrane. It controls the former by regulating channel trafficking and the latter by controlling channel kinetics and modulation by other PTMs. Ion channel function may be modulated by S-acylation of both pore-forming and regulatory subunits as well as through control of adapter, signaling, and scaffolding proteins in ion channel complexes. Importantly, cross-talk of S-acylation with other PTMs of both cysteine residues by themselves and neighboring sites of phosphorylation is an emerging concept in the control of ion channel physiology. In this review, I discuss the fundamentals of protein S-acylation and the tools available to investigate ion channel S-acylation. The mechanisms and role of S-acylation in controlling diverse stages of the ion channel life cycle and its effect on ion channel function are highlighted. Finally, I discuss future goals and challenges for the field to understand both the mechanistic basis for S-acylation control of ion channels and the functional consequence and implications for understanding the physiological function of ion channel S-acylation in health and disease.
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Affiliation(s)
- Michael J Shipston
- Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD Scotland, UK
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9
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Chaube R, Hess DT, Wang YJ, Plummer B, Sun QA, Laurita K, Stamler JS. Regulation of the skeletal muscle ryanodine receptor/Ca2+-release channel RyR1 by S-palmitoylation. J Biol Chem 2014; 289:8612-9. [PMID: 24509862 DOI: 10.1074/jbc.m114.548925] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The ryanodine receptor/Ca(2+)-release channels (RyRs) of skeletal and cardiac muscle are essential for Ca(2+) release from the sarcoplasmic reticulum that mediates excitation-contraction coupling. It has been shown that RyR activity is regulated by dynamic post-translational modifications of Cys residues, in particular S-nitrosylation and S-oxidation. Here we show that the predominant form of RyR in skeletal muscle, RyR1, is subject to Cys-directed modification by S-palmitoylation. S-Palmitoylation targets 18 Cys within the N-terminal, cytoplasmic region of RyR1, which are clustered in multiple functional domains including those implicated in the activity-governing protein-protein interactions of RyR1 with the L-type Ca(2+) channel CaV1.1, calmodulin, and the FK506-binding protein FKBP12, as well as in "hot spot" regions containing sites of mutations implicated in malignant hyperthermia and central core disease. Eight of these Cys have been identified previously as subject to physiological S-nitrosylation or S-oxidation. Diminishing S-palmitoylation directly suppresses RyR1 activity as well as stimulus-coupled Ca(2+) release through RyR1. These findings demonstrate functional regulation of RyR1 by a previously unreported post-translational modification and indicate the potential for extensive Cys-based signaling cross-talk. In addition, we identify the sarco/endoplasmic reticular Ca(2+)-ATPase 1A and the α1S subunit of the L-type Ca(2+) channel CaV1.1 as S-palmitoylated proteins, indicating that S-palmitoylation may regulate all principal governors of Ca(2+) flux in skeletal muscle that mediates excitation-contraction coupling.
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Affiliation(s)
- Ruchi Chaube
- From the Institute for Transformative Molecular Medicine and Department of Medicine, Case Western Reserve University School of Medicine and University Hospitals, Cleveland, Ohio 44106
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Vogl C, Mochida S, Wolff C, Whalley BJ, Stephens GJ. The synaptic vesicle glycoprotein 2A ligand levetiracetam inhibits presynaptic Ca2+ channels through an intracellular pathway. Mol Pharmacol 2012; 82:199-208. [PMID: 22554805 DOI: 10.1124/mol.111.076687] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Levetiracetam (LEV) is a prominent antiepileptic drug that binds to neuronal synaptic vesicle glycoprotein 2A protein and has reported effects on ion channels, but with a poorly defined mechanism of action. We investigated inhibition of voltage-dependent Ca(2+) (Ca(V)) channels as a potential mechanism through which LEV exerts effects on neuronal activity. We used electrophysiological methods to investigate the effects of LEV on cholinergic synaptic transmission and Ca(V) channel activity in superior cervical ganglion neurons (SCGNs). In parallel, we investigated the effects of the inactive LEV R-enantiomer, (R)-α-ethyl-2-oxo-1-pyrrolidine acetamide (UCB L060). LEV but not UCB L060 (each at 100 μM) inhibited synaptic transmission between SCGNs in long-term culture in a time-dependent manner, significantly reducing excitatory postsynaptic potentials after a ≥30-min application. In isolated SCGNs, LEV pretreatment (≥1 h) but not short-term application (5 min) significantly inhibited whole-cell Ba(2+) current (I(Ba)) amplitude. In current-clamp recordings, LEV reduced the amplitude of the afterhyperpolarizing potential in a Ca(2+)-dependent manner but also increased the action potential latency in a Ca(2+)-independent manner, which suggests additional mechanisms associated with reduced excitability. Intracellular LEV application (4-5 min) caused rapid inhibition of I(Ba) amplitude, to an extent comparable to that seen with extracellular LEV pretreatment (≥1 h). Neither pretreatment nor intracellular application of UCB L060 produced any inhibitory effects on I(Ba) amplitude. These results identify a stereospecific intracellular pathway through which LEV inhibits presynaptic Ca(V) channels; resultant reductions in neuronal excitability are proposed to contribute to the anticonvulsant effects of LEV.
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Affiliation(s)
- Christian Vogl
- School of Pharmacy, University of Reading, Whiteknights, Reading, UK
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11
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Palmitoylation influences the function and pharmacology of sodium channels. Proc Natl Acad Sci U S A 2011; 108:20213-8. [PMID: 22123950 DOI: 10.1073/pnas.1108497108] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Palmitoylation is a common lipid modification known to regulate the functional properties of various proteins and is a vital step in the biosynthesis of voltage-activated sodium (Nav) channels. We discovered a mutation in an intracellular loop of rNav1.2a (G1079C), which results in a higher apparent affinity for externally applied PaurTx3 and ProTx-II, two voltage sensor toxins isolated from tarantula venom. To explore whether palmitoylation of the introduced cysteine underlies this observation, we compared channel susceptibility to a range of animal toxins in the absence and presence of 2-Br-palmitate, a palmitate analog that prevents palmitate incorporation into proteins, and found that palmitoylation contributes to the increased affinity of PaurTx3 and ProTx-II for G1079C. Further investigations with 2-Br-palmitate revealed that palmitoylation can regulate the gating and pharmacology of wild-type (wt) rNav1.2a. To identify rNav1.2a palmitoylation sites contributing to these phenomena, we substituted three endogenous cysteines predicted to be palmitoylated and found that the gating behavior of this triple cysteine mutant is similar to wt rNav1.2a treated with 2-Br-palmitate. As with chemically depalmitoylated rNav1.2a channels, this mutant also exhibits an increased susceptibility for PaurTx3. Additional mutagenesis experiments showed that palmitoylation of one cysteine in particular (C1182) primarily influences PaurTx3 sensitivity and may enhance the inactivation process of wt rNav1.2a. Overall, our results demonstrate that lipid modifications are capable of altering the gating and pharmacological properties of rNav1.2a.
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12
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Bucci G, Mochida S, Stephens GJ. Inhibition of synaptic transmission and G protein modulation by synthetic CaV2.2 Ca²+ channel peptides. J Physiol 2011; 589:3085-101. [PMID: 21521766 PMCID: PMC3145926 DOI: 10.1113/jphysiol.2010.204735] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2011] [Accepted: 04/19/2011] [Indexed: 12/27/2022] Open
Abstract
Modulation of presynaptic voltage-dependent Ca2+ channels is a major means of controlling neurotransmitter release. The CaV2.2Ca2+ channel subunit contains several inhibitory interaction sites for Gβγ subunits, including the amino terminal (NT) and I-II loop. The NT and I-II loop have also been proposed to undergo a G protein-gated inhibitory interaction, whilst the NT itself has also been proposed to suppress CaV2 channel activity. Here, we investigate the effects of an amino terminal (CaV2.2[45-55]) 'NT peptide' and a I-II loop alpha interaction domain (CaV2.2[377-393]) 'AID peptide' on synaptic transmission, Ca2+ channel activity and G protein modulation in superior cervical ganglion neurones (SCGNs). Presynaptic injection of NT or AID peptide into SCGN synapses inhibited synaptic transmission and also attenuated noradrenaline-induced G protein modulation. In isolated SCGNs, NT and AID peptides reduced whole-cell Ca2+ current amplitude, modified voltage dependence of Ca2+ channel activation and attenuated noradrenaline-induced G protein modulation. Co-application of NT and AID peptide negated inhibitory actions. Together, these data favour direct peptide interaction with presynaptic Ca2+ channels, with effects on current amplitude and gating representing likely mechanisms responsible for inhibition of synaptic transmission. Mutations to residues reported as determinants of Ca2+ channel function within the NT peptide negated inhibitory effects on synaptic transmission, Ca2+ current amplitude and gating and G protein modulation. A mutation within the proposed QXXER motif for G protein modulation did not abolish inhibitory effects of the AID peptide. This study suggests that the CaV2.2 amino terminal and I-II loop contribute molecular determinants for Ca2+ channel function; the data favour a direct interaction of peptides with Ca2+ channels to inhibit synaptic transmission and attenuate G protein modulation.
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Affiliation(s)
- Giovanna Bucci
- School of Pharmacy, University of Reading, Whiteknights, Reading RG6 6AJ, UK
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13
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Abstract
Protein S-palmitoylation, the reversible thioester linkage of a 16-carbon palmitate lipid to an intracellular cysteine residue, is rapidly emerging as a fundamental, dynamic, and widespread post-translational mechanism to control the properties and function of ligand- and voltage-gated ion channels. Palmitoylation controls multiple stages in the ion channel life cycle, from maturation to trafficking and regulation. An emerging concept is that palmitoylation is an important determinant of channel regulation by other signaling pathways. The elucidation of enzymes controlling palmitoylation and developments in proteomics tools now promise to revolutionize our understanding of this fundamental post-translational mechanism in regulating ion channel physiology.
