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Tian Q, Tong P, Chen G, Deng M, Cai T, Tian R, Zhang Z, Xia K, Hu Z. GLRA2 gene mutations cause high myopia in humans and mice. J Med Genet 2023; 60:193-203. [PMID: 35396272 PMCID: PMC9887403 DOI: 10.1136/jmedgenet-2022-108425] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Accepted: 03/16/2022] [Indexed: 02/03/2023]
Abstract
BACKGROUND High myopia (HM) is a leading cause of blindness that has a strong genetic predisposition. However, its genetic and pathogenic mechanisms remain largely unknown. Thus, this study aims to determine the genetic profile of individuals from two large Chinese families with HM and 200 patients with familial/sporadic HM. We also explored the pathogenic mechanism of HM using HEK293 cells and a mouse model. METHODS The participants underwent genome-wide linkage analysis and exome sequencing. Visual acuity, electroretinogram response, refractive error, optical parameters and retinal rod cell genesis were measured in knockout mice. Immunofluorescent staining, biotin-labelled membrane protein isolation and electrophysiological characterisation were conducted in cells transfected with overexpression plasmids. RESULTS A novel HM locus on Xp22.2-p11.4 was identified. Variant c.539C>T (p.Pro180Leu) in GLRA2 gene was co-segregated with HM in the two families. Another variant, c.458G>A (p.Arg153Gln), was identified in a sporadic sample. The Glra2 knockout mice showed myopia-related phenotypes, decreased electroretinogram responses and impaired retinal rod cell genesis. Variants c.458G>A and c.539C>T altered the localisation of GlyRα2 on the cell membrane and decreased agonist sensitivity. CONCLUSION GLRA2 was identified as a novel HM-causing gene. Its variants would cause HM through altered visual experience by impairing photoperception and visual transmission.
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Affiliation(s)
- Qi Tian
- Center for Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China,Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China,Hunan Key Laboratory of Animal Models for Human Disease, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China
| | - Ping Tong
- Department of Ophthalmology, The Second Xiangya Hospital, Central South University, Changsha, Hunan, People's Republic of China
| | - Gong Chen
- Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China,Hunan Key Laboratory of Animal Models for Human Disease, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China,Hunan Province Key Laboratory of Basic and Applied Hematology, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China,Department of Biochemistry and Molecular Biology, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China
| | - Meichun Deng
- Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China,Hunan Key Laboratory of Animal Models for Human Disease, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China,Hunan Province Key Laboratory of Basic and Applied Hematology, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China,Department of Biochemistry and Molecular Biology, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China
| | - Tian'e Cai
- Reproductive Center, Sanya Central Hospital, Sanya, Hainan, People's Republic of China
| | - Runyi Tian
- Center for Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China,Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China,Hunan Key Laboratory of Animal Models for Human Disease, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China
| | - Zimin Zhang
- Center for Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China,Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China,Hunan Key Laboratory of Animal Models for Human Disease, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China
| | - Kun Xia
- Center for Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China .,Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China.,Hunan Key Laboratory of Animal Models for Human Disease, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China
| | - Zhengmao Hu
- Center for Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China .,Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China.,Hunan Key Laboratory of Animal Models for Human Disease, School of Life Sciences, Central South University, Changsha, Hunan, People's Republic of China
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2
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Lipovsek M, Marcovich I, Elgoyhen AB. The Hair Cell α9α10 Nicotinic Acetylcholine Receptor: Odd Cousin in an Old Family. Front Cell Neurosci 2021; 15:785265. [PMID: 34867208 PMCID: PMC8634148 DOI: 10.3389/fncel.2021.785265] [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: 09/28/2021] [Accepted: 10/25/2021] [Indexed: 11/13/2022] Open
Abstract
Nicotinic acetylcholine receptors (nAChRs) are a subfamily of pentameric ligand-gated ion channels with members identified in most eumetazoan clades. In vertebrates, they are divided into three subgroups, according to their main tissue of expression: neuronal, muscle and hair cell nAChRs. Each receptor subtype is composed of different subunits, encoded by paralogous genes. The latest to be identified are the α9 and α10 subunits, expressed in the mechanosensory hair cells of the inner ear and the lateral line, where they mediate efferent modulation. α9α10 nAChRs are the most divergent amongst all nicotinic receptors, showing marked differences in their degree of sequence conservation, their expression pattern, their subunit co-assembly rules and, most importantly, their functional properties. Here, we review recent advances in the understanding of the structure and evolution of nAChRs. We discuss the functional consequences of sequence divergence and conservation, with special emphasis on the hair cell α9α10 receptor, a seemingly distant cousin of neuronal and muscle nicotinic receptors. Finally, we highlight potential links between the evolution of the octavolateral system and the extreme divergence of vertebrate α9α10 receptors.
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Affiliation(s)
- Marcela Lipovsek
- Ear Institute, Faculty of Brain Sciences, University College London, London, United Kingdom
| | - Irina Marcovich
- Departments of Otolaryngology & Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA, United States
| | - Ana Belén Elgoyhen
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres" (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
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3
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Platholi J, Hemmings HC. Effects of general anesthetics on synaptic transmission and plasticity. Curr Neuropharmacol 2021; 20:27-54. [PMID: 34344292 PMCID: PMC9199550 DOI: 10.2174/1570159x19666210803105232] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2021] [Revised: 07/26/2021] [Accepted: 08/02/2021] [Indexed: 11/22/2022] Open
Abstract
General anesthetics depress excitatory and/or enhance inhibitory synaptic transmission principally by modulating the function of glutamatergic or GABAergic synapses, respectively, with relative anesthetic agent-specific mechanisms. Synaptic signaling proteins, including ligand- and voltage-gated ion channels, are targeted by general anesthetics to modulate various synaptic mechanisms, including presynaptic neurotransmitter release, postsynaptic receptor signaling, and dendritic spine dynamics to produce their characteristic acute neurophysiological effects. As synaptic structure and plasticity mediate higher-order functions such as learning and memory, long-term synaptic dysfunction following anesthesia may lead to undesirable neurocognitive consequences depending on the specific anesthetic agent and the vulnerability of the population. Here we review the cellular and molecular mechanisms of transient and persistent general anesthetic alterations of synaptic transmission and plasticity.
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Affiliation(s)
- Jimcy Platholi
- Cornell University Joan and Sanford I Weill Medical College Ringgold standard institution - Anesthesiology New York, New York. United States
| | - Hugh C Hemmings
- Cornell University Joan and Sanford I Weill Medical College Ringgold standard institution - Anesthesiology New York, New York. United States
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4
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Hussein RA, Ahmed M, Sticht H, Breitinger HG, Breitinger U. Fine-Tuning of Neuronal Ion Channels-Mapping of Residues Involved in Glucose Sensitivity of Recombinant Human Glycine Receptors. ACS Chem Neurosci 2020; 11:3474-3483. [PMID: 33007159 DOI: 10.1021/acschemneuro.0c00566] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The inhibitory glycine receptor (GlyR) mediates synaptic inhibition in the spinal cord, brain stem, and other regions of the mammalian central nervous system. Glucose was shown to potentiate α1 GlyRs by interacting with K143. Here, additional amino acids involved in glucose modulation were identified using a structure-based approach of site-directed mutagenesis followed by whole-cell patch-clamp analysis. We identified two additional lysine residues in the α1 GlyR extracellular domain, K16 and K281, that were involved in glucose modulation. Mutation of either residue to alanine abolished glucose potentiation. Residue K281 is located in the same pocket as K143 and could thus contribute to glucose binding. The double mutant K143A-K281A showed a 6-fold increase of EC50, while EC50 of both single mutants K143A and K281A was only slightly increased (1.7- and 1.3-fold, respectively). K16 is located at an analgesic binding site that is distant from the agonist or glucose sites, and the K16A mutation may generate a receptor species that is not potentiated. GlyR position α1-S267 is close to the postulated glucose binding site and known for interactions with ethanol and anesthetics. In the presence of glucose, GlyR α1 mutants S267A, S267I, and S267R showed potentiation, no effect, and reduction of current responses, respectively. This pattern follows that of ethanol modulation and suggests that the interaction sites of glucose and ethanol are identical or located close to each other. Our results support the presence of a distinct binding site for glucose on the glycine receptor, overlapping with the ivermectin/ethanol binding pocket near the transmembrane region and the TM2-3 loop.
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Affiliation(s)
- Rama Ashraf Hussein
- Department of Biochemistry, The German University in Cairo, Main Entrance of Al Tagamoa Al Khames, New Cairo 11835, Egypt
| | - Marwa Ahmed
- Department of Biochemistry, The German University in Cairo, Main Entrance of Al Tagamoa Al Khames, New Cairo 11835, Egypt
| | - Heinrich Sticht
- Division of Bioinformatics, Institute of Biochemistry, Friedrich-Alexander-Universität Erlangen-Nürnberg, Fahrstrasse 17, D-91054 Erlangen, Germany
| | - Hans-Georg Breitinger
- Department of Biochemistry, The German University in Cairo, Main Entrance of Al Tagamoa Al Khames, New Cairo 11835, Egypt
| | - Ulrike Breitinger
- Department of Biochemistry, The German University in Cairo, Main Entrance of Al Tagamoa Al Khames, New Cairo 11835, Egypt
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Han L, Shan Q. Pair of Residue Substitutions at the Outer Mouth of the Channel Pore Act as Inputs for a Boolean Logic "OR" Gate Based on the Glycine Receptor. ACS Chem Neurosci 2020; 11:3409-3417. [PMID: 32970400 DOI: 10.1021/acschemneuro.0c00522] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The glycine receptor (GlyR) is a ligand-activated chloride channel, whose mutations are the major cause of hereditary hyperekplexia. The hyperekplexia-causing R271Q mutation, which is located at the extracellular outer mouth of the channel pore, dramatically impairs the GlyR function manifesting a reduced sensitivity toward glycine. This study reports that a second mutation, S273D, rescues the function of the R271Q GlyR to that of the wild-type (WT) GlyR. Surprisingly, the S273D mutation, when introduced to the WT GlyR, does not further increase the receptor function. In other words, the compromised function of the 271Q 273S GlyR (i.e., the R271Q GlyR) can be rescued to WT levels by the introduction of either, or both, of the Q271R and S273D substitutions. From the perspective of Boolean logic gates, the Q271R and S273D substitutions act as inputs for an OR gate based on the GlyR. Further experiments revealed that the negative-charge carried by the 273 residue is essential for the expression of the OR gate and that the expression of the OR gate is residue-position-specific. In addition, mechanistic investigation implied that the 273 residue influences the 271 residue, which might underpin the unique nonadditive OR gate relationship between these two residues. Such an ion-channel-based OR gate, expressing output in the form of electrical current, could potentially be developed to digitally manipulate neuronal activity.
