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Yang Y, Arai T, Sasaki D, Kuramochi M, Inagaki H, Ohashi S, Sekiguchi H, Mio K, Kubo T, Sasaki YC. Real-time tilting and twisting motions of ligand-bound states of α7 nicotinic acetylcholine receptor. EUROPEAN BIOPHYSICS JOURNAL : EBJ 2024; 53:15-25. [PMID: 38233601 PMCID: PMC10853312 DOI: 10.1007/s00249-023-01693-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2023] [Revised: 11/29/2023] [Accepted: 12/01/2023] [Indexed: 01/19/2024]
Abstract
The α7 nicotinic acetylcholine receptor is a member of the nicotinic acetylcholine receptor family and is composed of five α7 subunits arranged symmetrically around a central pore. It is localized in the central nervous system and immune cells and could be a target for treating Alzheimer's disease and schizophrenia. Acetylcholine is a ligand that opens the channel, although prolonged application rapidly decreases the response. Ivermectin was reported as one of the positive allosteric modulators, since the binding of Ivermectin to the channel enhances acetylcholine-evoked α7 currents. One research has suggested that tilting motions of the nicotinic acetylcholine receptor are responsible for channel opening and activation. To verify this hypothesis applies to α7 nicotinic acetylcholine receptor, we utilized a diffracted X-ray tracking method to monitor the stable twisting and tilting motion of nAChR α7 without a ligand, with acetylcholine, with Ivermectin, and with both of them. The results show that the α7 nicotinic acetylcholine receptor twists counterclockwise with the channel transiently opening, transitioning to a desensitized state in the presence of acetylcholine and clockwise without the channel opening in the presence of Ivermectin. We propose that the conformational transition of ACh-bound nAChR α7 may be due to the collective twisting of the five α7 subunits, resulting in the compression and movement, either downward or upward, of one or more subunits, thus manifesting tilting motions. These tilting motions possibly represent the transition from the resting state to channel opening and potentially to the desensitized state.
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Affiliation(s)
- Yue Yang
- Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, 277-8561, Japan
| | - Tatsuya Arai
- Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, 277-8561, Japan
- AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory (OPERANDO-OIL), National Institute of Advanced Industrial Science and Technology (AIST), Kashiwa, 277-8565, Japan
| | - Daisuke Sasaki
- Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, 277-8561, Japan
| | - Masahiro Kuramochi
- Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, 277-8561, Japan
- Graduate School of Science and Engineering, Ibaraki University, Hitachi, 316-8511, Japan
| | - Hidetoshi Inagaki
- Biomedical Research Insitute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, 305-8566, Japan
| | - Sumiko Ohashi
- Biomedical Research Insitute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, 305-8566, Japan
| | - Hiroshi Sekiguchi
- Center for Synchrotron Radiation Research, Japan Synchrotron Radiation Research Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5198, Japan
| | - Kazuhiro Mio
- AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory (OPERANDO-OIL), National Institute of Advanced Industrial Science and Technology (AIST), Kashiwa, 277-8565, Japan
| | - Tai Kubo
- Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, 277-8561, Japan
- AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory (OPERANDO-OIL), National Institute of Advanced Industrial Science and Technology (AIST), Kashiwa, 277-8565, Japan
| | - Yuji C Sasaki
- Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, 277-8561, Japan.
- AIST-UTokyo Advanced Operando-Measurement Technology Open Innovation Laboratory (OPERANDO-OIL), National Institute of Advanced Industrial Science and Technology (AIST), Kashiwa, 277-8565, Japan.
- Center for Synchrotron Radiation Research, Japan Synchrotron Radiation Research Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5198, Japan.
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Goswami U, Rahman MM, Teng J, Hibbs RE. Structural interplay of anesthetics and paralytics on muscle nicotinic receptors. Nat Commun 2023; 14:3169. [PMID: 37264005 DOI: 10.1038/s41467-023-38827-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2023] [Accepted: 05/17/2023] [Indexed: 06/03/2023] Open
Abstract
General anesthetics and neuromuscular blockers are used together during surgery to stabilize patients in an unconscious state. Anesthetics act mainly by potentiating inhibitory ion channels and inhibiting excitatory ion channels, with the net effect of dampening nervous system excitability. Neuromuscular blockers act by antagonizing nicotinic acetylcholine receptors at the motor endplate; these excitatory ligand-gated ion channels are also inhibited by general anesthetics. The mechanisms by which anesthetics and neuromuscular blockers inhibit nicotinic receptors are poorly understood but underlie safe and effective surgeries. Here we took a direct structural approach to define how a commonly used anesthetic and two neuromuscular blockers act on a muscle-type nicotinic receptor. We discover that the intravenous anesthetic etomidate binds at an intrasubunit site in the transmembrane domain and stabilizes a non-conducting, desensitized-like state of the channel. The depolarizing neuromuscular blocker succinylcholine also stabilizes a desensitized channel but does so through binding to the classical neurotransmitter site. Rocuronium binds in this same neurotransmitter site but locks the receptor in a resting, non-conducting state. Together, this study reveals a structural mechanism for how general anesthetics work on excitatory nicotinic receptors and further rationalizes clinical observations in how general anesthetics and neuromuscular blockers interact.
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Affiliation(s)
- Umang Goswami
- Department of Neuroscience and O'Donnell Brain Institute, University of Texas Southwestern Medical Center, Dallas, TX, 75390, USA
| | - Md Mahfuzur Rahman
- Department of Neuroscience and O'Donnell Brain Institute, University of Texas Southwestern Medical Center, Dallas, TX, 75390, USA
- Thermo Fisher Scientific, Rockford, IL, 61101, USA
| | - Jinfeng Teng
- Department of Neurobiology, University of California, San Diego, La Jolla, CA, 92093, USA
| | - Ryan E Hibbs
- Department of Neuroscience and O'Donnell Brain Institute, University of Texas Southwestern Medical Center, Dallas, TX, 75390, USA.
- Department of Neurobiology, University of California, San Diego, La Jolla, CA, 92093, USA.
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Rodríguez Cruz PM, Ravenscroft G, Natera D, Carr A, Manzur A, Liu WW, Vella NR, Jericó I, Gonzalez-Quereda L, Gallano P, Montalto SA, Davis MR, Lamont PJ, Laing NG, Bourque P, Nascimento A, Muntoni F, Polavarapu K, Lochmüller H, Palace J, Beeson D. A novel phenotype of AChR-deficiency syndrome with predominant facial and distal weakness resulting from the inclusion of an evolutionary alternatively-spliced exon in CHRNA1. Neuromuscul Disord 2023; 33:161-168. [PMID: 36634413 DOI: 10.1016/j.nmd.2022.12.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2022] [Revised: 12/13/2022] [Accepted: 12/19/2022] [Indexed: 12/24/2022]
Abstract
Primary acetylcholine receptor deficiency is the most common subtype of congenital myasthenic syndrome, resulting in reduced amount of acetylcholine receptors expressed at the muscle endplate and impaired neuromuscular transmission. AChR deficiency is caused mainly by pathogenic variants in the ε-subunit of the acetylcholine receptor encoded by CHRNE, although pathogenic variants in other subunits are also seen. We report the clinical and molecular features of 13 patients from nine unrelated kinships with acetylcholine receptor deficiency harbouring the CHRNA1 variant NM_001039523.3:c.257G>A (p.Arg86His) in homozygosity or compound heterozygosity. This variant results in the inclusion of an alternatively-spliced evolutionary exon (P3A) that causes expression of a non-functional acetylcholine receptor α-subunit. We compare the clinical findings of this group to the other cases of acetylcholine receptor deficiency within our cohort. We report differences in phenotype, highlighting a predominant pattern of facial and distal weakness in adulthood, predominantly in the upper limbs, which is unusual for acetylcholine receptor deficiency syndromes, and more in keeping with slow-channel syndrome or distal myopathy. Finally, we stress the importance of including alternative exons in variant analysis to increase the probability of achieving a molecular diagnosis.
