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Abstract
G-protein-coupled receptors (GPCRs) constitute a large group of integral membrane proteins that transduce extracellular signals from a wide range of agonists into targeted intracellular responses. Although the responses can vary depending on the category of G-proteins activated by a particular receptor, responses were also found to be triggered by interactions of the receptor with β-arrestins. It was subsequently discovered that for the same receptor molecule (e.g., the β-adrenergic receptor), some agonists have a propensity to specifically favor responses by G-proteins, others by β-arrestins, as has now been extensively studied. This feature of the GPCR system is known as biased agonism and is subject to various interpretations, including agonist-induced conformational change versus selective stabilization of preexisting active conformations. Here, we explore a complete allosteric framework for biased agonism based on alternative preexisting conformations that bind more strongly, but nonexclusively, either G-proteins or β-arrestins. The framework incorporates reciprocal effects among all interacting molecules. As a result, G-proteins and β-arrestins are in steric competition for binding to the cytoplasmic surface of either the G-protein-favoring or β-arrestin-favoring GPCR conformation. Moreover, through linkage relations, the strength of the interactions of G-proteins or β-arrestins with the corresponding active conformation potentiates the apparent affinity for the agonist, effectively equating these two proteins to allosteric modulators. The balance between response alternatives can also be influenced by the physiological concentrations of either G-proteins or β-arrestins, as well as by phosphorylation or interactions with positive or negative allosteric modulators. The nature of the interactions in the simulations presented suggests novel experimental tests to distinguish more fully among alternative mechanisms.
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Kinde MN, Chen Q, Lawless MJ, Mowrey DD, Xu J, Saxena S, Xu Y, Tang P. Conformational Changes Underlying Desensitization of the Pentameric Ligand-Gated Ion Channel ELIC. Structure 2015; 23:995-1004. [PMID: 25960405 DOI: 10.1016/j.str.2015.03.017] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Revised: 03/24/2015] [Accepted: 03/30/2015] [Indexed: 11/18/2022]
Abstract
Structural rearrangements underlying functional transitions of pentameric ligand-gated ion channels (pLGICs) are not fully understood. Using (19)F nuclear magnetic resonance and electron spin resonance spectroscopy, we found that ELIC, a pLGIC from Erwinia chrysanthemi, expanded the extracellular end and contracted the intracellular end of its pore during transition from the resting to an apparent desensitized state. Importantly, the contraction at the intracellular end of the pore likely forms a gate to restrict ion transport in the desensitized state. This gate differs from the hydrophobic gate present in the resting state. Conformational changes of the TM2-TM3 loop were limited to the N-terminal end. The TM4 helices and the TM3-TM4 loop appeared relatively insensitive to agonist-mediated structural rearrangement. These results indicate that conformational changes accompanying functional transitions are not uniform among different ELIC regions. This work also revealed the co-existence of multiple conformations for a given state and suggested asymmetric conformational arrangements in a homomeric pLGIC.
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Affiliation(s)
- Monica N Kinde
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Qiang Chen
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Matthew J Lawless
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - David D Mowrey
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA; Department of Computational & Systems Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Jiawei Xu
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Sunil Saxena
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Yan Xu
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA; Department of Pharmacology & Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA; Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Pei Tang
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA; Department of Pharmacology & Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA; Department of Computational & Systems Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA.