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Affiliation(s)
- Lu Han
- Zhejiang Key Laboratory of Organ Development and Regeneration, College of Life and Environmental Sciences, Hangzhou Normal University, Hangzhou, Zhejiang 311121, China
| | - Qiang Shan
- Laboratory for Synaptic Plasticity, Shantou University Medical College, Shantou, Guangdong 515041, China
- School of Basic Medical Sciences, Wenzhou Medical University, Wenzhou, Zhejiang 325035, China
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6
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Theisen U, Hennig C, Ring T, Schnabel R, Köster RW. Neurotransmitter-mediated activity spatially controls neuronal migration in the zebrafish cerebellum. PLoS Biol 2018; 16:e2002226. [PMID: 29300740 PMCID: PMC5754045 DOI: 10.1371/journal.pbio.2002226] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Accepted: 11/22/2017] [Indexed: 11/27/2022] Open
Abstract
Neuronal migration during embryonic development contributes to functional brain circuitry. Many neurons migrate in morphologically distinct stages that coincide with differentiation, requiring tight spatial regulation. It had been proposed that neurotransmitter-mediated activity could exert this control. Here, we demonstrate that intracellular calcium transients occur in cerebellar neurons of zebrafish embryos during migration. We show that depolarization increases and hyperpolarization reduces the speed of tegmental hindbrain neurons using optogenetic tools and advanced track analysis optimized for in vivo migration. Finally, we introduce a compound screening assay to identify acetylcholine (ACh), glutamate, and glycine as regulators of migration, which act regionally along the neurons’ route. We summarize our findings in a model describing how different neurotransmitters spatially interact to control neuronal migration. The high evolutionary conservation of the cerebellum and hindbrain makes it likely that polarization state-driven motility constitutes an important principle in building a functional brain. Postmitotic neurons migrate from their site of origin to their final destination in the developing brain to form functional structures. These neurons typically follow defined routes through the tissue. Previous studies investigating progress along such route have identified neurotransmitters—chemicals that transmit the signals between neurons—as important regulators in neuronal migration using mostly rodent brain slice cultures and cultivated neurons. In this study, we use live zebrafish embryos to test the influence of neurotransmitters on migrating hindbrain neurons. First, we demonstrate that calcium transients can be measured in these neurons using genetically encoded reporters. Next, we use optogenetic channels to specifically de- or hyperpolarize the plasma membrane of the neurons to show that the polarization state is linked to migratory speed. Finally, we use a screening method to identify the neurotransmitter systems involved in migration progress control. We summarize these findings in a model that suggests that there are regions of influence for different neurotransmitters that act successively on the neurons to ensure their timely arrival at their destination.
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Affiliation(s)
- Ulrike Theisen
- Technische Universität Braunschweig, Zoological Institute, Cellular and Molecular Neurobiology, Braunschweig, Germany
| | - Christian Hennig
- Technische Universität Braunschweig, Institute for Genetics, Braunschweig, Germany
| | - Tobias Ring
- Technische Universität Braunschweig, Institute for Engineering Design, Vibroacoustics, Braunschweig, Germany
| | - Ralf Schnabel
- Technische Universität Braunschweig, Institute for Genetics, Braunschweig, Germany
| | - Reinhard W. Köster
- Technische Universität Braunschweig, Zoological Institute, Cellular and Molecular Neurobiology, Braunschweig, Germany
- * E-mail:
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7
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Burgos CF, Yévenes GE, Aguayo LG. Structure and Pharmacologic Modulation of Inhibitory Glycine Receptors. Mol Pharmacol 2016; 90:318-25. [PMID: 27401877 DOI: 10.1124/mol.116.105726] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2016] [Accepted: 07/08/2016] [Indexed: 01/08/2023] Open
Abstract
Glycine receptors (GlyR) are inhibitory Cys-loop ion channels that contribute to the control of excitability along the central nervous system (CNS). GlyR are found in the spinal cord and brain stem, and more recently they were reported in higher regions of the CNS such as the hippocampus and nucleus accumbens. GlyR are involved in motor coordination, respiratory rhythms, pain transmission, and sensory processing, and they are targets for relevant physiologic and pharmacologic modulators. Several studies with protein crystallography and cryoelectron microscopy have shed light on the residues and mechanisms associated with the activation, blockade, and regulation of pentameric Cys-loop ion channels at the atomic level. Initial studies conducted on the extracellular domain of acetylcholine receptors, ion channels from prokaryote homologs-Erwinia chrysanthemi ligand-gated ion channel (ELIC), Gloeobacter violaceus ligand-gated ion channel (GLIC)-and crystallized eukaryotic receptors made it possible to define the overall structure and topology of the Cys-loop receptors. For example, the determination of pentameric GlyR structures bound to glycine and strychnine have contributed to visualizing the structural changes implicated in the transition between the open and closed states of the Cys-loop receptors. In this review, we summarize how the new information obtained in functional, mutagenesis, and structural studies have contributed to a better understanding of the function and regulation of GlyR.
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Affiliation(s)
- Carlos F Burgos
- Laboratory of Neurophysiology (C.F.B., L.G.A.), and Laboratory of Neuropharmacology (G.E.Y.), Department of Physiology, University of Concepción, Concepción, Chile
| | - Gonzalo E Yévenes
- Laboratory of Neurophysiology (C.F.B., L.G.A.), and Laboratory of Neuropharmacology (G.E.Y.), Department of Physiology, University of Concepción, Concepción, Chile
| | - Luis G Aguayo
- Laboratory of Neurophysiology (C.F.B., L.G.A.), and Laboratory of Neuropharmacology (G.E.Y.), Department of Physiology, University of Concepción, Concepción, Chile
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8
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Jaiteh M, Taly A, Hénin J. Evolution of Pentameric Ligand-Gated Ion Channels: Pro-Loop Receptors. PLoS One 2016; 11:e0151934. [PMID: 26986966 PMCID: PMC4795631 DOI: 10.1371/journal.pone.0151934] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Accepted: 03/07/2016] [Indexed: 01/27/2023] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) are ubiquitous neurotransmitter receptors in Bilateria, with a small number of known prokaryotic homologues. Here we describe a new inventory and phylogenetic analysis of pLGIC genes across all kingdoms of life. Our main finding is a set of pLGIC genes in unicellular eukaryotes, some of which are metazoan-like Cys-loop receptors, and others devoid of Cys-loop cysteines, like their prokaryotic relatives. A number of such “Cys-less” receptors also appears in invertebrate metazoans. Together, those findings draw a new distribution of pLGICs in eukaryotes. A broader distribution of prokaryotic channels also emerges, including a major new archaeal taxon, Thaumarchaeota. More generally, pLGICs now appear nearly ubiquitous in major taxonomic groups except multicellular plants and fungi. However, pLGICs are sparsely present in unicellular taxa, suggesting a high rate of gene loss and a non-essential character, contrasting with their essential role as synaptic receptors of the bilaterian nervous system. Multiple alignments of these highly divergent sequences reveal a small number of conserved residues clustered at the interface between the extracellular and transmembrane domains. Only the “Cys-loop” proline is absolutely conserved, suggesting the more fitting name “Pro loop” for that motif, and “Pro-loop receptors” for the superfamily. The infered molecular phylogeny shows a Cys-loop and a Cys-less clade in eukaryotes, both containing metazoans and unicellular members. This suggests new hypotheses on the evolutionary history of the superfamily, such as a possible origin of the Cys-loop cysteines in an ancient unicellular eukaryote. Deeper phylogenetic relationships remain uncertain, particularly around the split between bacteria, archaea, and eukaryotes.
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Affiliation(s)
- Mariama Jaiteh
- Laboratoire de Biochimie Théorique, Institut de Biologie Physico-Chimique, CNRS and Université Paris Diderot, Paris, France
| | - Antoine Taly
- Laboratoire de Biochimie Théorique, Institut de Biologie Physico-Chimique, CNRS and Université Paris Diderot, Paris, France
| | - Jérôme Hénin
- Laboratoire de Biochimie Théorique, Institut de Biologie Physico-Chimique, CNRS and Université Paris Diderot, Paris, France
- * E-mail:
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9
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Glycine receptor mechanism elucidated by electron cryo-microscopy. Nature 2015; 526:224-9. [PMID: 26344198 DOI: 10.1038/nature14853] [Citation(s) in RCA: 305] [Impact Index Per Article: 33.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2015] [Accepted: 06/23/2015] [Indexed: 12/12/2022]
Abstract
The strychnine-sensitive glycine receptor (GlyR) mediates inhibitory synaptic transmission in the spinal cord and brainstem and is linked to neurological disorders, including autism and hyperekplexia. Understanding of molecular mechanisms and pharmacology of glycine receptors has been hindered by a lack of high-resolution structures. Here we report electron cryo-microscopy structures of the zebrafish α1 GlyR with strychnine, glycine, or glycine and ivermectin (glycine/ivermectin). Strychnine arrests the receptor in an antagonist-bound closed ion channel state, glycine stabilizes the receptor in an agonist-bound open channel state, and the glycine/ivermectin complex adopts a potentially desensitized or partially open state. Relative to the glycine-bound state, strychnine expands the agonist-binding pocket via outward movement of the C loop, promotes rearrangement of the extracellular and transmembrane domain 'wrist' interface, and leads to rotation of the transmembrane domain towards the pore axis, occluding the ion conduction pathway. These structures illuminate the GlyR mechanism and define a rubric to interpret structures of Cys-loop receptors.
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Yu R, Hurdiss E, Greiner T, Lape R, Sivilotti L, Biggin PC. Agonist and antagonist binding in human glycine receptors. Biochemistry 2014; 53:6041-51. [PMID: 25184435 DOI: 10.1021/bi500815f] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The human glycine receptor (hGlyR) is an anion-permeable ligand-gated channel that is part of a larger superfamily of receptors called the Cys-loop family. hGlyRs are particularly amenable to single-channel recordings, thus making them a model experimental system for understanding the Cys-loop receptor family in general. Understanding the relationship between agonist binding and efficacy in Cys-loop receptors should improve our future prospects for making specific agonists or antagonists. However, at present, there is no high-resolution structure for the complete hGlyR, and thus, modeling is needed to provide a physical framework on which to interpret single-channel data. The structure of the glutamate-gated chloride channel from Caenorhabditis elegans shows a much higher level of sequence identity to human hGlyR than previous templates such as AChBP or the bacterial channels, GLIC and ELIC. Thus, we constructed a model of the hGlyR and validated it against previously reported mutagenesis data. We used molecular dynamics to refine the model and to explore binding of both an agonist (glycine) and an antagonist (strychnine). The model shows excellent agreement with previous data but also suggests some unique features: (i) a water molecule that forms part of the binding site and allows us to account for some previous results that were difficult to reconcile, (ii) an interaction of the glycine agonist with S129, and (iii) an effect from E211, both of which we confirmed with new site-directed mutagenesis and patch clamp recordings. Finally, examination of the simulations suggests that strychnine binding induces movement to a conformational state distinct from the glycine-bound or apo state, not only within the ligand-binding domain but also in the transmembrane domain.
