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Lucaci AG, Brew WE, Lamanna J, Selberg A, Carnevale V, Moore AR, Kosakovsky Pond SL. The evolution of mammalian Rem2: unraveling the impact of purifying selection and coevolution on protein function, and implications for human disorders. FRONTIERS IN BIOINFORMATICS 2024; 4:1381540. [PMID: 38978817 PMCID: PMC11228553 DOI: 10.3389/fbinf.2024.1381540] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2024] [Accepted: 05/28/2024] [Indexed: 07/10/2024] Open
Abstract
Rad And Gem-Like GTP-Binding Protein 2 (Rem2), a member of the RGK family of Ras-like GTPases, is implicated in Huntington's disease and Long QT Syndrome and is highly expressed in the brain and endocrine cells. We examine the evolutionary history of Rem2 identified in various mammalian species, focusing on the role of purifying selection and coevolution in shaping its sequence and protein structural constraints. Our analysis of Rem2 sequences across 175 mammalian species found evidence for strong purifying selection in 70% of non-invariant codon sites which is characteristic of essential proteins that play critical roles in biological processes and is consistent with Rem2's role in the regulation of neuronal development and function. We inferred epistatic effects in 50 pairs of codon sites in Rem2, some of which are predicted to have deleterious effects on human health. Additionally, we reconstructed the ancestral evolutionary history of mammalian Rem2 using protein structure prediction of extinct and extant sequences which revealed the dynamics of how substitutions that change the gene sequence of Rem2 can impact protein structure in variable regions while maintaining core functional mechanisms. By understanding the selective pressures, protein- and gene - interactions that have shaped the sequence and structure of the Rem2 protein, we gain a stronger understanding of its biological and functional constraints.
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Affiliation(s)
- Alexander G Lucaci
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY, United States
- Weill Cornell Medicine, The HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute for Computational Biomedicine, New York, NY, United States
| | - William E Brew
- Department of Biology, Temple University, Philadelphia, PA, United States
| | - Jason Lamanna
- Department of Biology, Temple University, Philadelphia, PA, United States
- Institute for Computational Molecular Science, Temple University, Philadelphia, PA, United States
| | - Avery Selberg
- Department of Biology, Temple University, Philadelphia, PA, United States
- Institute for Genomics and Evolutionary Medicine, Temple University, Philadelphia, PA, United States
| | - Vincenzo Carnevale
- Department of Biology, Temple University, Philadelphia, PA, United States
- Institute for Computational Molecular Science, Temple University, Philadelphia, PA, United States
| | - Anna R Moore
- Department of Biology, Temple University, Philadelphia, PA, United States
| | - Sergei L Kosakovsky Pond
- Department of Biology, Temple University, Philadelphia, PA, United States
- Institute for Genomics and Evolutionary Medicine, Temple University, Philadelphia, PA, United States
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2
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Allam S, Levenson-Palmer R, Chia Chang Z, Kaur S, Cernuda B, Raman A, Booth A, Dobbins S, Suppa G, Yang J, Buraei Z. Inactivation influences the extent of inhibition of voltage-gated Ca +2 channels by Gem-implications for channelopathies. Front Physiol 2023; 14:1155976. [PMID: 37654674 PMCID: PMC10466392 DOI: 10.3389/fphys.2023.1155976] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Accepted: 07/21/2023] [Indexed: 09/02/2023] Open
Abstract
Voltage-gated Ca2+ channels (VGCC) directly control muscle contraction and neurotransmitter release, and slower processes such as cell differentiation, migration, and death. They are potently inhibited by RGK GTP-ases (Rem, Rem2, Rad, and Gem/Kir), which decrease Ca2+ channel membrane expression, as well as directly inhibit membrane-resident channels. The mechanisms of membrane-resident channel inhibition are difficult to study because RGK-overexpression causes complete or near complete channel inhibition. Using titrated levels of Gem expression in Xenopus oocytes to inhibit WT P/Q-type calcium channels by ∼50%, we show that inhibition is dependent on channel inactivation. Interestingly, fast-inactivating channels, including Familial Hemiplegic Migraine mutants, are more potently inhibited than WT channels, while slow-inactivating channels, such as those expressed with the Cavβ2a auxiliary subunit, are spared. We found similar results in L-type channels, and, remarkably, Timothy Syndrome mutant channels were insensitive to Gem inhibition. Further results suggest that RGKs slow channel recovery from inactivation and further implicate RGKs as likely modulating factors in channelopathies.
