1
|
Chan ES, Ge Y, So YW, Bai YF, Liu L, Wang YT. Allosteric potentiation of GABAA receptor single-channel conductance by netrin-1 during neuronal-excitation-induced inhibitory synaptic homeostasis. Cell Rep 2022; 41:111584. [DOI: 10.1016/j.celrep.2022.111584] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Revised: 07/13/2022] [Accepted: 10/08/2022] [Indexed: 11/06/2022] Open
|
2
|
Irwin BWJ, Wanjura CC, Molnar D, Rutter MJ, Payne MC, Chau PL. GABA receptor associated protein changes the electrostatic environment around the GABA type A receptor. Proteins 2021; 90:476-484. [PMID: 34546588 PMCID: PMC9293360 DOI: 10.1002/prot.26241] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Revised: 07/16/2021] [Accepted: 09/13/2021] [Indexed: 11/18/2022]
Abstract
We have performed fully atomistic molecular dynamics simulations of the intracellular domain of a model of the GABAA receptor with and without the GABA receptor associated protein (GABARAP) bound. We have also calculated the electrostatic potential due to the receptor, in the absence and presence of GABARAP. We find that GABARAP binding changes the electrostatic properties around the GABAA receptor and could lead to increased conductivity of chloride ions through the receptor. We also find that ion motions that would result in conducting currents are observed nearly twice as often when GABARAP binds. These results are consistent with data from electrophysiological experiments.
Collapse
Affiliation(s)
- Benedict W J Irwin
- Theory of Condensed Matter Group, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, UK
| | - Clara C Wanjura
- Theory of Condensed Matter Group, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, UK
| | - Daniel Molnar
- Theory of Condensed Matter Group, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, UK
| | - Michael J Rutter
- Theory of Condensed Matter Group, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, UK
| | - Michael C Payne
- Theory of Condensed Matter Group, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, UK
| | - P-L Chau
- Bioinformatique Structurale, Institut Pasteur, CNRS URA 3528, CB3I CNRS USR 3756, Paris, France
| |
Collapse
|
3
|
Gibbs E, Chakrapani S. Structure, Function and Physiology of 5-Hydroxytryptamine Receptors Subtype 3. Subcell Biochem 2021; 96:373-408. [PMID: 33252737 DOI: 10.1007/978-3-030-58971-4_11] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
5-hydroxytryptamine receptor subtype 3 (5-HT3R) is a pentameric ligand-gated ion channel (pLGIC) involved in neuronal signaling. It is best known for its prominent role in gut-CNS signaling though there is growing interest in its other functions, particularly in modulating non-serotonergic synaptic activity. Recent advances in structural biology have provided mechanistic understanding of 5-HT3R function and present new opportunities for the field. This chapter gives a broad overview of 5-HT3R from a physiological and structural perspective and then discusses the specific details of ion permeation, ligand binding and allosteric coupling between these two events. Biochemical evidence is summarized and placed within a physiological context. This perspective underscores the progress that has been made as well as outstanding challenges and opportunities for future 5-HT3R research.
Collapse
Affiliation(s)
- Eric Gibbs
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, 44106-4970, USA.
| | - Sudha Chakrapani
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, 44106-4970, USA. .,Department of Neuroscience, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106-4970, USA.
| |
Collapse
|
4
|
Irwin BWJ, Vukovič S, Payne MC, ElGamacy M, Chau PL. Prediction of GABARAP interaction with the GABA type A receptor. Proteins 2018; 86:1251-1264. [PMID: 30218455 PMCID: PMC6492159 DOI: 10.1002/prot.25589] [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: 02/27/2018] [Revised: 07/17/2018] [Accepted: 08/05/2018] [Indexed: 01/05/2023]
Abstract
We have performed docking simulations on GABARAP interacting with the GABA type A receptor using SwarmDock. We have also used a novel method to study hydration sites on the surface of these two proteins; this method identifies regions around proteins where desolvation is relatively easy, and these are possible locations where proteins can bind each other. There is a high degree of consistency between the predictions of these two methods. Moreover, we have also identified binding sites on GABARAP for other proteins, and listed possible binding sites for as yet unknown proteins on both GABARAP and the GABA type A receptor intracellular domain.