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Affiliation(s)
- Pedro M Rodríguez Cruz
- CNAG-CRG, Centro Nacional de Análisis Genómico - Centre for Genomic Regulation, Barcelona Institute of Science and Technology, Barcelona, Spain.
| | - Gianina Ravenscroft
- Harry Perkins Institute of Medical Research, Nedlands, WA, Australia; Centre of Medical Research, University of Western Australia, Nedlands, WA, Australia
| | - Daniel Natera
- Neuromuscular Unit, Hospital Sant Joan de Déu, Barcelona, Spain
| | - Aisling Carr
- Centre for Neuromuscular Diseases, UCL Queen Square Institute of Neurology, National Hospital for Neurology and Neurosurgery, Queen Square, London, UK
| | - Adnan Manzur
- Dubowitz Neuromuscular Centre, NIHR Biomedical Research Centre, UCL Great Ormond Street Institute of Child Health; Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK
| | - Wei Wei Liu
- Neurosciences Group, Weatherall Institute of Molecular Medicine, University of Oxford, The John Radcliffe Hospital, Oxford, UK
| | - Norbert R Vella
- Department of Neuroscience, Mater Dei Hospital, Msida, Malta
| | - Ivonne Jericó
- Department of Neurology, Hospital Universitario de Navarra, IdisNa (Instituto Investigación Sanitaria Navarra), Pamplona, Spain
| | - Lidia Gonzalez-Quereda
- Center for the Biomedical Research on Rare Diseases (CIBERER), ISCIII, Madrid, Spain; Department of Genetics, Hospital de Sant Pau, IIB Sant Pau, Barcelona, Spain
| | - Pia Gallano
- Center for the Biomedical Research on Rare Diseases (CIBERER), ISCIII, Madrid, Spain; Department of Genetics, Hospital de Sant Pau, IIB Sant Pau, Barcelona, Spain
| | | | - Mark R Davis
- Neurogenetic Unit, Department of Diagnostic Genomics, PathWest Laboratory Medicine, Western Australian Department of Health, Nedlands, WA, Australia
| | - Phillipa J Lamont
- Department of Neurology, Royal Perth Hospital, Nedlands, WA, Australia
| | - Nigel G Laing
- Harry Perkins Institute of Medical Research, Nedlands, WA, Australia; Centre of Medical Research, University of Western Australia, Nedlands, WA, Australia; Neurogenetic Unit, Department of Diagnostic Genomics, PathWest Laboratory Medicine, Western Australian Department of Health, Nedlands, WA, Australia
| | - Pierre Bourque
- Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Canada
| | | | - Francesco Muntoni
- Dubowitz Neuromuscular Centre, NIHR Biomedical Research Centre, UCL Great Ormond Street Institute of Child Health; Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK
| | - Kiran Polavarapu
- Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Canada
| | - Hanns Lochmüller
- CNAG-CRG, Centro Nacional de Análisis Genómico - Centre for Genomic Regulation, Barcelona Institute of Science and Technology, Barcelona, Spain; Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Canada; Division of Neurology, Department of Medicine, The Ottawa Hospital; and Brain and Mind Research Institute, University of Ottawa, Ottawa, Canada; Department of Neuropediatrics and Muscle Disorders, Medical Center-University of Freiburg, Faculty of Medicine, Freiburg, Germany.
| | - Jacqueline Palace
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - David Beeson
- Neurosciences Group, Weatherall Institute of Molecular Medicine, University of Oxford, The John Radcliffe Hospital, Oxford, UK; Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
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Rahman MM, Basta T, Teng J, Lee M, Worrell BT, Stowell MHB, Hibbs RE. Structural mechanism of muscle nicotinic receptor desensitization and block by curare. Nat Struct Mol Biol 2022; 29:386-394. [PMID: 35301478 DOI: 10.1038/s41594-022-00737-3] [Citation(s) in RCA: 38] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2021] [Accepted: 02/04/2022] [Indexed: 11/09/2022]
Abstract
Binding of the neurotransmitter acetylcholine to its receptors on muscle fibers depolarizes the membrane and thereby triggers muscle contraction. We sought to understand at the level of three-dimensional structure how agonists and antagonists alter nicotinic acetylcholine receptor conformation. We used the muscle-type receptor from the Torpedo ray to first define the structure of the receptor in a resting, activatable state. We then determined the receptor structure bound to the agonist carbachol, which stabilizes an asymmetric, closed channel desensitized state. We find conformational changes in a peripheral membrane helix are tied to recovery from desensitization. To probe mechanisms of antagonism, we obtained receptor structures with the active component of curare, a poison arrow toxin and precursor to modern muscle relaxants. d-Tubocurarine stabilizes the receptor in a desensitized-like state in the presence and absence of agonist. These findings define the transitions between resting and desensitized states and reveal divergent means by which antagonists block channel activity of the muscle-type nicotinic receptor.
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Affiliation(s)
- Md Mahfuzur Rahman
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Tamara Basta
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO, USA
| | - Jinfeng Teng
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX, USA
| | - Myeongseon Lee
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO, USA
| | - Brady T Worrell
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO, USA
| | - Michael H B Stowell
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO, USA.
| | - Ryan E Hibbs
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX, USA.
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5
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Li F, Egea PF, Vecchio AJ, Asial I, Gupta M, Paulino J, Bajaj R, Dickinson MS, Ferguson-Miller S, Monk BC, Stroud RM. Highlighting membrane protein structure and function: A celebration of the Protein Data Bank. J Biol Chem 2021; 296:100557. [PMID: 33744283 PMCID: PMC8102919 DOI: 10.1016/j.jbc.2021.100557] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2020] [Revised: 02/10/2021] [Accepted: 03/16/2021] [Indexed: 12/13/2022] Open
Abstract
Biological membranes define the boundaries of cells and compartmentalize the chemical and physical processes required for life. Many biological processes are carried out by proteins embedded in or associated with such membranes. Determination of membrane protein (MP) structures at atomic or near-atomic resolution plays a vital role in elucidating their structural and functional impact in biology. This endeavor has determined 1198 unique MP structures as of early 2021. The value of these structures is expanded greatly by deposition of their three-dimensional (3D) coordinates into the Protein Data Bank (PDB) after the first atomic MP structure was elucidated in 1985. Since then, free access to MP structures facilitates broader and deeper understanding of MPs, which provides crucial new insights into their biological functions. Here we highlight the structural and functional biology of representative MPs and landmarks in the evolution of new technologies, with insights into key developments influenced by the PDB in magnifying their impact.
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Affiliation(s)
- Fei Li
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, USA; Department of Neurology, University of California San Francisco, San Francisco, California, USA
| | - Pascal F Egea
- Department of Biological Chemistry, School of Medicine, University of California Los Angeles, Los Angeles, California, USA
| | - Alex J Vecchio
- Department of Biochemistry, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
| | | | - Meghna Gupta
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, USA
| | - Joana Paulino
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, USA
| | - Ruchika Bajaj
- Department of Bioengineering and Therapeutic Sciences, University of California San Francisco, San Francisco, California, USA
| | - Miles Sasha Dickinson
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, USA
| | - Shelagh Ferguson-Miller
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan, USA
| | - Brian C Monk
- Sir John Walsh Research Institute and Department of Oral Sciences, University of Otago, North Dunedin, Dunedin, New Zealand
| | - Robert M Stroud
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California, USA.
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6
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Phillips MB, Nigam A, Johnson JW. Interplay between Gating and Block of Ligand-Gated Ion Channels. Brain Sci 2020; 10:brainsci10120928. [PMID: 33271923 PMCID: PMC7760600 DOI: 10.3390/brainsci10120928] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 11/21/2020] [Accepted: 11/26/2020] [Indexed: 02/03/2023] Open
Abstract
Drugs that inhibit ion channel function by binding in the channel and preventing current flow, known as channel blockers, can be used as powerful tools for analysis of channel properties. Channel blockers are used to probe both the sophisticated structure and basic biophysical properties of ion channels. Gating, the mechanism that controls the opening and closing of ion channels, can be profoundly influenced by channel blocking drugs. Channel block and gating are reciprocally connected; gating controls access of channel blockers to their binding sites, and channel-blocking drugs can have profound and diverse effects on the rates of gating transitions and on the stability of channel open and closed states. This review synthesizes knowledge of the inherent intertwining of block and gating of excitatory ligand-gated ion channels, with a focus on the utility of channel blockers as analytic probes of ionotropic glutamate receptor channel function.
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Affiliation(s)
- Matthew B. Phillips
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA; (M.B.P.); (A.N.)
- Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Aparna Nigam
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA; (M.B.P.); (A.N.)
| | - Jon W. Johnson
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA; (M.B.P.); (A.N.)
- Center for Neuroscience, University of Pittsburgh, Pittsburgh, PA 15260, USA
- Correspondence: ; Tel.: +1-(412)-624-4295
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7
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Rahman MM, Teng J, Worrell BT, Noviello CM, Lee M, Karlin A, Stowell MHB, Hibbs RE. Structure of the Native Muscle-type Nicotinic Receptor and Inhibition by Snake Venom Toxins. Neuron 2020; 106:952-962.e5. [PMID: 32275860 DOI: 10.1016/j.neuron.2020.03.012] [Citation(s) in RCA: 129] [Impact Index Per Article: 32.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Revised: 01/13/2020] [Accepted: 03/15/2020] [Indexed: 12/28/2022]
Abstract
The nicotinic acetylcholine receptor, a pentameric ligand-gated ion channel, converts the free energy of binding of the neurotransmitter acetylcholine into opening of its central pore. Here we present the first high-resolution structure of the receptor type found in muscle-endplate membrane and in the muscle-derived electric tissues of fish. The native receptor was purified from Torpedo electric tissue and functionally reconstituted in lipids optimal for cryo-electron microscopy. The receptor was stabilized in a closed state by the binding of α-bungarotoxin. The structure reveals the binding of a toxin molecule at each of two subunit interfaces in a manner that would block the binding of acetylcholine. It also reveals a closed gate in the ion-conducting pore, formed by hydrophobic amino acid side chains, located ∼60 Å from the toxin binding sites. The structure provides a framework for understanding gating in ligand-gated channels and how mutations in the acetylcholine receptor cause congenital myasthenic syndromes.