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Affiliation(s)
- Salma Allam
- Department of Biology, Pace University, New York, NY, United States
| | - Rose Levenson-Palmer
- Department of Biological Sciences, Columbia University, New York, NY, United States
| | | | - Sukhjinder Kaur
- Department of Biology, Pace University, New York, NY, United States
| | - Bryan Cernuda
- Department of Biology, Pace University, New York, NY, United States
| | - Ananya Raman
- Department of Biology, Pace University, New York, NY, United States
| | - Audrey Booth
- Department of Biology, Pace University, New York, NY, United States
| | - Scott Dobbins
- Department of Biological Sciences, Columbia University, New York, NY, United States
| | - Gabrielle Suppa
- Department of Biology, Pace University, New York, NY, United States
| | - Jian Yang
- Department of Biological Sciences, Columbia University, New York, NY, United States
| | - Zafir Buraei
- Department of Biology, Pace University, New York, NY, United States
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3
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Agbu SO, Liang Y, Liu A, Anderson KV. The small GTPase RSG1 controls a final step in primary cilia initiation. J Cell Biol 2017; 217:413-427. [PMID: 29038301 PMCID: PMC5748968 DOI: 10.1083/jcb.201604048] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2016] [Revised: 08/18/2016] [Accepted: 09/21/2017] [Indexed: 12/11/2022] Open
Abstract
Primary cilia are essential for normal development and tissue homeostasis, but the mechanisms that remodel the centriole to promote cilia initiation are not well understood. Agbu et al. report that mouse RSG1, a small GTPase, regulates a late step in cilia initiation, downstream of TTBK2 and the CPLANE protein INTU. Primary cilia, which are essential for normal development and tissue homeostasis, are extensions of the mother centriole, but the mechanisms that remodel the centriole to promote cilia initiation are poorly understood. Here we show that mouse embryos that lack the small guanosine triphosphatase RSG1 die at embryonic day 12.5, with developmental abnormalities characteristic of decreased cilia-dependent Hedgehog signaling. Rsg1 mutant embryos have fewer primary cilia than wild-type embryos, but the cilia that form are of normal length and traffic Hedgehog pathway proteins within the cilium correctly. Rsg1 mother centrioles recruit proteins required for cilia initiation and dock onto ciliary vesicles, but axonemal microtubules fail to elongate normally. RSG1 localizes to the mother centriole in a process that depends on tau tubulin kinase 2 (TTBK2), the CPLANE complex protein Inturned (INTU), and its own GTPase activity. The data suggest a specific role for RSG1 in the final maturation of the mother centriole and ciliary vesicle that allows extension of the ciliary axoneme.
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Affiliation(s)
- Stephanie O Agbu
- Developmental Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, NY.,Biochemistry, Cell and Molecular Biology Program, Weill Graduate School of Medical Sciences of Cornell University, New York, NY
| | - Yinwen Liang
- Developmental Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, NY
| | - Aimin Liu
- Department of Biology, Eberly College of Science, The Pennsylvania State University, University Park, PA
| | - Kathryn V Anderson
- Developmental Biology Program, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, NY
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4
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Functional assessment of three Rem residues identified as critical for interactions with Ca(2+) channel β subunits. Pflugers Arch 2015; 467:2299-306. [PMID: 25771954 DOI: 10.1007/s00424-015-1700-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Accepted: 03/04/2015] [Indexed: 12/18/2022]
Abstract
Members of the Rem, Rem2, Rad, Gem/Kir (RGK) family of small GTP-binding proteins inhibit high-voltage-activated (HVA) Ca(2+) channels through interactions with both the principal α1 and the auxiliary β subunits of the channel complex. Three highly conserved residues of Rem (R200, L227, and H229) have been shown in vitro to be critical for interactions with β subunits. However, the functional significance of these residues is not known. To investigate the contributions of R200, L227, and H229 to β subunit-mediated RGK protein-dependent inhibition of HVA channels, we introduced alanine substitutions into all three positions of Venus fluorescent protein-tagged Rem (V-Rem AAA) and made three other V-Rem constructs with an alanine introduced at only one position (V-Rem R200A, V-Rem L227A, and V-Rem H229A). Confocal imaging and immunoblotting demonstrated that each Venus-Rem mutant construct had comparable expression levels to Venus-wild-type Rem when heterologously expressed in tsA201 cells. In electrophysiological experiments, V-Rem AAA failed to inhibit N-type Ca(2+) currents in tsA201 cells coexpressing CaV2.2 α1B, β3, and α2δ-1 channel subunits. The V-Rem L227A single mutant also failed to reduce N-type currents conducted by coexpressed CaV2.2 channels, a finding consistent with the previous observation that a leucine at position 227 is critical for Rem-β interactions. Rem-dependent inhibition of CaV2.2 channels was impaired to a much lesser extent by the R200A substitution. In contrast to the earlier work demonstrating that Rem H229A was unable to interact with β3 subunits in vitro, V-Rem H229A produced nearly complete inhibition of CaV2.2-mediated currents.