Collapse
Affiliation(s)
- B W J Irwin
- Department of Physics, Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
| | - Siniša Vukovič
- Department of Physics, Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
| | - M C Payne
- Department of Physics, Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
| | - Mohammad ElGamacy
- Abteilung Proteinevolution, Max-Planck-Institut für Entwicklungsbiologie, Tübingen, Germany
| | - P-L Chau
- Bioinformatique Structurale, CNRS URA 3528, Paris, France
| |
Collapse
|
5
|
Xu W, Wang K, Chen Y, Liang XT, Yu MK, Yue H, Tierney ML. Sperm gamma-aminobutyric acid type A receptor delta subunit (GABRD) and its interaction with purinergic P2X 2 receptors in progesterone-induced acrosome reaction and male fertility. Reprod Fertil Dev 2017; 29:2060-2072. [PMID: 28190421 DOI: 10.1071/rd16294] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Accepted: 12/22/2016] [Indexed: 11/23/2022] Open
Abstract
The mechanism underlying the non-genomic action of progesterone in sperm functions and related Ca2+ mobilisation remains elusive. Herein we report the expression of gamma-aminobutyric acid type A receptor delta subunit (GABRD) in human and rodent sperm and its involvement in mediating the progesterone-induced acrosome reaction. GABRD was localised in the sperm head/neck region. A δ(392-422)-specific inhibitory peptide against GABRD blocked the progesterone-induced acrosome reaction and the associated increase in intracellular Ca2+. Similarly, an inhibitory effect against both progesterone-induced Ca2+ influx and the acrosome reaction was observed with a P2X2 receptor antagonist. The lack of synergism between the GABRD and P2X2 inhibitors suggests that these two receptors are playing a role in the same pathway. Furthermore, a co-immunoprecipitation experiment demonstrated that GABRD could undergo protein-protein interactions with the Ca2+-conducting P2X2 receptor. This interaction between the receptors could be reduced following progesterone (10μM) inducement. Significantly reduced GABRD expression was observed in spermatozoa from infertile patients with reduced acrosome reaction capacity, suggesting that normal expression of GABRD is critical for the sperm acrosome reaction and thus male fertility. The results of the present study indicate that GABRD represents a novel progesterone receptor or modulator in spermatozoa that is responsible for the progesterone-induced Ca2+ influx required for the acrosome reaction through its interaction with the P2X2 receptor.
Collapse
Affiliation(s)
- Wenming Xu
- Joint Laboratory of Reproductive Medicine, Key Laboratory of Birth Defects and Related Diseases of Women and Children, Ministry of Education, (Sichuan University), West China Second University Hospital, Sichuan University, Renmin Lanlu, 3 duan, No.17, Chengdu, 610041, PR China
| | - Ke Wang
- Joint Laboratory of Reproductive Medicine, Key Laboratory of Birth Defects and Related Diseases of Women and Children, Ministry of Education, (Sichuan University), West China Second University Hospital, Sichuan University, Renmin Lanlu, 3 duan, No.17, Chengdu, 610041, PR China
| | - Yan Chen
- Joint Laboratory of Reproductive Medicine, Key Laboratory of Birth Defects and Related Diseases of Women and Children, Ministry of Education, (Sichuan University), West China Second University Hospital, Sichuan University, Renmin Lanlu, 3 duan, No.17, Chengdu, 610041, PR China
| | - Xiao Tong Liang
- Joint Laboratory of Reproductive Medicine, Key Laboratory of Birth Defects and Related Diseases of Women and Children, Ministry of Education, (Sichuan University), West China Second University Hospital, Sichuan University, Renmin Lanlu, 3 duan, No.17, Chengdu, 610041, PR China
| | - Mei Kuen Yu
- Epithelial Cell Biology Research Center, School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong SAR, China
| | - Huanxun Yue
- Andrology clinic, Department of Obstetric and Gynecologic Diseases, West China Second University Hospital, Sichuan University, Chengdu, 610041, PR China
| | - M Louise Tierney
- Membrane Physiology and Ion Channel Signalling Group, Division of Translational Bioscience, The John Curtin School of Medical Research, Building 54, Ward and Garran Roads, The Australian National University, Canberra, ACT 0200, Australia
| |
Collapse
|
6
|
Chua HC, Absalom NL, Hanrahan JR, Viswas R, Chebib M. The Direct Actions of GABA, 2'-Methoxy-6-Methylflavone and General Anaesthetics at β3γ2L GABAA Receptors: Evidence for Receptors with Different Subunit Stoichiometries. PLoS One 2015; 10:e0141359. [PMID: 26496640 PMCID: PMC4619705 DOI: 10.1371/journal.pone.0141359] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Accepted: 10/07/2015] [Indexed: 12/13/2022] Open