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Hossain S, Hashimoto M, Katakura M, Al Mamun A, Shido O. Medicinal value of asiaticoside for Alzheimer's disease as assessed using single-molecule-detection fluorescence correlation spectroscopy, laser-scanning microscopy, transmission electron microscopy, and in silico docking. Altern Ther Health Med 2015; 15:118. [PMID: 25880304 PMCID: PMC4422550 DOI: 10.1186/s12906-015-0620-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2014] [Accepted: 03/16/2015] [Indexed: 01/09/2023]
Abstract
BACKGROUND Identifying agents that inhibit amyloid beta peptide (Aβ) aggregation is the ultimate goal for slowing Alzheimer's disease (AD) progression. This study investigated whether the glycoside asiaticoside inhibits Aβ1-42 fibrillation in vitro. METHODS Fluorescence correlation spectroscopy (FCS), evaluating the Brownian diffusion times of moving particles in a small confocal volume at the single-molecule level, was used. If asiaticoside inhibits early Aβ1-42 fibrillation steps, more Aβs would remain free and rapidly diffuse in the confocal volume. In contrast, "weaker or no inhibition" permits a greater number of Aβs to polymerize into oligomers, leading to fibers and gives rise to slow diffusion times in the solution. Trace amounts of 5-carboxytetramethylrhodamine (TAMRA)-labeled Aβ1-42 in the presence of excess unlabeled Aβ1-42 (10 μM) was used as a fluorescent probe. Steady-state and kinetic-Thioflavin T (ThT) fluorospectroscopy, laser-scanning fluorescence microscopy (LSM), and transmission electron microscopy (TEM) were also used to monitor fibrillation. Binding of asiaticoside with Aβ1-42 at the atomic level was computationally examined using the Molegro Virtual Docker and PatchDock. RESULTS With 1 h of incubation time for aggregation, FCS data analysis revealed that the diffusion time of TAMRA-Aβ1-42 was 208 ± 4 μs, which decreased to 164 ± 8.0 μs in the presence of asiaticoside, clearly indicating that asiaticoside inhibited the early stages Aβ1-42 of fibrillation, leaving more free Aβs in the solution and permitting their rapid diffusion in the confocal volume. The inhibitory effects were also evidenced by reduced fiber formation as assessed by steady-state and kinetic ThT fluorospectroscopy, LSM, and TEM. Asiaticoside elongated the lag phase of Aβ1-42 fibrillation, indicating the formation of smaller amyloid species were impaired in the presence of asiaticoside. Molecular docking revealed that asiaticoside binds with amyloid intra- and inter-molecular amino acid residues, which are responsible for β-sheet formation and longitudinal extension of fibrils. CONCLUSION Finally, asiaticoside prevents amyloidogenesis that precedes neurodegeneration in patients with Alzheimer's disease.
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Dutta-Roy R, Rosenmund C, Edelstein SJ, Le Novère N. Ligand-dependent opening of the multiple AMPA receptor conductance states: a concerted model. PLoS One 2015; 10:e0116616. [PMID: 25629405 PMCID: PMC4309570 DOI: 10.1371/journal.pone.0116616] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2014] [Accepted: 11/21/2014] [Indexed: 01/27/2023] Open
Abstract
Modulation of the properties of AMPA receptors at the post-synaptic membrane is one of the main suggested mechanisms underlying fast synaptic transmission in the central nervous system of vertebrates. Electrophysiological recordings of single channels stimulated with agonists showed that both recombinant and native AMPA receptors visit multiple conductance states in an agonist concentration dependent manner. We propose an allosteric model of the multiple conductance states based on concerted conformational transitions of the four subunits, as an iris diaphragm. Our model predicts that the thermodynamic behaviour of the conductance states upon full and partial agonist stimulations can be described with increased affinity of receptors as they progress to higher conductance states. The model also predicts the existence of AMPA receptors in non-liganded conductive substates. However, the probability of spontaneous openings decreases with increasing conductances. Finally, we predict that the large conductance states are stabilized within the rise phase of a whole-cell EPSC in glutamatergic hippocampal neurons. Our model provides a mechanistic link between ligand concentration and conductance states that can explain thermodynamic and kinetic features of AMPA receptor gating.