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Affiliation(s)
- Michael J Shipston
- Centre for Integrative Physiology, College of Medicine and Veterinary Medicine, University of Edinburgh, Edinburgh EH8 9XD, Scotland, United Kingdom.
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14
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Abstract
Calcium regulates a wide spectrum of physiological processes such as heartbeat, muscle contraction, neuronal communication, hormone release, cell division, and gene transcription. Major entryways for Ca(2+) in excitable cells are high-voltage activated (HVA) Ca(2+) channels. These are plasma membrane proteins composed of several subunits, including α(1), α(2)δ, β, and γ. Although the principal α(1) subunit (Ca(v)α(1)) contains the channel pore, gating machinery and most drug binding sites, the cytosolic auxiliary β subunit (Ca(v)β) plays an essential role in regulating the surface expression and gating properties of HVA Ca(2+) channels. Ca(v)β is also crucial for the modulation of HVA Ca(2+) channels by G proteins, kinases, and the Ras-related RGK GTPases. New proteins have emerged in recent years that modulate HVA Ca(2+) channels by binding to Ca(v)β. There are also indications that Ca(v)β may carry out Ca(2+) channel-independent functions, including directly regulating gene transcription. All four subtypes of Ca(v)β, encoded by different genes, have a modular organization, consisting of three variable regions, a conserved guanylate kinase (GK) domain, and a conserved Src-homology 3 (SH3) domain, placing them into the membrane-associated guanylate kinase (MAGUK) protein family. Crystal structures of Ca(v)βs reveal how they interact with Ca(v)α(1), open new research avenues, and prompt new inquiries. In this article, we review the structure and various biological functions of Ca(v)β, with both a historical perspective as well as an emphasis on recent advances.
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Affiliation(s)
- Zafir Buraei
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
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15
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ORTIZ-MIRANDA SONIAI, DAYANITHI GOVINDAN, VELÁZQUEZ-MARRERO CRISTINA, CUSTER EDWARDE, TREISTMAN STEVENN, LEMOS JOSÉR. Differential modulation of N-type calcium channels by micro-opioid receptors in oxytocinergic versus vasopressinergic neurohypophysial terminals. J Cell Physiol 2010; 225:276-88. [PMID: 20509142 PMCID: PMC4060829 DOI: 10.1002/jcp.22263] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Opioids modulate the electrical activity of magnocellular neurons (MCN) and inhibit neuropeptide release at their terminals in the neurohypophysis. We have previously shown that micro-opioid receptor (MOR) activation induces a stronger inhibition of oxytocin (OT) than vasopressin (AVP) release from isolated MCN terminals. This higher sensitivity of OT release is due, at least in part, to the selective targeting of R-type calcium channels. We now describe the underlying basis for AVP's weaker inhibition by MOR activation and provide a more complete explanation of the complicated effects on neuropeptide release. We found that N-type calcium channels in AVP terminals are differentially modulated by MOR; enhanced at lower concentrations but increasingly inhibited at higher concentrations of agonists. On the other hand, N-type calcium channels in OT terminals were always inhibited. The response pattern in co-labeled terminals was analogous to that observed in AVP-containing terminals. Changes in intracellular calcium concentration and neuropeptide release corroborated these results as they showed a similar pattern of enhancement and inhibition in AVP terminals contrasting with solely inhibitory responses in OT terminals to MOR agonists. We established that fast translocation of Ca(2+) channels to the plasma membrane was not mediating current increments and thus, changes in channel kinetic properties are most likely involved. Finally, we reveal a distinct Ca-channel beta-subunit expression between each type of nerve endings that could explain some of the differences in responses to MOR activation. These results help advance our understanding of the complex modulatory mechanisms utilized by MORs in regulating presynaptic neuropeptide release.
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Affiliation(s)
- SONIA I. ORTIZ-MIRANDA
- Department of Physiology & Program in Neuroscience, University of Massachusetts Medical School, Worcester, Massachusetts
| | | | - CRISTINA VELÁZQUEZ-MARRERO
- Department of Physiology & Program in Neuroscience, University of Massachusetts Medical School, Worcester, Massachusetts
| | - EDWARD E. CUSTER
- Department of Physiology & Program in Neuroscience, University of Massachusetts Medical School, Worcester, Massachusetts
| | - STEVEN N. TREISTMAN
- Brudnick Neuropsychiatric Institute, University of Massachusetts Medical School, Worcester, Massachusetts
| | - JOSÉ R. LEMOS
- Department of Physiology & Program in Neuroscience, University of Massachusetts Medical School, Worcester, Massachusetts
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16
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Walsh CP, Davies A, Butcher AJ, Dolphin AC, Kitmitto A. Three-dimensional structure of CaV3.1: comparison with the cardiac L-type voltage-gated calcium channel monomer architecture. J Biol Chem 2009; 284:22310-22321. [PMID: 19520861 PMCID: PMC2755954 DOI: 10.1074/jbc.m109.017152] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calcium entry through voltage-gated calcium channels has widespread cellular effects upon a host of physiological processes including neuronal excitability, muscle excitation-contraction coupling, and secretion. Using single particle analysis methods, we have determined the first three-dimensional structure, at 23 A resolution, for a member of the low voltage-activated voltage-gated calcium channel family, CaV3.1, a T-type channel. CaV3.1 has dimensions of approximately 115x85x95 A, composed of two distinct segments. The cytoplasmic densities form a vestibule below the transmembrane domain with the C terminus, unambiguously identified by the presence of a His tag being approximately 65 A long and curling around the base of the structure. The cytoplasmic assembly has a large exposed surface area that may serve as a signaling hub with the C terminus acting as a "fishing rod" to bind regulatory proteins. We have also determined a three-dimensional structure, at a resolution of 25 A, for the monomeric form of the cardiac L-type voltage-gated calcium (high voltage-activated) channel with accessory proteins beta and alpha2delta bound to the ion channel polypeptide CaV1.2. Comparison with the skeletal muscle isoform finds a good match particularly with respect to the conformation, size, and shape of the domain identified as that formed by alpha2. Furthermore, modeling of the CaV3.1 structure (analogous to CaV1.2 at these resolutions) into the heteromeric L-type voltage-gated calcium channel complex volume reveals multiple interaction sites for beta-CaV1.2 binding and for the first time identifies the size and organization of the alpha2delta polypeptides.
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Affiliation(s)
- Conor P Walsh
- Cardiovascular Medicine, School of Clinical and Laboratory Sciences, Faculty of Medical and Human Sciences, University of Manchester, Manchester M13 9NT
| | - Anthony Davies
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Adrian J Butcher
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Annette C Dolphin
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Ashraf Kitmitto
- Cardiovascular Medicine, School of Clinical and Laboratory Sciences, Faculty of Medical and Human Sciences, University of Manchester, Manchester M13 9NT
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17
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Roberts-Crowley ML, Mitra-Ganguli T, Liu L, Rittenhouse AR. Regulation of voltage-gated Ca2+ channels by lipids. Cell Calcium 2009; 45:589-601. [PMID: 19419761 PMCID: PMC2964877 DOI: 10.1016/j.ceca.2009.03.015] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2009] [Revised: 03/23/2009] [Accepted: 03/24/2009] [Indexed: 11/23/2022]
Abstract
Great skepticism has surrounded the question of whether modulation of voltage-gated Ca(2+) channels (VGCCs) by the polyunsaturated free fatty acid arachidonic acid (AA) has any physiological basis. Here we synthesize findings from studies of both native and recombinant channels where micromolar concentrations of AA consistently inhibit both native and recombinant activity by stabilizing VGCCs in one or more closed states. Structural requirements for these inhibitory actions include a chain length of at least 18 carbons and multiple double bonds located near the fatty acid's carboxy terminus. Acting at a second site, AA increases the rate of VGCC activation kinetics, and in Ca(V)2.2 channels, increases current amplitude. We present evidence that phosphatidylinositol 4,5-bisphosphate (PIP(2)), a palmitoylated accessory subunit (beta(2a)) of VGCCs and AA appear to have overlapping sites of action giving rise to complex channel behavior. Their actions converge in a physiologically relevant manner during muscarinic modulation of VGCCs. We speculate that M(1) muscarinic receptors may stimulate multiple lipases to break down the PIP(2) associated with VGCCs and leave PIP(2)'s freed fatty acid tails bound to the channels to confer modulation. This unexpectedly simple scheme gives rise to unanticipated predictions and redirects thinking about lipid regulation of VGCCs.
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Affiliation(s)
- Mandy L. Roberts-Crowley
- Program in Neuroscience, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 USA
- Department of Physiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 USA
| | - Tora Mitra-Ganguli
- Program in Neuroscience, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 USA
- Department of Physiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 USA
| | - Liwang Liu
- Department of Physiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 USA
| | - Ann R. Rittenhouse
- Program in Neuroscience, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 USA
- Department of Physiology, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 USA
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18
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Karunasekara Y, Dulhunty AF, Casarotto MG. The voltage-gated calcium-channel beta subunit: more than just an accessory. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:75-81. [PMID: 19455319 DOI: 10.1007/s00249-009-0467-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2009] [Revised: 04/22/2009] [Accepted: 04/29/2009] [Indexed: 11/25/2022]
Abstract
Voltage-gated Ca(2+) channels (VGCCs) are involved in a number of excitatory processes in the cell that regulate muscle contraction, neurotransmitter release, gene regulation, and neuronal migration. They consist of a central pore-forming alpha(1) subunit together with a number of associated auxiliary subunits including a cytoplasmic beta subunit. With the aid of X-ray crystallography, it has been found that the beta subunits of VGCCs (beta(2a), beta(3), and beta(4)) interact strongly with the I-II loop of the pore-forming alpha(1) subunit. Here we discuss the potential interaction sites of beta(1a) with its alpha(1) subunit as well as the skeletal ryanodine receptor. We suggest that not only can beta(1a) interact with the alpha(1) subunit I-II loop, but more subtle interactions may be possible through the II-III loop via the beta(1a) SH3 domain. Such findings could have important implications with respect to EC coupling.
