1
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Mukhtasimova N, Bouzat C, Sine SM. Novel interplay between agonist and calcium binding sites modulates drug potentiation of α7 acetylcholine receptor. Cell Mol Life Sci 2024; 81:332. [PMID: 39110172 PMCID: PMC11335256 DOI: 10.1007/s00018-024-05374-1] [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: 05/17/2024] [Revised: 07/15/2024] [Accepted: 07/18/2024] [Indexed: 08/22/2024]
Abstract
Drug modulation of the α7 acetylcholine receptor has emerged as a therapeutic strategy for neurological, neurodegenerative, and inflammatory disorders. α7 is a homo-pentamer containing topographically distinct sites for agonists, calcium, and drug modulators with each type of site present in five copies. However, functional relationships between agonist, calcium, and drug modulator sites remain poorly understood. To investigate these relationships, we manipulated the number of agonist binding sites, and monitored potentiation of ACh-elicited single-channel currents through α7 receptors by PNU-120596 (PNU) both in the presence and absence of calcium. When ACh is present alone, it elicits brief, sub-millisecond channel openings, however when ACh is present with PNU it elicits long clusters of potentiated openings. In receptors harboring five agonist binding sites, PNU potentiates regardless of the presence or absence of calcium, whereas in receptors harboring one agonist binding site, PNU potentiates in the presence but not the absence of calcium. By varying the numbers of agonist and calcium binding sites we show that PNU potentiation of α7 depends on a balance between agonist occupancy of the orthosteric sites and calcium occupancy of the allosteric sites. The findings suggest that in the local cellular environment, fluctuations in the concentrations of neurotransmitter and calcium may alter this balance and modulate the ability of PNU to potentiate α7.
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Affiliation(s)
- Nuriya Mukhtasimova
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine and Science, Rochester, MN, USA
| | - Cecilia Bouzat
- Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur and Instituto de Investigaciones Bioquímicas de Bahía Blanca, Consejo Nacional de Investigaciones Científicas y Técnicas, Bahía Blanca, Argentina
| | - Steven M Sine
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine and Science, Rochester, MN, USA.
- Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic College of Medicine and Science, Rochester, MN, USA.
- Department of Neurology, Mayo Clinic College of Medicine and Science, Rochester, MN, USA.
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2
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Davolio AJ, J. Jankowski W, Várnai C, Irwin BWJ, Payne MC, Chau PL. Efficiently Differentiating Agonists and Competitive Antagonists for Weak Allosteric Protein-Ligand Interactions with Linear Response Theory. ACS OMEGA 2023; 8:44537-44544. [PMID: 38046342 PMCID: PMC10688131 DOI: 10.1021/acsomega.3c03503] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/19/2023] [Accepted: 09/05/2023] [Indexed: 12/05/2023]
Abstract
What makes an agonist and a competitive antagonist? In this work, we aim to answer this question by performing parallel tempering Monte Carlo simulations on the serotonin type 3A (5-HT3A) receptor. We use linear response theory to predict conformational changes in the 5-HT3A receptor active site after weak perturbations are applied to its allosteric binding sites. A covariance tensor is built from conformational sampling of its apo state, and a harmonic approximation allows us to substitute the calculation of ligand-induced forces with the binding site's displacement vector. Remarkably, our study demonstrates the feasibility of effectively discerning between agonists and competitive antagonists for multiple ligands, requiring computationally expensive calculations only once per protein.
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Affiliation(s)
- Anthony J. Davolio
- Theory
of Condensed Matter Group, Department of Physics, University of Cambridge, Cambridge CB3 0HE, U.K.
| | - Wojciech J. Jankowski
- Theory
of Condensed Matter Group, Department of Physics, University of Cambridge, Cambridge CB3 0HE, U.K.
| | - Csilla Várnai
- Centre
for Computational Biology, University of
Birmingham, Birmingham B15 2TT, U.K.
- Institute
of Cancer and Genomic Sciences, University of Birmingham, Birmingham B15 2SY, U.K.
| | - Benedict W. J. Irwin
- Theory
of Condensed Matter Group, Department of Physics, University of Cambridge, Cambridge CB3 0HE, U.K.
| | - Michael C. Payne
- Theory
of Condensed Matter Group, Department of Physics, University of Cambridge, Cambridge CB3 0HE, U.K.
| | - Pak-Lee Chau
- Bioinformatique
Structurale, Institut Pasteur, CNRS URA
3528, CB3I CNRS USR 3756, 75724 Paris, France
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3
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Kinoshita M, Okamoto H. Acetylcholine potentiates glutamate transmission from the habenula to the interpeduncular nucleus in losers of social conflict. Curr Biol 2023:S0960-9822(23)00445-1. [PMID: 37105168 DOI: 10.1016/j.cub.2023.03.087] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Revised: 03/02/2023] [Accepted: 03/31/2023] [Indexed: 04/29/2023]
Abstract
Switching behaviors from aggression to submission in losers at the end of conspecific social fighting is essential to avoid serious injury or death. We have previously shown that the experience of defeat induces a loser-specific potentiation in the habenula (Hb)-interpeduncular nucleus (IPN) and show here that this is induced by acetylcholine. Calcium imaging and electrophysiological recording using acute brain slices from winners and losers of fighting behavior in zebrafish revealed that the ventral IPN (vIPN) dominates over the dorsal IPN in the neural response to Hb stimulation in losers. We also show that GluA1 α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits on the postsynaptic membrane increased in the vIPN of losers. Furthermore, these loser-specific neural properties disappeared in the presence of an α7 nicotinic acetylcholine receptor (nAChR) antagonist and, conversely, were induced in brain slices of winners treated with α7 nAChR agonists. These data suggest that acetylcholine released from Hb terminals in the vIPN induces activation of α7 nAChR followed by an increase in postsynaptic membrane GluA1. This results in an increase in active synapses on postsynaptic neurons, resulting in the potentiation of neurotransmissions to the vIPN. This acetylcholine-induced neuromodulation could be the neural foundation for behavioral switching in losers. Our results could increase our understanding of the mechanisms of various mood disorders such as social anxiety disorder and social withdrawal.