Abstract
2'-Methoxy-6-methylflavone (2'MeO6MF) is an anxiolytic flavonoid which has been shown to display GABAA receptor (GABAAR) β2/3-subunit selectivity, a pharmacological profile similar to that of the general anaesthetic etomidate. Electrophysiological studies suggest that the full agonist action of 2'MeO6MF at α2β3γ2L GABAARs may mediate the flavonoid's in vivo effects. However, we found variations in the relative efficacy of 2'MeO6MF (2'MeO6MF-elicited current responses normalised to the maximal GABA response) at α2β3γ2L GABAARs due to the presence of mixed receptor populations. To understand which receptor subpopulation(s) underlie the variations observed, we conducted a systematic investigation of 2'MeO6MF activity at all receptor combinations that could theoretically form (α2, β3, γ2L, α2β3, α2γ2L, β3γ2L and α2β3γ2L) in Xenopus oocytes using the two-electrode voltage clamp technique. We found that 2'MeO6MF activated non-α-containing β3γ2L receptors. In an attempt to establish the optimal conditions to express a uniform population of these receptors, we found that varying the relative amounts of β3:γ2L subunit mRNAs resulted in differences in the level of constitutive activity, the GABA concentration-response relationships, and the relative efficacy of 2'MeO6MF activation. Like 2'MeO6MF, general anaesthetics such as etomidate and propofol also showed distinct levels of relative efficacy across different injection ratios. Based on these results, we infer that β3γ2L receptors may form with different subunit stoichiometries, resulting in the complex pharmacology observed across different injection ratios. Moreover, the discovery that GABA and etomidate have direct actions at the α-lacking β3γ2L receptors raises questions about the structural requirements for their respective binding sites at GABAARs.
Collapse
Affiliation(s)
- Han Chow Chua
- Faculty of Pharmacy, University of Sydney, Sydney, New South Wales, Australia
| | - Nathan L Absalom
- Faculty of Pharmacy, University of Sydney, Sydney, New South Wales, Australia
| | - Jane R Hanrahan
- Faculty of Pharmacy, University of Sydney, Sydney, New South Wales, Australia
| | - Raja Viswas
- Faculty of Pharmacy, University of Sydney, Sydney, New South Wales, Australia
| | - Mary Chebib
- Faculty of Pharmacy, University of Sydney, Sydney, New South Wales, Australia
| |
Collapse
|
7
|
Burgos CF, Muñoz B, Guzman L, Aguayo LG. Ethanol effects on glycinergic transmission: From molecular pharmacology to behavior responses. Pharmacol Res 2015; 101:18-29. [PMID: 26158502 DOI: 10.1016/j.phrs.2015.07.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2015] [Revised: 07/01/2015] [Accepted: 07/01/2015] [Indexed: 10/23/2022]
Abstract
It is well accepted that ethanol is able to produce major health and economic problems associated to its abuse. Because of its intoxicating and addictive properties, it is necessary to analyze its effect in the central nervous system. However, we are only now learning about the mechanisms controlling the modification of important membrane proteins such as ligand-activated ion channels by ethanol. Furthermore, only recently are these effects being correlated to behavioral changes. Current studies show that the glycine receptor (GlyR) is a susceptible target for low concentrations of ethanol (5-40mM). GlyRs are relevant for the effects of ethanol because they are found in the spinal cord and brain stem where they primarily express the α1 subunit. More recently, the presence of GlyRs was described in higher regions, such as the hippocampus and nucleus accumbens, with a prevalence of α2/α3 subunits. Here, we review data on the following aspects of ethanol effects on GlyRs: (1) direct interaction of ethanol with amino acids in the extracellular or transmembrane domains, and indirect mechanisms through the activation of signal transduction pathways; (2) analysis of α2 and α3 subunits having different sensitivities to ethanol which allows the identification of structural requirements for ethanol modulation present in the intracellular domain and C-terminal region; (3) Genetically modified knock-in mice for α1 GlyRs that have an impaired interaction with G protein and demonstrate reduced ethanol sensitivity without changes in glycinergic transmission; and (4) GlyRs as potential therapeutic targets.