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Affiliation(s)
- Rilei Yu
- Structural Bioinformatics and Computational Biochemistry, Department of Biochemistry, University of Oxford , South Parks Road, Oxford OX1 3QU, United Kingdom
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Han L, Talwar S, Wang Q, Shan Q, Lynch JW. Phosphorylation of α3 glycine receptors induces a conformational change in the glycine-binding site. ACS Chem Neurosci 2013; 4:1361-70. [PMID: 23834509 DOI: 10.1021/cn400097j] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Inflammatory pain sensitization is initiated by prostaglandin-induced phosphorylation of α3 glycine receptors (GlyRs) that are specifically located in inhibitory synapses on spinal pain sensory neurons. Phosphorylation reduces the magnitude of glycinergic synaptic currents, thereby disinhibiting nociceptive neurons. Although α1 and α3 subunits are both expressed on spinal nociceptive neurons, α3 is a more promising therapeutic target as its sparse expression elsewhere implies a reduced risk of side-effects. Here we compared glycine-mediated conformational changes in α1 and α3 GlyRs to identify structural differences that might be exploited in designing α3-specific analgesics. Using voltage-clamp fluorometry, we show that glycine-mediated conformational changes in the extracellular M2-M3 domain were significantly different between the two GlyR isoforms. Using a chimeric approach, we found that structural variations in the intracellular M3-M4 domain were responsible for this difference. This prompted us to test the hypothesis that phosphorylation of S346 in α3 GlyR might also induce extracellular conformation changes. We show using both voltage-clamp fluorometry and pharmacology that Ser346 phosphorylation elicits structural changes in the α3 glycine-binding site. These results provide the first direct evidence for phosphorylation-mediated extracellular conformational changes in pentameric ligand-gated ion channels, and thus suggest new loci for investigating how phosphorylation modulates structure and function in this receptor family. More importantly, by demonstrating that phosphorylation alters α3 GlyR glycine-binding site structure, they raise the possibility of developing analgesics that selectively target inflammation-modulated GlyRs.
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Affiliation(s)
- Lu Han
- Queensland Brain Institute and ‡School of Biomedical Sciences, The University of Queensland, Brisbane
QLD 4072, Australia
| | - Sahil Talwar
- Queensland Brain Institute and ‡School of Biomedical Sciences, The University of Queensland, Brisbane
QLD 4072, Australia
| | - Qian Wang
- Queensland Brain Institute and ‡School of Biomedical Sciences, The University of Queensland, Brisbane
QLD 4072, Australia
| | - Qiang Shan
- Queensland Brain Institute and ‡School of Biomedical Sciences, The University of Queensland, Brisbane
QLD 4072, Australia
| | - Joseph W. Lynch
- Queensland Brain Institute and ‡School of Biomedical Sciences, The University of Queensland, Brisbane
QLD 4072, Australia
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Pless SA, Hanek AP, Price KL, Lynch JW, Lester HA, Dougherty DA, Lummis SCR. A cation-π interaction at a phenylalanine residue in the glycine receptor binding site is conserved for different agonists. Mol Pharmacol 2011; 79:742-8. [PMID: 21266487 DOI: 10.1124/mol.110.069583] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cation-π interactions have been demonstrated to play a major role in agonist-binding in Cys-loop receptors. However, neither the aromatic amino acid contributing to this interaction nor its location is conserved among Cys-loop receptors. Likewise, it is not clear how many different agonists of a given receptor form a cation-π interaction or, if they do, whether it is with the same aromatic amino acid as the major physiological agonist. We demonstrated previously that Phe159 in the glycine receptor (GlyR) α1 subunit forms a strong cation-π interaction with the principal agonist, glycine. In the current study, we investigated whether the lower efficacy agonists of the human GlyR β-alanine and taurine also form cation-π interactions with Phe159. By incorporating a series of unnatural amino acids, we found cation-π interactions between Phe159 and the amino groups of β-alanine and taurine. The strengths of these interactions were significantly weaker than for glycine. Modeling studies suggest that β-alanine and taurine are orientated subtly differently in the binding pocket, with their amino groups further from Phe159 than that of glycine. These data therefore show that similar agonists can have similar but not identical orientations and interactions in the binding pocket and provide a possible explanation for the lower potencies of β-alanine and taurine.
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Affiliation(s)
- Stephan A Pless
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia
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Lynagh T, Lynch JW. An improved ivermectin-activated chloride channel receptor for inhibiting electrical activity in defined neuronal populations. J Biol Chem 2010; 285:14890-14897. [PMID: 20308070 PMCID: PMC2865309 DOI: 10.1074/jbc.m110.107789] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2010] [Revised: 03/02/2010] [Indexed: 11/06/2022] Open
Abstract
The ability to silence the electrical activity of defined neuronal populations in vivo is dramatically advancing our understanding of brain function. This technology may eventually be useful clinically for treating a variety of neuropathological disorders caused by excessive neuronal activity. Several neuronal silencing methods have been developed, with the bacterial light-activated halorhodopsin and the invertebrate allatostatin-activated G protein-coupled receptor proving the most successful to date. However, both techniques may be difficult to implement clinically due to their requirement for surgically implanted stimulus delivery methods and their use of nonhuman receptors. A third silencing method, an invertebrate glutamate-gated chloride channel receptor (GluClR) activated by ivermectin, solves the stimulus delivery problem as ivermectin is a safe, well tolerated drug that reaches the brain following systemic administration. However, the limitations of this method include poor functional expression, possibly due to the requirement to coexpress two different subunits in individual neurons, and the nonhuman origin of GluClR. Here, we describe the development of a modified human alpha1 glycine receptor as an improved ivermectin-gated silencing receptor. The crucial development was the identification of a mutation, A288G, which increased ivermectin sensitivity almost 100-fold, rendering it similar to that of GluClR. Glycine sensitivity was eliminated via the F207A mutation. Its large unitary conductance, homomeric expression, and human origin may render the F207A/A288G alpha1 glycine receptor an improved silencing receptor for neuroscientific and clinical purposes. As all known highly ivermectin-sensitive GluClRs contain an endogenous glycine residue at the corresponding location, this residue appears essential for exquisite ivermectin sensitivity.
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Affiliation(s)
- Timothy Lynagh
- Queensland Brain Institute and School of Biomedical Sciences, The University of Queensland, Brisbane QLD 4072, Australia
| | - Joseph W Lynch
- Queensland Brain Institute and School of Biomedical Sciences, The University of Queensland, Brisbane QLD 4072, Australia.
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14
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Disruption of an intersubunit electrostatic bond is a critical step in glycine receptor activation. Proc Natl Acad Sci U S A 2010; 107:7987-92. [PMID: 20385800 DOI: 10.1073/pnas.1001845107] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Proper regulation of neurotransmission requires that ligand-activated ion channels remain closed until agonist binds. How channels then open remains poorly understood. Glycine receptor (GlyR) gating is initiated by agonist binding at interfaces between adjacent subunits in the extracellular domain. Aspartate-97, located at the alpha1 GlyR interface, is a conserved residue in the cys-loop receptor superfamily. The mutation of D97 to arginine (D97R) causes spontaneous channel opening, with open and closed dwell times similar to those of maximally activated WT GlyR. Using a model of the N-terminal domain of the alpha1 GlyR, we hypothesized that an arginine-119 residue was forming intersubunit electrostatic bonds with D97. The D97R/R119E charge reversal restored this interaction, stabilizing channels in their closed states. Cysteine substitution shows that this link occurs between adjacent subunits. This intersubunit electrostatic interaction among GlyR subunits thus contributes to the stabilization of the closed channel state, and its disruption represents a critical step in GlyR activation.
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15
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Vogel N, Kluck CJ, Melzer N, Schwarzinger S, Breitinger U, Seeber S, Becker CM. Mapping of disulfide bonds within the amino-terminal extracellular domain of the inhibitory glycine receptor. J Biol Chem 2009; 284:36128-36136. [PMID: 19861413 DOI: 10.1074/jbc.m109.043448] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The strychnine-sensitive glycine receptor (GlyR) is a ligand-gated chloride channel and a member of the superfamily of cysteine loop (Cys-loop) neurotransmitter receptors, which also comprises the nicotinic acetylcholine receptor (nAChR). Within the extracellular domain (ECD), the eponymous Cys-loop harbors two conserved cysteines, assumed to be linked by a superfamily-specific disulfide bond. The GlyR ECD carries three additional cysteine residues, two are predicted to form a second, GlyR-specific bond. The configuration of none of the cysteines of GlyR, however, had been determined directly. Based on a crystal structure of the nAChRalpha1 ECD, we generated a model of the human GlyRalpha1 where close proximity of the respective cysteines was consistent with the formation of both the Cys-loop and the GlyR-specific disulfide bonds. To identify native disulfide bonds, the GlyRalpha1 ECD was heterologously expressed and refolded under oxidative conditions. By matrix-assisted laser desorption ionization time-of-flight mass spectrometry, we detected tryptic fragments of the ECD indicative of disulfide bond formation for both pairs of cysteines, as proposed by modeling. The identity of tryptic fragments was confirmed using chemical modification of cysteine and lysine residues. As evident from circular dichroism spectroscopy, mutagenesis of single cysteines did not impair refolding of the ECD in vitro, whereas it led to partial or complete intracellular retention and consequently to a loss of function of full-length GlyR subunits in human embryonic kidney 293 cells. Our results indicate that the GlyR ECD forms both a Cys-loop and a GlyR-specific disulfide bond. In addition, cysteine residues appear to be important for protein maturation in vivo.
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Affiliation(s)
- Nicolas Vogel
- Institut für Biochemie, Emil-Fischer-Zentrum, Universität Erlangen-Nürnberg, Erlangen 91054
| | - Christoph J Kluck
- Institut für Biochemie, Emil-Fischer-Zentrum, Universität Erlangen-Nürnberg, Erlangen 91054
| | - Nima Melzer
- Institut für Biochemie, Emil-Fischer-Zentrum, Universität Erlangen-Nürnberg, Erlangen 91054
| | | | - Ulrike Breitinger
- Institut für Biochemie, Emil-Fischer-Zentrum, Universität Erlangen-Nürnberg, Erlangen 91054
| | - Silke Seeber
- Institut für Biochemie, Emil-Fischer-Zentrum, Universität Erlangen-Nürnberg, Erlangen 91054
| | - Cord-Michael Becker
- Institut für Biochemie, Emil-Fischer-Zentrum, Universität Erlangen-Nürnberg, Erlangen 91054.