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Affiliation(s)
- Md Mahfuzur Rahman
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Jinfeng Teng
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Brady T Worrell
- Department of Molecular, Cellular & Developmental Biology, University of Colorado, Boulder, CO 80309, USA
| | - Colleen M Noviello
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Myeongseon Lee
- Department of Molecular, Cellular & Developmental Biology, University of Colorado, Boulder, CO 80309, USA
| | - Arthur Karlin
- Center for Molecular Recognition & Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Michael H B Stowell
- Department of Molecular, Cellular & Developmental Biology, University of Colorado, Boulder, CO 80309, USA.
| | - Ryan E Hibbs
- Department of Neuroscience, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
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8
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Progress in nicotinic receptor structural biology. Neuropharmacology 2020; 171:108086. [PMID: 32272141 DOI: 10.1016/j.neuropharm.2020.108086] [Citation(s) in RCA: 58] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2020] [Accepted: 03/31/2020] [Indexed: 02/07/2023]
Abstract
Here we begin by briefly reviewing landmark structural studies on the nicotinic acetylcholine receptor. We highlight challenges that had to be overcome to push through resolution barriers, then focus on what has been gleaned in the past few years from crystallographic and single particle cryo-EM studies of different nicotinic receptor subunit assemblies and ligand complexes. We discuss insights into ligand recognition, ion permeation, and allosteric gating. We then highlight some foundational aspects of nicotinic receptor structural biology that remain unresolved and are areas ripe for future exploration. This article is part of the special issue on 'Contemporary Advances in Nicotine Neuropharmacology'.
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9
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Changeux JP. Discovery of the First Neurotransmitter Receptor: The Acetylcholine Nicotinic Receptor. Biomolecules 2020; 10:E547. [PMID: 32260196 PMCID: PMC7226243 DOI: 10.3390/biom10040547] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2020] [Revised: 03/04/2020] [Accepted: 03/10/2020] [Indexed: 11/16/2022] Open
Abstract
The concept of pharmacological receptor was proposed at the turn of the 20th century but it took almost 70 years before the first receptor for a neurotransmitter was isolated and identified as a protein. This review retraces the history of the difficulties and successes in the identification of the nicotinic acetylcholine receptor, the first neurotransmitter receptor to be identified.
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Affiliation(s)
- Jean-Pierre Changeux
- Department of Neuroscience, CNRS UMR 3571, Institut Pasteur & Collège de France, 75015 Paris, France
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10
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Abstract
The pentameric γ-aminobutyric acid type A receptors are ion channels activated by ligands, which intervene in the rapid inhibitory transmission in the mammalian CNS. Due to their rich pharmacology and therapeutic potential, it is essential to understand their structure and function thoroughly. This deep characterization was hampered by the lack of experimental structural information for many years. Thus, computational techniques have been extensively combined with experimental data, in order to undertake the study of γ-aminobutyric acid type A receptors and their interaction with drugs. Here, we review the exciting journey made to assess the structures of these receptors and outline major outcomes. Finally, we discuss the brand new structure of the α1β2γ2 subtype and the amazing advances it brings to the field.
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11
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Bouzat C, Sine SM. Nicotinic acetylcholine receptors at the single-channel level. Br J Pharmacol 2018; 175:1789-1804. [PMID: 28261794 PMCID: PMC5979820 DOI: 10.1111/bph.13770] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 02/21/2017] [Accepted: 02/24/2017] [Indexed: 01/28/2023] Open
Abstract
Over the past four decades, the patch clamp technique and nicotinic ACh (nACh) receptors have established an enduring partnership. Like all good partnerships, each partner has proven significant in its own right, while their union has spurred innumerable advances in life science research. A member and prototype of the superfamily of pentameric ligand-gated ion channels, the nACh receptor is a chemo-electric transducer, binding ACh released from nerves and rapidly opening its channel to cation flow to elicit cellular excitation. A subject of a Nobel Prize in Physiology or Medicine, the patch clamp technique provides unprecedented resolution of currents through single ion channels in their native cellular environments. Here, focusing on muscle and α7 nACh receptors, we describe the extraordinary contribution of the patch clamp technique towards understanding how they activate in response to neurotransmitter, how subtle structural and mechanistic differences among nACh receptor subtypes translate into significant physiological differences, and how nACh receptors are being exploited as therapeutic drug targets. LINKED ARTICLES This article is part of a themed section on Nicotinic Acetylcholine Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.11/issuetoc/.
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Affiliation(s)
- Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, INIBIBB (CONICET‐UNS), Departamento de Biología, Bioquímica y FarmaciaUniversidad Nacional del SurBahía BlancaArgentina
| | - Steven M Sine
- Receptor Biology Laboratory, Department of Physiology and Biomedical EngineeringMayo Clinic College of MedicineRochesterMN55905USA
- Department of NeurologyMayo Clinic College of MedicineRochesterMN55905USA
- Department of Pharmacology and Experimental TherapeuticsMayo Clinic College of MedicineRochesterMN55905USA
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He LL, Zhang QF, Wang LC, Dai JX, Wang CH, Zheng LH, Zhou Z. Muscarinic inhibition of nicotinic transmission in rat sympathetic neurons and adrenal chromaffin cells. Philos Trans R Soc Lond B Biol Sci 2016; 370:rstb.2014.0188. [PMID: 26009767 DOI: 10.1098/rstb.2014.0188] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Little is known about the interactions between nicotinic and muscarinic acetylcholine receptors (nAChRs and mAChRs). Here we report that methacholine (MCh), a selective agonist of mAChRs, inhibited up to 80% of nicotine-induced nAChR currents in sympathetic superior cervical ganglion neurons and adrenal chromaffin cells. The muscarine-induced inhibition (MiI) substantially reduced ACh-induced membrane currents through nAChRs and quantal neurotransmitter release. The MiI was time- and temperature-dependent. The slow recovery of nAChR current after washout of MCh, as well as the high value of Q10 (3.2), suggested, instead of a direct open-channel blockade, an intracellular metabotropic process. The effects of GTP-γ-S, GDP-β-S and pertussis toxin suggested that MiI was mediated by G-protein signalling. Inhibitors of protein kinase C (bisindolymaleimide-Bis), protein kinase A (H89) and PIP2 depletion attenuated the MiI, indicating that a second messenger pathway is involved in this process. Taken together, these data suggest that mAChRs negatively modulated nAChRs via a G-protein-mediated second messenger pathway. The time dependence suggests that MiI may provide a novel mechanism for post-synaptic adaptation in all cells/neurons and synapses expressing both types of AChRs.
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Affiliation(s)
- Lin-Ling He
- State Key Laboratory of Biomembrane and Membrane Biotechnology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine and PKU-IDG/McGovern Institute for Brain Research and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, People's Republic of China Department of Immunology and Microbial Science, The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Quan-Feng Zhang
- State Key Laboratory of Biomembrane and Membrane Biotechnology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine and PKU-IDG/McGovern Institute for Brain Research and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, People's Republic of China
| | - Lie-Cheng Wang
- State Key Laboratory of Biomembrane and Membrane Biotechnology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine and PKU-IDG/McGovern Institute for Brain Research and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, People's Republic of China
| | - Jing-Xia Dai
- State Key Laboratory of Biomembrane and Membrane Biotechnology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine and PKU-IDG/McGovern Institute for Brain Research and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, People's Republic of China
| | - Chang-He Wang
- State Key Laboratory of Biomembrane and Membrane Biotechnology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine and PKU-IDG/McGovern Institute for Brain Research and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, People's Republic of China
| | - Liang-Hong Zheng
- State Key Laboratory of Biomembrane and Membrane Biotechnology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine and PKU-IDG/McGovern Institute for Brain Research and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, People's Republic of China
| | - Zhuan Zhou
- State Key Laboratory of Biomembrane and Membrane Biotechnology and Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine and PKU-IDG/McGovern Institute for Brain Research and Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, People's Republic of China
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13
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Moczydlowski E. On the Natural and Unnatural History of the Voltage-Gated Na+ Channel. NA CHANNELS FROM PHYLA TO FUNCTION 2016; 78:3-36. [DOI: 10.1016/bs.ctm.2016.06.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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14
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Wever CM, Farrington D, Dent JA. The Validation of Nematode-Specific Acetylcholine-Gated Chloride Channels as Potential Anthelmintic Drug Targets. PLoS One 2015; 10:e0138804. [PMID: 26393923 PMCID: PMC4578888 DOI: 10.1371/journal.pone.0138804] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Accepted: 09/03/2015] [Indexed: 01/06/2023] Open
Abstract
New compounds are needed to treat parasitic nematode infections in humans, livestock and plants. Small molecule anthelmintics are the primary means of nematode parasite control in animals; however, widespread resistance to the currently available drug classes means control will be impossible without the introduction of new compounds. Adverse environmental effects associated with nematocides used to control plant parasitic species are also motivating the search for safer, more effective compounds. Discovery of new anthelmintic drugs in particular has been a serious challenge due to the difficulty of obtaining and culturing target parasites for high-throughput screens and the lack of functional genomic techniques to validate potential drug targets in these pathogens. We present here a novel strategy for target validation that employs the free-living nematode Caenorhabditis elegans to demonstrate the value of new ligand-gated ion channels as targets for anthelmintic discovery. Many successful anthelmintics, including ivermectin, levamisole and monepantel, are agonists of pentameric ligand-gated ion channels, suggesting that the unexploited pentameric ion channels encoded in parasite genomes may be suitable drug targets. We validated five members of the nematode-specific family of acetylcholine-gated chloride channels as targets of agonists with anthelmintic properties by ectopically expressing an ivermectin-gated chloride channel, AVR-15, in tissues that endogenously express the acetylcholine-gated chloride channels and using the effects of ivermectin to predict the effects of an acetylcholine-gated chloride channel agonist. In principle, our strategy can be applied to validate any ion channel as a putative anti-parasitic drug target.