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Affiliation(s)
- Masae Kinoshita
- Laboratory for Neural Circuit Dynamics of Decision Making, RIKEN Center for Brain Science, Saitama 351-0198, Japan
| | - Hitoshi Okamoto
- Laboratory for Neural Circuit Dynamics of Decision Making, RIKEN Center for Brain Science, Saitama 351-0198, Japan; RIKEN CBS-Kao Collaboration Center, Saitama 351-0198, Japan.
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4
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Tessier CJG, Emlaw JR, Sturgeon RM, daCosta CJB. Derepression may masquerade as activation in ligand-gated ion channels. Nat Commun 2023; 14:1907. [PMID: 37019877 PMCID: PMC10076327 DOI: 10.1038/s41467-023-36770-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2022] [Accepted: 02/16/2023] [Indexed: 04/07/2023] Open
Abstract
Agonists are ligands that bind to receptors and activate them. In the case of ligand-gated ion channels, such as the muscle-type nicotinic acetylcholine receptor, mechanisms of agonist activation have been studied for decades. Taking advantage of a reconstructed ancestral muscle-type β-subunit that forms spontaneously activating homopentamers, here we show that incorporation of human muscle-type α-subunits appears to repress spontaneous activity, and furthermore that the presence of agonist relieves this apparent α-subunit-dependent repression. Our results demonstrate that rather than provoking channel activation/opening, agonists may instead 'inhibit the inhibition' of intrinsic spontaneous activity. Thus, agonist activation may be the apparent manifestation of agonist-induced derepression. These results provide insight into intermediate states that precede channel opening and have implications for the interpretation of agonism in ligand-gated ion channels.
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Affiliation(s)
- Christian J G Tessier
- Department of Chemistry and Biomolecular Sciences, Centre for Chemical and Synthetic Biology, University of Ottawa, Ottawa, ON, Canada
| | - Johnathon R Emlaw
- Department of Chemistry and Biomolecular Sciences, Centre for Chemical and Synthetic Biology, University of Ottawa, Ottawa, ON, Canada
| | - Raymond M Sturgeon
- Department of Chemistry and Biomolecular Sciences, Centre for Chemical and Synthetic Biology, University of Ottawa, Ottawa, ON, Canada
| | - Corrie J B daCosta
- Department of Chemistry and Biomolecular Sciences, Centre for Chemical and Synthetic Biology, University of Ottawa, Ottawa, ON, Canada.
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5
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Sanders VR, Millar NS. Potentiation and allosteric agonist activation of α7 nicotinic acetylcholine receptors: binding sites and hypotheses. Pharmacol Res 2023; 191:106759. [PMID: 37023990 DOI: 10.1016/j.phrs.2023.106759] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/06/2023] [Revised: 03/27/2023] [Accepted: 03/30/2023] [Indexed: 04/07/2023]
Abstract
Considerable progress has been made in recent years towards the identification and characterisation of novel subtype-selective modulators of nicotinic acetylcholine receptors (nAChRs). In particular, this has focussed on modulators of α7 nAChRs, a nAChR subtype that has been identified as a target for drug discovery in connection with a range of potential therapeutic applications. This review focusses upon α7-selective modulators that bind to receptor sites other than the extracellular 'orthosteric' agonist binding site for the endogenous agonist acetylcholine (ACh). Such compounds include those that are able to potentiate responses evoked by orthosteric agonists such as ACh (positive allosteric modulators; PAMs) and those that are able to activate α7 nAChRs by direct allosteric activation in the absence of an orthosteric agonist (allosteric agonists or 'ago-PAMs'). There has been considerable debate about the mechanism of action of α7-selective PAMs and allosteric agonists, much of which has centred around identifying the location of their binding sites on α7 nAChRs. Based on a variety of experimental evidence, including recent structural data, there is now clear evidence indicating that at least some α7-selective PAMs bind to an inter-subunit site located in the transmembrane domain. In contrast, there are differing hypotheses about the site or sites at which allosteric agonists bind to α7 nAChRs. It will be argued that the available evidence supports the conclusion that direct allosteric activation by allosteric agonists/ago-PAMs occurs via the same inter-subunit transmembrane site that has been identified for several α7-selective PAMs.
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Affiliation(s)
- Victoria R Sanders
- Division of Biosciences, University College London, London WC1E 6BT, United Kingdom
| | - Neil S Millar
- Division of Biosciences, University College London, London WC1E 6BT, United Kingdom.