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16
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Chen X, Cromer BA, Lynch JW. Molecular determinants of beta-carboline inhibition of the glycine receptor. J Neurochem 2009; 110:1685-94. [PMID: 19619142 DOI: 10.1111/j.1471-4159.2009.06273.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
beta-Carbolines are potent modulators of GABA type A receptors and they have recently been shown to inhibit glycine receptors in a subunit-specific manner. The present study screened four structurally similar beta-carbolines, 1,2,3,4-tetrahydronorharmane, norharmane, harmane and 6-methoxyharmalan, at recombinantly expressed alpha1, alpha1beta, alpha2 and alpha3 glycine receptors with the aims of identifying structural elements of both the receptor and the compounds that are important for binding and subunit specificity. The four compounds exhibited only weak subunit specificity, rendering them unsuitable as pharmacological probes. Because they displayed competitive antagonist activity, we investigated the roles of known glycine binding residues in coordinating the four compounds. The structural similarity of the compounds, coupled with the differential effects of C-loop mutations (T204A, F207Y) on compound potency, implied direct interactions between variable beta-carboline groups and mutated residues. Mutant cycle analysis employing harmane and norharmane revealed a strong pairwise interaction between the harmane methyl group and the C-loop in the region T204 and F207. These results which define the orientation of the bound beta-carbolines were supported by molecular docking simulations. The information may also be relevant to understanding the mechanism beta-carboline of binding to GABA type A receptors where they are potent pharmacological probes.
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Affiliation(s)
- Xuebin Chen
- Queensland Brain Institute and School of Biomedical Sciences, University of Queensland, Brisbane, Queensland 4072, Australia
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17
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Kehoe J, Buldakova S, Acher F, Dent J, Bregestovski P, Bradley J. Aplysia cys-loop glutamate-gated chloride channels reveal convergent evolution of ligand specificity. J Mol Evol 2009; 69:125-41. [PMID: 19554247 DOI: 10.1007/s00239-009-9256-z] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2009] [Revised: 05/15/2009] [Accepted: 06/01/2009] [Indexed: 12/20/2022]
Abstract
Among the members of the superfamily of cys-loop ligand-gated ion channels (LGICs) are receptors distinguished by the presence of two cys-loops in the ligand-binding domain, for example, the glycine receptor. Such receptors have thus far been cloned only from vertebrates and from ecdysozoa (arthropods and nematodes). We have now cloned and expressed two 2-cys-loop receptors from Aplysia californica, a lophotrocozoan, and have shown that they form homomeric glutamate receptors. We have also built up a database including the two receptors cloned here, previously cloned vertebrate and ecdysozoan 2-cys-loop receptors taken from GenBank, and the same type of receptors obtained by a search of recently cloned genomes, including two non-vertebrate chordates, an echinoderm, a crustacean, an annelid, and another mollusk. We subjected these receptors to phylogenetic analysis, alone and in combination with GABA-A receptors from the same phyla and from a recently cloned cnidarian. The phylogenetic analysis revealed the presence of two independent clades of glutamate receptors: one from lophotrocozoa and other from ecdysozoa, and suggests that the ancestors of the current 2-cys-loop receptor types diverged from the GABA-A receptors and from each other before the bilateria-cnidaria split. Finally, combining the results from the phylogenetic analysis with those obtained from an analysis of the 2-cys-loop receptors in light of recently published hypotheses concerning the glycine binding pocket, we predict that glycine receptors are not exclusively a vertebrate-receptor type.
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18
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Pless SA, Lynch JW. Ligand-specific conformational changes in the alpha1 glycine receptor ligand-binding domain. J Biol Chem 2009; 284:15847-56. [PMID: 19286654 DOI: 10.1074/jbc.m809343200] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Understanding the activation mechanism of Cys loop ion channel receptors is key to understanding their physiological and pharmacological properties under normal and pathological conditions. The ligand-binding domains of these receptors comprise inner and outer beta-sheets and structural studies indicate that channel opening is accompanied by conformational rearrangements in both beta-sheets. In an attempt to resolve ligand-dependent movements in the ligand-binding domain, we employed voltage-clamp fluorometry on alpha1 glycine receptors to compare changes mediated by the agonist, glycine, and by the antagonist, strychnine. Voltage-clamp fluorometry involves labeling introduced cysteines with environmentally sensitive fluorophores and inferring structural rearrangements from ligand-induced fluorescence changes. In the inner beta-sheet, we labeled residues in loop 2 and in binding domain loops D and E. At each position, strychnine and glycine induced distinct maximal fluorescence responses. The pre-M1 domain responded similarly; at each of four labeled positions glycine produced a strong fluorescence signal, whereas strychnine did not. This suggests that glycine induces conformational changes in the inner beta-sheet and pre-M1 domain that may be important for activation, desensitization, or both. In contrast, most labeled residues in loops C and F yielded fluorescence changes identical in magnitude for glycine and strychnine. A notable exception was H201C in loop C. This labeled residue responded differently to glycine and strychnine, thus underlining the importance of loop C in ligand discrimination. These results provide an important step toward mapping the domains crucial for ligand discrimination in the ligand-binding domain of glycine receptors and possibly other Cys loop receptors.
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Affiliation(s)
- Stephan A Pless
- Queensland Brain Institute and School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia
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19
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Pless SA, Lynch JW. Distinct conformational changes in activated agonist-bound and agonist-free glycine receptor subunits. J Neurochem 2009; 108:1585-94. [DOI: 10.1111/j.1471-4159.2009.05930.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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20
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A novel member of the ligand-gated chloride channel gene family from Haemonchus contortus. Parasitology 2007; 135:539-45. [DOI: 10.1017/s0031182007004088] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
SUMMARYLigand-gated chloride channels (LGCCs) are key components of the nervous system of parasitic nematodes and important targets for anthelmintics. Here, we describe the isolation and characterization of a novel member of the LGCC gene family (HcLGCC1) from the parasitic nematode Haemonchus contortus. Sequence analysis revealed that the channel subunit encoded by HcLGCC1 is anion selective and a member of a group of channels characterized as having two Cys-loops in the N-terminal ligand-binding domain†. Although the overall function of HcLGCC1 is presently unknown, the gene may play a key role in the early developmental stages of the parasite. Further investigations into the function of LGCCs, such as HcLGCC1, in parasitic nematodes should have implications for the discovery of new anthelmintic targets.
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21
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Zhang CG, Kim SJ. Taurine Induces Anti-Anxiety by Activating Strychnine-Sensitive Glycine Receptor in vivo. ANNALS OF NUTRITION AND METABOLISM 2007; 51:379-86. [PMID: 17728537 DOI: 10.1159/000107687] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2006] [Accepted: 03/09/2007] [Indexed: 11/19/2022]
Abstract
Taurine has a variety of actions in the body such as cardiotonic, host-defensive, radioprotective and glucose-regulatory effects. However, its action in the central nervous system remains to be characterized. In the present study, we tested to see whether taurine exerts anti-anxiety effects and to explore its mechanism of anti-anxiety activity in vivo. The staircase test and elevated plus maze test were performed to test the anti-anxiety action of taurine. Convulsions induced by strychnine, picrotoxin, yohimbine and isoniazid were tested to explore the mechanism of anti-anxiety activity of taurine. The Rotarod test was performed to test muscle relaxant activity and the passive avoidance test was carried out to test memory activity in response to taurine. Taurine (200 mg/kg, p.o.) significantly reduced rearing numbers in the staircase test while it increased the time spent in the open arms as well as the number of entries to the open arms in the elevated plus maze test, suggesting that it has a significant anti-anxiety activity. Taurine's action could be due to its binding to and activating of strychnine-sensitive glycine receptor in vivo as it inhibited convulsion caused by strychnine; however, it has little effect on picrotoxin-induced convulsion, suggesting its anti-anxiety activity may not be linked to GABA receptor. It did not alter memory function and muscle activity. Taken together, these results suggest that taurine could be beneficial for the control of anxiety in the clinical situations.
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Affiliation(s)
- Cheng Gao Zhang
- Department of Pharmacology and Metabolic Diseases Research Laboratory, School of Dentistry, Kyung Hee University, Seoul, Korea
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22
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Yang Z, Ney A, Cromer BA, Ng HL, Parker MW, Lynch JW. Tropisetron modulation of the glycine receptor: femtomolar potentiation and a molecular determinant of inhibition. J Neurochem 2006; 100:758-69. [PMID: 17181559 DOI: 10.1111/j.1471-4159.2006.04242.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The 5-hydroxytryptamine type-3 receptor antagonist tropisetron is in clinical use as an anti-emetic drug. This compound also exerts both potentiating and inhibitory effects on the glycine receptor chloride channel. The inhibitory effects occur at micromolar concentrations, whereas the potentiating effects are shown here to occur at femtomolar concentrations at the homomeric alpha1 receptor. Potentiation occurred only when tropisetron was applied in the presence of glycine. We also sought to identify molecular determinants of tropisetron inhibition at the alpha1 glycine receptor by serially mutating residues located in or near known ligand-binding sites. We discovered that conservative mutations to N102 ablated tropisetron inhibition without affecting the magnitude or sensitivity of tropisetron potentiation. Several lines of evidence, including a structure-activity analysis of tropisetron, atropine and SB203186, suggest that N102 may bind to the tropisetron tropane nitrogen via H-bonding. Mutation of the N125 residue in the beta subunit, which corresponds to N102 in the alpha1 subunit, had little effect on tropisetron inhibitory potency. These results show that N102 is required for tropisetron inhibition but not potentiation and that inhibitory tropisetron binds in different orientations at different subunit interfaces. To our knowledge, tropisetron is the most exquisitely sensitive modulator yet identified for a cys-loop receptor.
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Affiliation(s)
- Zhe Yang
- School of Biomedical Sciences, University of Queensland, Brisbane, QLD, Australia
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23
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Dent JA. Evidence for a Diverse Cys-Loop Ligand-Gated Ion Channel Superfamily in Early Bilateria. J Mol Evol 2006; 62:523-35. [PMID: 16586016 DOI: 10.1007/s00239-005-0018-2] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2005] [Accepted: 11/30/2005] [Indexed: 10/24/2022]
Abstract
The genome sequences of Caenorhabditis elegans and Drosophila melanogaster reveal a diversity of cysteine-loop ligand-gated ion channels (Cys-loop LGICs) not found in vertebrates. To better understand the evolution of this gene superfamily, I compared all Cys-loop LGICs from rat, the primitive chordate Ciona intestinalis, Drosophila, and C. elegans. There are two clades of GABA receptor subunits that include both vertebrate and invertebrate orthologues. In addition, I identified nine clades of anion channel subunits found only in invertebrates, including three that are specific to C. elegans and two found only in Drosophila. One well-defined clade of vertebrate cation channel subunits, the alpha 7 nicotinic acetylcholine receptor subunits (nAChR), includes invertebrate orthologues. There are two clades of invertebrate nAChRs, one of alpha-type subunits and one of non-alpha subunits, that are most similar to the two clades of vertebrate neuronal and muscle alpha and non-alpha subunits. There is a large group of divergent C. elegans nAChR-like subunits partially resolved into clades but no orthologues of 5HT3-type serotonin receptors in the invertebrates. The topology of the trees suggests that most of the invertebrate-specific Cys-loop LGIC clades were present in the common ancestor of chordates and ecdysozoa. Many of these disappeared from the chordates. Subsequently, selected subunit genes expanded to form large subfamilies.