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Affiliation(s)
- Claudia M. Wever
- Department of Biology, McGill University, Montreal, Quebec, Canada
| | | | - Joseph A. Dent
- Department of Biology, McGill University, Montreal, Quebec, Canada
- * E-mail:
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15
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Isacoff EY, Jan LY, Minor DL. Conduits of life's spark: a perspective on ion channel research since the birth of neuron. Neuron 2013; 80:658-74. [PMID: 24183018 DOI: 10.1016/j.neuron.2013.10.040] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Heartbeats, muscle twitches, and lightning-fast thoughts are all manifestations of bioelectricity and rely on the activity of a class of membrane proteins known as ion channels. The basic function of an ion channel can be distilled into, "The hole opens. Ions go through. The hole closes." Studies of the fundamental mechanisms by which this process happens and the consequences of such activity in the setting of excitable cells remains the central focus of much of the field. One might wonder after so many years of detailed poking at such a seemingly simple process, is there anything left to learn?
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Affiliation(s)
- Ehud Y Isacoff
- Helen Wills Neuroscience Institute, University of California, Berkeley, CA 94720, USA; Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA; Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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16
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Nicotinic acetylcholine receptor and the structural basis of neuromuscular transmission: insights from Torpedo postsynaptic membranes. Q Rev Biophys 2013; 46:283-322. [PMID: 24050525 PMCID: PMC3820380 DOI: 10.1017/s0033583513000061] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The nicotinic acetylcholine (ACh) receptor, at the neuromuscular junction, is a neurotransmitter-gated ion channel that has been fine-tuned through evolution to transduce a chemical signal into an electrical signal with maximum efficiency and speed. It is composed from three similar and two identical polypeptide chains, arranged in a ring around a narrow membrane pore. Central to the design of this assembly is a hydrophobic gate in the pore, more than 50 Å away from sites in the extracellular domain where ACh binds. Although the molecular properties of the receptor have been explored intensively over the last few decades, only recently have structures emerged revealing its complex architecture and illuminating how ACh entering the binding sites opens the distant gate. Postsynaptic membranes isolated from the (muscle-derived) electric organ of the Torpedo ray have underpinned most of the structural studies: the membranes form tubular vesicles having receptors arranged on a regular surface lattice, which can be imaged directly in frozen physiological solutions. Advances in electron crystallographic techniques have also been important, enabling analysis of the closed- and open-channel forms of the receptor in unreacted tubes or tubes reacted briefly with ACh. The structural differences between these two forms show that all five subunits participate in a concerted conformational change communicating the effect of ACh binding to the gate, but that three of them (αγ, β and δ) play a dominant role. Flexing of oppositely facing pore-lining α-helices is the principal motion determining the closed/open state of the gate. These results together with the findings of biochemical, biophysical and other structural studies allow an integrated description of the receptor and of its mode of action at the synapse.
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17
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Changeux JP. The concept of allosteric interaction and its consequences for the chemistry of the brain. J Biol Chem 2013; 288:26969-26986. [PMID: 23878193 DOI: 10.1074/jbc.x113.503375] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Throughout this Reflections article, I have tried to follow up on the genesis in the 1960s and subsequent evolution of the concept of allosteric interaction and to examine its consequences within the past decades, essentially in the field of the neuroscience. The main conclusion is that allosteric mechanisms built on similar structural principles operate in bacterial regulatory enzymes, gene repressors (and the related nuclear receptors), rhodopsin, G-protein-coupled receptors, neurotransmitter receptors, ion channels, and so on from prokaryotes up to the human brain yet with important features of their own. Thus, future research on these basic cybernetic sensors is expected to develop in two major directions: at the elementary level, toward the atomic structure and molecular dynamics of the conformational changes involved in signal recognition and transduction, but also at a higher level of organization, the contribution of allosteric mechanisms to the modulation of brain functions.
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Affiliation(s)
- Jean-Pierre Changeux
- Collège de France, 75005 Paris and the Institut Pasteur, 75724 Paris Cedex 15, France.
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18
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Mallipeddi PL, Pedersen SE, Briggs JM. Interactions of acetylcholine binding site residues contributing to nicotinic acetylcholine receptor gating: role of residues Y93, Y190, K145 and D200. J Mol Graph Model 2013; 44:145-54. [PMID: 23831994 DOI: 10.1016/j.jmgm.2013.05.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Revised: 05/24/2013] [Accepted: 05/27/2013] [Indexed: 10/26/2022]
Abstract
The nicotinic acetylcholine receptor exhibits multiple conformational states, resting (channel closed), active (channel open) and desensitized (channel closed). The resting state may be distinguished from the active and desensitized states by the orientation of loop C in the extracellular ligand binding domain (LBD). Homology modeling was used to generate structures of the Torpedo californica α2βδγ nAChR that initially represent the resting state (loop C open) and the desensitized state (loop C closed). Molecular dynamics (MD) simulations were performed on the extracellular LBD on each nAChR conformational state, with and without the agonist anabaseine present in each binding site (the αγ and the αδ sites). Three MD simulations of 10ns each were performed for each of the four conditions. Comparison of dynamics revealed that in the presence of agonist, loop C was drawn inward and attains a more stable conformation. Examination of side-chain interactions revealed that residue αY190 exhibited hydrogen-bonding interactions either with residue αY93 in the ligand binding site or with residue αK145 proximal to the binding site. αK145 also exhibited side chain (salt bridge) interactions with αD200 and main chain interactions with αY93. Residues αW149, αY198, γY116/δT119, γL118/δL121 and γL108/δL111 appear to play the role of stabilizing ligand in the binding site. In MD simulations for the desensitized state, the effect of ligand upon the interactions among αK145, αY190, and αY93 as well as ligand-hydrogen-bonding to αW149 were more pronounced at the αγ interface than at the αδ interface. Differences in affinity for the desensitized state were determined experimentally to be 10-fold. The changes in side chain interactions observed for the two conformations and induced by ligand support a model wherein hydrogen bond interactions between αD200 and αY93 are broken and rearrange to form a salt-bridge between αK145 and αD200 and hydrogen bond interactions between αY93 and αY190 and between αK145 and αY190.
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Affiliation(s)
- Prema L Mallipeddi
- Department of Biology and Biochemistry, University of Houston, Houston, TX 77204, USA
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19
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Abstract
Molecular pain research is a relatively new and rapidly expanding field that represents advancement in conventional pain research. One of the fundamentals of molecular pain involves the cloning of genes and especially the ion channels specifically involved in nociceptive processing at the periphery and centrally. A variety of approaches were used to isolate these critically important genes. Cloning of these genes involved innovative strategies based on existing molecular approaches. This review will discuss well-utilized cloning approaches and their exploitation in molecular pain research.
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Affiliation(s)
- Armen N Akopian
- Department of Endodontics, Dental School, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
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20
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Changeux JP. The nicotinic acetylcholine receptor: the founding father of the pentameric ligand-gated ion channel superfamily. J Biol Chem 2012; 287:40207-15. [PMID: 23038257 DOI: 10.1074/jbc.r112.407668] [Citation(s) in RCA: 164] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A critical event in the history of biological chemistry was the chemical identification of the first neurotransmitter receptor, the nicotinic acetylcholine receptor. Disciplines as diverse as electrophysiology, pharmacology, and biochemistry joined together in a unified and rational manner with the common goal of successfully identifying the molecular device that converts a chemical signal into an electrical one in the nervous system. The nicotinic receptor has become the founding father of a broad family of pentameric membrane receptors, paving the way for their identification, including that of the GABA(A) receptors.