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6
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Li Z, Chan KC, Nickels JD, Cheng X. Molecular Dynamics Refinement of Open State Serotonin 5-HT 3A Receptor Structures. J Chem Inf Model 2023; 63:1196-1207. [PMID: 36757760 DOI: 10.1021/acs.jcim.2c01441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Abstract
Pentameric ligand-gated ion channels play an important role in mediating fast neurotransmissions. As a member of this receptor family, cation-selective 5-HT3 receptors are a clinical target for treating nausea and vomiting associated with chemotherapy and radiation therapy (Thompson and Lummis, 2006). Multiple cryo-electron microscopy (cryo-EM) structures of 5-HT3 receptors have been determined in distinct functional states (e.g., open, closed, etc.) (Basak et al., 2018; Basak et al., 2018; Polovinkin et al., 2018; Zhang et al., 2015). However, recent work has shown that the transmembrane pores of the open 5-HT3 receptor structures rapidly collapse and become artificially asymmetric in molecular dynamics (MD) simulations. To avoid this hydrophobic collapse, Dämgen and Biggin developed an equilibration protocol that led to a stable open state structure of the glycine receptor in MD simulations (Dämgen and Biggin, 2020). However, the protocol failed to yield open-like structures of the 5-HT3 receptor in our simulations. Here, we present a refined equilibration protocol that involves the rearrangement of the transmembrane helices to achieve stable open state structures of the 5-HT3 receptor that allow both water and ion permeation through the channel. Notably, channel gating is mediated through collective movement of the transmembrane helices, involving not only pore lining M2 helices but also their cross-talk with the adjacent M1 and M3 helices. Thus, the successful application of our refined equilibration protocol underscores the importance of the conformational coupling between the transmembrane helices in stabilizing open-like structures of the 5-HT3 receptor.
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Affiliation(s)
- Zoe Li
- Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy at The Ohio State University, Columbus, Ohio 43210, United States
| | - Kevin C Chan
- Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy at The Ohio State University, Columbus, Ohio 43210, United States
| | - Jonathan D Nickels
- Department of Chemical and Environmental Engineering, University of Cincinnati, Cincinnati, Ohio 45221, United States
| | - Xiaolin Cheng
- Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy at The Ohio State University, Columbus, Ohio 43210, United States.,Translational Data Analytics Institute (TDAI) at The Ohio State University, Columbus, Ohio 43210, United States
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7
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Asymmetric opening of the homopentameric 5-HT 3A serotonin receptor in lipid bilayers. Nat Commun 2021; 12:1074. [PMID: 33594077 PMCID: PMC7887223 DOI: 10.1038/s41467-021-21016-7] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Accepted: 01/06/2021] [Indexed: 12/13/2022] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) of the Cys-loop receptor family are key players in fast signal transduction throughout the nervous system. They have been shown to be modulated by the lipid environment, however the underlying mechanism is not well understood. We report three structures of the Cys-loop 5-HT3A serotonin receptor (5HT3R) reconstituted into saposin-based lipid bilayer discs: a symmetric and an asymmetric apo state, and an asymmetric agonist-bound state. In comparison to previously published 5HT3R conformations in detergent, the lipid bilayer stabilises the receptor in a more tightly packed, ‘coupled’ state, involving a cluster of highly conserved residues. In consequence, the agonist-bound receptor conformation adopts a wide-open pore capable of conducting sodium ions in unbiased molecular dynamics (MD) simulations. Taken together, we provide a structural basis for the modulation of 5HT3R by the membrane environment, and a model for asymmetric activation of the receptor. Pentameric ligand-gated ion channels (pLGICs) are key players in neurotransmission and have been shown to be modulated by the lipid environment, however the underlying mechanism is not well understood. Here, the authors report structures of the pLGIC 5-HT3A serotonin receptor reconstituted into lipid bilayer discs and reveal lipid–protein interactions as well as asymmetric activation of the homopentameric receptor.
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8
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Gibbs E, Chakrapani S. Structure, Function and Physiology of 5-Hydroxytryptamine Receptors Subtype 3. Subcell Biochem 2021; 96:373-408. [PMID: 33252737 DOI: 10.1007/978-3-030-58971-4_11] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
5-hydroxytryptamine receptor subtype 3 (5-HT3R) is a pentameric ligand-gated ion channel (pLGIC) involved in neuronal signaling. It is best known for its prominent role in gut-CNS signaling though there is growing interest in its other functions, particularly in modulating non-serotonergic synaptic activity. Recent advances in structural biology have provided mechanistic understanding of 5-HT3R function and present new opportunities for the field. This chapter gives a broad overview of 5-HT3R from a physiological and structural perspective and then discusses the specific details of ion permeation, ligand binding and allosteric coupling between these two events. Biochemical evidence is summarized and placed within a physiological context. This perspective underscores the progress that has been made as well as outstanding challenges and opportunities for future 5-HT3R research.
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Affiliation(s)
- Eric Gibbs
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, 44106-4970, USA.
| | - Sudha Chakrapani
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, 44106-4970, USA. .,Department of Neuroscience, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106-4970, USA.