Collapse
Affiliation(s)
- Carlos F Burgos
- Laboratory of Neurophysiology, Department of Physiology, University of Concepción, Chile
| | - Braulio Muñoz
- Laboratory of Neurophysiology, Department of Physiology, University of Concepción, Chile
| | - Leonardo Guzman
- Laboratory of Molecular Neurobiology, Department of Physiology, University of Concepción, Chile
| | - Luis G Aguayo
- Laboratory of Neurophysiology, Department of Physiology, University of Concepción, Chile.
| |
Collapse
|
8
|
Burgos CF, Castro PA, Mariqueo T, Bunster M, Guzmán L, Aguayo LG. Evidence for α-helices in the large intracellular domain mediating modulation of the α1-glycine receptor by ethanol and Gβγ. J Pharmacol Exp Ther 2015; 352:148-55. [PMID: 25339760 PMCID: PMC4279101 DOI: 10.1124/jpet.114.217976] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2014] [Accepted: 10/21/2014] [Indexed: 12/19/2022] Open
Abstract
The α1-subunit containing glycine receptors (GlyRs) is potentiated by ethanol, in part, by intracellular Gβγ actions. Previous studies have suggested that molecular requirements in the large intracellular domain are involved; however, the lack of structural data about this region has made it difficult to describe a detailed mechanism. Using circular dichroism and molecular modeling, we generated a full model of the α1-GlyR, which includes the large intracellular domain and provides new information on structural requirements for allosteric modulation by ethanol and Gβγ. The data strongly suggest the existence of an α-helical conformation in the regions near transmembrane (TM)-3 and TM4 of the large intracellular domain. The secondary structure in the N-terminal region of the large intracellular domain near TM3 appeared critical for ethanol action, and this was tested using the homologous domain of the γ2-subunit of the GABAA receptor predicted to have little helical conformation. This region of γ2 was able to bind Gβγ and form a functional channel when combined with α1-GlyR, but it was not sensitive to ethanol. Mutations in the N- and C-terminal regions introduced to replace corresponding amino acids of the α1-GlyR sequence restored the ability to be modulated by ethanol and Gβγ. Recovery of the sensitivity to ethanol was associated with the existence of a helical conformation similar to α1-GlyR, thus being an essential secondary structural requirement for GlyR modulation by ethanol and G protein.
Collapse
Affiliation(s)
- Carlos F Burgos
- Laboratory of Neurophysiology, Department of Physiology (C.F.B., .P.A.C., T.M., L.G.A.), Laboratory of Molecular Neurobiology, Department of Physiology (L.G.), Laboratory of Molecular Biophysics, Department of Biochemistry and Molecular Biology (M.B.), and Ph.D. program in Pharmacology (T.M.), University of Concepción, Concepción, Chile
| | - Patricio A Castro
- Laboratory of Neurophysiology, Department of Physiology (C.F.B., .P.A.C., T.M., L.G.A.), Laboratory of Molecular Neurobiology, Department of Physiology (L.G.), Laboratory of Molecular Biophysics, Department of Biochemistry and Molecular Biology (M.B.), and Ph.D. program in Pharmacology (T.M.), University of Concepción, Concepción, Chile
| | - Trinidad Mariqueo
- Laboratory of Neurophysiology, Department of Physiology (C.F.B., .P.A.C., T.M., L.G.A.), Laboratory of Molecular Neurobiology, Department of Physiology (L.G.), Laboratory of Molecular Biophysics, Department of Biochemistry and Molecular Biology (M.B.), and Ph.D. program in Pharmacology (T.M.), University of Concepción, Concepción, Chile
| | - Marta Bunster
- Laboratory of Neurophysiology, Department of Physiology (C.F.B., .P.A.C., T.M., L.G.A.), Laboratory of Molecular Neurobiology, Department of Physiology (L.G.), Laboratory of Molecular Biophysics, Department of Biochemistry and Molecular Biology (M.B.), and Ph.D. program in Pharmacology (T.M.), University of Concepción, Concepción, Chile
| | - Leonardo Guzmán
- Laboratory of Neurophysiology, Department of Physiology (C.F.B., .P.A.C., T.M., L.G.A.), Laboratory of Molecular Neurobiology, Department of Physiology (L.G.), Laboratory of Molecular Biophysics, Department of Biochemistry and Molecular Biology (M.B.), and Ph.D. program in Pharmacology (T.M.), University of Concepción, Concepción, Chile
| | - Luis G Aguayo
- Laboratory of Neurophysiology, Department of Physiology (C.F.B., .P.A.C., T.M., L.G.A.), Laboratory of Molecular Neurobiology, Department of Physiology (L.G.), Laboratory of Molecular Biophysics, Department of Biochemistry and Molecular Biology (M.B.), and Ph.D. program in Pharmacology (T.M.), University of Concepción, Concepción, Chile