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Affiliation(s)
- Yamuna Karunasekara
- The John Curtin School of Medical Research, Australian National University, GPO Box 334, Canberra, ACT, 2601, Australia
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19
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Chen YH, He LL, Buchanan DR, Zhang Y, Fitzmaurice A, Yang J. Functional dissection of the intramolecular Src homology 3-guanylate kinase domain coupling in voltage-gated Ca2+ channel beta-subunits. FEBS Lett 2009; 583:1969-75. [PMID: 19427861 DOI: 10.1016/j.febslet.2009.05.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2009] [Revised: 03/25/2009] [Accepted: 05/04/2009] [Indexed: 11/19/2022]
Abstract
The beta-subunit of voltage-gated Ca(2+) channels is essential for trafficking the channels to the plasma membrane and regulating their gating. It contains a Src homology 3 (SH3) domain and a guanylate kinase (GK) domain, which interact intramolecularly. We investigated the structural underpinnings of this intramolecular coupling and found that in addition to a previously described SH3 domain beta strand, two structural elements are crucial for maintaining a strong and yet potentially modifiable SH3-GK intramolecular coupling: an intrinsically weak SH3-GK interface and a direct connection of the SH3 and GK domains. Alterations of these elements uncouple the two functions of the beta-subunit, degrading its ability to regulate gating while leaving its chaperone effect intact.
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Affiliation(s)
- Yu-hang Chen
- Department of Biological Sciences, 917 Fairchild Center, MC2462, Columbia University, New York, NY 10027, USA
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20
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Orientation of the calcium channel beta relative to the alpha(1)2.2 subunit is critical for its regulation of channel activity. PLoS One 2008; 3:e3560. [PMID: 18958281 PMCID: PMC2570331 DOI: 10.1371/journal.pone.0003560] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2008] [Accepted: 10/09/2008] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The Ca(v)beta subunits of high voltage-activated Ca(2+) channels control the trafficking and biophysical properties of the alpha(1) subunit. The Ca(v)beta-alpha(1) interaction site has been mapped by crystallographic studies. Nevertheless, how this interaction leads to channel regulation has not been determined. One hypothesis is that betas regulate channel gating by modulating movements of IS6. A key requirement for this direct-coupling model is that the linker connecting IS6 to the alpha-interaction domain (AID) be a rigid structure. METHODOLOGY/PRINCIPAL FINDINGS The present study tests this hypothesis by altering the flexibility and orientation of this region in alpha(1)2.2, then testing for Ca(v)beta regulation using whole cell patch clamp electrophysiology. Flexibility was induced by replacement of the middle six amino acids of the IS6-AID linker with glycine (PG6). This mutation abolished beta2a and beta3 subunits ability to shift the voltage dependence of activation and inactivation, and the ability of beta2a to produce non-inactivating currents. Orientation of Ca(v)beta with respect to alpha(1)2.2 was altered by deletion of 1, 2, or 3 amino acids from the IS6-AID linker (Bdel1, Bdel2, Bdel3, respectively). Again, the ability of Ca(v)beta subunits to regulate these biophysical properties were totally abolished in the Bdel1 and Bdel3 mutants. Functional regulation by Ca(v)beta subunits was rescued in the Bdel2 mutant, indicating that this part of the linker forms beta-sheet. The orientation of beta with respect to alpha was confirmed by the bimolecular fluorescence complementation assay. CONCLUSIONS/SIGNIFICANCE These results show that the orientation of the Ca(v)beta subunit relative to the alpha(1)2.2 subunit is critical, and suggests additional points of contact between these subunits are required for Ca(v)beta to regulate channel activity.
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21
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Dresviannikov AV, Page KM, Leroy J, Pratt WS, Dolphin AC. Determinants of the voltage dependence of G protein modulation within calcium channel beta subunits. Pflugers Arch 2008; 457:743-56. [PMID: 18651169 PMCID: PMC2686087 DOI: 10.1007/s00424-008-0549-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2008] [Accepted: 06/17/2008] [Indexed: 11/21/2022]
Abstract
CaVβ subunits of voltage-gated calcium channels contain two conserved domains, a src-homology-3 (SH3) domain and a guanylate kinase-like (GK) domain with an intervening HOOK domain. We have shown in a previous study that, although Gβγ-mediated inhibitory modulation of CaV2.2 channels did not require the interaction of a CaVβ subunit with the CaVα1 subunit, when such interaction was prevented by a mutation in the α1 subunit, G protein modulation could not be removed by a large depolarization and showed voltage-independent properties (Leroy et al., J Neurosci 25:6984–6996, 2005). In this study, we have investigated the ability of mutant and truncated CaVβ subunits to support voltage-dependent G protein modulation in order to determine the minimal domain of the CaVβ subunit that is required for this process. We have coexpressed the CaVβ subunit constructs with CaV2.2 and α2δ-2, studied modulation by the activation of the dopamine D2 receptor, and also examined basal tonic modulation. Our main finding is that the CaVβ subunit GK domains, from either β1b or β2, are sufficient to restore voltage dependence to G protein modulation. We also found that the removal of the variable HOOK region from β2a promotes tonic voltage-dependent G protein modulation. We propose that the absence of the HOOK region enhances Gβγ binding affinity, leading to greater tonic modulation by basal levels of Gβγ. This tonic modulation requires the presence of an SH3 domain, as tonic modulation is not supported by any of the CaVβ subunit GK domains alone.
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Affiliation(s)
- Andriy V Dresviannikov
- Laboratory of Cellular and Molecular Neuroscience, Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
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22
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Cheng X, Liu J, Asuncion-Chin M, Blaskova E, Bannister JP, Dopico AM, Jaggar JH. A novel Ca(V)1.2 N terminus expressed in smooth muscle cells of resistance size arteries modifies channel regulation by auxiliary subunits. J Biol Chem 2007; 282:29211-21. [PMID: 17699517 PMCID: PMC2276565 DOI: 10.1074/jbc.m610623200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Voltage-dependent L-type Ca(2+) (Ca(V)1.2) channels are the principal Ca(2+) entry pathway in arterial myocytes. Ca(V)1.2 channels regulate multiple vascular functions and are implicated in the pathogenesis of human disease, including hypertension. However, the molecular identity of Ca(V)1.2 channels expressed in myocytes of myogenic arteries that regulate vascular pressure and blood flow is unknown. Here, we cloned Ca(V)1.2 subunits from resistance size cerebral arteries and demonstrate that myocytes contain a novel, cysteine rich N terminus that is derived from exon 1 (termed "exon 1c"), which is located within CACNA1C, the Ca(V)1.2 gene. Quantitative PCR revealed that exon 1c was predominant in arterial myocytes, but rare in cardiac myocytes, where exon 1a prevailed. When co-expressed with alpha(2)delta subunits, Ca(V)1.2 channels containing the novel exon 1c-derived N terminus exhibited: 1) smaller whole cell current density, 2) more negative voltages of half activation (V(1/2,act)) and half-inactivation (V(1/2,inact)), and 3) reduced plasma membrane insertion, when compared with channels containing exon 1b. beta(1b) and beta(2a) subunits caused negative shifts in the V(1/2,act) and V(1/2,inact) of exon 1b-containing Ca(V)1.2alpha(1)/alpha(2)delta currents that were larger than those in exon 1c-containing Ca(V)1.2alpha(1)/alpha(2)delta currents. In contrast, beta(3) similarly shifted V(1/2,act) and V(1/2,inact) of currents generated by exon 1b- and exon 1c-containing channels. beta subunits isoform-dependent differences in current inactivation rates were also detected between N-terminal variants. Data indicate that through novel alternative splicing at exon 1, the Ca(V)1.2 N terminus modifies regulation by auxiliary subunits. The novel exon 1c should generate distinct voltage-dependent Ca(2+) entry in arterial myocytes, resulting in tissue-specific Ca(2+) signaling.
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Affiliation(s)
- Xiaoyang Cheng
- Department of Physiology, University of Tennessee Health Science Center, Memphis, Tennessee 38163
| | - Jianxi Liu
- Department of Pharmacology, University of Tennessee Health Science Center, Memphis, Tennessee 38163
| | - Maria Asuncion-Chin
- Department of Pharmacology, University of Tennessee Health Science Center, Memphis, Tennessee 38163
| | - Eva Blaskova
- Department of Physiology, University of Tennessee Health Science Center, Memphis, Tennessee 38163
| | - John P. Bannister
- Department of Physiology, University of Tennessee Health Science Center, Memphis, Tennessee 38163
| | - Alejandro M. Dopico
- Department of Pharmacology, University of Tennessee Health Science Center, Memphis, Tennessee 38163
| | - Jonathan H. Jaggar
- Department of Physiology, University of Tennessee Health Science Center, Memphis, Tennessee 38163
- To whom correspondence should be addressed: Dept. of Physiology, University of Tennessee Health Science Center, 894 Union Ave., Memphis, TN 38163. Tel.: 901-448-1208; Fax: 901-448-7126; E-mail:
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23
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He LL, Zhang Y, Chen YH, Yamada Y, Yang J. Functional modularity of the beta-subunit of voltage-gated Ca2+ channels. Biophys J 2007; 93:834-45. [PMID: 17496037 PMCID: PMC1913152 DOI: 10.1529/biophysj.106.101691] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The beta-subunit of voltage-gated Ca(2+) channels plays a dual role in chaperoning the channels to the plasma membrane and modulating their gating. It contains five distinct modular domains/regions, including the variable N- and C-terminus, a conserved Src homology 3 (SH3) domain, a conserved guanylate kinase (GK) domain, and a connecting variable and flexible HOOK region. Recent crystallographic studies revealed a highly conserved interaction between the GK domain and alpha interaction domain (AID), the high-affinity binding site in the pore-forming alpha(1) subunit. Here we show that the AID-GK domain interaction is necessary for beta-subunit-stimulated Ca(2+) channel surface expression and that the GK domain alone can carry out this function. We also examined the role of each region of all four beta-subunit subfamilies in modulating P/Q-type Ca(2+) channel gating and demonstrate that the beta-subunit functions modularly. Our results support a model that the conserved AID-GK domain interaction anchors the beta-subunit to the alpha(1) subunit, enabling alpha(1)-beta pair-specific low-affinity interactions involving the N-terminus and the HOOK region, which confer on each of the four beta-subunit subfamilies its distinctive modulatory properties.