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9
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Moglie MJ, Marcovich I, Corradi J, Carpaneto Freixas AE, Gallino S, Plazas PV, Bouzat C, Lipovsek M, Elgoyhen AB. Loss of Choline Agonism in the Inner Ear Hair Cell Nicotinic Acetylcholine Receptor Linked to the α10 Subunit. Front Mol Neurosci 2021; 14:639720. [PMID: 33613194 PMCID: PMC7892445 DOI: 10.3389/fnmol.2021.639720] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2020] [Accepted: 01/11/2021] [Indexed: 11/13/2022] Open
Abstract
The α9α10 nicotinic acetylcholine receptor (nAChR) plays a fundamental role in inner ear physiology. It mediates synaptic transmission between efferent olivocochlear fibers that descend from the brainstem and hair cells of the auditory sensory epithelium. The α9 and α10 subunits have undergone a distinct evolutionary history within the family of nAChRs. Predominantly in mammalian vertebrates, the α9α10 receptor has accumulated changes at the protein level that may ultimately relate to the evolutionary history of the mammalian hearing organ. In the present work, we investigated the responses of α9α10 nAChRs to choline, the metabolite of acetylcholine degradation at the synaptic cleft. Whereas choline is a full agonist of chicken α9α10 receptors it is a partial agonist of the rat receptor. Making use of the expression of α9α10 heterologous receptors, encompassing wild-type, heteromeric, homomeric, mutant, chimeric, and hybrid receptors, and in silico molecular docking, we establish that the mammalian (rat) α10 nAChR subunit underscores the reduced efficacy of choline. Moreover, we show that whereas the complementary face of the α10 subunit does not play an important role in the activation of the receptor by ACh, it is strictly required for choline responses. Thus, we propose that the evolutionary changes acquired in the mammalian α9α10 nAChR resulted in the loss of choline acting as a full agonist at the efferent synapse, without affecting the triggering of ACh responses. This may have accompanied the fine-tuning of hair cell post-synaptic responses to the high-frequency activity of efferent medial olivocochlear fibers that modulate the cochlear amplifier.
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Affiliation(s)
- Marcelo J. Moglie
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular “Dr. Héctor N. Torres” (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
| | - Irina Marcovich
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular “Dr. Héctor N. Torres” (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
| | - Jeremías Corradi
- Departamento de Biología, Bioquímica y Farmacia, Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Universidad Nacional del Sur y Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| | - Agustín E. Carpaneto Freixas
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular “Dr. Héctor N. Torres” (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
| | - Sofía Gallino
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular “Dr. Héctor N. Torres” (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
| | - Paola V. Plazas
- Instituto de Farmacología, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Cecilia Bouzat
- Departamento de Biología, Bioquímica y Farmacia, Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Universidad Nacional del Sur y Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| | - Marcela Lipovsek
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular “Dr. Héctor N. Torres” (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
- Centre for Developmental Neurobiology, King’s College London, Institute of Psychiatry, Psychology, and Neuroscience, Guy’s Campus, London, United Kingdom
| | - Ana Belén Elgoyhen
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular “Dr. Héctor N. Torres” (INGEBI), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina
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10
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Prevost MS, Bouchenaki H, Barilone N, Gielen M, Corringer PJ. Concatemers to re-investigate the role of α5 in α4β2 nicotinic receptors. Cell Mol Life Sci 2021; 78:1051-1064. [PMID: 32472188 PMCID: PMC11071962 DOI: 10.1007/s00018-020-03558-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Revised: 05/15/2020] [Accepted: 05/22/2020] [Indexed: 01/08/2023]
Abstract
Nicotinic acetylcholine receptors (nAChRs) are pentameric ion channels expressed in the central nervous systems. nAChRs containing the α4, β2 and α5 subunits are specifically involved in addictive processes, but their functional architecture is poorly understood due to the intricacy of assembly of these subunits. Here we constrained the subunit assembly by designing fully concatenated human α4β2 and α4β2α5 receptors and characterized their properties by two-electrodes voltage-clamp electrophysiology in Xenopus oocytes. We found that α5-containing nAChRs are irreversibly blocked by methanethiosulfonate (MTS) reagents through a covalent reaction with a cysteine present only in α5. MTS-block experiments establish that the concatemers are expressed in intact form at the oocyte surface, but that reconstitution of nAChRs from loose subunits show inefficient and highly variable assembly of α5 with α4 and β2. Mutational analysis shows that the concatemers assemble both in clockwise and anticlockwise orientations, and that α5 does not contribute to ACh binding from its principal (+) site. Reinvestigation of suspected α5-ligands such as galantamine show no specific effect on α5-containing concatemers. Analysis of the α5-D398N mutation that is linked to smoking and lung cancer shows no significant effect on the electrophysiological function, suggesting that its effect might arise from alteration of other cellular processes. The concatemeric strategy provides a well-characterized platform for mechanistic analysis and screening of human α5-specific ligands.
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Affiliation(s)
- Marie S Prevost
- Unité Récepteurs-Canaux, Institut Pasteur, UMR 3571, CNRS, 75015, Paris, France
| | - Hichem Bouchenaki
- Unité Récepteurs-Canaux, Institut Pasteur, UMR 3571, CNRS, 75015, Paris, France
| | - Nathalie Barilone
- Unité Récepteurs-Canaux, Institut Pasteur, UMR 3571, CNRS, 75015, Paris, France
| | - Marc Gielen
- Unité Récepteurs-Canaux, Institut Pasteur, UMR 3571, CNRS, 75015, Paris, France.
- Sorbonne Université, 21, rue de l'école de médecine, 75006, Paris, France.