| |
Collapse
|
9
|
Kozuska JL, Paulsen IM, Belfield WJ, Martin IL, Cole DJ, Holt A, Dunn SMJ. Impact of intracellular domain flexibility upon properties of activated human 5-HT3 receptors. Br J Pharmacol 2014; 171:1617-28. [PMID: 24283776 PMCID: PMC3966743 DOI: 10.1111/bph.12536] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2013] [Revised: 09/09/2013] [Accepted: 09/14/2013] [Indexed: 12/20/2022] Open
Abstract
Background and Purpose It has been proposed that arginine residues lining the intracellular portals of the homomeric 5-HT3A receptor cause electrostatic repulsion of cation flow, accounting for a single-channel conductance substantially lower than that of the 5-HT3AB heteromer. However, comparison of receptor homology models for wild-type pentamers suggests that salt bridges in the intracellular domain of the homomer may impart structural rigidity, and we hypothesized that this rigidity could account for the low conductance. Experimental Approach Mutations were introduced into the portal region of the human 5-HT3A homopentamer, such that putative salt bridges were broken by neutralizing anionic partners. Single-channel and whole cell currents were measured in transfected tsA201 cells and in Xenopus oocytes respectively. Computational simulations of protein flexibility facilitated comparison of wild-type and mutant receptors. Key Results Single-channel conductance was increased substantially, often to wild-type heteromeric receptor values, in most 5-HT3A mutants. Conversely, introduction of arginine residues to the portal region of the heteromer, conjecturally creating salt bridges, decreased conductance. Gating kinetics varied significantly between different mutant receptors. EC50 values for whole-cell responses to 5-HT remained largely unchanged, but Hill coefficients for responses to 5-HT were usually significantly smaller in mutants. Computational simulations suggested increased flexibility throughout the protein structure as a consequence of mutations in the intracellular domain. Conclusions and Implications These data support a role for intracellular salt bridges in maintaining the quaternary structure of the 5-HT3 receptor and suggest a role for the intracellular domain in allosteric modulation of cooperativity and agonist efficacy. Linked Article This article is commented on by Vardy and Kenakin, pp. 1614–1616 of volume 171 issue 7. To view this commentary visit http://dx.doi.org/10.1111/bph.12550.
Collapse
Affiliation(s)
- J L Kozuska
- Department of Pharmacology, University of Alberta, Edmonton, AB, Canada
| | | | | | | | | | | | | |
Collapse
|
10
|
Xie HB, Sha Y, Wang J, Cheng MS. Some insights into the binding mechanism of the GABAA receptor: a combined docking and MM-GBSA study. J Mol Model 2013; 19:5489-500. [DOI: 10.1007/s00894-013-2049-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 10/21/2013] [Indexed: 02/02/2023]
|
11
|
Chaumont S, André C, Perrais D, Boué-Grabot E, Taly A, Garret M. Agonist-dependent endocytosis of γ-aminobutyric acid type A (GABAA) receptors revealed by a γ2(R43Q) epilepsy mutation. J Biol Chem 2013; 288:28254-65. [PMID: 23935098 DOI: 10.1074/jbc.m113.470807] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
GABA-gated chloride channels (GABAARs) trafficking is involved in the regulation of fast inhibitory transmission. Here, we took advantage of a γ2(R43Q) subunit mutation linked to epilepsy in humans that considerably reduces the number of GABAARs on the cell surface to better understand the trafficking of GABAARs. Using recombinant expression in cultured rat hippocampal neurons and COS-7 cells, we showed that receptors containing γ2(R43Q) were addressed to the cell membrane but underwent clathrin-mediated dynamin-dependent endocytosis. The γ2(R43Q)-dependent endocytosis was reduced by GABAAR antagonists. These data, in addition to a new homology model, suggested that a conformational change in the extracellular domain of γ2(R43Q)-containing GABAARs increased their internalization. This led us to show that endogenous and recombinant wild-type GABAAR endocytosis in both cultured neurons and COS-7 cells can be amplified by their agonists. These findings revealed not only a direct relationship between endocytosis of GABAARs and a genetic neurological disorder but also that trafficking of these receptors can be modulated by their agonist.