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Affiliation(s)
- Lin-Ling He
- Department of Biological Sciences, Columbia University, New York, New York 10027, USA
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24
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Abstract
Triggered activity in cardiac muscle and intracellular Ca2+ have been linked in the past. However, today not only are there a number of cellular proteins that show clear Ca2+ dependence but also there are a number of arrhythmias whose mechanism appears to be linked to Ca2+-dependent processes. Thus we present a systematic review of the mechanisms of Ca2+ transport (forward excitation-contraction coupling) in the ventricular cell as well as what is known for other cardiac cell types. Second, we review the molecular nature of the proteins that are involved in this process as well as the functional consequences of both normal and abnormal Ca2+ cycling (e.g., Ca2+ waves). Finally, we review what we understand to be the role of Ca2+ cycling in various forms of arrhythmias, that is, those associated with inherited mutations and those that are acquired and resulting from reentrant excitation and/or abnormal impulse generation (e.g., triggered activity). Further solving the nature of these intricate and dynamic interactions promises to be an important area of research for a better recognition and understanding of the nature of Ca2+ and arrhythmias. Our solutions will provide a more complete understanding of the molecular basis for the targeted control of cellular calcium in the treatment and prevention of such.
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Affiliation(s)
- Henk E D J Ter Keurs
- Department of Medicine, Physiology and Biophysics, University of Calgary, Alberta, Canada
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25
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Weiss N, Tadmouri A, Mikati M, Ronjat M, De Waard M. Importance of voltage-dependent inactivation in N-type calcium channel regulation by G-proteins. Pflugers Arch 2006; 454:115-29. [PMID: 17171365 PMCID: PMC2703660 DOI: 10.1007/s00424-006-0184-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2006] [Accepted: 10/29/2006] [Indexed: 10/23/2022]
Abstract
Direct regulation of N-type calcium channels by G-proteins is essential to control neuronal excitability and neurotransmitter release. Binding of the G(betagamma) dimer directly onto the channel is characterized by a marked current inhibition ("ON" effect), whereas the pore opening- and time-dependent dissociation of this complex from the channel produce a characteristic set of biophysical modifications ("OFF" effects). Although G-protein dissociation is linked to channel opening, the contribution of channel inactivation to G-protein regulation has been poorly studied. Here, the role of channel inactivation was assessed by examining time-dependent G-protein de-inhibition of Ca(v)2.2 channels in the presence of various inactivation-altering beta subunit constructs. G-protein activation was produced via mu-opioid receptor activation using the DAMGO agonist. Whereas the "ON" effect of G-protein regulation is independent of the type of beta subunit, the "OFF" effects were critically affected by channel inactivation. Channel inactivation acts as a synergistic factor to channel activation for the speed of G-protein dissociation. However, fast inactivating channels also reduce the temporal window of opportunity for G-protein dissociation, resulting in a reduced extent of current recovery, whereas slow inactivating channels undergo a far more complete recovery from inhibition. Taken together, these results provide novel insights on the role of channel inactivation in N-type channel regulation by G-proteins and contribute to the understanding of the physiological consequence of channel inactivation in the modulation of synaptic activity by G-protein coupled receptors.
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Affiliation(s)
- Norbert Weiss
- Canaux calciques , fonctions et pathologies
INSERM : U607CEA : DSV/IRTSVUniversité Joseph Fourier - Grenoble I17, rue des martyrs 38054 Grenoble,FR
| | - Abir Tadmouri
- Canaux calciques , fonctions et pathologies
INSERM : U607CEA : DSV/IRTSVUniversité Joseph Fourier - Grenoble I17, rue des martyrs 38054 Grenoble,FR
| | - Mohamad Mikati
- Department of Pediatrics
American University of Beirut Medical CenterBeyrouth,LB
| | - Michel Ronjat
- Canaux calciques , fonctions et pathologies
INSERM : U607CEA : DSV/IRTSVUniversité Joseph Fourier - Grenoble I17, rue des martyrs 38054 Grenoble,FR
| | - Michel De Waard
- Canaux calciques , fonctions et pathologies
INSERM : U607CEA : DSV/IRTSVUniversité Joseph Fourier - Grenoble I17, rue des martyrs 38054 Grenoble,FR
- * Correspondence should be adressed to: Michel De Waard
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Leroy J, Richards MW, Richards MS, Butcher AJ, Nieto-Rostro M, Pratt WS, Davies A, Dolphin AC. Interaction via a key tryptophan in the I-II linker of N-type calcium channels is required for beta1 but not for palmitoylated beta2, implicating an additional binding site in the regulation of channel voltage-dependent properties. J Neurosci 2006; 25:6984-96. [PMID: 16049174 PMCID: PMC6724838 DOI: 10.1523/jneurosci.1137-05.2005] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The CaVbeta subunits of voltage-gated calcium channels regulate these channels in several ways. Here we investigate the role of these auxiliary subunits in the expression of functional N-type channels at the plasma membrane and in the modulation by G-protein-coupled receptors of this neuronal channel. To do so, we mutated tryptophan 391 to an alanine within the alpha-interacting domain (AID) in the I-II linker of CaV2.2. We showed that the mutation W391 virtually abolishes the binding of CaVbeta1b and CaVbeta2a to the CaV2.2 I-II linker and strongly reduced current density and cell surface expression of both CaV2.2/alpha2delta-2/beta1b and/beta2a channels. When associated with CaVbeta1b, the W391A mutation also prevented the CaVbeta1b-mediated hyperpolarization of CaV2.2 channel activation and steady-state inactivation. However, the mutated CaV2.2W391A/beta1b channels were still inhibited to a similar extent by activation of the D2 dopamine receptor with the agonist quinpirole. Nevertheless, key hallmarks of G-protein modulation of N-type currents, such as slowed activation kinetics and prepulse facilitation, were not observed for the mutated channel. In contrast, CaVbeta2a was still able to completely modulate the biophysical properties of CaV2.2W391A channel and allow voltage-dependent G-protein modulation of CaV2.2W391A. Additional data suggest that the concentration of CaVbeta2a in the proximity of the channel is enhanced independently of its binding to the AID by its palmitoylation. This is essentially sufficient for all of the functional effects of CaVbeta2a, which may occur via a second lower-affinity binding site, except trafficking the channel to the plasma membrane, which requires interaction with the AID region.
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Affiliation(s)
- Jérôme Leroy
- Department of Pharmacology, University College London, London WC1E 6BT, United Kingdom.
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27
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Boyden PA, ter Keurs H. Would modulation of intracellular Ca2+ be antiarrhythmic? Pharmacol Ther 2005; 108:149-79. [PMID: 16038982 DOI: 10.1016/j.pharmthera.2005.03.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2005] [Accepted: 03/22/2005] [Indexed: 01/10/2023]
Abstract
Under several types of conditions, reversal of steps of excitation-contraction coupling (RECC) can give rise to nondriven electrical activity. In this review we explore those conditions for several cardiac cell types (SA, atrial, Purkinje, ventricular cells). We find that abnormal spontaneous Ca2+ release from intracellular Ca2+ stores, aberrant Ca2+ influx from sarcolemmal channels or abnormal Ca2+ surges in nonuniform muscle can be the initiators of the RECC. Often, with such increases in Ca2+, spontaneous Ca2+ waves occur and lead to membrane depolarizations. Because the change in membrane voltage is produced by Ca2+-dependent changes in ion channel function, we also review here what is known about the molecular interaction of Ca2+ and several Ca2+-dependent processes, including the intracellular Ca2+ release channels implicated in the genetic basis of some forms of human arrhythmias. Finally, we review what is known about the effectiveness of several agents in modifying such Ca2+-dependent arrhythmias.
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Affiliation(s)
- Penelope A Boyden
- Department of Pharmacology, Center for Molecular Therapeutics, Columbia University, NY 10032, USA.
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28
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De Waard M, Hering J, Weiss N, Feltz A. How do G proteins directly control neuronal Ca2+ channel function? Trends Pharmacol Sci 2005; 26:427-36. [PMID: 16009433 DOI: 10.1016/j.tips.2005.06.008] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2004] [Revised: 05/03/2005] [Accepted: 06/22/2005] [Indexed: 10/25/2022]
Abstract
Ca2+ entry into neuronal cells is modulated by the activation of numerous G-protein-coupled receptors (GPCRs). Much effort has been invested in studying direct G-protein-mediated inhibition of voltage-dependent CaV2 Ca2+ channels. This inhibition occurs through a series of convergent modifications in the biophysical properties of the channels. An integrated view of the structural organization of the Gbetagamma-dimer binding-site pocket within the channel is emerging. In this review, we discuss how variable geometry of the Gbetagamma binding pocket can yield distinct sets of channel inhibition. In addition, we propose specific mechanisms for the regulation of the channel by G proteins that take into account the regulatory input of each Gbetagamma binding element.