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Affiliation(s)
- Joseph A Dent
- Department of Biology, McGill University, 1205 Dr. Penfield Avenue, Montreal, Quebec H3A 1B1, Canada.
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24
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Pan C, Bai X, Fan L, Ji Y, Li X, Chen Q. Cytoprotection by glycine against ATP-depletion-induced injury is mediated by glycine receptor in renal cells. Biochem J 2006; 390:447-53. [PMID: 15836436 PMCID: PMC1198924 DOI: 10.1042/bj20050141] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
It is known that glycine protects mammalian cells against ischaemic cell injury by preventing cellular membrane leakage. However, the molecular mechanisms have not yet been clearly elucidated. The purpose of the present study was to clarify whether GlyR (glycine receptor) acts as a key mediator in cytoprotection of glycine. cDNA encoding human GlyRa1 (a1-subunit of glycine receptor) was transfected into HEK-293 cells. The membrane integrity of the cells with or without GlyRa1 was examined by the uptake of marker compounds, the release of LDH (lactate dehydrogenase) and the exclusion of Trypan Blue. Glycine prevented the permeability of 70 kDa dextrans and 140 kDa LDH in the cells in which GlyR was expressed under conditions of ATP depletion. The inhibition of endogenous GlyR expression by RNA interference attenuated the cytoprotection by glycine. Furthermore, the mutation of Tyr202 to phenylalanine in GlyRa1 blocked the glycine-mediated cytoprotection, while the mutation of Tyr202 to leucine abolished the cytoprotection by strychnine. Our results suggested that the cytoprotection of glycine against ATP-depletion-induced injury might be mediated by GlyR.
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Affiliation(s)
- Chao Pan
- *Atherosclerosis Research Centre, Laboratory of Reproductive Medicine, Nanjing Medical University, Nanjing 210029, People's Republic of China
| | - Xiaoming Bai
- *Atherosclerosis Research Centre, Laboratory of Reproductive Medicine, Nanjing Medical University, Nanjing 210029, People's Republic of China
| | - Leming Fan
- *Atherosclerosis Research Centre, Laboratory of Reproductive Medicine, Nanjing Medical University, Nanjing 210029, People's Republic of China
| | - Yong Ji
- †Provincial Laboratory of Human Functional Genomics, Nanjing Medical University, Nanjing 210029, People's Republic of China
| | - Xiaoyu Li
- †Provincial Laboratory of Human Functional Genomics, Nanjing Medical University, Nanjing 210029, People's Republic of China
| | - Qi Chen
- *Atherosclerosis Research Centre, Laboratory of Reproductive Medicine, Nanjing Medical University, Nanjing 210029, People's Republic of China
- To whom correspondence should be addressed (email )
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25
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Lobo IA, Harris RA. Sites of alcohol and volatile anesthetic action on glycine receptors. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2005; 65:53-87. [PMID: 16140053 DOI: 10.1016/s0074-7742(04)65003-3] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
Affiliation(s)
- Ingrid A Lobo
- Institute for Cellular and Molecular Biology, Waggoner Center for Alcohol and Addiction Research, Section of Neurobiology, University of Texas at Austin, Austin, Texas 78712, USA
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26
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O'Mara M, Cromer B, Parker M, Chung SH. Homology model of the GABAA receptor examined using Brownian dynamics. Biophys J 2005; 88:3286-99. [PMID: 15749776 PMCID: PMC1305477 DOI: 10.1529/biophysj.104.051664] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have developed a homology model of the GABA(A) receptor, using the subunit combination of alpha1beta2gamma2, the most prevalent type in the mammalian brain. The model is produced in two parts: the membrane-embedded channel domain and the extracellular N-terminal domain. The pentameric transmembrane domain model is built by modeling each subunit by homology with the equivalent subunit of the heteropentameric acetylcholine receptor transmembrane domain. This segment is then joined with the extracellular domain built by homology with the acetylcholine binding protein. The all-atom model forms a wide extracellular vestibule that is connected to an oval chamber near the external surface of the membrane. A narrow, cylindrical transmembrane channel links the outer segment of the pore to a shallow intracellular vestibule. The physiological properties of the model so constructed are examined using electrostatic calculations and Brownian dynamics simulations. A deep energy well of approximately 80 kT accommodates three Cl(-) ions in the narrow transmembrane channel and seven Cl(-) ions in the external vestibule. Inward permeation takes place when one of the ions queued in the external vestibule enters the narrow segment and ejects the innermost ion. The model, when incorporated into Brownian dynamics, reproduces key experimental features, such as the single-channel current-voltage-concentration profiles. Finally, we simulate the gamma2 K289M epilepsy inducing mutation and examine Cl(-) ion permeation through the mutant receptor.
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Affiliation(s)
- Megan O'Mara
- Department of Theoretical Physics, Research School of Physical Sciences, Australian National University, Canberra, Australia
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27
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Grudzinska J, Schemm R, Haeger S, Nicke A, Schmalzing G, Betz H, Laube B. The β Subunit Determines the Ligand Binding Properties of Synaptic Glycine Receptors. Neuron 2005; 45:727-39. [PMID: 15748848 DOI: 10.1016/j.neuron.2005.01.028] [Citation(s) in RCA: 281] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2004] [Revised: 12/23/2004] [Accepted: 01/20/2005] [Indexed: 11/26/2022]
Abstract
Inhibitory glycine receptors (GlyRs) regulate motor coordination and sensory signal processing in spinal cord and other brain regions. GlyRs are pentameric proteins composed of membrane-spanning alpha and beta subunits. Here, site-directed mutagenesis combined with homology modeling based on the crystal structure of the acetylcholine binding protein identified key ligand binding residues of recombinant homooligomeric alpha1 and heterooligomeric alpha1beta GlyRs. This disclosed two highly conserved, oppositely charged residues located on adjacent subunit interfaces as being crucial for agonist binding. In addition, the beta subunit was found to determine the ligand binding properties of heterooligomeric GlyRs. Expression of an alpha1beta tandem construct and affinity purification of metabolically labeled GlyRs confirmed a subunit stoichiometry of 2alpha3beta. Because the beta subunit anchors GlyRs at synaptic sites, our results have important implications for the biosynthesis, clustering, and pharmacology of synaptic GlyRs.
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Affiliation(s)
- Joanna Grudzinska
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrasse 46, D-60528 Frankfurt am Main, Germany
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28
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Engelberg H. Pathogenic factors in vascular dementia and Alzheimer's disease. Multiple actions of heparin that probably are beneficial. Dement Geriatr Cogn Disord 2005; 18:278-98. [PMID: 15286460 DOI: 10.1159/000080034] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 02/04/2004] [Indexed: 12/22/2022] Open
Abstract
The following areas are discussed in this review: atherogenesis; cerebrovascular factors; hypoperfusion; beta-amyloid production; beta-amyloid fibril formation; beta-sheets; metal cations; reactive oxygen species/free radicals; chronic inflammatory factors; endogenous plasma heparin; lipoprotein lipase; polyamines; protein kinase C; casein kinases; phospholipase A2; serine proteases; myeloperoxidase; cyclooxygenase 2; cysteine proteases; caspases; proprotein convertases; aspartic proteases; cyclin proteinases; thrombin; tau hyperphosphorylation; advanced glycosylation end products; activator protein 1; calcium; apolipoprotein E epsilon4; histamine; blood-brain barrier; glutamate; transglutaminase; insulin-like growth factor 1.
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29
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Abstract
The glycine receptor chloride channel (GlyR) is a member of the nicotinic acetylcholine receptor family of ligand-gated ion channels. Functional receptors of this family comprise five subunits and are important targets for neuroactive drugs. The GlyR is best known for mediating inhibitory neurotransmission in the spinal cord and brain stem, although recent evidence suggests it may also have other physiological roles, including excitatory neurotransmission in embryonic neurons. To date, four alpha-subunits (alpha1 to alpha4) and one beta-subunit have been identified. The differential expression of subunits underlies a diversity in GlyR pharmacology. A developmental switch from alpha2 to alpha1beta is completed by around postnatal day 20 in the rat. The beta-subunit is responsible for anchoring GlyRs to the subsynaptic cytoskeleton via the cytoplasmic protein gephyrin. The last few years have seen a surge in interest in these receptors. Consequently, a wealth of information has recently emerged concerning GlyR molecular structure and function. Most of the information has been obtained from homomeric alpha1 GlyRs, with the roles of the other subunits receiving relatively little attention. Heritable mutations to human GlyR genes give rise to a rare neurological disorder, hyperekplexia (or startle disease). Similar syndromes also occur in other species. A rapidly growing list of compounds has been shown to exert potent modulatory effects on this receptor. Since GlyRs are involved in motor reflex circuits of the spinal cord and provide inhibitory synapses onto pain sensory neurons, these agents may provide lead compounds for the development of muscle relaxant and peripheral analgesic drugs.
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Affiliation(s)
- Joseph W Lynch
- School of Biomedical Sciences, Univ. of Queensland, Brisbane QLD 4072, Australia.
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30
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Han NLR, Clements JD, Lynch JW. Comparison of Taurine- and Glycine-induced Conformational Changes in the M2-M3 Domain of the Glycine Receptor. J Biol Chem 2004; 279:19559-65. [PMID: 14981077 DOI: 10.1074/jbc.m400548200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the ionotropic glutamate receptor, the global conformational changes induced by partial agonists are smaller than those induced by full agonists. However, in the pentameric ligand-gated ion channel receptor family, the structural basis of partial agonism is not understood. This study investigated whether full and partial agonists induce different conformation changes in the glycine receptor chloride channel (GlyR). A substituted cysteine accessibility analysis demonstrated previously that glycine binding induced an increase in surface accessibility of all residues from Arg(271) to Lys(276) in the M2-M3 domain of the homomeric alpha1 GlyR. Here we compare the surface accessibility changes induced by the full agonist, glycine, and the partial agonist, taurine. In GlyRs incorporating the A272C, S273C, L274C, or P275C mutation, the reaction rate of the cysteine-specific compound, methanethiosulfonate ethyltrimethylammonium, depended on how strongly the receptors were activated but was agonist-independent. Reaction rates could not be compared in the R271C and K276C mutant GlyRs because methanethiosulfonate ethyltrimethylammonium did not modify the extremely small currents induced by saturating taurine or equivalent low glycine concentrations. The results indicate that bound taurine and glycine molecules impose identical conformational changes to the M2-M3 domain. We therefore conclude that the higher efficacy of glycine is due to an increased ability to stabilize a common activated configuration.