Collapse
Affiliation(s)
- Severine Chaumont
- From the Université Bordeaux, Institut de Neurosciences Cognitives et Intégratives d'Aquitaine (INCIA), UMR 5287, F-33000 Bordeaux, France
| | | | | | | | | | | |
Collapse
|
12
|
Takano K, Liu D, Tarpey P, Gallant E, Lam A, Witham S, Alexov E, Chaubey A, Stevenson RE, Schwartz CE, Board PG, Dulhunty AF. An X-linked channelopathy with cardiomegaly due to a CLIC2 mutation enhancing ryanodine receptor channel activity. Hum Mol Genet 2012; 21:4497-507. [PMID: 22814392 DOI: 10.1093/hmg/dds292] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Chloride intracellular channel 2 (CLIC2) protein is a member of the glutathione transferase class of proteins. Its' only known function is the regulation of ryanodine receptor (RyR) intracellular Ca(2+) release channels. These RyR proteins play a major role in the regulation of Ca(2+) signaling in many cells. Utilizing exome capture and deep sequencing of genes on the X-chromosome, we have identified a mutation in CLIC2 (c.303C>G, p.H101Q) which is associated with X-linked intellectual disability (ID), atrial fibrillation, cardiomegaly, congestive heart failure (CHF), some somatic features and seizures. Functional studies of the H101Q variant indicated that it stimulated rather than inhibited the action of RyR channels, with channels remaining open for longer times and potentially amplifying Ca(2+) signals dependent on RyR channel activity. The overly active RyRs in cardiac and skeletal muscle cells and neuronal cells would result in abnormal cardiac function and trigger post-synaptic pathways and neurotransmitter release. The presence of both cardiomegaly and CHF in the two affected males and atrial fibrillation in one are consistent with abnormal RyR2 channel function. Since the dysfunction of RyR2 channels in the brain via 'leaky mutations' can result in mild developmental delay and seizures, our data also suggest a vital role for the CLIC2 protein in maintaining normal cognitive function via its interaction with RyRs in the brain. Therefore, our patients appear to suffer from a new channelopathy comprised of ID, seizures and cardiac problems because of enhanced Ca(2+) release through RyRs in neuronal cells and cardiac muscle cells.
Collapse
Affiliation(s)
- Kyoko Takano
- JC Self Research Institute, Greenwood Genetic Center, Greenwood, SC 29646, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
13
|
Seymour VAL, Curmi JP, Howitt SM, Casarotto MG, Laver DR, Tierney ML. Selective modulation of different GABAA receptor isoforms by diazepam and etomidate in hippocampal neurons. Int J Biochem Cell Biol 2012; 44:1491-500. [PMID: 22704937 DOI: 10.1016/j.biocel.2012.06.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2011] [Revised: 05/29/2012] [Accepted: 06/04/2012] [Indexed: 10/28/2022]
Abstract
Diazepam modulation of native γ2-containing GABA(A) (γGABA(A)) receptors increases channel conductance by facilitating protein interactions involving the γ2-subunit amphipathic (MA) region, which is found in the cytoplasmic loop between transmembrane domains 3 and 4 (Everitt et al., 2009). However, many drugs, predicted to act on different GABA(A) receptor subtypes, increase channel conductance leading us to hypothesize that conductance variation in GABA(A) receptors may be a general property, mediated by protein interactions involving the cytoplasmic MA stretch of amino acids. In this study we have tested this hypothesis by potentiating extrasynaptic GABA(A) currents with etomidate and examining the ability of peptides mimicking either the γ2- or δ-subunit MA region to affect conductance. In inside-out hippocampal patches from newborn rats the general anesthetic etomidate potentiated GABA currents, producing either an increase in open probability and single-channel conductance or an increase in open probability, as described previously (Seymour et al., 2009). In patches displaying high conductance channels application of a δ((392-422)) MA peptide, but not a scrambled version or the equivalent γ2((381-403)) MA peptide, reduced the potentiating effects of etomidate, significantly reducing single-channel conductance. In contrast, when GABA currents were potentiated by the γ2-specific drug diazepam the δ MA peptide had no effect. These data reveal that diazepam and etomidate potentiate different extrasynaptic GABA(A) receptor subtypes but both drugs modulate conductance similarly. One interpretation of the data is that these drugs elicit potentiation through protein interactions and that the MA peptides compete with these interactions to disrupt this process.