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Affiliation(s)
- Michel De Waard
- Laboratoire Canaux Calciques, Fonctions et Pathologies, Inserm U607, CEA, DRDC, 17 rue des Martyrs, 38054 Grenoble Cedex 09, France.
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Herlitze S, Xie M, Han J, Hümmer A, Melnik-Martinez KV, Moreno RL, Mark MD. Targeting mechanisms of high voltage-activated Ca2+ channels. J Bioenerg Biomembr 2004; 35:621-37. [PMID: 15000523 DOI: 10.1023/b:jobb.0000008027.19384.c0] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Functional voltage-dependent Ca2+ channel complexes are assembled by three to four subunits: alpha1, beta, alpha2delta subunits (C. Leveque et al., 1994, J. Biol Chem. 269, 6306-6312; M. W. McEnery et al., 1991, Proc. Natl. Acad. Sci. U.S.A. 88, 11095-11099) and at least in muscle cells also y subunits (B. M. Curtis and W. A. Catterall, 1984, Biochemistry 23, 2113-2118). Ca2+ channels mediate the voltage-dependent Ca2+ influx in subcellular compartments, triggering such diverse processes as neurotransmitter release, dendritic action potentials, excitation-contraction, and excitation-transcription coupling. The targeting of biophysically defined Ca2+ channel complexes to the correct subcellular structures is, thus, critical to proper cell and physiological functioning. Despite their importance, surprisingly little is known about the targeting mechanisms by which Ca2+ channel complexes are transported to their site of function. Here we summarize what we know about the targeting of Ca2+ channel complexes through the cell to the plasma membrane and subcellular structures.
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Affiliation(s)
- Stefan Herlitze
- Department of Neurosciences, Case Western Reserve University, School of Medicine, Room E604, 10900 Euclid Avenue, Cleveland, Ohio 44106-4975, USA.
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Dafi O, Berrou L, Dodier Y, Raybaud A, Sauvé R, Parent L. Negatively charged residues in the N-terminal of the AID helix confer slow voltage dependent inactivation gating to CaV1.2. Biophys J 2004; 87:3181-92. [PMID: 15339810 PMCID: PMC1304788 DOI: 10.1529/biophysj.104.045559] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The E462R mutation in the fifth position of the AID (alpha1 subunit interaction domain) region in the I-II linker is known to significantly accelerate voltage-dependent inactivation (VDI) kinetics of the L-type CaV1.2 channel, suggesting that the AID region could participate in a hinged-lid type inactivation mechanism in these channels. The recently solved crystal structures of the AID-CaVbeta regions in L-type CaV1.1 and CaV1.2 channels have shown that in addition to E462, positions occupied by Q458, Q459, E461, K465, L468, D469, and T472 in the rabbit CaV1.2 channel could also potentially contribute to a hinged-lid type mechanism. A mutational analysis of these residues shows that Q458A, Q459A, K465N, L468R, D469A, and T472D did not significantly alter VDI gating. In contrast, mutations of the negatively charged E461, E462, and D463 to neutral or positively charged residues increased VDI gating, suggesting that the cluster of negatively charged residues in the N-terminal end of the AID helix could account for the slower VDI kinetics of CaV1.2. A mutational analysis at position 462 (R, K, A, G, D, N, Q) further confirmed that E462R yielded faster VDI kinetics at +10 mV than any other residue with E462R >> E462K approximately E462A > E462N > wild-type approximately E462Q approximately E462G > E462D (from the fastest to the slowest). E462R was also found to increase the VDI gating of the slow CEEE chimera that includes the I-II linker from CaV1.2 into a CaV2.3 background. The fast VDI kinetics of the CaV1.2 E462R and the CEEE + E462R mutants were abolished by the CaVbeta2a subunit and reinstated when using the nonpalmitoylated form of CaVbeta2a C3S + C4S (CaVbeta2a CS), confirming that CaVbeta2a and E462R modulate VDI through a common pathway, albeit in opposite directions. Altogether, these results highlight the unique role of E461, E462, and D463 in the I-II linker in the VDI gating of high-voltage activated CaV1.2 channels.
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Affiliation(s)
- Omar Dafi
- Département de Physiologie, Membrane Protein Research Group, Université de Montréal, Montréal, Québec H3C 3J7, Canada
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Viard P, Butcher AJ, Halet G, Davies A, Nürnberg B, Heblich F, Dolphin AC. PI3K promotes voltage-dependent calcium channel trafficking to the plasma membrane. Nat Neurosci 2004; 7:939-46. [PMID: 15311280 DOI: 10.1038/nn1300] [Citation(s) in RCA: 200] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2004] [Accepted: 07/07/2004] [Indexed: 01/01/2023]
Abstract
Phosphatidylinositol 3-kinase (PI3K) has been shown to enhance native voltage-dependent calcium channel (Ca(v)) currents both in myocytes and in neurons; however, the mechanism(s) responsible for this regulation were not known. Here we show that PI3K promotes the translocation of GFP-tagged Ca(v) channels to the plasma membrane in both COS-7 cells and neurons. We show that the effect of PI3K is mediated by Akt/PKB and specifically requires Ca(v)beta(2) subunits. The mutations S574A and S574E in Ca(v)beta(2a) prevented and mimicked, respectively, the effect of PI3K/Akt-PKB, indicating that phosphorylation of Ser574 on Ca(v)beta(2a) is necessary and sufficient to promote Ca(v) channel trafficking.
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Affiliation(s)
- Patricia Viard
- Department of Pharmacology, University College London, London WC1E 6BT, UK.
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Yasuda T, Chen L, Barr W, McRory JE, Lewis RJ, Adams DJ, Zamponi GW. Auxiliary subunit regulation of high-voltage activated calcium channels expressed in mammalian cells. Eur J Neurosci 2004; 20:1-13. [PMID: 15245474 DOI: 10.1111/j.1460-9568.2004.03434.x] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The effects of auxiliary calcium channel subunits on the expression and functional properties of high-voltage activated (HVA) calcium channels have been studied extensively in the Xenopus oocyte expression system, but are less completely characterized in a mammalian cellular environment. Here, we provide the first systematic analysis of the effects of calcium channel beta and alpha(2)-delta subunits on expression levels and biophysical properties of three different types (Ca(v)1.2, Ca(v)2.1 and Ca(v)2.3) of HVA calcium channels expressed in tsA-201 cells. Our data show that Ca(v)1.2 and Ca(v)2.3 channels yield significant barium current in the absence of any auxiliary subunits. Although calcium channel beta subunits were in principle capable of increasing whole cell conductance, this effect was dependent on the type of calcium channel alpha(1) subunit, and beta(3) subunits altogether failed to enhance current amplitude irrespective of channel subtype. Moreover, the alpha(2)-delta subunit alone is capable of increasing current amplitude of each channel type examined, and at least for members of the Ca(v)2 channel family, appears to act synergistically with beta subunits. In general agreement with previous studies, channel activation and inactivation gating was regulated both by beta and by alpha(2)-delta subunits. However, whereas pronounced regulation of inactivation characteristics was seen with the majority of the auxiliary subunits, effects on voltage dependence of activation were only small (< 5 mV). Overall, through a systematic approach, we have elucidated a previously underestimated role of the alpha(2)-delta(1) subunit with regard to current enhancement and kinetics. Moreover, the effects of each auxiliary subunit on whole cell conductance and channel gating appear to be specifically tailored to subsets of calcium channel subtypes.
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Affiliation(s)
- Takahiro Yasuda
- Department of Physiology and Biophysics, Cellular and Molecular Neurobiology Research Group, University of Calgary, 3330 Hospital Dr. NW, Calgary, T2N 4 N1, Canada
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Park JY, Kang HW, Jeong SW, Lee JH. Multiple Structural Elements Contribute to the Slow Kinetics of the Cav3.3 T-type Channel. J Biol Chem 2004; 279:21707-13. [PMID: 15016809 DOI: 10.1074/jbc.m400684200] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Molecular cloning and expression studies established the existence of three T-type Ca(2+) channel (Ca(v)3) alpha(1) subunits: Ca(v)3.1 (alpha(1G)), Ca(v)3.2 (alpha(1H)), and Ca(v)3.3 (alpha(1I)). Although all three channels are low voltage-activated, they display considerable differences in their kinetics, with Ca(v)3.1 and Ca(v)3.2 channels activating and inactivating much faster than Ca(v)3.3 channels. The goal of the present study was to determine the structural elements that confer the distinctively slow kinetics of Ca(v)3.3 channels. To address this question, a series of chimeric channels between Ca(v)3.1 and Ca(v)3.3 channels were constructed and expressed in Xenopus oocytes. Kinetic analysis showed that the slow activation and inactivation kinetics of the Ca(v)3.3 channel were not completely abolished by substitution with any one portion of the Ca(v)3.1 channel. Likewise, the Ca(v)3.1 channel failed to acquire the slow kinetics by simply adopting one portion of the Ca(v)3.3 channel. These findings suggest that multiple structural elements contribute to the slow kinetics of Ca(v)3.3 channels.