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5
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Buraei Z, Lumen E, Kaur S, Yang J. RGK regulation of voltage-gated calcium channels. SCIENCE CHINA-LIFE SCIENCES 2015; 58:28-38. [PMID: 25576452 PMCID: PMC9074095 DOI: 10.1007/s11427-014-4788-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/15/2014] [Accepted: 09/02/2014] [Indexed: 01/01/2023]
Abstract
Voltage-gated calcium channels (VGCCs) play critical roles in cardiac and skeletal muscle contractions, hormone and neurotransmitter release, as well as slower processes such as cell proliferation, differentiation, migration and death. Mutations in VGCCs lead to numerous cardiac, muscle and neurological disease, and their physiological function is tightly regulated by kinases, phosphatases, G-proteins, calmodulin and many other proteins. Fifteen years ago, RGK proteins were discovered as the most potent endogenous regulators of VGCCs. They are a family of monomeric GTPases (Rad, Rem, Rem2, and Gem/Kir), in the superfamily of Ras GTPases, and they have two known functions: regulation of cytoskeletal dynamics including dendritic arborization and inhibition of VGCCs. Here we review the mechanisms and molecular determinants of RGK-mediated VGCC inhibition, the physiological impact of this inhibition, and recent evidence linking the two known RGK functions.
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Affiliation(s)
- Zafir Buraei
- Department of Biology, Pace University, New York, NY, 10038, USA,
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6
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Xu X, Zhang F, Zamponi GW, Horne WA. Solution NMR and calorimetric analysis of Rem2 binding to the Ca2+ channel β4 subunit: a low affinity interaction is required for inhibition of Cav2.1 Ca2+ currents. FASEB J 2015; 29:1794-804. [PMID: 25563298 DOI: 10.1096/fj.14-264499] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Accepted: 12/22/2014] [Indexed: 12/20/2022]
Abstract
Rem, Rad, Kir/Gem (RGK) proteins, including Rem2, mediate profound inhibition of high-voltage activated Ca(2+) channels containing intracellular regulatory β subunits. All RGK proteins bind to voltage-gated Ca(2+) channel β subunit (Cavβ) subunits in vitro, but the necessity of the interaction for current inhibition remains controversial. This study applies NMR and calorimetric techniques to map the binding site for Rem2 on human Cavβ4a and measure its binding affinity. Our experiments revealed 2 binding surfaces on the β4 guanylate kinase domain contributing to a 156 ± 18 µM Kd interaction: a hydrophobic pocket lined by 4 critical residues (L173, N261, H262, and V303), mutation of any of which completely disrupted binding, and a nearby surface containing 3 residues (D206, L209, and D258) that when individually mutated decreased affinity. Voltage-gated Ca(2+) channel α1A subunit (Cav2.1) Ca(2+) currents were completely inhibited by Rem2 when co-expressed with wild-type Cavβ4a, but were unaffected by Rem2 when coexpressed with a Cavβ4a site 1 (L173A/V303A) or site 2 (D258A) mutant. These results provide direct evidence for a low-affinity Rem2/Cavβ4 interaction and show definitively that the interaction is required for Cav2.1 inhibition.