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Affiliation(s)
- Nian-Lin R Han
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland 4072, Australia
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31
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Young TL, Cepko CL. A Role for Ligand-Gated Ion Channels in Rod Photoreceptor Development. Neuron 2004; 41:867-79. [PMID: 15046720 DOI: 10.1016/s0896-6273(04)00141-2] [Citation(s) in RCA: 118] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2003] [Revised: 12/04/2003] [Accepted: 01/29/2004] [Indexed: 11/30/2022]
Abstract
Neurotransmitter receptors are central to communication at synapses. Many components of the machinery for neurotransmission are present prior to synapse formation, suggesting a developmental role. Here, evidence is presented that signaling through glycine receptor alpha2 (GlyRalpha2) and GABA(A) receptors plays a role in photoreceptor development in the vertebrate retina. The signaling is likely mediated by taurine, which is present at high levels throughout the developing central nervous system (CNS). Taurine potentiates the production of rod photoreceptors, and this induction is inhibited by strychnine, an antagonist of glycine receptors, and bicuculline, an antagonist of GABA receptors. Gain-of-function experiments showed that signaling through GlyRalpha2 induced exit from mitosis and an increase in rod photoreceptors. Furthermore, targeted knockdown of GlyRalpha2 decreased the number of photoreceptors while increasing the number of other retinal cell types. These data support a previously undescribed role for these ligand-gated ion channels during the early stages of CNS development.
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Affiliation(s)
- Tracy L Young
- Department of Genetics, Howard Hughes Medical Institute, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
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32
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Chen Z, Dillon GH, Huang R. Molecular Determinants of Proton Modulation of Glycine Receptors. J Biol Chem 2004; 279:876-83. [PMID: 14563849 DOI: 10.1074/jbc.m307684200] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Extracellular pH regulates glycine receptors through an unknown mechanism. Here we demonstrate that acidic pH remarkably inhibited glycine-activated whole-cell currents in recombinant glycine alpha1 and alpha1beta receptors transiently expressed in human embryonic kidney 293 cells. The proton effect was voltage-independent and pharmacologically competed with glycine receptor agonist glycine and antagonist strychnine. Using site-directed mutagenesis, we have identified an N-terminal domain that is essential for proton-induced inhibition of glycine current. In alpha1 homomers, removal of the hydroxyl group by mutation of residue Thr-112 to Ala or Phe abolished inhibition of glycine currents by acidification. In contrast, mutation of Thr-112 to another hydroxylated residue (Tyr) produced receptors that retained partial proton sensitivity. In alpha1beta heteromers, a single mutation of the beta subunit T135A, which is homologous to alpha1 Thr-112, reduced proton sensitivity, whereas the double mutation alpha1(T112A)beta(T135A) almost completely eliminated the proton sensitivity. In addition, the mutation alpha1 H109A greatly reduced sensitivity to protons in homomeric alpha1 receptors. The results demonstrate that extracellular pH can regulate the function of glycine alpha1 and alpha1beta receptors. An extracellular domain consisting of Thr-112 and His-109 at the alpha1 subunit and Thr-135 at the beta subunit plays a critical role in determining proton modulation of glycine receptor function.
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Affiliation(s)
- Zhenglan Chen
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, Texas 76107, USA
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33
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Abstract
Retinal ganglion cells exhibit fast and slow inhibitory synaptic glycine currents that can be selectively inhibited by strychnine and 5,7-dichlorokynurenic acid (DCKA), respectively. In this study we examined whether strychnine and DCKA selectivity correlated with the subunit composition of the glycine receptor. Homomeric alpha1, alpha2 or alpha2* glycine subunits were in vitro expressed in human embryonic kidney cells (HEK 293). In cells expressing the alpha1 subunit, responses to 200 microm glycine were blocked by 1 microm strychnine but not by 500 microm DCKA. In cells expressing the alpha2 subunit, both 1 microm strychnine and 500 microm DCKA were effective antagonists of 200 microm glycine. In cells expressing alpha2* subunits, which are much less glycine-sensitive, 10 mm glycine was inhibited by 500 microm DCKA but not by 1 microm strychnine. A single amino acid mutation in the alpha1 subunit (R196G), converted this subunit from DCKA-insensitive to DCKA-sensitive. In conclusion, the comparative effectiveness of strychnine and DCKA can be used to distinguish between the alpha1, alpha2 and alpha2* receptor responses. Furthermore, a single amino acid near the glycine receptor's putative agonist binding site may account for differences in DCKA sensitivity amongst the alpha subunits.
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Affiliation(s)
- Yi Han
- University at Buffalo School of Medicine, Department of Physiology & Biophysics, 124 Sherman Hall, 3435 Main Street, Buffalo, NY 14214, USA
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34
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Kirchner A, Breustedt J, Rosche B, Heinemann UF, Schmieden V. Effects of taurine and glycine on epileptiform activity induced by removal of Mg2+ in combined rat entorhinal cortex-hippocampal slices. Epilepsia 2003; 44:1145-52. [PMID: 12919385 DOI: 10.1046/j.1528-1157.2003.01603.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
PURPOSE The imbalance between neuronal inhibition and excitation contributes to epileptogenesis. Inhibition in the central nervous system (CNS) is mediated by gamma-aminobutyric acid (GABA) and glycine. Recent studies indicate the expression of glycine receptor (GlyR) in hippocampus and neocortex. However, the function of GlyR in these regions is not clarified completely. The aim of this study was to investigate whether the GlyR agonists glycine and taurine promote an anticonvulsive effect. METHODS We induced epileptiform discharges by reducing extracellular Mg2+ concentration in combined rat entorhinal cortex-hippocampal slices (400 micro m). Epileptiform discharges were detected by using extracellular recording techniques. RESULTS Seizure-like events were suppressed by taurine, exhibiting a half-maximal inhibitory effect (IC50) of 0.9 mM. Suppression of late recurrent discharges in the medial entorhinal cortex and recurrent short discharges in the hippocampus was obtained at an IC50 value of 1.6 and 2.1 mM, respectively. Strychnine at concentrations <1 micro M abolished these effects. Likewise glycine, after an initial proconvulsant effect, suppressed epileptiform discharges. CONCLUSIONS These findings show that GlyR agonists, in particular taurine, could serve as potential anticonvulsants and suggest an important role of GlyR in cortical function and dysfunction.
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Affiliation(s)
- Anne Kirchner
- Johannes Müller Institut für Physiologie, Universitätsklinikum Charité, Humboldt Universität, Berlin, Germany.
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35
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Shan Q, Nevin ST, Haddrill JL, Lynch JW. Asymmetric contribution of alpha and beta subunits to the activation of alphabeta heteromeric glycine receptors. J Neurochem 2003; 86:498-507. [PMID: 12871591 DOI: 10.1046/j.1471-4159.2003.01872.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
This study investigated the role of beta subunits in the activation of alphabeta heteromeric glycine receptor (GlyR) chloride channels recombinantly expressed in HEK293 cells. The approach involved incorporating mutations into corresponding positions in alpha and beta subunits and comparing their effects on receptor function. Although cysteine-substitution mutations to residues in the N-terminal half of the alpha subunit M2-M3 loop dramatically impaired the gating efficacy, the same mutations exerted little effect when incorporated into corresponding positions of the beta subunit. Furthermore, although the alpha subunit M2-M3 loop cysteines were modified by a cysteine-specific reagent, the corresponding beta subunit cysteines showed no evidence of reactivity. These observations suggest structural or functional differences between alpha and beta subunit M2-M3 loops. In addition, a threonine-->leucine mutation at the 9' position in the beta subunit M2 pore-lining domain dramatically increased the glycine sensitivity. By analogy with the effects of the same mutation in other ligand-gated ion channels, it was concluded that the mutation affected the GlyR activation mechanism. This supports the idea that the GlyR beta subunit is involved in receptor gating. In conclusion, this study demonstrates that beta subunits contribute to the activation of the GlyR, but that their involvement in this process is significantly different to that of the alpha subunit.
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Affiliation(s)
- Qiang Shan
- Department of Physiology and Pharmacology, School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia
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36
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Romanelli MN, Gualtieri F. Cholinergic nicotinic receptors: competitive ligands, allosteric modulators, and their potential applications. Med Res Rev 2003; 23:393-426. [PMID: 12710018 DOI: 10.1002/med.10037] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Discovery of the important role played by nicotinic acetylcholine receptors (nAChRs) in several CNS disorders has called attention to these membrane proteins and to ligands able to modulate their functions. The existence of different subtypes at multiple levels has complicated the understanding of this receptor's physiological role, but at the same time has increased the efforts to discover selective compounds in order to improve the pharmacological characterization of this kind of receptor and to make the possible therapeutical use of its modulators safer. This review focuses on the structure of new ligands for nAChRs, agonists, antagonists and allosteric modulators, and on their possible applications.
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Affiliation(s)
- M Novella Romanelli
- Dipartimento di Scienze Farmaceutiche, Università di Firenze, via Gino Capponi 9, 50121 Firenze, Italy.
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37
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Lewis TM, Schofield PR, McClellan AML. Kinetic determinants of agonist action at the recombinant human glycine receptor. J Physiol 2003; 549:361-74. [PMID: 12679369 PMCID: PMC2342959 DOI: 10.1113/jphysiol.2002.037796] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The amino acids glycine, beta-alanine and taurine are all endogenous agonists of the glycine receptor. In this study, a combination of rapid agonist application onto macropatches and steady-state single-channel recordings was used to compare the actions of glycine, beta-alanine and taurine upon homomeric alpha1 human glycine receptors transiently expressed in human embryonic kidney (HEK 293) cells. The 10-90 % rise times determined from rapid application of 100 microM of each agonist were indistinguishable, indicating each agonist has a similar association rate. At saturating concentrations (30 mM) the rise time for glycine (0.26 ms) was 1.8-fold faster than that for beta-alanine (0.47 ms) and 3.9-fold faster than that for taurine (1.01 ms), indicating clear differences in the maximum opening rate between agonists. The relaxation following rapid removal of agonist was fitted with a single exponential for beta-alanine (3.0 ms) and taurine (2.2 ms), and two exponential components for glycine with a weighted mean time constant of 27.1 ms. This was consistent with differences in dissociation rates estimated from analysis of bursts, with taurine > beta-alanine > glycine. Exponential fits to the open period distributions gave time constants that did not differ between agonists and the geometric distribution for the number of openings per burst indicated that all three agonists had a significant component of single-opening bursts. Based upon these data, we propose a kinetic scheme with three independent open states, where the opening rates are dependent upon the activating agonist, while the closing rates are an intrinsic characteristic of the receptor.
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Affiliation(s)
- Trevor M Lewis
- Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, Sydney, NSW 2010, Australia.