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Affiliation(s)
- Jin-Yong Park
- Department of Life Science, Sogang University, Shinsu-dong, Seoul 121-742, Korea
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Opatowsky Y, Chen CC, Campbell KP, Hirsch JA. Structural Analysis of the Voltage-Dependent Calcium Channel β Subunit Functional Core and Its Complex with the α1 Interaction Domain. Neuron 2004; 42:387-99. [PMID: 15134636 DOI: 10.1016/s0896-6273(04)00250-8] [Citation(s) in RCA: 216] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2004] [Revised: 03/23/2004] [Accepted: 04/12/2004] [Indexed: 11/21/2022]
Abstract
Voltage-dependent calcium channels (VDCC) are multiprotein assemblies that regulate the entry of extracellular calcium into electrically excitable cells and serve as signal transduction centers. The alpha1 subunit forms the membrane pore while the intracellular beta subunit is responsible for trafficking of the channel to the plasma membrane and modulation of its electrophysiological properties. Crystallographic analyses of a beta subunit functional core alone and in complex with a alpha1 interaction domain (AID) peptide, the primary binding site of beta to the alpha1 subunit, reveal that beta represents a novel member of the MAGUK protein family. The findings illustrate how the guanylate kinase fold has been fashioned into a protein-protein interaction module by alteration of one of its substrate sites. Combined results indicate that the AID peptide undergoes a helical transition in binding to beta. We outline the mechanistic implications for understanding the beta subunit's broad regulatory role of the VDCC, particularly via the AID.
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Affiliation(s)
- Yarden Opatowsky
- Department of Biochemistry, Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel
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Sandoz G, Lopez-Gonzalez I, Stamboulian S, Weiss N, Arnoult C, De Waard M. Repositioning of charged I-II loop amino acid residues within the electric field by beta subunit as a novel working hypothesis for the control of fast P/Q calcium channel inactivation. Eur J Neurosci 2004; 19:1759-72. [PMID: 15078550 DOI: 10.1111/j.1460-9568.2004.03216.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We have investigated the contribution of the Ca(v)beta subunits to the process of inactivation dependent of the I-II loop of Ca(v)alpha(2.1). Two amino acid residues located in the alpha1 interaction domain (AID) of the I-II loop of Ca(v)alpha(2.1) (Arg(387) and Glu(388)) have been directly implicated in voltage-dependent inactivation of this channel. Various point mutations of these residues disrupt the interaction between the I-II loop and the III-IV loop, and thereby modify the inactivation properties of the channel by accelerating its kinetics and shifting the steady-state inactivation curve towards hyperpolarized potentials. A similar disruption is produced by Ca(v)beta(4) subunit association with the I-II loop. Moreover, in the presence of Ca(v)beta(4) subunit, introducing negatively charged residues at positions 387 or 388 slows inactivation kinetics down, whereas introducing positive charges has the opposite effect. The shift of the steady-state inactivation curve is also amino acid charge-dependent. In contrast, mutation of Arg(387) or Glu(388) does not alter the differential regulation of the different Ca(v)beta isoforms on inactivation. These results suggest that the expression of Ca(v)beta(4) alters the contribution of charged residues at positions 387 and 388 to inactivation. We discuss these results with regard to the actual hypotheses on the mechanisms of calcium channel inactivation. We introduce the working concept that Ca(v)beta-subunits produce a conformational repositioning of charged AID residues within the electric field.
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Affiliation(s)
- Guillaume Sandoz
- INSERM Unité, CEA, Laboratoire Canaux Calciques, Fonctions et Pathologies, DRDC, 17 Rue des Martyrs, 38054 Grenoble Cedex 9, France
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Yasuda T, Lewis RJ, Adams DJ. Overexpressed Ca(v)beta3 inhibits N-type (Cav2.2) calcium channel currents through a hyperpolarizing shift of ultra-slow and closed-state inactivation. ACTA ACUST UNITED AC 2004; 123:401-16. [PMID: 15024042 PMCID: PMC2217459 DOI: 10.1085/jgp.200308967] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
It has been shown that β auxiliary subunits increase current amplitude in voltage-dependent calcium channels. In this study, however, we found a novel inhibitory effect of β3 subunit on macroscopic Ba2+ currents through recombinant N- and R-type calcium channels expressed in Xenopus oocytes. Overexpressed β3 (12.5 ng/cell cRNA) significantly suppressed N- and R-type, but not L-type, calcium channel currents at “physiological” holding potentials (HPs) of −60 and −80 mV. At a HP of −80 mV, coinjection of various concentrations (0–12.5 ng) of the β3 with Cav2.2α1 and α2δ enhanced the maximum conductance of expressed channels at lower β3 concentrations but at higher concentrations (>2.5 ng/cell) caused a marked inhibition. The β3-induced current suppression was reversed at a HP of −120 mV, suggesting that the inhibition was voltage dependent. A high concentration of Ba2+ (40 mM) as a charge carrier also largely diminished the effect of β3 at −80 mV. Therefore, experimental conditions (HP, divalent cation concentration, and β3 subunit concentration) approaching normal physiological conditions were critical to elucidate the full extent of this novel β3 effect. Steady-state inactivation curves revealed that N-type channels exhibited “closed-state” inactivation without β3, and that β3 caused an ∼40-mV negative shift of the inactivation, producing a second component with an inactivation midpoint of approximately −85 mV. The inactivation of N-type channels in the presence of a high concentration (12.5 ng/cell) of β3 developed slowly and the time-dependent inactivation curve was best fit by the sum of two exponential functions with time constants of 14 s and 8.8 min at −80 mV. Similar “ultra-slow” inactivation was observed for N-type channels without β3. Thus, β3 can have a profound negative regulatory effect on N-type (and also R-type) calcium channels by causing a hyperpolarizing shift of the inactivation without affecting “ultra-slow” and “closed-state” inactivation properties.
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Stotz SC, Jarvis SE, Zamponi GW. Functional roles of cytoplasmic loops and pore lining transmembrane helices in the voltage-dependent inactivation of HVA calcium channels. J Physiol 2004; 554:263-73. [PMID: 12815185 PMCID: PMC1664770 DOI: 10.1113/jphysiol.2003.047068] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Voltage-dependent inactivation of calcium channels is a key mechanism for regulating intracellular calcium levels and neuronal excitability. In sodium and potassium channels, the molecular determinants that govern fast inactivation involve pore block by a cytoplasmic gating particle. As we discuss here, there is an increasing body of evidence that is consistent with a qualitatively similar inactivation mechanism in high-voltage-activated calcium channels. Work from a number of laboratories has implicated both cytoplasmic regions and the pore-lining S6 transmembrane helices in the inactivation process. Together with our recent findings, this leads us to propose a model in which the intracellular domain I-II linker region acts as a 'hinged lid' that physically occludes the pore by docking to the cytoplasmic ends of the S6 segments. We further propose that the ancillary calcium channel Beta subunits differentially modulate inactivation kinetics by binding to and thereby regulating the mobility of the putative inactivation gate. Indeed, additional evidence suggests that the carboxy terminus, amino terminus and domain III-IV linker regions of the channel modulate inactivation rates through interactions with the I-II linker per se, or indirectly via the ancillary Beta subunits. Taken together, the fast voltage-dependent inactivation of calcium channels appears reminiscent of that of sodium channels, but appears to show a more complex regulation through intramolecular interactions between the putative inactivation gate and other cytoplasmic regions.
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Affiliation(s)
- Stephanie C Stotz
- Department of Physiology and Biophysics, University of Calgary, 3330 Hospital Drive NW, Calgary T2N 4N1, Canada
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Stotz SC, Barr W, McRory JE, Chen L, Jarvis SE, Zamponi GW. Several Structural Domains Contribute to the Regulation of N-type Calcium Channel Inactivation by the β3 Subunit. J Biol Chem 2004; 279:3793-800. [PMID: 14602720 DOI: 10.1074/jbc.m308991200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calcium channel beta subunits are essential regulatory elements of the gating properties of high voltage-activated calcium channels. Co-expression with beta(3) subunits typically accelerates inactivation, whereas co-expression with beta(4) subunits results in a slowly inactivating phenotype. Here, we have examined the molecular basis of the differential effect of these two subunits on the inactivation characteristics of Ca(v)2.2 + alpha(2)-delta(1) N-type calcium channels by creating a series of 22 chimeric beta subunits that are based on various combinations of variable and conserved regions of the parent beta subunit isoforms. Our data show that replacement of the N terminus region of beta(4) with a corresponding 14-amino acid stretch of beta(3) sequence accelerates the inactivation kinetics to levels seen with wild type beta(3). A similar kinetic speeding is observed by a concomitant substitution of the second conserved and variable regions, but not when these regions are substituted individually, suggesting that 1) the second variable and conserved regions cooperatively regulate N-type calcium channel inactivation and 2) that there are two redundant mechanisms that allow the beta(3) subunit to accelerate N-type channel inactivation. In contrast with previous reports in Ca(v)2.1 calcium channels, deletion of the C-terminal region of Ca(v)2.2 did not alter the regulation of the channel by wild type and chimeric beta subunits. Hence, the molecular underpinnings of beta subunit regulation of voltage-gated calcium channels appear to vary with calcium channel subtype.
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Affiliation(s)
- Stephanie C Stotz
- Department of Physiology and Biophysics. Cellular and Molecular Neurobiology Research Group, University of Calgary, Calgary, Alberta T2N 4N1, Canada
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Abstract
Calcium influx into any cell requires fine tuning to guarantee the correct balance between activation of calcium-dependent processes, such as muscle contraction and neurotransmitter release, and calcium-induced cell damage. G protein-coupled receptors play a critical role in negative feedback to modulate the activity of the CaV2 subfamily of the voltage-dependent calcium channels, which are largely situated on neuronal and neuro-endocrine cells. The basis for the specificity of the relationships among membrane receptors, G proteins, and effector calcium channels will be discussed, as well as the mechanism by which G protein-mediated inhibition is thought to occur. The inhibition requires free G beta gamma dimers, and the cytoplasmic linker between domains I and II of the CaV2 alpha 1 subunits binds G beta gamma dimers, whereas the intracellular N terminus of CaV2 alpha 1 subunits provides essential determinants for G protein modulation. Evidence suggests a key role for the beta subunits of calcium channels in the process of G protein modulation, and the role of a class of proteins termed "regulators of G protein signaling" will also be described.