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Affiliation(s)
- Xingfu Xu
- *Department of Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA; and Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Fangxiong Zhang
- *Department of Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA; and Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Gerald W Zamponi
- *Department of Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA; and Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - William A Horne
- *Department of Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA; and Department of Physiology and Pharmacology, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
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7
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Beqollari D, Romberg CF, Meza U, Papadopoulos S, Bannister RA. Differential effects of RGK proteins on L-type channel function in adult mouse skeletal muscle. Biophys J 2014; 106:1950-7. [PMID: 24806927 DOI: 10.1016/j.bpj.2014.03.033] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2013] [Revised: 02/24/2014] [Accepted: 03/25/2014] [Indexed: 11/19/2022] Open
Abstract
Work in heterologous systems has revealed that members of the Rad, Rem, Rem2, Gem/Kir (RGK) family of small GTP-binding proteins profoundly inhibit L-type Ca(2+) channels via three mechanisms: 1), reduction of membrane expression; 2), immobilization of the voltage-sensors; and 3), reduction of Po without impaired voltage-sensor movement. However, the question of which mode is the critical one for inhibition of L-type channels in their native environments persists. To address this conundrum in skeletal muscle, we overexpressed Rad and Rem in flexor digitorum brevis (FDB) fibers via in vivo electroporation and examined the abilities of these two RGK isoforms to modulate the L-type Ca(2+) channel (CaV1.1). We found that Rad and Rem both potently inhibit L-type current in FDB fibers. However, intramembrane charge movement was only reduced in fibers transfected with Rad; charge movement for Rem-expressing fibers was virtually identical to charge movement observed in naïve fibers. This result indicated that Rem supports inhibition solely through a mechanism that allows for translocation of CaV1.1's voltage-sensors, whereas Rad utilizes at least one mode that limits voltage-sensor movement. Because Rad and Rem differ significantly only in their amino-termini, we constructed Rad-Rem chimeras to probe the structural basis for the distinct specificities of Rad- and Rem-mediated inhibition. Using this approach, a chimera composed of the amino-terminus of Rem and the core/carboxyl-terminus of Rad inhibited L-type current without reducing charge movement. Conversely, a chimera having the amino-terminus of Rad fused to the core/carboxyl-terminus of Rem inhibited L-type current with a concurrent reduction in charge movement. Thus, we have identified the amino-termini of Rad and Rem as the structural elements dictating the specific modes of inhibition of CaV1.1.
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Affiliation(s)
- D Beqollari
- Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, Aurora, Colorado
| | - C F Romberg
- Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, Aurora, Colorado
| | - U Meza
- Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, Aurora, Colorado; Departamento de Fisiología y Biofísica, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, San Luis Potosí, México
| | - S Papadopoulos
- Institute of Vegetative Physiology, University Hospital of Cologne, Cologne, Germany
| | - R A Bannister
- Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, Aurora, Colorado.
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8
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Moore AR, Ghiretti AE, Paradis S. A loss-of-function analysis reveals that endogenous Rem2 promotes functional glutamatergic synapse formation and restricts dendritic complexity. PLoS One 2013; 8:e74751. [PMID: 23991227 PMCID: PMC3753333 DOI: 10.1371/journal.pone.0074751] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2013] [Accepted: 08/06/2013] [Indexed: 12/28/2022] Open
Abstract
Rem2 is a member of the RGK family of small Ras-like GTPases whose expression and function is regulated by neuronal activity in the brain. A number of questions still remain as to the endogenous functions of Rem2 in neurons. RNAi-mediated Rem2 knockdown leads to an increase in dendritic complexity and a decrease in functional excitatory synapses, though a recent report challenged the specificity of Rem2-targeted RNAi reagents. In addition, overexpression in a number of cell types has shown that Rem2 can inhibit voltage-gated calcium channel (VGCC) function, while studies employing RNAi-mediated knockdown of Rem2 have failed to observe a corresponding enhancement of VGCC function. To further investigate these discrepancies and determine the endogenous function of Rem2, we took a comprehensive, loss-of-function approach utilizing two independent, validated Rem2-targeted shRNAs to analyze Rem2 function. We sought to investigate the consequence of endogenous Rem2 knockdown by focusing on the three reported functions of Rem2 in neurons: regulation of synapse formation, dendritic morphology, and voltage-gated calcium channels. We conclude that endogenous Rem2 is a positive regulator of functional, excitatory synapse development and a negative regulator of dendritic complexity. In addition, while we are unable to reach a definitive conclusion as to whether the regulation of VGCCs is an endogenous function of Rem2, our study reports important data regarding RNAi reagents for use in future investigation of this issue.