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21
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Lemoine D, Jiang R, Taly A, Chataigneau T, Specht A, Grutter T. Ligand-gated ion channels: new insights into neurological disorders and ligand recognition. Chem Rev 2012; 112:6285-318. [PMID: 22988962 DOI: 10.1021/cr3000829] [Citation(s) in RCA: 115] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Damien Lemoine
- Laboratoire de Biophysicochimie des Récepteurs Canaux, UMR 7199 CNRS, Conception et Application de Molécules Bioactives, Faculté de Pharmacie, Université de Strasbourg , 67400 Illkirch, France
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22
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Abstract
The synapse is a localized neurohumoral contact between a neuron and an effector cell and may be considered the quantum of fast intercellular communication. Analogously, the postsynaptic neurotransmitter receptor may be considered the quantum of fast chemical to electrical transduction. Our understanding of postsynaptic receptors began to develop about a hundred years ago with the demonstration that electrical stimulation of the vagus nerve released acetylcholine and slowed the heart beat. During the past 50 years, advances in understanding postsynaptic receptors increased at a rapid pace, owing largely to studies of the acetylcholine receptor (AChR) at the motor endplate. The endplate AChR belongs to a large superfamily of neurotransmitter receptors, called Cys-loop receptors, and has served as an exemplar receptor for probing fundamental structures and mechanisms that underlie fast synaptic transmission in the central and peripheral nervous systems. Recent studies provide an increasingly detailed picture of the structure of the AChR and the symphony of molecular motions that underpin its remarkably fast and efficient chemoelectrical transduction.
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Affiliation(s)
- Steven M Sine
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA.
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23
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Sources of energy for gating by neurotransmitters in acetylcholine receptor channels. Proc Natl Acad Sci U S A 2012; 109:9384-9. [PMID: 22647603 DOI: 10.1073/pnas.1203633109] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nicotinic acetylcholine receptors (AChRs) mediate signaling in the central and peripheral nervous systems. The AChR gating conformational change is powered by a low- to high-affinity change for neurotransmitters at two transmitter binding sites. We estimated (from single-channel currents) the components of energy for gating arising from binding site aromatic residues in the α-subunit. All mutations reduced the energy (TyrC1>>TrpB≈TyrC2>TyrA), with TyrC1 providing ~40% of the total. Considered one at a time, the fractional energy contributions from the aromatic rings were TrpB ~35%, TyrC1 ~28%, TyrC2 ~28%, and TyrA ~10%. Together, TrpB, TyrC1, and TyrC2 comprise an "aromatic triad" that provides much of the total energy from the transmitter for gating. Analysis of mutant pairs suggests that the energy contributions from some residues are nearly independent. Mutations of TyrC1 cause particularly large energy reductions because they remove two favorable and approximately equal interactions between the aromatic ring and the quaternary amine of the agonist and between the hydroxyl and αLysβ7.
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24
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Kozuska JL, Paulsen IM. The Cys-loop pentameric ligand-gated ion channel receptors: 50 years on. Can J Physiol Pharmacol 2012; 90:771-82. [PMID: 22493950 DOI: 10.1139/y2012-018] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This year, 2011, the Department of Pharmacology at the University of Alberta celebrated its 50th anniversary. This timeframe covers nearly the entire history of Cys-loop pentameric ligand-gated ion channel (pLGIC) research. In this review we consider how major technological advancements affected our current understanding of pLGICs, and highlight the contributions made by members of our department. The individual at the center of our story is Susan Dunn; her passing earlier this year has robbed the Department of Pharmacology and the research community of a most insightful colleague. Her dissection of ligand interactions with the nAChR, together with their interpretation, was the hallmark of her extensive collaborations with Michael Raftery. Here, we highlight some electrophysiological studies from her laboratory over the last few years, using the technique that she introduced to the department in Edmonton, the 2-electrode voltage-clamp of Xenopus oocytes. Finally, we discuss some single-channel studies of the anionic GlyR and GABA(A)R that prefaced the introduction of this technique to her laboratory.
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Affiliation(s)
- Janna L Kozuska
- Department of Pharmacology, University of Alberta, 9-55 Medical Sciences Building, Edmonton, AB T6G2H7, Canada.
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25
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Tochitsky I, Banghart MR, Mourot A, Yao JZ, Gaub B, Kramer RH, Trauner D. Optochemical control of genetically engineered neuronal nicotinic acetylcholine receptors. Nat Chem 2012; 4:105-11. [PMID: 22270644 DOI: 10.1038/nchem.1234] [Citation(s) in RCA: 142] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2011] [Accepted: 11/21/2011] [Indexed: 12/21/2022]
Abstract
Advances in synthetic chemistry, structural biology, molecular modelling and molecular cloning have enabled the systematic functional manipulation of transmembrane proteins. By combining genetically manipulated proteins with light-sensitive ligands, innately 'blind' neurobiological receptors can be converted into photoreceptors, which allows them to be photoregulated with high spatiotemporal precision. Here, we present the optochemical control of neuronal nicotinic acetylcholine receptors (nAChRs) with photoswitchable tethered agonists and antagonists. Using structure-based design, we produced heteromeric α3β4 and α4β2 nAChRs that can be activated or inhibited with deep-violet light, but respond normally to acetylcholine in the dark. The generation of these engineered receptors should facilitate investigation of the physiological and pathological functions of neuronal nAChRs and open a general pathway to photosensitizing pentameric ligand-gated ion channels.
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Affiliation(s)
- Ivan Tochitsky
- Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA
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26
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O'Toole KK, Jenkins A. Discrete M3-M4 intracellular loop subdomains control specific aspects of γ-aminobutyric acid type A receptor function. J Biol Chem 2011; 286:37990-37999. [PMID: 21903587 DOI: 10.1074/jbc.m111.258012] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The GABA type A receptor (GABA(A)R) is a member of the pentameric ligand gated ion channel (pLGIC) family that mediates ionotropic neurotransmission. Residues in the intracellular loop domain (ILD) have recently been shown to define part of the ion permeation pathway in several closely related members of the pentameric ligand gated ion channel family. In this study, we investigated the role the ILD of the GABA(A)R α1 subunit plays in channel function. Deletion of the α1 ILD resulted in a significant increase in GABA EC(50) and maximal current amplitude, suggesting that the ILD must be intact for proper receptor function. To test this hypothesis, we conducted a mutagenic screen of all amino acids harboring ionizable side chains within this domain to investigate the contribution of individual charged residues to ion permeation. Using macroscopic and single channel voltage-clamp recording techniques, we found that mutations within a subdomain of the α1 ILD near M3 altered GABA apparent affinity; interestingly, α1(K312E) exhibited reduced partial agonist efficacy. We introduced point mutations near M4, including α1(K383E) and α1(K384E), that enhanced receptor desensitization. Mutation of 5 charged residues within a 39-residue span contiguous with M4 reduced relative anion permeability of the channel and may represent a weak intracellular selectivity filter. Within this subdomain, the α1(K378E) mutation induced a significant reduction in single channel conductance, consistent with our hypothesis that the GABA(A)R α1 ILD contributes directly to the permeation pathway.
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Affiliation(s)
- Kate K O'Toole
- Departments of Anesthesiology and Pharmacology, Emory University, Atlanta, Georgia 30322
| | - Andrew Jenkins
- Departments of Anesthesiology and Pharmacology, Emory University, Atlanta, Georgia 30322.
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27
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28
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Kosower EM. A molecular model for an acetylcholine binding site: ion channel and the bilayer helices of the acetylcholine receptor assigned using single group rotation theory and electrostatic interactions. Biophys J 2010; 45:13-4. [PMID: 19431537 DOI: 10.1016/s0006-3495(84)84088-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
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29
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Kawai H, Raftery MA. Kinetics of agonist-induced intrinsic fluorescence changes in the Torpedo acetylcholine receptor. J Biochem 2010; 147:743-9. [PMID: 20123701 DOI: 10.1093/jb/mvq007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The nicotinic acetylcholine receptor from Torpedo electric organs is a ligand-gated ion channel that undergoes conformational transitions for activation and/or desensitization. Earlier work suggested that intrinsic fluorescence changes of the receptor monitors kinetic transitions toward the high-affinity, desensitized state. Here, using highly purified membrane preparations to minimize contaminating fluorescence, we examined kinetic mechanisms of the receptor as monitored by its intrinsic fluorescence. Fluorescence changes were specific to the receptor as they were blocked by alpha-bungarotoxin and were induced by agonists, but not by the antagonist hexamethonium. Acetylcholine, carbamylcholine and suberyldicholine showed only one kinetic phase with relatively fast rates (t(1/2) = 0.2-1.2 s). Effective dissociation constants were at least an order of magnitude higher than the high affinity, equilibrium binding constants for these agonists. A semirigid agonist isoarecolone-methiodide, whose activation constant was approximately 3-fold lower than acetylcholine, induced an additional slow phase (t(1/2) = 4.5-9 s) with apparent rates that increased and then decreased in a concentration dependent manner, revealing a branched mechanism for conformational transitions. We propose that the intrinsic fluorescence changes of the receptor describe a process(es) toward a fast desensitization state prior to the formation of the high affinity state.