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11
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Rodriguez Araujo N, Fabiani C, Mazzarini Dimarco A, Bouzat C, Corradi J. Orthosteric and Allosteric Activation of Human 5-HT 3A Receptors. Biophys J 2020; 119:1670-1682. [PMID: 32946769 DOI: 10.1016/j.bpj.2020.08.029] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Revised: 07/18/2020] [Accepted: 08/24/2020] [Indexed: 12/24/2022] Open
Abstract
The serotonin type 3 receptor (5-HT3) is a ligand-gated ion channel that converts the binding of the neurotransmitter serotonin (5-HT) into a transient cation current that mediates fast excitatory responses in peripheral and central nervous systems. Information regarding the activation and modulation of the human 5-HT3 type A receptor has been based only on macroscopic current measurements because of its low ion conductance. By constructing a high-conductance human 5-HT3A receptor, we here revealed mechanistic information regarding the orthosteric activation by 5-HT and by the partial agonist tryptamine, and the allosteric activation by the terpenoids, carvacrol, and thymol. Terpenoids potentiated macroscopic currents elicited by the orthosteric agonist and directly elicited currents with slow-rising phases and submaximal amplitudes. At the single-channel level, activation by orthosteric and allosteric agonists appeared as openings in quick succession (bursts) that showed no ligand concentration dependence. Bursts were grouped into long-duration clusters in the presence of 5-HT and even longer in the presence of terpenoids, whereas they remained isolated in the presence of tryptamine. Kinetic analysis revealed that allosteric and orthosteric activation mechanisms can be described by the same scheme that includes transitions of the agonist-bound receptor to closed intermediate states before opening (priming). Reduced priming explained the partial agonism of tryptamine; however, equilibrium constants for gating and priming were similar for 5-HT and terpenoid activation. Thus, our kinetic analysis revealed that terpenoids are efficacious agonists for 5-HT3A receptors. These findings not only extend our knowledge about the human 5-HT3A molecular function but also provide novel insights into the mechanisms of action of allosteric ligands, which are of increasing interest as therapeutic drugs in all the superfamily.
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Affiliation(s)
- Noelia Rodriguez Araujo
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur (UNS)-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina
| | - Camila Fabiani
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur (UNS)-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina
| | - Albano Mazzarini Dimarco
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur (UNS)-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina
| | - Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur (UNS)-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina.
| | - Jeremías Corradi
- Instituto de Investigaciones Bioquímicas de Bahía Blanca (INIBIBB), Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur (UNS)-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Bahía Blanca, Argentina.
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12
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Absalom NL, Liao VW, Chebib M. Ligand-gated ion channels in genetic disorders and the question of efficacy. Int J Biochem Cell Biol 2020; 126:105806. [DOI: 10.1016/j.biocel.2020.105806] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2020] [Revised: 07/06/2020] [Accepted: 07/13/2020] [Indexed: 01/13/2023]
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13
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Papke RL, Lindstrom JM. Nicotinic acetylcholine receptors: Conventional and unconventional ligands and signaling. Neuropharmacology 2020; 168:108021. [PMID: 32146229 PMCID: PMC7610230 DOI: 10.1016/j.neuropharm.2020.108021] [Citation(s) in RCA: 66] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2019] [Revised: 02/05/2020] [Accepted: 02/25/2020] [Indexed: 12/28/2022]
Abstract
Postsynaptic nAChRs in the peripheral nervous system are critical for neuromuscular and autonomic neurotransmission. Pre- and peri-synaptic nAChRs in the brain modulate neurotransmission and are responsible for the addictive effects of nicotine. Subtypes of nAChRs in lymphocytes and non-synaptic locations may modulate inflammation and other cellular functions. All AChRs that function as ligand-gated ion channels are formed from five homologous subunits organized to form a central cation channel whose opening is regulated by ACh bound at extracellular subunit interfaces. nAChR subtype subunit composition can range from α7 homomers to α4β2α6β2β3 heteromers. Subtypes differ in affinities for ACh and other agonists like nicotine and in efficiencies with which their channels are opened and desensitized. Subtypes also differ in affinities for antagonists and for positive and negative allosteric modulators. Some agonists are "silent" with respect to channel opening, and AChRs may be able to signal metabotropic pathways by releasing G-proteins independent of channel opening. Electrophysiological studies that can resolve single-channel openings and molecular genetic approaches have allowed characterization of the structures of ligand binding sites, the cation channel, and the linkages between them, as well as the organization of AChR subunits and their contributions to function. Crystallography and cryo-electron-microscopy are providing increasing insights into the structures and functions of AChRs. However, much remains to be learned about both AChR structure and function, the in vivo functional roles of some AChR subtypes, and the development of better pharmacological tools directed at AChRs to treat addiction, pain, inflammation, and other medically important issues. This article is part of the special issue on 'Contemporary Advances in Nicotine Neuropharmacology'.
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Affiliation(s)
- Roger L Papke
- Department of Pharmacology and Therapeutics, University of Florida, P.O. Box 100267, Gainesville, FL, 32610-0267, USA.
| | - Jon M Lindstrom
- Department of Neuroscience, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
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van Goethem NP, Paes D, Puzzo D, Fedele E, Rebosio C, Gulisano W, Palmeri A, Wennogle LP, Peng Y, Bertrand D, Prickaerts J. Antagonizing α7 nicotinic receptors with methyllycaconitine (MLA) potentiates receptor activity and memory acquisition. Cell Signal 2019; 62:109338. [PMID: 31176021 DOI: 10.1016/j.cellsig.2019.06.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Revised: 06/03/2019] [Accepted: 06/03/2019] [Indexed: 12/11/2022]
Abstract
α7 nicotinic acetylcholine receptors (α7nAChRs) have been targeted to improve cognition in different neurological and psychiatric disorders. Nevertheless, no α7nAChR activating ligand has been clinically approved. Here, we investigated the effects of antagonizing α7nAChRs using the selective antagonist methyllycaconitine (MLA) on receptor activity in vitro and cognitive functioning in vivo. Picomolar concentrations of MLA significantly potentiated receptor responses in electrophysiological experiments mimicking the in vivo situation. Furthermore, microdialysis studies showed that MLA administration substantially increased hippocampal glutamate efflux which is related to memory processes. Accordingly, pre-tetanus administration of low MLA concentrations produced longer lasting potentiation (long-term potentiation, LTP) in studies examining hippocampal plasticity. Moreover, low doses of MLA improved acquisition, but not consolidation memory processes in rats. While the focus to enhance cognition by modulating α7nAChRs lies on agonists and positive modulators, antagonists at low doses should provide a novel approach to improve cognition in neurological and psychiatric disorders.