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38
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Li P, Slimko EM, Lester HA. Selective elimination of glutamate activation and introduction of fluorescent proteins into a Caenorhabditis elegans chloride channel. FEBS Lett 2002; 528:77-82. [PMID: 12297283 DOI: 10.1016/s0014-5793(02)03245-3] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Glutamate-gated chloride (GluCl) channels from invertebrates can be activated by ivermectin (IVM) to produce electrical silencing in mammalian neurons. To improve this GluCl/IVM strategy, we sought to mutate the Caenorhabditis elegans GluCl channels so that they become insensitive to glutamate but retain their sensitivity to IVM. Based on structure-function studies of nicotinic acetylcholine receptor superfamily members, we tested in oocytes 19 point mutants at 16 residues in the beta-subunit likely to be involved in the response to glutamate. Y182F reduces the glutamate response by greater than six-fold, with little change to IVM responses, when coexpressed with wild-type (WT) GluCl alpha. For GluCl alphabeta(Y182F), the EC(50) and Hill coefficient for glutamate are similar to those of WT, indicating that the mutant decreases the efficacy of glutamate, but not the potency. Also, fluorescent proteins (enhanced green fluorescent protein, enhanced yellow fluorescent protein, enhanced cyan fluorescent protein; XFP) were inserted into the M3-M4 loop of the GluCl alpha, beta and beta(Y182F). We found no significant functional difference between these XFP-tagged receptors and WT receptors. The modified GluCl channel, without glutamate sensitivity but with a fluorescent tag, may be more useful in GluCl silencing strategies.
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Affiliation(s)
- Ping Li
- Division of Biology, M/C 156-29, California Institute of Technology, Pasadena 91125, USA
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39
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Beckstead MJ, Phelan R, Trudell JR, Bianchini MJ, Mihic SJ. Anesthetic and ethanol effects on spontaneously opening glycine receptor channels. J Neurochem 2002; 82:1343-51. [PMID: 12354281 DOI: 10.1046/j.1471-4159.2002.01086.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Strychnine-sensitive glycine receptors mediate inhibitory neurotransmission occurring in the brain stem and spinal cord. Alcohols, volatile anesthetics and inhaled drugs of abuse are positive allosteric modulators of glycine receptor function, normally enhancing function only in the presence of glycine. A complication in studying allosteric actions on ligand-gated ion channels is in the dissection of their effects on neurotransmitter binding from their effects on channel opening. Mutation of an aspartate residue at position 97 to arginine in the glycine receptor alpha1 subunit simulated the effects of glycine binding, producing receptors that exhibited tonic channel opening in the absence of neurotransmitter; i.e. these receptors demonstrated a dissociation of channel opening from neurotransmitter binding. In these receptors, ethanol, enflurane, chloroform, halothane, 1,1,1-trichloroethane and toluene elicited inward currents in the absence of glycine. We previously identified mutations on ligand-gated ion channels that eliminate ethanol, anesthetic and inhalant actions (such as S267I on alpha1 glycine receptors). The double mutant (D97R and S267I) receptors were both constitutively active and resistant to the enhancing effects of ethanol and enflurane. These data demonstrate that ethanol and volatile anesthetics can affect glycine receptor channel opening independently of their effects on enhancing neurotransmitter binding.
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Affiliation(s)
- Michael J Beckstead
- Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, North Carolina, USA
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40
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Maksay G, Bíró T, Laube B. Hyperekplexia mutation of glycine receptors: decreased gating efficacy with altered binding thermodynamics. Biochem Pharmacol 2002; 64:285-8. [PMID: 12123749 DOI: 10.1016/s0006-2952(02)01111-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
[(3)H]Strychnine binding was studied to recombinant human alpha(1) and the hyperekplexia mutant alpha(1)R271L glycine receptors (GlyRs) transiently expressed in human embryonic kidney (HEK)-293 cell cultures at 0, 18 and 37 degrees. The alpha(1)R271L mutation did not affect the linear van't Hoff plots of the exothermic binding of the antagonist [3H]strychnine while it turned taurine into an antagonist with exothermic binding. The inhibition constants of the agonist glycine showed opposite temperature dependence on alpha(1) GlyRs, corresponding to endothermic binding driven by large entropic increases. The temperature dependence of displacement by the partial agonists taurine on alpha(1) GlyRs and glycine on alpha(1)R271L GlyRs was biphasic reflecting negative heat capacity changes, dehydration changes and/or a complex binding mechanism. The thermodynamic discrimination of efficacy is valid for native rat spinal and recombinant human GlyRs. The alpha(1)R271L mutation impairs the transduction mechanism and distorts gating of GlyRs. Thereby it reduces the potency and efficacy of agonists and affects their thermodynamic parameters of binding. The hyperekplexia mutation offers a model system to demonstrate the correlation among pathophysiology, gating efficacy and binding thermodynamics of GlyRs.
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Affiliation(s)
- Gábor Maksay
- Department of Molecular Pharmacology, Chemical Research Centre, Hungarian Academy of Sciences, P.O. Box 17, H-1525 Budapest, Hungary.
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41
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Gisselmann G, Galler A, Friedrich F, Hatt H, Bormann J. Cloning and functional characterization of two glycine receptor alpha-subunits from the perch retina. Eur J Neurosci 2002; 16:69-80. [PMID: 12153532 DOI: 10.1046/j.1460-9568.2002.02070.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Glycine receptors are ligand-gated ion channel proteins mediating synaptic inhibition in the spinal cord, retina and brain of vertebrates. We have cloned and functionally characterized two glycine receptor alpha-subunits from the perch (Roccus americana) retina. Based on sequence homology with the mammalian counterparts, we termed these subunits alpha 1 and alpha 3. RT-PCR revealed the presence of both subunits in retina and brain, whereas alpha1 was predominant in spinal cord. A short splice variant of alpha1 was detected in the brain but not in the retina. Functional expression of the perch subunits in HEK-293 cells yielded robust glycine-gated currents sensitive to strychnine. The perch receptors displayed a high efficacy for taurine and GABA and thus differ from the mammalian counterparts. Because the retina is a rich source for taurine, this finding could be of physiological importance. The structural features of the ligand binding domain strongly support the notion of increased glycine/GABA discrimination in higher vertebrates.
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Affiliation(s)
- G Gisselmann
- Ruhr-University Bochum, Department of Cell Physiology, ND4, D-44780 Bochum, Germany
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42
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Gálvez-Ruano E, Iriepa I, Morreale A, Boyd DB. Superimposition-based protocol as a tool for determining bioactive conformations. I. Application to ligands of the glycinergic receptor (GlyR). J Mol Graph Model 2002; 19:331-7, 391-5. [PMID: 11449572 DOI: 10.1016/s1093-3263(00)00081-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The natural templates (NT) approach, which is a superimposition-based protocol that has been successfully employed in several studies, is here applied to ligands of the glycine ligand-gated ion channel receptor. Bioactive conformations for glycine and its analogs were obtained using strychnine (a natural and specific competitive antagonist) as template. Experimental evidence was used to guide the superimposition protocol. Three essential regions have been defined in strychnine's structure that serve as a pharmacophore for agonist and antagonist activities. Reasonable alignments of known ligands were found in the majority of the cases. Molecular mechanics (i.e., conformational searches for the relatively flexible ligands) and molecular dynamics (for relatively rigid ligands such as strychnine and 5,6,7,8-tetrahydro-4H-isoxazolo[3,4-d]azepin-3-ol) were used to assess the energetic accessibility of the proposed bioactive conformations.
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Affiliation(s)
- E Gálvez-Ruano
- Departamento de Química Orgánica, Universidad de Alcalá de Henares, Ctra. Madrid-Barcelona Km. 33,600, Alcalá de Henares, 28871 Madrid, Spain.
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43
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Han NL, Haddrill JL, Lynch JW. Characterization of a glycine receptor domain that controls the binding and gating mechanisms of the beta-amino acid agonist, taurine. J Neurochem 2001; 79:636-47. [PMID: 11701767 DOI: 10.1046/j.1471-4159.2001.00601.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The beta-amino acid, taurine, is a full agonist of the human glycine receptor alpha1 subunit when recombinantly expressed in a mammalian (HEK293) cell line, but a partial agonist of the same receptor when expressed in Xenopus oocytes. Several residues in the Ala101-Thr112 domain have previously been identified as determinants of beta-amino acid binding and gating mechanisms in Xenopus oocyte-expressed receptors. The present study used the substituted cysteine accessibility method to investigate the role of this domain in controlling taurine-specific binding and gating mechanisms of glycine receptors recombinantly expressed in mammalian cells. Asn102 and Glu103 are identified as taurine and glycine binding sites, whereas Ala101 is eliminated as a possible binding site. The N102C mutation also abolished the antagonistic actions of taurine, indicating that this site does not discriminate between the putative agonist- and antagonist-bound conformations of beta-amino acids. The effects of mutations from Lys104-Thr112 indicate that the mechanism by which this domain controls beta-amino acid-specific binding and gating processes differs substantially depending on whether the receptor is expressed in mammalian cells or Xenopus oocytes. Thr112 is the only domain element in mammalian cell-expressed GlyRs which was demonstrated to discriminate between glycine and taurine.
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Affiliation(s)
- N L Han
- Department of Physiology and Pharmacology, School of Biomedical Sciences, University of Queensland, Brisbane, Australia
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44
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Leite JF, Cascio M. Structure of ligand-gated ion channels: critical assessment of biochemical data supports novel topology. Mol Cell Neurosci 2001; 17:777-92. [PMID: 11358478 DOI: 10.1006/mcne.2001.0984] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Rapid signaling across the synaptic junction is partially mediated by the ligand-gated ion channel superfamily (LGICS), which includes inhibitory glycine and GABA receptors and excitatory acetylcholine and serotonin receptors. The glycine receptor (GlyR) can assemble as homopentamers of alpha subunits, and baculovirus expression systems are capable of overexpressing large quantities of active receptors. Limited proteolysis coupled to mass spectrometry on reconstituted alpha1 GlyR homopentamers identified proteolytic cleavages within proposed transmembrane domains postulated to fold as bilayer-spanning alpha helices in the "classical" model and identified unexpected membrane-associated regions in the N-terminal domain (J. F. Leite et al., 2000, J. Biol. Chem. 275, 13683-13689). In this review, optimized sequence alignments were used to integrate these proteolysis data with biochemical information determined in studies of all the LGICS members in order to construct a novel topological model.
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Affiliation(s)
- J F Leite
- Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
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45
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Imboden M, De Saint Jan D, Leulier F, Korn H, Goblet C, Bregestovski P. Isolation and characterization of an alpha 2-type zebrafish glycine receptor subunit. Neuroscience 2001; 103:799-810. [PMID: 11274795 DOI: 10.1016/s0306-4522(00)00575-3] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The complementary DNA for a novel alpha subunit of the glycine receptor, alphaZ2, was isolated from a zebrafish adult brain library. The molecular characteristics, phylogenetic relationships and messenger RNA length of this alphaZ2 subunit show it to be an alpha2-type glycine receptor subunit isoform. The leader peptide however, diverges from those of known glycine receptor alpha isoforms. Recombinantly expressed in Xenopus oocytes, alphaZ2 formed functional glycine receptor channels. These homomeric channels were activated by glycine and taurine, with apparent affinities similar to those reported for zebrafish alphaZ1 glycine receptor, and were also effectively antagonized by nanomolar concentrations of strychnine. However, during prolonged applications of agonists, ionic currents of alphaZ2 receptor channels declined to a much lower steady-state level than those of alphaZ1, indicating different desensitization properties. Analysis of messenger RNA revealed that alphaZ2 is specifically expressed in adult brain tissue and present in both adult and embryonic zebrafish. This report contributes to the characterization of the diversity of glycine receptor isoforms in vertebrates.