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Affiliation(s)
- Anna R. Moore
- Department of Biology, National Center for Behavioral Genomics and Volen Center for Complex Systems, Brandeis University, Waltham, Massachusetts, United States of America
| | - Amy E. Ghiretti
- Department of Biology, National Center for Behavioral Genomics and Volen Center for Complex Systems, Brandeis University, Waltham, Massachusetts, United States of America
| | - Suzanne Paradis
- Department of Biology, National Center for Behavioral Genomics and Volen Center for Complex Systems, Brandeis University, Waltham, Massachusetts, United States of America
- * E-mail:
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9
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Meza U, Beqollari D, Romberg CF, Papadopoulos S, Bannister RA. Potent inhibition of L-type Ca2+ currents by a Rad variant associated with congestive heart failure. Biochem Biophys Res Commun 2013; 439:270-4. [PMID: 23973784 DOI: 10.1016/j.bbrc.2013.08.044] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2013] [Accepted: 08/13/2013] [Indexed: 10/26/2022]
Abstract
Ca(2+) influx via L-type voltage-gated Ca(2+) channels supports the plateau phase of ventricular action potentials and is the trigger for excitation-contraction (EC) coupling in the myocardium. Rad, a member of the RGK (Rem, Rem2, Rad, Gem/Kir) family of monomeric G proteins, regulates ventricular action potential duration and EC coupling gain through its ability to inhibit cardiac L-type channel activity. In this study, we have investigated the potential dysfunction of a naturally occurring Rad variant (Q66P) that has been associated with congestive heart failure in humans. Specifically, we have tested whether Rad Q66P limits, or even eliminates, the inhibitory actions of Rad on CaV1.2 and CaV1.3, the two L-type channel isoforms known to be expressed in the heart. We have found that mouse Rad Q65P (the murine equivalent of human Rad Q66P) inhibits L-type currents conducted by CaV1.2 or CaV1.3 channels as potently as wild-type Rad (>95% inhibition of both channels). In addition, Rad Q65P attenuates the gating movement of both channels as effectively as wild-type Rad, indicating that the Q65P substitution does not differentially impair any of the three described modes of L-type channel inhibition by RGK proteins. Thus, we conclude that if Rad Q66P contributes to cardiomyopathy, it does so via a mechanism that is not related to its ability to inhibit L-type channel-dependent processes per se. However, our results do not rule out the possibility that decreased expression, mistargeting or altered regulation of Rad Q66P may reduce the RGK protein's efficacy in vivo.
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Affiliation(s)
- U Meza
- Department of Medicine-Cardiology Division, University of Colorado Denver-Anschutz Medical Campus, 12700 East 19th Avenue, P15-8006, B-139, Aurora, CO 80045, USA; Departamento de Fisiología y Biofísica, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, Venustiano Carranza #2405, San Luis Potosí, SLP 78210, México.
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10
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Yang T, Colecraft HM. Regulation of voltage-dependent calcium channels by RGK proteins. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:1644-54. [PMID: 23063948 DOI: 10.1016/j.bbamem.2012.10.005] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2012] [Revised: 10/04/2012] [Accepted: 10/05/2012] [Indexed: 12/28/2022]
Abstract
RGK proteins belong to the Ras superfamily of monomeric G-proteins, and currently include four members - Rad, Rem, Rem2, and Gem/Kir. RGK proteins are broadly expressed, and are the most potent known intracellular inhibitors of high-voltage-activated Ca²⁺ (Ca(V)1 and Ca(V)2) channels. Here, we review and discuss the evidence in the literature regarding the functional mechanisms, structural determinants, physiological role, and potential practical applications of RGK-mediated inhibition of Ca(V)1/Ca(V)2 channels. This article is part of a Special Issue entitled: Calcium channels.
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Affiliation(s)
- Tingting Yang
- Department of Physiology and Cellular Biophysics, Columbia University, College of Physicians and Surgeons, 1150 St. Nicholas Avenue, New York, NY 10032, USA
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11
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Fan M, Zhang WK, Buraei Z, Yang J. Molecular determinants of Gem protein inhibition of P/Q-type Ca2+ channels. J Biol Chem 2012; 287:22749-58. [PMID: 22589533 DOI: 10.1074/jbc.m111.291872] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The RGK family of monomeric GTP-binding proteins potently inhibits high voltage-activated Ca(2+) channels. The molecular mechanisms of this inhibition are largely unclear. In Xenopus oocytes, Gem suppresses the activity of P/Q-type Ca(2+) channels on the plasma membrane. This is presumed to occur through direct interactions of one or more Gem inhibitory sites and the pore-forming Ca(v)2.1 subunit in a manner dependent on the Ca(2+) channel subunit β (Ca(v)β). In this study we investigated the molecular determinants in Gem that are critical for this inhibition. Like other RGK proteins, Gem contains a conserved Ras-like core and extended N and C termini. A 12-amino acid fragment in the C terminus was found to be crucial for and sufficient to produce Ca(v)β-dependent inhibition, suggesting that this region forms an inhibitory site. A three-amino acid motif in the core was also found to be critical, possibly forming another inhibitory site. Mutating either site individually did not hamper Gem inhibition, but mutating both sites together completely abolished Gem inhibition without affecting Gem protein expression level or disrupting Gem interaction with Ca(v)2.1 or Ca(v)β. Mutating Gem residues that are crucial for interactions with previously demonstrated RGK modulators such as calmodulin, 14-3-3, and phosphatidylinositol lipids did not significantly affect Gem inhibition. These results suggest that Gem contains two candidate inhibitory sites, each capable of producing full inhibition of P/Q-type Ca(2+) channels.