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Affiliation(s)
- Nick P van Goethem
- Department of Psychiatry and Neuropsychology, School for Mental Health and Neuroscience, Maastricht University, 6200, MD, Maastricht, The Netherlands
| | - Dean Paes
- Department of Psychiatry and Neuropsychology, School for Mental Health and Neuroscience, Maastricht University, 6200, MD, Maastricht, The Netherlands
| | - Daniela Puzzo
- Department of Biomedical and Biotechnological Sciences, Section of Physiology, University of Catania, 95124 Catania, Italy
| | - Ernesto Fedele
- Department of Pharmacy, Section of Pharmacology and Toxicology, School of Medical and Pharmaceutical Sciences, Centre of Excellence for Biomedical Research, University of Genoa, 16148 Genoa, Italy; IRCCS Polyclinic Hospital San Martino, 16132 Genoa, Italy
| | - Claudia Rebosio
- Department of Pharmacy, Section of Pharmacology and Toxicology, School of Medical and Pharmaceutical Sciences, Centre of Excellence for Biomedical Research, University of Genoa, 16148 Genoa, Italy
| | - Walter Gulisano
- Department of Biomedical and Biotechnological Sciences, Section of Physiology, University of Catania, 95124 Catania, Italy
| | - Agostino Palmeri
- Department of Biomedical and Biotechnological Sciences, Section of Physiology, University of Catania, 95124 Catania, Italy
| | | | - Youyi Peng
- Intra-Cellular Therapies, Inc., New York 10016, United States
| | - Daniel Bertrand
- HiQScreen Sàrl, 6, rte de Compois, 1222, Vésenaz, Geneva, Switzerland
| | - Jos Prickaerts
- Department of Psychiatry and Neuropsychology, School for Mental Health and Neuroscience, Maastricht University, 6200, MD, Maastricht, The Netherlands.
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15
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Toxins for decoding interface selectivity in nicotinic acetylcholine receptors. Biochem J 2019; 476:1515-1520. [PMID: 31138769 DOI: 10.1042/bcj20190255] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2019] [Revised: 04/29/2019] [Accepted: 05/03/2019] [Indexed: 01/25/2023]
Abstract
Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels that play crucial roles in neurotransmission and regulate complex processes in brain functions, including anxiety, learning and memory, food intake, drug addiction, cognition and nociception. To perform these and other functions, a diverse array of nAChR subtypes are generated by homomeric or heteromeric assembly of 17 homologous nAChR subunits. Agonists, acetylcholine and nicotine, bind to the interface formed between two α subunits and between α and non-α subunits to activate the nAChR and allow cation influx. The diversity of subunit interfaces determines the channel properties, the responses to different agonists/antagonists, desensitization and downstream signaling and thus, define specialized properties and functions. Over the last several decades, snake venom neurotoxins have contributed to the purification, localization and characterization of molecular details of various nAChRs. Utkin et al. have described the purification and characterization of αδ-bungarotoxins, a novel class of neurotoxins in a recent paper published in the Biochemical Journal [Biochem. J. (2019) 476, 1285-1302]. These toxins from Bungarus candidus venom preferably bind to α-δ site with two orders of magnitude higher affinity compared with α-γ or α-ε sites. The subtle changes in the structure of αδ-bungarotoxins led to variation in interface selectivity. Such new classes of antagonists will offer us great opportunity to delineate the pharmacophores and design new highly selective antagonists. Thus, their findings provide new impetus to re-evaluate molecular details of pharmacological properties of α-neurotoxins with careful consideration towards subtype-, interface- and species-selectivity.
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Oakes V, Domene C. Capturing the Molecular Mechanism of Anesthetic Action by Simulation Methods. Chem Rev 2018; 119:5998-6014. [DOI: 10.1021/acs.chemrev.8b00366] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Victoria Oakes
- Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
| | - Carmen Domene
- Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
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17
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Ladefoged LK, Munro L, Pedersen AJ, Lummis SCR, Bang-Andersen B, Balle T, Schiøtt B, Kristensen AS. Modeling and Mutational Analysis of the Binding Mode for the Multimodal Antidepressant Drug Vortioxetine to the Human 5-HT3A Receptor. Mol Pharmacol 2018; 94:1421-1434. [DOI: 10.1124/mol.118.113530] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Accepted: 09/19/2018] [Indexed: 12/23/2022] Open
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Zoli M, Pucci S, Vilella A, Gotti C. Neuronal and Extraneuronal Nicotinic Acetylcholine Receptors. Curr Neuropharmacol 2018; 16:338-349. [PMID: 28901280 PMCID: PMC6018187 DOI: 10.2174/1570159x15666170912110450] [Citation(s) in RCA: 159] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Revised: 08/08/2017] [Accepted: 09/03/2017] [Indexed: 02/08/2023] Open
Abstract
Neuronal nicotinic acetylcholine receptors (nAChRs) belong to a super-family of Cys-loop ligand-gated ion chan-nels that respond to endogenous acetylcholine (ACh) or other cholinergic ligands. These receptors are also the targets of drugs such as nicotine (the main addictive agent delivered by cigarette smoke) and are involved in a variety of physiological and pathophysiological processes. Numerous studies have shown that the expression and/or function of nAChRs is com-promised in many neurological and psychiatric diseases. Furthermore, recent studies have shown that neuronal nAChRs are found in a large number of non-neuronal cell types in-cluding endothelial cells, glia, immune cells, lung epithelia and cancer cells where they regulate cell differentiation, prolifera-tion and inflammatory responses. The aim of this review is to describe the most recent findings concerning the structure and function of native nAChRs inside and outside the nervous system.