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Affiliation(s)
- Ranjita Dutta-Roy
- Department of Medicine Solna, Karolinska Insitutet, 171 76 Stockholm, Sweden
- NWFZ, Charite Universitatsmedizin, 101 17 Berlin, Germany
- European Bioinformatics Institute (EMBL-EBI), Wellcome Trust Genome Campus, Hinxton, Cambridgeshire CB10 1SD, UK
| | | | | | - Nicolas Le Novère
- European Bioinformatics Institute (EMBL-EBI), Wellcome Trust Genome Campus, Hinxton, Cambridgeshire CB10 1SD, UK
- The Babraham Institute, Babraham, Cambridgeshire CB22 3AT, UK
- * E-mail:
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Weatherill EE, Wallace MI. Combining Single-Molecule Imaging and Single-Channel Electrophysiology. J Mol Biol 2015; 427:146-57. [DOI: 10.1016/j.jmb.2014.07.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Revised: 07/07/2014] [Accepted: 07/07/2014] [Indexed: 12/29/2022]
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Hellyer SD, Selwood AI, van Ginkel R, Munday R, Sheard P, Miles CO, Rhodes L, Kerr DS. In vitro labelling of muscle type nicotinic receptors using a fluorophore-conjugated pinnatoxin F derivative. Toxicon 2014; 87:17-25. [DOI: 10.1016/j.toxicon.2014.05.013] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Revised: 05/02/2014] [Accepted: 05/07/2014] [Indexed: 11/30/2022]
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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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8
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Schmauder R, Kosanic D, Hovius R, Vogel H. Correlated optical and electrical single-molecule measurements reveal conformational diffusion from ligand binding to channel gating in the nicotinic acetylcholine receptor. Chembiochem 2011; 12:2431-4. [PMID: 21915985 DOI: 10.1002/cbic.201100302] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2011] [Indexed: 11/11/2022]
Affiliation(s)
- Ralf Schmauder
- Laboratory of Physical Chemistry of Polymers and Membranes, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
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Taly A, Colas C, Malliavin T, Blondel A, Nilges M, Corringer PJ, Joseph D. Discrimination of agonists versus antagonists of nicotinic ligands based on docking onto AChBP structures. J Mol Graph Model 2011; 30:100-9. [PMID: 21764343 DOI: 10.1016/j.jmgm.2011.06.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2011] [Revised: 05/27/2011] [Accepted: 06/22/2011] [Indexed: 11/26/2022]
Abstract
Numerous high-resolution crystallographic structures of the acetylcholine binding protein (AChBP), a molluscan cholinergic protein, homologous to the extracellular domain of nicotinic acetylcholine receptors, are available. This offers opportunities to model the interaction between various ligands and the acetylcholine binding site. Herein we present a study of the interplay between ligand binding and motions of the C-loop capping the binding site. Nicotinic agonists and antagonists were docked on AChBP X-ray structures. It is shown that the studied agonists and antagonists can be discriminated according to their higher affinities for structures respectively obtained in the presence of agonists or antagonists, highlighting the fact that AChBP structures retain a pharmacological footprint of the compound used in crystallography experiments. A detailed analysis of the binding site cavities suggests that this property is mainly related to the shape of the cavities.
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Affiliation(s)
- Antoine Taly
- Laboratoire de Conception et Application de Molécules Bioactives, UMR 7199 CNRS-Université de Strasbourg, 74 Route du Rhin-BP 60024, 67401 Illkirch Cedex, France.
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10
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Ide T. Simultaneous Optical and Electrical Recording of Single Molecule Bonding to Single Channel Proteins. Chemphyschem 2010; 11:3408-11. [DOI: 10.1002/cphc.201000560] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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11
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Gleitsman KR, Shanata JAP, Frazier SJ, Lester HA, Dougherty DA. Long-range coupling in an allosteric receptor revealed by mutant cycle analysis. Biophys J 2009; 96:3168-78. [PMID: 19383461 DOI: 10.1016/j.bpj.2008.12.3949] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2008] [Revised: 12/12/2008] [Accepted: 12/15/2008] [Indexed: 11/26/2022] Open
Abstract
The functional coupling of residues that are far apart in space is the quintessential property of allosteric proteins. For example, in Cys-loop receptors, the gating of an intrinsic ion channel is allosterically regulated by the binding of small molecule neurotransmitters 50-60 A from the channel gate. Some residues near the binding site must have as their primary function the communication of the binding event to the gating region. These gating pathway residues are essential to function, but their identification and characterization can be challenging. This work introduces a simple strategy, derived from mutant cycle analysis, for identifying gating pathway residues using macroscopic measurements alone. In the exemplar Cys-loop receptor, the nicotinic acetylcholine receptor, a well-characterized reporter mutation (betaL9'S) known to impact gating, was combined with mutations of target residues in the ligand-binding domain hypothesized or previously found to be functionally significant. A mutant cycle analysis of the macroscopic EC(50) measurements can then provide insights into the role of the target residue. This new method, elucidating long-range functional coupling in allosteric receptors, can be applied to several reporter mutations in a wide variety of receptors to identify previously characterized and novel mutations that impact the gating pathway. We support our interpretation of macroscopic data with single-channel studies. Elucidating long-range functional coupling in allosteric receptors should be broadly applicable to determining functional roles of residues in allosteric receptors.