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Affiliation(s)
- Mingming Fan
- Department of Biological Sciences, Columbia University, New York, New York 10027, USA
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12
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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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13
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Direct inhibition of P/Q-type voltage-gated Ca2+ channels by Gem does not require a direct Gem/Cavbeta interaction. Proc Natl Acad Sci U S A 2010; 107:14887-92. [PMID: 20679232 DOI: 10.1073/pnas.1007543107] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The Rem, Rem2, Rad, and Gem/Kir (RGK) family of small GTP-binding proteins potently inhibits high voltage-activated (HVA) Ca(2+) channels, providing a powerful means of modulating neural, endocrine, and muscle functions. The molecular mechanisms of this inhibition are controversial and remain largely unclear. RGK proteins associate directly with Ca(2+) channel beta subunits (Ca(v)beta), and this interaction is widely thought to be essential for their inhibitory action. In this study, we investigate the molecular underpinnings of Gem inhibition of P/Q-type Ca(2+) channels. We find that a purified Gem protein markedly and acutely suppresses P/Q channel activity in inside-out membrane patches, that this action requires Ca(v)beta but not the Gem/Ca(v)beta interaction, and that Gem coimmunoprecipitates with the P/Q channel alpha(1) subunit (Ca(v)alpha(1)) in a Ca(v)beta-independent manner. By constructing chimeras between P/Q channels and Gem-insensitive low voltage-activated T-type channels, we identify a region encompassing transmembrane segments S1, S2, and S3 in the second homologous repeat of Ca(v)alpha(1) critical for Gem inhibition. Exchanging this region between P/Q and T channel Ca(v)alpha(1) abolishes Gem inhibition of P/Q channels and confers Ca(v)beta-dependent Gem inhibition to a chimeric T channel that also carries the P/Q I-II loop (a cytoplasmic region of Ca(v)alpha(1) that binds Ca(v)beta). Our results challenge the prevailing view regarding the role of Ca(v)beta in RGK inhibition of high voltage-activated Ca(2+) channels and prompt a paradigm in which Gem directly binds and inhibits Ca(v)beta-primed Ca(v)alpha(1) on the plasma membrane.
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14
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Leyris JP, Gondeau C, Charnet A, Delattre C, Rousset M, Cens T, Charnet P. RGK GTPase-dependent CaV2.1 Ca2+ channel inhibition is independent of CaVbeta-subunit-induced current potentiation. FASEB J 2009; 23:2627-38. [PMID: 19332647 DOI: 10.1096/fj.08-122135] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
RGK (Rad-Gem-Rem) GTPases have been described as potent negative regulators of the Ca(2+) influx via high-threshold voltage-activated Ca(2+) channels. Recent work, mostly performed on Ca(V)1.2 Ca(2+) channels, has highlighted the crucial role played by the channel auxiliary Ca(V)beta subunits and identified several GTPase and beta-subunit protein domains involved in this regulation. We now extend these conclusions by producing the first complete characterization of the effects of Gem, Rem, and Rem2 on the neuronal Ca(V)2.1 Ca(2+) channels expressed with Ca(V)beta(1) or Ca(V)beta(2) subunits. Current inhibition is limited to a decrease in amplitude with no modification in the voltage dependence or kinetics of the current. We demonstrate that this inhibition can occur for Ca(V)beta constructs with impaired capacity to induce current potentiation, but that it is lost for Ca(V)beta constructs deleted for their beta-interaction domain. The RGK C-terminal last approximately 80 amino acids are sufficient to allow potent current inhibition and in vivo beta-subunit/Gem interaction. Interestingly, although Gem and Gem carboxy-terminus induce a completely different pattern of beta-subunit cellular localization, they both potently inhibit Ca(V)2.1 channels. These data therefore set the status of neuronal Ca(V)2.1 Ca(2+) channel inhibition by RGK GTPases, emphasizing the role of short amino acid sequences of both proteins in beta-subunit binding and channel inhibition and revealing a new mechanism for channel inhibition.
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Affiliation(s)
- J-P Leyris
- CRBM, CNRS UMR 5237, Université de Montpellier 1, 34293 Montpellier cedex, France
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