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Affiliation(s)
- Michele Zoli
- Department of Biomedical, Metabolic and Neural Sciences, Center for Neuroscience and Neurotechnology, University of Modena and Reggio Emilia, Modena, Italy
| | - Susanna Pucci
- CNR, Neuroscience Institute-Milano, Biometra University of Milan, Milan, Italy
| | - Antonietta Vilella
- Department of Biomedical, Metabolic and Neural Sciences, Center for Neuroscience and Neurotechnology, University of Modena and Reggio Emilia, Modena, Italy
| | - Cecilia Gotti
- CNR, Neuroscience Institute-Milano, Biometra University of Milan, Milan, Italy
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19
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Nielsen BE, Minguez T, Bermudez I, Bouzat C. Molecular function of the novel α7β2 nicotinic receptor. Cell Mol Life Sci 2018; 75:2457-2471. [PMID: 29313059 PMCID: PMC11105712 DOI: 10.1007/s00018-017-2741-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2017] [Revised: 11/30/2017] [Accepted: 12/27/2017] [Indexed: 01/03/2023]
Abstract
The α7 nicotinic receptor is a promising drug target for neurological and inflammatory disorders. Although it is the homomeric member of the family, a novel α7β2 heteromeric receptor has been discovered. To decipher the functional contribution of the β2 subunit, we generated heteromeric receptors with fixed stoichiometry by two different approaches comprising concatenated and unlinked subunits. Receptors containing up to three β2 subunits are functional. As the number of β2 subunits increases in the pentameric arrangement, the durations of channel openings and activation episodes increase progressively probably due to decreased desensitization. The prolonged activation episodes conform the kinetic signature of α7β2 and may have an impact on neuronal excitability. For activation of α7β2 receptors, an α7/α7 binding-site interface is required, thus indicating that the three β2 subunits are located consecutively in the pentameric arrangement. α7-positive allosteric modulators (PAMs) are emerging as novel therapeutic drugs. The presence of β2 in the pentamer affects neither type II PAM potentiation nor activation by an allosteric agonist whereas it impairs type I PAM potentiation. This first single-channel study provides fundamental basis required to decipher the role and function of the novel α7β2 receptor and opens doors to develop selective therapeutic drugs.
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Affiliation(s)
- Beatriz E Nielsen
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (UNS-CONICET), 8000, Bahía Blanca, Argentina
| | - Teresa Minguez
- Department of Medical and Biological Sciences, Oxford Brookes University, Oxford, OX3 0BP, UK
| | - Isabel Bermudez
- Department of Medical and Biological Sciences, Oxford Brookes University, Oxford, OX3 0BP, UK
| | - Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (UNS-CONICET), 8000, Bahía Blanca, Argentina.
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20
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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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21
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Lasala M, Corradi J, Bruzzone A, Esandi MDC, Bouzat C. A human-specific, truncated α7 nicotinic receptor subunit assembles with full-length α7 and forms functional receptors with different stoichiometries. J Biol Chem 2018; 293:10707-10717. [PMID: 29784875 DOI: 10.1074/jbc.ra117.001698] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2017] [Revised: 05/15/2018] [Indexed: 11/06/2022] Open
Abstract
The cholinergic α7 nicotinic receptor gene, CHRNA7, encodes a subunit that forms the homopentameric α7 receptor, involved in learning and memory. In humans, exons 5-10 in CHRNA7 are duplicated and fused to the FAM7A genetic element, giving rise to the hybrid gene CHRFAM7A Its product, dupα7, is a truncated subunit lacking part of the N-terminal extracellular ligand-binding domain and is associated with neurological disorders, including schizophrenia, and immunomodulation. We combined dupα7 expression on mammalian cells with patch clamp recordings to understand its functional role. Transfected cells expressed dupα7 protein, but they exhibited neither surface binding of the α7 antagonist α-bungarotoxin nor responses to acetylcholine (ACh) or to an allosteric agonist that binds to the conserved transmembrane region. To determine whether dupα7 assembles with α7, we generated receptors comprising α7 and dupα7 subunits, one of which was tagged with conductance substitutions that report subunit stoichiometry and monitored ACh-elicited channel openings in the presence of a positive allosteric α7 modulator. We found that α7 and dupα7 subunits co-assemble into functional heteromeric receptors, which require at least two α7 subunits for channel opening, and that dupα7's presence in the pentameric arrangement does not affect the duration of the potentiated events compared with that of α7. Using an α7 subunit mutant, we found that activation of (α7)2(dupα7)3 receptors occurs through ACh binding at the α7/α7 interfacial binding site. Our study contributes to the understanding of the modulation of α7 function by the human specific, duplicated subunit, associated with human disorders.