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Affiliation(s)
- Annette C Dolphin
- Department of Pharmacology, University College London, Gower St., London WC1E 6BT, UK.
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40
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Opatowsky Y, Chomsky-Hecht O, Kang MG, Campbell KP, Hirsch JA. The voltage-dependent calcium channel beta subunit contains two stable interacting domains. J Biol Chem 2003; 278:52323-32. [PMID: 14559910 DOI: 10.1074/jbc.m303564200] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Voltage-dependent calcium channels selectively enable Ca2+ ion movement through cellular membranes. These multiprotein complexes are involved in a wide spectrum of biological processes such as signal transduction and cellular homeostasis. alpha1 is the membrane pore-forming subunit, whereas beta is an intracellular subunit that binds to alpha1, facilitating and modulating channel function. We have expressed, purified, and characterized recombinant beta3 and beta2a using both biochemical and biophysical methods, including electrophysiology, to better understand the beta family's protein structural and functional correlates. Our results indicate that the beta protein is composed of two distinct domains that associate with one another in a stable manner. The data also suggest that the polypeptide regions outside these domains are not structured when beta is not in complex with the channel. In addition, the beta structural core, comprised of just these two domains without other sequences, binds tightly to the alpha interaction domain (AID) motif, a sequence derived from the alpha1 subunit and the principal anchor site of beta. Domain II is responsible for this binding, but domain I enhances it.
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Affiliation(s)
- Yarden Opatowsky
- Department of Biochemistry, Faculty of Life Sciences, Tel Aviv University, Sherman Bldg., Rm. 621, Ramat Aviv 69978, Israel
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Abstract
Ca(2+) channel blockers such as 1,4-dihydropyridines, phenylalkylamines, diltiazem and mibefradil exert their anti-arrhythmic and anti-hypertensive action by restricting Ca(2+) entry into myocardial cells and smooth muscle cells. Binding sites for these drugs are present on the pore-forming alpha(1)-subunits of voltage-dependent Ca(2+) (Ca(v)) channels. However, striking new data show that auxillary beta-subunits also influence drug sensitivity significantly. These findings are summarized and the underlying molecular mechanisms and their pharmacological relevance are discussed.
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Affiliation(s)
- Steffen Hering
- Institut für Biochemische Pharmakologie, Peter Mayr Strasse 1, A-6020, Innsbruck, Austria.
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Berrou L, Klein H, Bernatchez G, Parent L. A specific tryptophan in the I-II linker is a key determinant of beta-subunit binding and modulation in Ca(V)2.3 calcium channels. Biophys J 2002; 83:1429-42. [PMID: 12202369 PMCID: PMC1302242 DOI: 10.1016/s0006-3495(02)73914-3] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The ancillary beta subunits modulate the activation and inactivation properties of high-voltage activated (HVA) Ca(2+) channels in an isoform-specific manner. The beta subunits bind to a high-affinity interaction site, alpha-interaction domain (AID), located in the I-II linker of HVA alpha1 subunits. Nine residues in the AID motif are absolutely conserved in all HVA channels (QQxExxLxGYxxWIxxxE), but their contribution to beta-subunit binding and modulation remains to be established in Ca(V)2.3. Mutations of W386 to either A, G, Q, R, E, F, or Y in Ca(V)2.3 disrupted [(35)S]beta3-subunit overlay binding to glutathione S-transferase fusion proteins containing the mutated I-II linker, whereas mutations (single or multiple) of nonconserved residues did not affect the protein-protein interaction with beta3. The tryptophan residue at position 386 appears to be an essential determinant as substitutions with hydrophobic (A and G), hydrophilic (Q, R, and E), or aromatic (F and Y) residues yielded the same results. beta-Subunit modulation of W386 (A, G, Q, R, E, F, and Y) and Y383 (A and S) mutants was investigated after heterologous expression in Xenopus oocytes. All mutant channels expressed large inward Ba(2+) currents with typical current-voltage properties. Nonetheless, the typical hallmarks of beta-subunit modulation, namely the increase in peak currents, the hyperpolarization of peak voltages, and the modulation of the kinetics and voltage dependence of inactivation, were eliminated in all W386 mutants, although they were preserved in part in Y383 (A and S) mutants. Altogether these results suggest that W386 is critical for beta-subunit binding and modulation of HVA Ca(2+) channels.
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Affiliation(s)
- L Berrou
- Département de Physiologie, Membrane Transport Research Group, Université de Montréal, Montréal, Quebec H3C 3J7, Canada
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43
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Fitzgerald EM. The presence of Ca2+ channel beta subunit is required for mitogen-activated protein kinase (MAPK)-dependent modulation of alpha1B Ca2+ channels in COS-7 cells. J Physiol 2002; 543:425-37. [PMID: 12205179 PMCID: PMC2290524 DOI: 10.1113/jphysiol.2002.022822] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
In rat sensory neurones, voltage-dependent calcium channels (VDCCs), including the N-type, are tonically up-regulated via Ras/mitogen-activated protein kinase (MAPK) signalling. To determine whether VDCC beta subunit is involved in this process, the role of the four neuronal betas (beta1b, beta2a, beta3, beta4) in MAPK-dependent modulation of alpha1B (Ca(v)2.2, N-type) Ca(2+) channels has been examined in COS-7 cells. MAPK is exclusively activated by MAPK kinase (MEK), and here, acute application of a MEK-specific inhibitor UO126, significantly inhibited peak alpha1B Ca2+ channel current (I(max)) within a period of 5-10 min, regardless of which beta subunit was co-expressed (25-50 %, P < 0.01). With beta2a however, the percentage inhibition of I(max) was less than that observed with any other beta (ANOVA: F(3,34) = 6.48, P < 0.01). UO126 also caused a hyperpolarising shift (6 +/- 1 mV, P < 0.001) in the voltage dependence of beta2a current activation, such that inhibition occurred only at depolarised potentials (> +5 mV) whereas at more negative potentials the current amplitude was enhanced. A marked change in beta2a current kinetics, perceived either as decreased activation or increased inactivation, was also associated with UO126 application. A similar effect of UO126 on beta4 current kinetics was also observed. The beta2a-specific effects of UO126 on current inhibition and voltage dependence of activation were abolished when alpha1B was co-expressed with de-palmitoylated beta2a(C3,4S), in which amino terminal cysteines 3 and 4 had been mutated to serines. In the absence of beta subunit, UO126 had no effect on alpha1B Ca2+ channel current. Together, these data suggest an absolute requirement for beta in MAPK-dependent modulation of these channels. Since beta subunits vary both in their temporal expression and localisation within neurones, beta subunit-dependent modulation of N-type Ca2+ channels via MAPK could provide an important new mechanism by which to fine-tune neurotransmitter release.
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Affiliation(s)
- Elizabeth M Fitzgerald
- Department of Pharmacology, University College London, Gower Street, London WC1E 6BT, UK.
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44
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Hitzl M, Striessnig J, Neuhuber B, Flucher BE. A mutation in the beta interaction domain of the Ca(2+) channel alpha(1C) subunit reduces the affinity of the (+)-[(3)H]isradipine binding site. FEBS Lett 2002; 524:188-92. [PMID: 12135765 DOI: 10.1016/s0014-5793(02)03054-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The molecular mechanisms of how alpha(1) and beta subunits of voltage-gated Ca(2+) channels interact with one another are still controversial. Here we show that despite a mutation in the beta interaction domain that has previously been shown to disrupt binding, alpha(1C)Y467S and beta(1a-myc) still formed immunoprecipitable complexes when coexpressed in tsA201 cells. However, the alpha(1C)Y467S-beta(1a-myc) complexes had a decreased affinity to (+)-[(3)H]isradipine. This indicates that the beta interaction domain in the I-II loop of the alpha(1) subunit is not merely an anchor required for the functional interaction of the two Ca(2+) channel subunits but is itself part of the effector pathway for beta-induced channel modulation.
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Affiliation(s)
- Monika Hitzl
- Department of Biochemical Pharmacology, University of Innsbruck, A-6020 Innsbruck, Austria
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45
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Geib S, Sandoz G, Cornet V, Mabrouk K, Fund-Saunier O, Bichet D, Villaz M, Hoshi T, Sabatier JM, De Waard M. The interaction between the I-II loop and the III-IV loop of Cav2.1 contributes to voltage-dependent inactivation in a beta -dependent manner. J Biol Chem 2002; 277:10003-13. [PMID: 11790766 DOI: 10.1074/jbc.m106231200] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have investigated the molecular mechanisms whereby the I-II loop controls voltage-dependent inactivation in P/Q calcium channels. We demonstrate that the I-II loop is localized in a central position to control calcium channel activity through the interaction with several cytoplasmic sequences; including the III-IV loop. Several experiments reveal the crucial role of the interaction between the I-II loop and the III-IV loop in channel inactivation. First, point mutations of two amino acid residues of the I-II loop of Ca(v)2.1 (Arg-387 or Glu-388) facilitate voltage-dependent inactivation. Second, overexpression of the III-IV loop, or injection of a peptide derived from this loop, produces a similar inactivation behavior than the mutated channels. Third, the III-IV peptide has no effect on channels mutated in the I-II loop. Thus, both point mutations and overexpression of the III-IV loop appear to act similarly on inactivation, by competing off the native interaction between the I-II and the III-IV loops of Ca(v)2.1. As they are known to affect inactivation, we also analyzed the effects of beta subunits on these interactions. In experiments in which the beta(4) subunit is co-expressed, the III-IV peptide is no longer able to regulate channel inactivation. We conclude that (i) the contribution of the I-II loop to inactivation is partly mediated by an interaction with the III-IV loop and (ii) the beta subunits partially control inactivation by modifying this interaction. These data provide novel insights into the mechanisms whereby the beta subunit, the I-II loop, and the III-IV loop altogether can contribute to regulate inactivation in high voltage-activated calcium channels.