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Affiliation(s)
- Kristin R Gleitsman
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA
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Grandl J, Sakr E, Kotzyba-Hibert F, Krieger F, Bertrand S, Bertrand D, Vogel H, Goeldner M, Hovius R. Fluorescent Epibatidine Agonists for Neuronal and Muscle-Type Nicotinic Acetylcholine Receptors. Angew Chem Int Ed Engl 2007. [DOI: 10.1002/ange.200604807] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Grandl J, Sakr E, Kotzyba-Hibert F, Krieger F, Bertrand S, Bertrand D, Vogel H, Goeldner M, Hovius R. Fluorescent Epibatidine Agonists for Neuronal and Muscle-Type Nicotinic Acetylcholine Receptors. Angew Chem Int Ed Engl 2007; 46:3505-8. [PMID: 17385777 DOI: 10.1002/anie.200604807] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Jörg Grandl
- Laboratoire de Chimie Physique des Polymères et Membranes, Ecole Polytechniques Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
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Danelon C, Grandl J, Hovius R, Vogel H. Modulation of proton-induced current fluctuations in the human nicotinic acetylcholine receptor channel. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:76-89. [PMID: 16956576 DOI: 10.1016/j.bbamem.2006.07.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2006] [Revised: 06/12/2006] [Accepted: 07/13/2006] [Indexed: 02/03/2023]
Abstract
The nicotinic acetylcholine receptor (nAChR) is a ligand-gated ion channel that switches upon activation from a closed state to a full conducting state. We found that the mutation delta S268K, located at 12' position of the second transmembrane domain of the delta subunit of the human nAChR generates a long-lived intermediate conducting state, from which openings to a wild-type like conductance level occur on a submillisecond time scale. Aiming to understand the interplay between structural changes near the 12' position and channel gating, we investigated the influence of various parameters: different ligands (acetylcholine, choline and epibatidine), ligand concentrations, transmembrane voltages and both fetal and adult nAChRs. Since sojourns in the high conductance state are not fully resolved in time, spectral noise analysis was used as a complement to dwell time analysis to determine the gating rate constants. Open channel current fluctuations are described by a two-state Markov model. The characteristic time of the process is markedly influenced by the ligand and the receptor type, whereas the frequency of openings to the high conductance state increases with membrane hyperpolarization. Conductance changes are discussed with regard to reversible transfer reaction of single protons at the lysine 12' side chain.
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Affiliation(s)
- Christophe Danelon
- Laboratory of Physical Chemistry of Polymers and Membranes, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
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Changeux JP, Edelstein SJ. Allosteric receptors after 30 years. RENDICONTI LINCEI-SCIENZE FISICHE E NATURALI 2006. [DOI: 10.1007/bf02904502] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Abstract
The members of the pentameric ligand-gated receptor channel family are involved in information transfer in synapses and the neuromuscular junction. They often contain several copies of the same subunit isoform. Here, we present a method to functionally dissect the role of individual subunits that occur in multiple copies in these receptors. Opening of the inherent chloride channel in the GABA(A) receptor is achieved through the binding of two agonist molecules; however, it has been difficult to obtain information on the contribution of the two individual binding sites. The sites are both located at beta+/alpha- subunit interfaces, suggesting similar properties. One pair of subunits is flanked by gamma and beta (site 1) and the other by alpha and gamma (site 2), the different environment possibly affecting the binding sites. Here, we used concatenated subunits and two point mutations of amino acid residues, each in alpha and beta subunits, both located in the agonist binding pocket, to investigate the properties of these two sites. The sites were individually mutated, and consequences of these mutations on GABA and muscimol-induced channel opening and its competitive inhibition by bicuculline were studied. A model predicts that opening also occurs for receptors occupied with a single agonist molecule but is promoted approximately 60-fold in those occupied by two agonists and that site 2 has an approximately threefold higher affinity for GABA than site 1, whereas muscimol and bicuculline show some preference for site 1.