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Affiliation(s)
- Hideki Kawai
- Department of Pharmacology, University of Minnesota Medical School, Minneapolis, MN 55455, USA.
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30
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The evolution of pentameric ligand-gated ion channels. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 683:11-23. [PMID: 20737785 DOI: 10.1007/978-1-4419-6445-8_2] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Fast, ionotropic neurotransmission mediated by ligand-gated ion channels is essential for timely behavioral responses in multicellular organisms. Metazoa employ more ionotropic neurotransmitters in more types of synapses, inhibitory or excitatory, than is generally appreciated. It is becoming increasingly clear that the adaptability of a single neurotransmitter receptor superfamily, the pentameric ligand-gated ion channels (pLGICs), makes the diversity in ionotropic neurotransmission possible. Modification ofa common pLGIC structure generates channels that are gated by ligands as different as protons, histamine or zinc and that pair common neurotransmitters with both cation and anion permeability. A phylogeny of the pLGIC gene family from representative metazoa suggests that pLGIC diversity is ancient and evolution of contemporary phyla was characterized by a surprising loss of pLGIC diversity. The pLGIC superfamily reveals aspects of early metazoan evolution, may help us identify novel neurotransmitters and can inform our exploration of structure/function relationships.
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31
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De Almeida RFM, Loura LMS, Prieto M, Watts A, Fedorov A, Barrantes FJ. Structure and dynamics of the γM4 transmembrane domain of the acetylcholine receptor in lipid bilayers: insights into receptor assembly and function. Mol Membr Biol 2009; 23:305-15. [PMID: 16923724 DOI: 10.1080/09687860600703613] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
A 28-mer peptide (gammaM4) corresponding to the fourth transmembrane segment of the nicotinic acetylcholine receptor (AChR) gamma-subunit, with a single tryptophan residue (Trp6), was reconstituted into lipid bilayers of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), loaded with either high or low amounts of cholesterol, i.e., in the conjugated liquid-ordered and liquid-disordered phases, respectively, at room temperature. By making use of the Trp intrinsic fluorescence, both steady-state and time-resolved fluorescence techniques were employed, namely, red-edge excitation shift effect, decay-associated spectra (DAS), and time-resolved anisotropy. The results obtained here, together with previous studies on the same reconstituted peptide, indicate that: (i) Trp6 is strongly anchored in the bilayer with a defined transverse location; (ii) the modifications in the measured DAS are related to the complex result of a self-quenching process on the decay parameters; (iii) the wobbling movement of the indole moiety of Trp6 is fast but severely restricted in amplitude; and, (iv) in the liquid-ordered phase, the bilayer properties and the tilt angle of the peptide enhance peptide-peptide interactions, with the formation of peptide rich patches and possibly some anti-parallel helix-helix aggregates, showing different dynamics from that of the peptide in the liquid-disordered phase where the peptide is randomly distributed.
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Affiliation(s)
- Rodrigo F M De Almeida
- Centro de Química e Bioquímica, Faculdade de Ciências de Lisboa, Campo Grande, Lisboa, Portugal.
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32
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Millar NS. A review of experimental techniques used for the heterologous expression of nicotinic acetylcholine receptors. Biochem Pharmacol 2009; 78:766-76. [PMID: 19540210 DOI: 10.1016/j.bcp.2009.06.015] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2009] [Revised: 06/08/2009] [Accepted: 06/10/2009] [Indexed: 11/18/2022]
Abstract
Nicotinic acetylcholine receptors (nAChRs) are members of the Cys-loop family of neurotransmitter-gated ion channels, a family that also includes receptors for gamma-aminobutyric acid, glycine and 5-hydroxytryptamine. In humans, nAChRs have been implicated in several neurological and psychiatric disorders and are major targets for pharmaceutical drug discovery. In addition, nAChRs are important targets for neuroactive pesticides in insects and in other invertebrates. Historically, nAChRs have been one of the most intensively studied families of neurotransmitter receptors. They were the first neurotransmitter receptors to be biochemically purified and the first to be characterized by molecular cloning and heterologous expression. Although much has been learnt from studies of native nAChRs, the expression of recombinant nAChRs has provided dramatic advances in the characterization of these important receptors. This review will provide a brief history of the characterization of nAChRs by heterologous expression. It will focus, in particular, upon studies of recombinant nAChRs, work that has been conducted by many hundreds of scientists during a period of almost 30 years since the molecular cloning of nAChR subunits in the early 1980s.
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Affiliation(s)
- Neil S Millar
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK.
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33
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Albuquerque EX, Pereira EFR, Alkondon M, Rogers SW. Mammalian nicotinic acetylcholine receptors: from structure to function. Physiol Rev 2009; 89:73-120. [PMID: 19126755 PMCID: PMC2713585 DOI: 10.1152/physrev.00015.2008] [Citation(s) in RCA: 1241] [Impact Index Per Article: 82.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The classical studies of nicotine by Langley at the turn of the 20th century introduced the concept of a "receptive substance," from which the idea of a "receptor" came to light. Subsequent studies aided by the Torpedo electric organ, a rich source of muscle-type nicotinic receptors (nAChRs), and the discovery of alpha-bungarotoxin, a snake toxin that binds pseudo-irreversibly to the muscle nAChR, resulted in the muscle nAChR being the best characterized ligand-gated ion channel hitherto. With the advancement of functional and genetic studies in the late 1980s, the existence of nAChRs in the mammalian brain was confirmed and the realization that the numerous nAChR subtypes contribute to the psychoactive properties of nicotine and other drugs of abuse and to the neuropathology of various diseases, including Alzheimer's, Parkinson's, and schizophrenia, has since emerged. This review provides a comprehensive overview of these findings and the more recent revelations of the impact that the rich diversity in function and expression of this receptor family has on neuronal and nonneuronal cells throughout the body. Despite these numerous developments, our understanding of the contributions of specific neuronal nAChR subtypes to the many facets of physiology throughout the body remains in its infancy.
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Affiliation(s)
- Edson X Albuquerque
- Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore, MD, USA
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Higuchi M, Kinoshita T. Specific Permeability of Chiral Amino Acids through Functional Molecular Membranes Composed of an Amphiphilic Graft Peptide. Chemphyschem 2008; 9:1110-3. [DOI: 10.1002/cphc.200800164] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Sine SM, Gao F, Lee WY, Mukhtasimova N, Wang HL, Engel AG. Recent Structural and Mechanistic Insights into Endplate Acetylcholine Receptors. Ann N Y Acad Sci 2008; 1132:53-60. [DOI: 10.1196/annals.1405.041] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Rodriguez-Boulan E, Misek DE, Salas DVD, Salas PJI, Bard E. Chapter 6 Protein Sorting in the Secretory Pathway. CURRENT TOPICS IN MEMBRANES AND TRANSPORT 2008; 24:251-294. [PMID: 32287478 PMCID: PMC7146842 DOI: 10.1016/s0070-2161(08)60328-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
This chapter focuses on protein sorting in the secretory pathway. From primary and secondary biosynthetic sites in the cytosol and mitochondrial matrix, respectively, proteins and lipids are distributed to more than 30 final destinations in membranes or membrane-bound spaces, where they carry out their programmed function. Molecular sorting is defined, in its most general sense, as the sum of the mechanisms that determine the distribution of a given molecule from its site of synthesis to its site of function in the cell. The final site of residence of a protein in a eukaryotic cell is determined by a combination of various factors, acting in concert: (1) site of synthesis, (2) sorting signals or zip codes, (3) signal recognition or decoding mechanisms, (4) cotranslational or posttranslational mechanisms for translocation across membranes, (5) specific fusion-fission interactions between intracellular vesicular compartments, and (6) restrictions to the lateral mobility in the plane of the bilayer. Improvements in cell fractionation, protein separation, and immune precipitation procedures in the past decade have made them possible. Very little is known about the mechanisms that mediate the localization and concentration of specific proteins and lipids within organelles. Various experimental model systems have become available for their study. The advent of recombinant DNA technology has shortened the time needed for obtaining the primary structure of proteins to a few months.