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Affiliation(s)
- Sandrine Geib
- INSERM Unité 464, Laboratoire de Neurobiologie des Canaux Ioniques, Faculté de Médecine Nord, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
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46
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Dominant-negative synthesis suppression of voltage-gated calcium channel Cav2.2 induced by truncated constructs. J Neurosci 2001. [PMID: 11606638 DOI: 10.1523/jneurosci.21-21-08495.2001] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Voltage-gated calcium channel alpha1 subunits consist of four domains (I-IV), each with six transmembrane segments. A number of truncated isoforms have been identified to occur as a result of alternative splicing or mutation. We have examined the functional consequences for expression of full-length Ca(v)2.2 (alpha1B) of its coexpression with truncated constructs of Ca(v)2.2. Domains I-II or domains III-IV, when expressed individually, together with the accessory subunits beta1b and alpha2delta-1, did not form functional channels. When they were coexpressed, low-density whole-cell currents and functional channels with properties similar to wild-type channels were observed. However, when domain I-II, domain III-IV, or domain I alone were coexpressed with full-length Ca(v)2.2, they markedly suppressed its functional expression, although at the single channel level, when channels were recorded, there were no differences in their biophysical properties. Furthermore, when it was coexpressed with either domain I-II or domain I, the fluorescence of green fluorescent protein (GFP)-Ca(v)2.2 and expression of Ca(v)2.2 protein was almost abolished. Suppression does not involve sequestration of the Ca(v)beta subunit, because loss of GFP-Ca(v)2.2 expression also occurred in the absence of beta subunit, and the effect of domain I-II or domain I could not be mimicked by the cytoplasmic I-II loop of Ca(v)2.2. It requires transmembrane segments, because the isolated Ca(v)2.2 N terminus did not have any effect. Our results indicate that the mechanism of suppression of Ca(v)2.2 by truncated constructs containing domain I involves inhibition of channel synthesis, which may represent a role of endogenously expressed truncated Ca(v) isoforms.
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47
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Marksteiner R, Schurr P, Berjukow S, Margreiter E, Perez-Reyes E, Hering S. Inactivation determinants in segment IIIS6 of Ca(v)3.1. J Physiol 2001; 537:27-34. [PMID: 11711558 PMCID: PMC2278921 DOI: 10.1111/j.1469-7793.2001.0027k.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. Low threshold, T-type, Ca(2+) channels of the Ca(v)3 family display the fastest inactivation kinetics among all voltage-gated Ca(2+) channels. The molecular inactivation determinants of this channel family are largely unknown. Here we investigate whether segment IIIS6 plays a role in Ca(v)3.1 inactivation as observed previously in high voltage-activated Ca(2+) channels. 2. Amino acids that are identical in IIIS6 segments of all Ca(2+) channel subtypes were mutated to alanine (F1505A, F1506A, N1509A, F1511A, V1512A, F1519A, FV1511/1512AA). Additionally M1510 was mutated to isoleucine and alanine. 3. The kinetic properties of the mutants were analysed with the two-microelectrode voltage-clamp technique after expression in Xenopus oocytes. The time constant for the barium current (I(Ba)) inactivation, tau(inact), of wild-type channels at -20 mV was 9.5 +/- 0.4 ms; the corresponding time constants of the mutants ranged from 9.2 +/- 0.4 ms in V1512A to 45.7 +/- 5.2 ms (4.8-fold slowing) in M1510I. Recovery at -80 mV was most significantly slowed by V1512A and accelerated by F1511A. 4. We conclude that amino acids M1510, F1511 and V1512 corresponding to previously identified inactivation determinants in IIIS6 of Ca(v)2.1 (Hering et al. 1998) have a significant role in Ca(v)3.1 inactivation. These data suggest common elements in the molecular architecture of the inactivation mechanism in high and low threshold Ca(2+) channels.
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Affiliation(s)
- R Marksteiner
- Institut für Biochemische Pharmakologie, Peter-Mayr-Strasse 1, A-6020 Innsbruck, Austria
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48
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Raghib A, Bertaso F, Davies A, Page KM, Meir A, Bogdanov Y, Dolphin AC. Dominant-negative synthesis suppression of voltage-gated calcium channel Cav2.2 induced by truncated constructs. J Neurosci 2001; 21:8495-504. [PMID: 11606638 PMCID: PMC6762802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2001] [Revised: 08/15/2001] [Accepted: 08/23/2001] [Indexed: 02/21/2023] Open
Abstract
Voltage-gated calcium channel alpha1 subunits consist of four domains (I-IV), each with six transmembrane segments. A number of truncated isoforms have been identified to occur as a result of alternative splicing or mutation. We have examined the functional consequences for expression of full-length Ca(v)2.2 (alpha1B) of its coexpression with truncated constructs of Ca(v)2.2. Domains I-II or domains III-IV, when expressed individually, together with the accessory subunits beta1b and alpha2delta-1, did not form functional channels. When they were coexpressed, low-density whole-cell currents and functional channels with properties similar to wild-type channels were observed. However, when domain I-II, domain III-IV, or domain I alone were coexpressed with full-length Ca(v)2.2, they markedly suppressed its functional expression, although at the single channel level, when channels were recorded, there were no differences in their biophysical properties. Furthermore, when it was coexpressed with either domain I-II or domain I, the fluorescence of green fluorescent protein (GFP)-Ca(v)2.2 and expression of Ca(v)2.2 protein was almost abolished. Suppression does not involve sequestration of the Ca(v)beta subunit, because loss of GFP-Ca(v)2.2 expression also occurred in the absence of beta subunit, and the effect of domain I-II or domain I could not be mimicked by the cytoplasmic I-II loop of Ca(v)2.2. It requires transmembrane segments, because the isolated Ca(v)2.2 N terminus did not have any effect. Our results indicate that the mechanism of suppression of Ca(v)2.2 by truncated constructs containing domain I involves inhibition of channel synthesis, which may represent a role of endogenously expressed truncated Ca(v) isoforms.
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Affiliation(s)
- A Raghib
- Department of Pharmacology, University College London, London WC1E6BT, United Kingdom
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49
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Cantí C, Davies A, Berrow NS, Butcher AJ, Page KM, Dolphin AC. Evidence for two concentration-dependent processes for beta-subunit effects on alpha1B calcium channels. Biophys J 2001; 81:1439-51. [PMID: 11509358 PMCID: PMC1301623 DOI: 10.1016/s0006-3495(01)75799-2] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
beta-Subunits of voltage-dependent Ca(2+) channels regulate both their expression and biophysical properties. We have injected a range of concentrations of beta3-cDNA into Xenopus oocytes, with a fixed concentration of alpha1B (Ca(V)2.2) cDNA, and have quantified the corresponding linear increase of beta3 protein. The concentration dependence of a number of beta3-dependent processes has been studied. First, the dependence of the a1B maximum conductance on beta3-protein occurs with a midpoint around the endogenous concentration of beta3 (approximately 17 nM). This may represent the interaction of the beta-subunit, responsible for trafficking, with the I-II linker of the nascent channel. Second, the effect of beta3-subunits on the voltage dependence of steady-state inactivation provides evidence for two channel populations, interpreted as representing alpha1B without or with a beta3-subunit, bound with a lower affinity of 120 nM. Third, the effect of beta3 on the facilitation rate of G-protein-modulated alpha1B currents during a depolarizing prepulse to +100 mV provides evidence for the same two populations, with the rapid facilitation rate being attributed to Gbetagamma dissociation from the beta-subunit-bound alpha1B channels. The data are discussed in terms of two hypotheses, either binding of two beta-subunits to the alpha1B channel or a state-dependent alteration in affinity of the channel for the beta-subunit.
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Affiliation(s)
- C Cantí
- Department of Pharmacology, University College London, London WC1E 6BT, United Kingdom
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50
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Berrou L, Bernatchez G, Parent L. Molecular determinants of inactivation within the I-II linker of alpha1E (CaV2.3) calcium channels. Biophys J 2001; 80:215-28. [PMID: 11159396 PMCID: PMC1301227 DOI: 10.1016/s0006-3495(01)76008-0] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Voltage-dependent inactivation of CaV2.3 channels was investigated using point mutations in the beta-subunit-binding site (AID) of the I-II linker. The quintuple mutant alpha1E N381K + R384L + A385D + D388T + K389Q (NRADK-KLDTQ) inactivated like the wild-type alpha1E. In contrast, mutations of alpha1E at position R378 (position 5 of AID) into negatively charged residues Glu (E) or Asp (D) significantly slowed inactivation kinetics and shifted the voltage dependence of inactivation to more positive voltages. When co-injected with beta3, R378E inactivated with tau(inact) = 538 +/- 54 ms (n = 14) as compared with 74 +/- 4 ms (n = 21) for alpha1E (p < 0.001) with a mid-potential of inactivation E(0.5) = -44 +/- 2 mV (n = 10) for R378E as compared with E(0.5) = -64 +/- 3 mV (n = 9) for alpha1E. A series of mutations at position R378 suggest that positively charged residues could promote voltage-dependent inactivation. R378K behaved like the wild-type alpha1E whereas R378Q displayed intermediate inactivation kinetics. The reverse mutation E462R in the L-type alpha1C (CaV1.2) produced channels with inactivation properties comparable to alpha1E R378E. Hence, position 5 of the AID motif in the I-II linker could play a significant role in the inactivation of Ca(V)1.2 and CaV2.3 channels.
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Affiliation(s)
- L Berrou
- Department of Physiology, Membrane Transport Research Group, Université de Montréal, Montréal, Québec H3C 3J7 Canada
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