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Changeux J, Edelstein SJ. Allosteric mechanisms in normal and pathological nicotinic acetylcholine receptors. Curr Opin Neurobiol 2001; 11:369-77. [PMID: 11399437 DOI: 10.1016/s0959-4388(00)00221-x] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Recent chemical and advanced structural studies on site-directed and naturally occurring pathological mutants of individual members of the multigene family of nicotinic acetylcholine receptors have yielded structure-function relationships supporting indirect 'allosteric' interactions between the acetylcholine-binding sites and the ion channel in signal transduction.
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Affiliation(s)
- J Changeux
- Laboratoire de Neurobiologie Moléculaire, Institut Pasteur, 25 rue du Dr Roux, 75724 Cedex 15, Paris, France.
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Schmidt C, Mayer M, Vogel H. A Chip-Based Biosensor for the Functional Analysis of Single Ion Channels We thank E. Ermanntraut, L. Giovangrandi, T. Wohland, A. Brecht, M. Köhler, C. Bieri, D. Stamou, and R. Hovius for advice. This work was supported by the Swiss National Science Foundation (Priority Program for Biotechnology) and by an interdepartmental grant of the Swiss Federal Institute of Technology Lausanne (EPFL, Project Microtechnique 96). Angew Chem Int Ed Engl 2000; 39:3137-3140. [PMID: 11028058 DOI: 10.1002/1521-3773(20000901)39:17<3137::aid-anie3137>3.0.co;2-d] [Citation(s) in RCA: 191] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- C Schmidt
- Institute of Physical Chemistry Swiss Federal Institute of Technology 1015 Lausanne (Switzerland)
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Wohland T, Friedrich K, Hovius R, Vogel H. Study of ligand-receptor interactions by fluorescence correlation spectroscopy with different fluorophores: evidence that the homopentameric 5-hydroxytryptamine type 3As receptor binds only one ligand. Biochemistry 1999; 38:8671-81. [PMID: 10393542 DOI: 10.1021/bi990366s] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The 5-hydroxytryptamine receptor of type 3 was investigated by fluorescence correlation spectroscopy (FCS). Binding constants of fluorescently labeled ligands, the stoichiometry, and the mass of the receptor are readily accessible by this technique, while the duration of measurement is on the order of seconds to minutes. The receptor antagonist 1,2,3, 9-tetrahydro-3-[(5-methyl-1H-imidazol-4-yl)methyl]-9-(3-aminopropyl)- 4H-carbazol-4-one (GR-H) was labeled with the fluorophores rhodamine 6G, fluorescein, N-[7-nitrobenz-2-oxa-1,3-diazol-4-yl], and the cyanine dye Cy5. These labels cover a large part of the visible electromagnetic spectrum. It is shown that the photophysical and chemical properties have a direct influence on the measurement quality (duration of measurement, signal-to-noise ratio) and the ligand-receptor interactions (dissociation constants), respectively. This makes it necessary to choose a suitable label or a combination of labels for receptor studies. The affinities of the fluorescently labeled ligands determined by FCS were virtually identical to the values obtained by radioligand binding experiments. Moreover, the dissociation constant of a nonfluorescent receptor ligand was determined successfully by an FCS competition assay. The experimental results showed that only one antagonist binds to the receptor, in agreement with measurements previously published [Tairi et al. (1998) Biochemistry 37, 15850-15864].