Collapse
Affiliation(s)
- Victoria A L Seymour
- The John Curtin School of Medical Research, The Australian National University, Canberra, ACT 2601, Australia
| | | | | | | | | | | |
Collapse
|
14
|
Karim N, Curmi J, Gavande N, Johnston GA, Hanrahan JR, Tierney ML, Chebib M. 2'-Methoxy-6-methylflavone: a novel anxiolytic and sedative with subtype selective activating and modulating actions at GABA(A) receptors. Br J Pharmacol 2012; 165:880-96. [PMID: 21797842 DOI: 10.1111/j.1476-5381.2011.01604.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
BACKGROUND AND PURPOSE Flavonoids are known to have anxiolytic and sedative effects mediated via actions on ionotropic GABA receptors. We sought to investigate this further. EXPERIMENTAL APPROACH We evaluated the effects of 2'-methoxy-6-methylflavone (2'MeO6MF) on native GABA(A) receptors in new-born rat hippocampal neurons and determined specificity from 18 human recombinant GABA(A) receptor subtypes expressed in Xenopus oocytes. We used ligand binding, two-electrode voltage clamp and patch clamp studies together with behavioural studies. KEY RESULTS 2'MeO6MF potentiated GABA at α2β1γ2L and all α1-containing GABA(A) receptor subtypes. At α2β2/3γ2L GABA(A) receptors, however, 2'MeO6MF directly activated the receptors without potentiating GABA. This activation was attenuated by bicuculline and gabazine but not flumazenil indicating a novel site. Mutation studies showed position 265 in the β1/2 subunit was key to whether 2'MeO6MF was an activator or a potentiator. In hippocampal neurons, 2'MeO6MF directly activated single-channel currents that showed the hallmarks of GABA(A) Cl(-) currents. In the continued presence of 2'MeO6MF the single-channel conductance increased and these high conductance channels were disrupted by the γ2(381-403) MA peptide, indicating that such currents are mediated by α2/γ2-containing GABA(A) receptors. In mice, 2'MeO6MF (1-100 mg·kg(-1) ; i.p.) displayed anxiolytic-like effects in two unconditioned models of anxiety: the elevated plus maze and light/dark tests. 2'MeO6MF induced sedative effects at higher doses in the holeboard, actimeter and barbiturate-induced sleep time tests. No myorelaxant effects were observed in the horizontal wire test. CONCLUSIONS AND IMPLICATIONS 2'MeO6MF will serve as a tool to study the complex nature of the activation and modulation of GABA(A) receptor subtypes.
Collapse
Affiliation(s)
- Nasiara Karim
- Faculty of Pharmacy A15, University of Sydney, Sydney, NSW, Australia
| | | | | | | | | | | | | |
Collapse
|
15
|
Tierney ML. Insights into the biophysical properties of GABA(A) ion channels: modulation of ion permeation by drugs and protein interactions. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1808:667-73. [PMID: 21126507 DOI: 10.1016/j.bbamem.2010.11.022] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2010] [Revised: 11/17/2010] [Accepted: 11/19/2010] [Indexed: 01/10/2023]
Abstract
The fundamental properties of ion channels assure their selectivity for a particular ion, its rapid permeation through a central pore and that such electrical activity is modulated by factors that control the opening and closing (gating) of the channel. All cell types possess ion channels and their regulated flux of ions across the membrane play critical roles in all steps of life. An ion channel does not act alone to control cell excitability but rather forms part of larger protein complexes. The identification of protein interaction partners of ion channels and their influence on both the fundamental biophysical properties of the channel and its expression in the membrane are revealing the many ways in which electrical activity may be regulated. Highlighted here is the novel use of the patch clamp method to dissect out the influence of protein interactions on the activity of individual GABA(A) receptors. The studies demonstrate that ion conduction is a dynamic property of a channel and that protein interactions in a cytoplasmic domain underlie the channel's ability to alter ion permeation. A structural model describing a reorganisation of the conserved cytoplasmic gondola domain and the influence of drugs on this process are presented.