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Affiliation(s)
| | - David E Misek
- Department of Pathology, State University of New York, Downstate Medical Center, Brooklyn, New York
| | - Dora Vega De Salas
- Department of Cell Biology and Anatomy, Cornell University Medical College, New York, New York
| | - Pedro J I Salas
- Department of Cell Biology and Anatomy, Cornell University Medical College, New York, New York
| | - Enzo Bard
- Department of Pathology, State University of New York, Downstate Medical Center, Brooklyn, New York
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Sommer N, Tackenberg B, Hohlfeld R. The immunopathogenesis of myasthenia gravis. HANDBOOK OF CLINICAL NEUROLOGY 2008; 91:169-212. [PMID: 18631843 DOI: 10.1016/s0072-9752(07)01505-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Affiliation(s)
- Norbert Sommer
- Clinical Neuroimmunology Group, Philipps-University, Marburg, Germany
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Changeux JP, Devillers-Thiéry A, Galzi JL, Revah F. The acetylcholine receptor: a model of an allosteric membrane protein mediating intercellular communication. CIBA FOUNDATION SYMPOSIUM 2007; 164:66-89; discussion 87-97. [PMID: 1395936 DOI: 10.1002/9780470514207.ch6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Over the past 20 years the nicotinic acetylcholine receptor has become the prototype of a superfamily of ligand-gated ion channels. As a single macromolecular entity of M(r) about 300,000, the receptor protein mediates, altogether, the activation and the desensitization of the associated ion channel and the regulation of these processes by extracellular and intracellular signals. The notion is discussed that the acetylcholine receptor is a membrane-bound allosteric protein which possesses several categories of specific sites for neurotransmitters and for regulatory ligands, and undergoes conformational transitions which link these diverse sites together. At this elementary molecular level, interactions between signalling pathways may be mediated by membrane-bound allosteric receptors and/or by other categories of cytoplasmic allosteric proteins.
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Affiliation(s)
- J P Changeux
- Institut Pasteur, Neurobiologie Moléculaire, Bâtiment des Biotechnologies, Paris, France
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Romanelli MN, Gratteri P, Guandalini L, Martini E, Bonaccini C, Gualtieri F. Central Nicotinic Receptors: Structure, Function, Ligands, and Therapeutic Potential. ChemMedChem 2007; 2:746-67. [PMID: 17295372 DOI: 10.1002/cmdc.200600207] [Citation(s) in RCA: 145] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The growing interest in nicotinic receptors, because of their wide expression in neuronal and non-neuronal tissues and their involvement in several important CNS pathologies, has stimulated the synthesis of a high number of ligands able to modulate their function. These membrane proteins appear to be highly heterogeneous, and still only incomplete information is available on their structure, subunit composition, and stoichiometry. This is due to the lack of selective ligands to study the role of nAChR under physiological or pathological conditions; so far, only compounds showing selectivity between alpha4beta2 and alpha7 receptors have been obtained. The nicotinic receptor ligands have been designed starting from lead compounds from natural sources such as nicotine, cytisine, or epibatidine, and, more recently, through the high-throughput screening of chemical libraries. This review focuses on the structure of the new agonists, antagonists, and allosteric ligands of nicotinic receptors, it highlights the current knowledge on the binding site models as a molecular modeling approach to design new compounds, and it discusses the nAChR modulators which have entered clinical trials.
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Affiliation(s)
- M Novella Romanelli
- Laboratory of Design, Synthesis, and Study of Biologically Active Heterocycles (HeteroBioLab), Department of Pharmaceutical Sciences, University of Florence, via Ugo Schiff 6, 50019 Sesto Fiorentino, Italy.
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Guzmán GR, Ortiz-Acevedo A, Ricardo A, Rojas LV, Lasalde-Dominicci JA. The Polarity of Lipid-Exposed Residues Contributes to the Functional Differences between Torpedo and Muscle-Type Nicotinic Receptors. J Membr Biol 2007; 214:131-8. [PMID: 17530159 DOI: 10.1007/s00232-006-0051-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2006] [Revised: 11/27/2006] [Indexed: 10/23/2022]
Abstract
A comparison between the Torpedo and muscle-type acetylcholine receptors (AChRs) reveals differences in several lipid-exposed amino acids, particularly in the polarity of those residues. The goal of this study was to characterize the role of eight lipid-exposed residues in the functional differences between the Torpedo and muscle-type AChRs. To this end, residues alphaS287, alphaC412, betaY441, gammaM299, gammaS460, deltaM293, deltaS297 and deltaN305 in the Torpedo AChR were replaced with those found in the muscle-type receptor. Mutant receptor expression was measured in Xenopus oocytes using [(125)I]-alpha-bungarotoxin, and AChR ion channel function was evaluated using the two-electrode voltage clamp. Eight mutant combinations resulted in an increase (1.5- to 5.2-fold) in AChR expression. Four mutant combinations produced a significant 46% decrease in the ACh 50% inhibitory concentration (EC(50)), while three mutant combinations resulted in 1.7- to 2-fold increases in ACh EC(50). Finally, seven mutant combinations resulted in a decrease in normalized, ACh-induced currents. Our results suggest that these residues, although remote from the ion channel pore, (1) contribute to ion channel gating, (2) may affect trafficking of AChR into specialized membrane domains and (3) account for the functional differences between Torpedo and muscle-type AChR. These findings emphasize the importance of the lipid-protein interface in the functional differences between the Torpedo and muscle-type AChRs.
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Affiliation(s)
- Gisila R Guzmán
- Department of Biology, University of Puerto Rico, San Juan, Puerto Rico 00931-3360.
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Halliwell RF. A short history of the rise of the molecular pharmacology of ionotropic drug receptors. Trends Pharmacol Sci 2007; 28:214-9. [PMID: 17416425 DOI: 10.1016/j.tips.2007.03.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2006] [Revised: 02/12/2007] [Accepted: 03/23/2007] [Indexed: 11/17/2022]
Abstract
Remarkably, perhaps, for many pharmacologists today, just over 25 years ago, receptors were still considered hypothetical entities. The isolation and identification of Langley's receptive substance (Ehrlich's side-chains) required efforts from diverse groups; serendipity also facilitated its purification and subsequent biochemical and molecular characterization. In this review, I consider some of the key individuals and breakthrough technical developments from the late 1950s to the early 1990s that lead to the cloning of the first receptors. I focus on the nicotinic acetylcholine receptor to illustrate the complexities in this field and because it was the first receptor to be cloned. This brief history will also touch upon the implications of the rise of molecular pharmacology for the development of new drugs.
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Affiliation(s)
- Robert F Halliwell
- T.J. Long School of Pharmacy and Health Sciences, University of the Pacific, Stockton, CA 95211, USA.
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Millar NS, Denholm I. Nicotinic acetylcholine receptors: targets for commercially important insecticides. INVERTEBRATE NEUROSCIENCE 2007; 7:53-66. [PMID: 17216290 DOI: 10.1007/s10158-006-0040-0] [Citation(s) in RCA: 176] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2006] [Accepted: 12/18/2006] [Indexed: 12/20/2022]
Abstract
Nicotinic acetylcholine receptors (nAChRs) are major excitatory neurotransmitter receptors in both vertebrates and invertebrates. In insects, nAChRs are the target site for several naturally occurring and synthetic compounds that exhibit potent insecticidal activity. Several compounds isolated from plants are potent agonists or antagonists of nAChRs, suggesting that these may have evolved as a defence mechanism against insects and other herbivores. Nicotine, isolated from the tobacco plant, has insecticidal activity and has been used extensively as a commercial insecticide. Spinosad, a naturally occurring mixture of two macrocyclic lactones isolated from the microorganism Saccharopolyspora spinosa, acts upon nAChRs and has been developed as a commercial insecticide. Since the early 1990s, one of the most widely used and rapidly growing classes of insecticides has been the neonicotinoids. Neonicotinoid insecticides are potent selective agonists of insect nAChRs and are used extensively in both crop protection and animal health applications. As with other classes of insecticides, there is growing evidence for the evolution of resistance to insecticides that act on nAChRs.
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Affiliation(s)
- Neil S Millar
- Department of Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK.