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Affiliation(s)
- T Wohland
- Laboratory of Physical Chemistry of Polymers and Membranes, Chemistry Department, Swiss Federal Institute of Technology, Lausanne, Switzerland
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21
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Affiliation(s)
- J P Changeux
- Neurobiologie Moléculaire Institut Pasteur, Paris, France.
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22
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Edelstein SJ, Changeux JP. Allosteric transitions of the acetylcholine receptor. ADVANCES IN PROTEIN CHEMISTRY 1998; 51:121-84. [PMID: 9615170 DOI: 10.1016/s0065-3233(08)60652-x] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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Soper SA, Warner IM, McGown LB. Molecular Fluorescence, Phosphorescence, and Chemiluminescence Spectrometry. Anal Chem 1998. [DOI: 10.1021/a1980019y] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Steven A. Soper
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, and Department of Chemistry, Duke University, Box 90346, Durham, North Carolina 27708-0346
| | - Isiah M. Warner
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, and Department of Chemistry, Duke University, Box 90346, Durham, North Carolina 27708-0346
| | - Linda B. McGown
- Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, and Department of Chemistry, Duke University, Box 90346, Durham, North Carolina 27708-0346
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Léna C, Changeux JP. Allosteric nicotinic receptors, human pathologies. JOURNAL OF PHYSIOLOGY, PARIS 1998; 92:63-74. [PMID: 9782446 DOI: 10.1016/s0928-4257(98)80140-x] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Nicotinic acetylcholine receptors are ligand-gated ion channels present in muscle and brain. These allosteric oligomers may exist in several conformational states which include a resting state, an open-channel state, and a desensitized refractory state. Recent work has shown that point mutations in the nicotinic receptor may, altogether, abolish desensitization, increase apparent affinity for agonists and convert the effect of a competitive antagonist into an agonist response. These pleiotropic effects are interpreted in terms of the allosteric model. This paper reviews recent evidence that such mutations occur spontaneously in humans and may cause diseases such as congenital myasthenia or familial frontal lobe epilepsy. In addition, nicotinic receptors are involved in tobacco smoking. Accumulating evidence, including experiments with knock-out animals, indicates that addiction to nicotine is linked to the activation of beta 2-subunit containing nicotinic receptors in the dopaminergic mesolimbic neurons which are part of the reward systems in the brain. Current research also indicates that nicotinic agonists might serve as therapeutic agents for Alzheimer's disease and Tourette's syndrome, as well as for schizophrenia. This paper extends and updates a recently published review.
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Affiliation(s)
- C Léna
- CNRS UA 1284, Institut Pasteur, Paris, France
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Edelstein SJ, Schaad O, Changeux JP. Myasthenic nicotinic receptor mutant interpreted in terms of the allosteric model. COMPTES RENDUS DE L'ACADEMIE DES SCIENCES. SERIE III, SCIENCES DE LA VIE 1997; 320:953-61. [PMID: 9587473 DOI: 10.1016/s0764-4469(97)82468-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
An extended Monod-Wyman-Changeux allosteric-type model is applied to human muscle nicotinic acetylcholine receptors expressed in HEK cells, for both the normal form and the high-affinity human myasthenic mutant, epsilon T264P. The model is based on a concerted transition between the basal (resting) B state and the active (open-channel) A state, with the equilibrium in the absence of ligand determined by the allosteric constant, L0 = [B0]/[A0]. For wild-type receptors the model with L0 = 9 x 10(8) provides a satisfactory representation of published patch-clamp recordings that yields a distribution of open-channel dwell times with a single peak at 0.7 ms. For the epsilon T264P mutant, the model with L0 = 100 accounts for the trimodal distribution reported for open-channel dwell times, with peaks at 0.15, 3.8 and 60 ms that correspond to non-, mono- and bi-liganded receptors, respectively. Possible applications of the allosteric model to other myasthenic mutants are considered.
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Affiliation(s)
- S J Edelstein
- Département de biochimie, université de Genève, Switzerland
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