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Affiliation(s)
- M Imboden
- Laboratoire de Biologie Cellulaire et Moléculaire du Neurone, INSERM U261, Institut Pasteur, 25, Rue du Dr Roux, F-75724, Paris Cedex 15, France
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46
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Cascio M, Shenkel S, Grodzicki RL, Sigworth FJ, Fox RO. Functional reconstitution and characterization of recombinant human alpha 1-glycine receptors. J Biol Chem 2001; 276:20981-8. [PMID: 11145968 DOI: 10.1074/jbc.m010968200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
By utilizing a baculoviral expression system described previously (Cascio, M., Schoppa, N. E., Grodzicki, R. L., Sigworth, F. J., and Fox, R. O. (1993) J. Biol. Chem. 268, 22135-22142), functional recombinant homomeric human alpha(1)-glycine receptors (GlyR) were overexpressed in insect cell culture, solubilized, purified, and reconstituted into lipid vesicles via gel filtration. Reconstituted GlyR channels were observed to retain native-like activity in single channel recordings of planar bilayers and in flux assays of small unilamellar vesicles, providing evidence that the recombinant homomeric receptor may be functionally reconstituted. This reconstitution is significant in that it indicates that the overexpressed homomeric receptor is an appropriate substrate for subsequent biophysical characterization aimed at the general elucidation of structure-function. Circular dichroism spectroscopy of reconstituted GlyR indicated a low alpha-helical content and a significant fraction of polyproline structure. The small fraction of observed alpha-helix is insufficient to accommodate the four helical transmembrane domains proposed in models for this receptor. By inference, other members of the homologous ligand-gated channel superfamily, which include the ionotropic gamma-aminobutyric acid, acetylcholine, and serotonin receptors, may also be erroneously modeled, and alternate models should be considered.
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Affiliation(s)
- M Cascio
- Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA
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47
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Shan Q, Haddrill JL, Lynch JW. Ivermectin, an unconventional agonist of the glycine receptor chloride channel. J Biol Chem 2001; 276:12556-64. [PMID: 11278873 DOI: 10.1074/jbc.m011264200] [Citation(s) in RCA: 162] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The effects of the antihelmintic, ivermectin, were investigated in recombinantly expressed human alpha(1) homomeric and alpha(1)beta heteromeric glycine receptors (GlyRs). At low (0.03 microm) concentrations ivermectin potentiated the response to sub-saturating glycine concentrations, and at higher (> or =0.03 microm) concentrations it irreversibly activated both alpha(1) homomeric and alpha(1)beta heteromeric GlyRs. Relative to glycine-gated currents, ivermectin-gated currents exhibited a dramatically reduced sensitivity to inhibition by strychnine, picrotoxin, and zinc. The insensitivity to strychnine could not be explained by ivermectin preventing the access of strychnine to its binding site. Furthermore, the elimination of a known glycine- and strychnine-binding site by site-directed mutagenesis had little effect on ivermectin sensitivity, demonstrating that the ivermectin- and glycine-binding sites were not identical. Ivermectin strongly and irreversibly activated a fast-desensitizing mutant GlyR after it had been completely desensitized by a saturating concentration of glycine. Finally, a mutation known to impair dramatically the glycine signal transduction mechanism had little effect on the apparent affinity or efficacy of ivermectin. Together, these findings indicate that ivermectin activates the GlyR by a novel mechanism.
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Affiliation(s)
- Q Shan
- Department of Physiology and Pharmacology, University of Queensland, Brisbane, Queensland 4072, Australia
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Lynch JW, Han NL, Haddrill J, Pierce KD, Schofield PR. The surface accessibility of the glycine receptor M2-M3 loop is increased in the channel open state. J Neurosci 2001; 21:2589-99. [PMID: 11306612 PMCID: PMC6762528] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/19/2023] Open
Abstract
Mutations in the extracellular M2-M3 loop of the glycine receptor (GlyR) alpha1 subunit have been shown previously to affect channel gating. In this study, the substituted cysteine accessibility method was used to investigate whether a structural rearrangement of the M2-M3 loop accompanies GlyR activation. All residues from R271C to V277C were covalently modified by both positively charged methanethiosulfonate ethyltrimethylammonium (MTSET) and negatively charged methanethiosulfonate ethylsulfonate (MTSES), implying that these residues form an irregular surface loop. The MTSET modification rate of all residues from R271C to K276C was faster in the glycine-bound state than in the unliganded state. MTSES modification of A272C, L274C, and V277C was also faster in the glycine-bound state. These results demonstrate that the surface accessibility of the M2-M3 loop is increased as the channel transitions from the closed to the open state, implying that either the loop itself or an overlying domain moves during channel activation.
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Affiliation(s)
- J W Lynch
- Department of Physiology and Pharmacology, University of Queensland, Brisbane, QLD, 4072, Australia.
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Abbott CA, Yu DM, Woollatt E, Sutherland GR, McCaughan GW, Gorrell MD. Cloning, expression and chromosomal localization of a novel human dipeptidyl peptidase (DPP) IV homolog, DPP8. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:6140-50. [PMID: 11012666 DOI: 10.1046/j.1432-1327.2000.01617.x] [Citation(s) in RCA: 214] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Dipeptidyl peptidase (DPP) IV has roles in T-cell costimulation, chemokine biology, type-II diabetes and tumor biology. Fibroblast activation protein (FAP) has been implicated in tumor growth and cirrhosis. Here we describe DPP8, a novel human postproline dipeptidyl aminopeptidase that is homologous to DPPIV and FAP. Northern-blot hybridization showed that the tissue expression of DPP8 mRNA is ubiquitous, similar to that of DPPIV. The DPP8 gene was localized to chromosome 15q22, distinct from a closely related gene at 19p13.3 which we named DPP9. The full-length DPP8 cDNA codes for an 882-amino-acid protein that has about 27% identity and 51% similarity to DPPIV and FAP, but no transmembrane domain and no N-linked or O-linked glycosylation. Western blots and confocal microscopy of transfected COS-7 cells showed DPP8 to be a 100-kDa monomeric protein expressed in the cytoplasm. Purified recombinant DPP8 hydrolyzed the DPPIV substrates Ala-Pro, Arg-Pro and Gly-Pro. Thus recombinant DPP8 shares a postproline dipeptidyl aminopeptidase activity with DPPIV and FAP. DPP8 enzyme activity had a neutral pH optimum consistent with it being nonlysosomal. The similarities between DPP8 and DPPIV in tissue expression pattern and substrates suggests a potential role for DPP8 in T-cell activation and immune function.
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Affiliation(s)
- C A Abbott
- A. W. Morrow Gastroenterology and Liver Centre, Royal Prince Alfred Hospital, Centenary Institute of Cancer Medicine and Cell Biologyand The University of Sydney, NSW, Australia.
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50
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Arias HR. Localization of agonist and competitive antagonist binding sites on nicotinic acetylcholine receptors. Neurochem Int 2000; 36:595-645. [PMID: 10771117 DOI: 10.1016/s0197-0186(99)00154-0] [Citation(s) in RCA: 156] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Identification of all residues involved in the recognition and binding of cholinergic ligands (e.g. agonists, competitive antagonists, and noncompetitive agonists) is a primary objective to understand which structural components are related to the physiological function of the nicotinic acetylcholine receptor (AChR). The picture for the localization of the agonist/competitive antagonist binding sites is now clearer in the light of newer and better experimental evidence. These sites are located mainly on both alpha subunits in a pocket approximately 30-35 A above the surface membrane. Since both alpha subunits are identical, the observed high and low affinity for different ligands on the receptor is conditioned by the interaction of the alpha subunit with other non-alpha subunits. This molecular interaction takes place at the interface formed by the different subunits. For example, the high-affinity acetylcholine (ACh) binding site of the muscle-type AChR is located on the alphadelta subunit interface, whereas the low-affinity ACh binding site is located on the alphagamma subunit interface. Regarding homomeric AChRs (e.g. alpha7, alpha8, and alpha9), up to five binding sites may be located on the alphaalpha subunit interfaces. From the point of view of subunit arrangement, the gamma subunit is in between both alpha subunits and the delta subunit follows the alpha aligned in a clockwise manner from the gamma. Although some competitive antagonists such as lophotoxin and alpha-bungarotoxin bind to the same high- and low-affinity sites as ACh, other cholinergic drugs may bind with opposite specificity. For instance, the location of the high- and the low-affinity binding site for curare-related drugs as well as for agonists such as the alkaloid nicotine and the potent analgesic epibatidine (only when the AChR is in the desensitized state) is determined by the alphagamma and the alphadelta subunit interface, respectively. The case of alpha-conotoxins (alpha-CoTxs) is unique since each alpha-CoTx from different species is recognized by a specific AChR type. In addition, the specificity of alpha-CoTxs for each subunit interface is species-dependent. In general terms we may state that both alpha subunits carry the principal component for the agonist/competitive antagonist binding sites, whereas the non-alpha subunits bear the complementary component. Concerning homomeric AChRs, both the principal and the complementary component exist on the alpha subunit. The principal component on the muscle-type AChR involves three loops-forming binding domains (loops A-C). Loop A (from mouse sequence) is mainly formed by residue Y(93), loop B is molded by amino acids W(149), Y(152), and probably G(153), while loop C is shaped by residues Y(190), C(192), C(193), and Y(198). The complementary component corresponding to each non-alpha subunit probably contributes with at least four loops. More specifically, the loops at the gamma subunit are: loop D which is formed by residue K(34), loop E that is designed by W(55) and E(57), loop F which is built by a stretch of amino acids comprising L(109), S(111), C(115), I(116), and Y(117), and finally loop G that is shaped by F(172) and by the negatively-charged amino acids D(174) and E(183). The complementary component on the delta subunit, which corresponds to the high-affinity ACh binding site, is formed by homologous loops. Regarding alpha-neurotoxins, several snake and alpha-CoTxs bear specific residues that are energetically coupled with their corresponding pairs on the AChR binding site. The principal component for snake alpha-neurotoxins is located on the residue sequence alpha1W(184)-D(200), which includes loop C. In addition, amino acid sequence 55-74 from the alpha1 subunit (which includes loop E), and residues gammaL(119) (close to loop F) and gammaE(176) (close to loop G) at the low-affinity binding site, or deltaL(121) (close to the homologous region of loop G) at the high-affinity binding site, are i
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Affiliation(s)
- H R Arias
- Instituto de Matemática de Bahía Blanca, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahía Blanca, Argentina.
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