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Carter CRJ, Cao L, Kawai H, Smith PA, Dryden WF, Raftery MA, Dunn SMJ. Chain length dependence of the interactions of bisquaternary ligands with the Torpedo nicotinic acetylcholine receptor. Biochem Pharmacol 2006; 73:417-26. [PMID: 17118342 DOI: 10.1016/j.bcp.2006.10.011] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2006] [Revised: 09/29/2006] [Accepted: 10/16/2006] [Indexed: 11/23/2022]
Abstract
The interactions of a series of bisholine esters [(CH3)3N+CH(2)CH2OCO-(CH2)n-COOCH2CH2N+(CH3)3] with the Torpedo nicotinic acetylcholine receptor have been investigated. In equilibrium binding studies, [3H]-suberyldicholine (n=6) binds to an equivalent number of sites as [3H]-acetylcholine and with similar affinity (KD approximately 15 nM). In competition studies, all bischoline esters examined displaced both radioligands in an apparently simple competitive manner. Estimated dissociation constants (KI) showed clear chain length dependence. Short chain molecules (n<or=2) were of lower affinity (KI's of 150-300 nM), whereas longer ligands (n>6) had high affinity similar to suberyldicholine. Functional responses were measured by either rapid flux techniques using Torpedo membrane vesicles or voltage-clamp analyses of recombinant receptors expressed in Xenopus oocytes. Both approaches revealed that suberyldicholine (EC50 approximately 3.4 microM) is 14-25-fold more potent than acetylcholine. However, suberyldicholine elicited only about 45% of the maximum response of the natural ligand, i.e., it is a partial agonist. The potency of this bischoline series increased with chain length. Whereas the shorter ligands (n<or=3) displayed potencies similar to acetylcholine, longer ligands (n>or=4) had similar (or higher) potency to suberyldicholine. Ligand efficacy had an approximately bell-shaped dependence on chain length and compounds where n<or=3 and >or=8 were very poor partial agonists. Based on estimates of interonium distances, we suggest that bisquaternary ligands can interact with multiple binding sites on the nAChR and, depending on the conformational state of the receptor, these sites are 15-20A apart.
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Affiliation(s)
- Chris R J Carter
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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Meltzer RH, Vila-Carriles W, Ebalunode JO, Briggs JM, Pedersen SE. Computed pore potentials of the nicotinic acetylcholine receptor. Biophys J 2006; 91:1325-35. [PMID: 16751248 PMCID: PMC1518625 DOI: 10.1529/biophysj.106.081455] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Electrostatic surface potentials in the vestibule of the nicotinic acetylcholine receptor (nAChR) were computed from structural models using the University of Houston Brownian Dynamics program to determine their effect on ion conduction and ionic selectivity. To further determine whether computed potentials accurately reflect the electrostatic environment of the channel, the potentials were used to predict the rate constants for diffusion-enhanced fluorescence energy transfer; the calculated energy transfer rates are directly comparable with those determined experimentally (see companion article by Meltzer et al. in this issue). To include any effects on the local potentials by the bound acceptor fluorophore crystal violet, its binding site was first localized within the pore by fluorescence energy transfer measurements from dansyl-C6-choline bound to the agonist sites and also by simulations of binding using Autodock. To compare the computed potentials with those determined experimentally, we used the predicted energy transfer rates from Tb3+ chelates of varying charge to calculate an expected potential using the Boltzmann relationship. This expected potential (from -20 to -40 mV) overestimates the values determined experimentally (from -10 to -25 mV) by two- to fourfold at similar conditions of ionic strength. Although the results indicate a basic discrepancy between experimental and computed surface potentials, both methods demonstrate that the vestibular potential has a relatively small effect on conduction and selectivity.
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Affiliation(s)
- Robert H Meltzer
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77035, USA
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Hill DG, Baenziger JE. The net orientation of nicotinic receptor transmembrane alpha-helices in the resting and desensitized states. Biophys J 2006; 91:705-14. [PMID: 16648164 PMCID: PMC1483077 DOI: 10.1529/biophysj.106.082693] [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: 11/18/2022] Open
Abstract
The net orientation of nicotinic acetylcholine receptor transmembrane alpha-helices has been probed in both the activatable resting and nonactivatable desensitized states using linear dichroism Fourier-transform infrared spectroscopy. Infrared spectra recorded from reconstituted nicotinic acetylcholine receptor membranes after 72 h exposure to (2)H2O exhibit an intense amide I component band near 1655 cm(-1) that is due predominantly to hydrogen-exchange-resistant transmembrane peptides in an alpha-helical conformation. The measured dichroism of this band is 2.37, suggesting a net tilt of the transmembrane alpha-helices of roughly 40 degrees from the bilayer normal, although this value overestimates the tilt angle because the measured dichroism at 1655 cm(-1) also reflects the dichroism of overlapping amide I component bands. Significantly, no change in the net orientation of the transmembrane alpha-helices is observed upon agonist binding. In fact, the main changes in structure and orientation detected upon desensitization involve highly solvent accessible regions of the polypeptide backbone. Our data are consistent with a capping of the ligand binding site by the solvent accessible C-loop with little change in the structure of the transmembrane domain in the desensitized state. Changes in structure at the interface between the ligand-binding and transmembrane domains may uncouple binding from gating.
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Affiliation(s)
- Danny G Hill
- Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario, Canada
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Luebke AE, Maroni PD, Guth SM, Lysakowski A. Alpha-9 nicotinic acetylcholine receptor immunoreactivity in the rodent vestibular labyrinth. J Comp Neurol 2005; 492:323-33. [PMID: 16217793 PMCID: PMC3221517 DOI: 10.1002/cne.20739] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Vestibular tissues (cristae ampullares, macular otolithic organs, and Scarpa's ganglia) in chinchilla, rat, and guinea pig were examined for immunoreactivity to the alpha9 nicotinic acetylcholine receptor (nAChR) subunit. The alpha9 antibody was generated against a conserved peptide present in the intracellular loop of the predicted protein sequence of the guinea pig alpha9 nAChR subunit. In the vestibular periphery, staining was observed in calyces around type I hair cells, at the synaptic pole of type II hair cells, and in varying levels in Scarpa's ganglion cells. Ganglion cells were also triply labeled to detect alpha9, calretinin, and peripherin. Calretinin labels calyx-only afferents. Peripherin labels bouton-only afferents. Dimorphic afferents, which have both calyx and bouton endings, are not labeled by calretinin or peripherin. In these experiments, alpha9 was expressed in both calyx and dimorphic afferents. A subpopulation of small ganglion cells did not contain the alpha9 nAChR but did stain for peripherin. We surmise that these are bouton-only afferents. Bouton (regularly discharging) afferents also show efferent responses, although they are qualitatively different from those in irregularly discharging (calyx and dimorphic) afferents, much slower and longer lasting. Thus, regular afferents are probably more affected via a muscarinic cholinergic or a peptidergic mechanism, with a much smaller superimposed fast nicotinic-type response. This latter response could be due to one of the other nicotinic receptors that have been described in studies from other laboratories.
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Affiliation(s)
- Anne E. Luebke
- Departments of Biomedical Engineering and Neurobiology and Anatomy, University of Rochester School of Medicine, Rochester, New York 14642
| | - Paul D. Maroni
- Department of Anatomy and Cell Biology, University of Illinois College of Medicine, Chicago, Illinois 60612
| | - Scott M. Guth
- Department of Anatomy and Cell Biology, University of Illinois College of Medicine, Chicago, Illinois 60612
| | - Anna Lysakowski
- Department of Anatomy and Cell Biology, University of Illinois College of Medicine, Chicago, Illinois 60612
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Abstract
Most currently used therapeutic drugs have an enzyme or a membrane-bound receptor as site of action. The sequencing of the human and other genomes has provided a potential to identify many hitherto unknown proteins that might serve as new drug targets. To achieve this, knowledge about three-dimensional protein structures is crucial for the understanding of their functional mechanisms, and for a rational drug design. Over the last decade atomic resolution crystal structures of soluble proteins have been reported in a rapidly increasing number, but the detailed three-dimensional structures are still unknown for the majority of membrane proteins since their membrane association makes experimental structure determinations complicated. Computerized modelling of protein structures, based on experimentally determined structures of homologue proteins, may be a useful methodological alternative, especially for membrane proteins. In the past, molecular modelling of transporters and G-protein-coupled receptors was based on low-resolution structural data obtained by cryo-electron microscopy. Recent high-resolution crystal structure determinations of a G-protein-coupled receptor, rhodopsin, and several different transporter proteins and ion channels have enabled construction of more accurate receptor and transporter models. For the future, collaborative structural genomics initiatives aim at determining the three-dimensional structure of all known proteins, based on a combination of experimental structure determination and molecular modelling. Development of still more powerful computer hardware and software will enable extensive studies of the protein structure and dynamics of new potential drug targets, but raises a new challenge in the validation and calibration of computerized methods of biosimulations.
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Affiliation(s)
- Svein G Dahl
- Department of Pharmacology, Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway.
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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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Abstract
Fifty years ago, ion channels were but a reasonable hypothesis. I outline some major steps in transforming this idea from a plausible description of the biological assemblies responsible for controlling passive ion transport across membranes to established fact. Important electrophysiological, biochemical, molecular biological, structural, and theoretical tools are discussed in the context of the transition from studying whole cell preparations, containing many channels, to investigating single channel behavior. Six channel families are exemplified: the model peptide, gramicidin, the acetylcholine receptor, and the sodium, potassium, calcium, and chloride channels. Some questions of current interest are posed.
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Affiliation(s)
- Peter C Jordan
- Department of Chemistry, Brandeis University, Waltham, MA 02454-9110, USA.
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50
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Lin NH, Meyer MD. Recent developments in neuronal nicotinic acetylcholine receptor modulators. Expert Opin Ther Pat 2005. [DOI: 10.1517/13543776.8.8.991] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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