Collapse
Affiliation(s)
- M Louise Tierney
- Membrane Physiology and Ion Channel Signaling Group, The John Curtin School of Medical Research, Building 54, Garran Road, The Australian National University, Canberra 0200, Australia.
| |
Collapse
|
16
|
Abstract
Cys-loop receptors are membrane-spanning neurotransmitter-gated ion channels that are responsible for fast excitatory and inhibitory transmission in the peripheral and central nervous systems. The best studied members of the Cys-loop family are nACh, 5-HT3, GABAA and glycine receptors. All these receptors share a common structure of five subunits, pseudo-symmetrically arranged to form a rosette with a central ion-conducting pore. Some are cation selective (e.g. nACh and 5-HT3) and some are anion selective (e.g. GABAA and glycine). Each receptor has an extracellular domain (ECD) that contains the ligand-binding sites, a transmembrane domain (TMD) that allows ions to pass across the membrane, and an intracellular domain (ICD) that plays a role in channel conductance and receptor modulation. Cys-loop receptors are the targets for many currently used clinically relevant drugs (e.g. benzodiazepines and anaesthetics). Understanding the molecular mechanisms of these receptors could therefore provide the catalyst for further development in this field, as well as promoting the development of experimental techniques for other areas of neuroscience.In this review, we present our current understanding of Cys-loop receptor structure and function. The ECD has been extensively studied. Research in this area has been stimulated in recent years by the publication of high-resolution structures of nACh receptors and related proteins, which have permitted the creation of many Cys loop receptor homology models of this region. Here, using the 5-HT3 receptor as a typical member of the family, we describe how homology modelling and ligand docking can provide useful but not definitive information about ligand interactions. We briefly consider some of the many Cys-loop receptors modulators. We discuss the current understanding of the structure of the TMD, and how this links to the ECD to allow channel gating, and consider the roles of the ICD, whose structure is poorly understood. We also describe some of the current methods that are beginning to reveal the differences between different receptor states, and may ultimately show structural details of transitions between them.
Collapse
|
17
|
Peters JA, Cooper MA, Carland JE, Livesey MR, Hales TG, Lambert JJ. Novel structural determinants of single channel conductance and ion selectivity in 5-hydroxytryptamine type 3 and nicotinic acetylcholine receptors. J Physiol 2010; 588:587-96. [PMID: 19933751 PMCID: PMC2828133 DOI: 10.1113/jphysiol.2009.183137] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Nicotinic acetylcholine (nACh) and 5-hydroxytryptamine type 3 (5-HT(3)) receptors are cation-selective ion channels of the pentameric ligand-gated ion channel (pLGIC) superfamily. Multiple lines of evidence adduced over the last 30 years indicate that the lining of the channel of such receptors is formed by the alpha-helical second transmembrane (TM2) domain and flanking sequences contributed by each of the five subunits present within the receptor complex. Specific amino acid residues within, and adjacent to, the TM2 domain influence single channel conductance, ion selectivity, and other aspects of receptor function that include gating and desensitization. However, more recent work has revealed important structural determinants of single channel conductance and ion selectivity that are not associated with the TM2 domain. Direct experimental evidence indicates that the intracellular domain of eukaryotic pLGICs, in particular a region of the loop linking TM3 and TM4 termed the membrane-associated (MA) stretch, exerts a strong influence upon ion channel biophysics. Moreover, recent computational approaches, complemented by experimentation, implicate the extracellular domain as an additional important determinant of ion conduction. This brief review describes how our knowledge of ion conduction and selectivity in cation-selective pLGICs has evolved beyond TM2.
Collapse
Affiliation(s)
- John A Peters
- Centre for Neuroscience, Division of Medical Sciences, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK.
| | | | | | | | | | | |
Collapse
|