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Affiliation(s)
- Matías Lasala
- From the Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 8000 Bahía Blanca, Argentina
| | - Jeremías Corradi
- From the Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 8000 Bahía Blanca, Argentina
| | - Ariana Bruzzone
- From the Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 8000 Bahía Blanca, Argentina
| | - María Del Carmen Esandi
- From the Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 8000 Bahía Blanca, Argentina
| | - Cecilia Bouzat
- From the Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 8000 Bahía Blanca, Argentina
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22
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Gielen M, Corringer P. The dual-gate model for pentameric ligand-gated ion channels activation and desensitization. J Physiol 2018; 596:1873-1902. [PMID: 29484660 PMCID: PMC5978336 DOI: 10.1113/jp275100] [Citation(s) in RCA: 75] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2018] [Revised: 01/17/2018] [Accepted: 01/17/2018] [Indexed: 12/15/2022] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) mediate fast neurotransmission in the nervous system. Their dysfunction is associated with psychiatric, neurological and neurodegenerative disorders such as schizophrenia, epilepsy and Alzheimer's disease. Understanding their biophysical and pharmacological properties, at both the functional and the structural level, thus holds many therapeutic promises. In addition to their agonist-elicited activation, most pLGICs display another key allosteric property, namely desensitization, in which they enter a shut state refractory to activation upon sustained agonist binding. While the activation mechanisms of several pLGICs have been revealed at near-atomic resolution, the structural foundation of desensitization has long remained elusive. Recent structural and functional data now suggest that the activation and desensitization gates are distinct, and are located at both sides of the ion channel. Such a 'dual gate mechanism' accounts for the marked allosteric effects of channel blockers, a feature illustrated herein by theoretical kinetics simulations. Comparison with other classes of ligand- and voltage-gated ion channels shows that this dual gate mechanism emerges as a common theme for the desensitization and inactivation properties of structurally unrelated ion channels.
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Affiliation(s)
- Marc Gielen
- Channel Receptors UnitInstitut PasteurCNRS UMR 3571ParisFrance
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23
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Abstract
The precise mechanism by which propofol enhances GABAergic transmission remains unclear, but much progress has been made regarding the underlying structural and dynamic mechanisms. Furthermore, it is now clear that propofol has additional molecular targets, many of which are functionally influenced at concentrations achieved clinically. Focusing primarily on molecular targets, this brief review attempts to summarize some of this recent progress while pointing out knowledge gaps and controversies. It is not intended to be comprehensive but rather to stimulate further thought, discussion, and study on the mechanisms by which propofol produces its pleiotropic effects.
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Affiliation(s)
- Pei Tang
- Department of Anesthesiology, University of Pittsburgh, 3550 Terrace Street, Pittsburgh, PA, 15261, USA
| | - Roderic Eckenhoff
- Department of Anesthesiology & Critical Care, University of Pennsylvania, 3400 Spruce St, Philadelphia, PA, 19104, USA
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Bouzat C, Lasala M, Nielsen BE, Corradi J, Esandi MDC. Molecular function of α7 nicotinic receptors as drug targets. J Physiol 2017; 596:1847-1861. [PMID: 29131336 DOI: 10.1113/jp275101] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Accepted: 11/02/2017] [Indexed: 12/20/2022] Open
Abstract
Nicotinic acetylcholine receptors (nAChRs) are pentameric ligand-gated ion channels involved in many physiological and pathological processes. In vertebrates, there are seventeen different nAChR subunits that combine to yield a variety of receptors with different pharmacology, function, and localization. The homomeric α7 receptor is one of the most abundant nAChRs in the nervous system and it is also present in non-neuronal cells. It plays important roles in cognition, memory, pain, neuroprotection, and inflammation. Its diverse physiological actions and associated disorders have made of α7 an attractive novel target for drug modulation. Potentiation of the α7 receptor has emerged as a novel therapeutic strategy for several neurological diseases, such as Alzheimer's and Parkinson's diseases, and inflammatory disorders. In contrast, increased α7 activity has been associated with cancer cell proliferation. The presence of different drug target sites offers a great potential for α7 modulation in different pathological contexts. In particular, compounds that target allosteric sites offer significant advantages over orthosteric agonists due to higher selectivity and a broader spectrum of degrees and mechanisms of modulation. Heterologous expression of α7, together with chaperone proteins, combined with patch clamp recordings have provided important advances in our knowledge of the molecular basis of α7 responses and their potential modulation for pathological processes. This review gives a synthetic view of α7 and its molecular function, focusing on how its unique activation and desensitization features can be modified by pharmacological agents. This fundamental information offers insights into therapeutic strategies.
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Affiliation(s)
- Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, CONICET/UNS, 8000, Bahía Blanca, Argentina
| | - Matías Lasala
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, CONICET/UNS, 8000, Bahía Blanca, Argentina
| | - Beatriz Elizabeth Nielsen
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, CONICET/UNS, 8000, Bahía Blanca, Argentina
| | - Jeremías Corradi
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, CONICET/UNS, 8000, Bahía Blanca, Argentina
| | - María Del Carmen Esandi
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, CONICET/UNS, 8000, Bahía Blanca, Argentina
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25
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Signalling assemblies: the odds of symmetry. Biochem Soc Trans 2017; 45:599-611. [PMID: 28620024 DOI: 10.1042/bst20170009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2017] [Revised: 02/27/2017] [Accepted: 02/28/2017] [Indexed: 02/06/2023]
Abstract
The assembly of proteins into complexes is fundamental to nearly all biological signalling processes. Symmetry is a dominant feature of the structures of experimentally determined protein complexes, observed in the vast majority of homomers and many heteromers. However, some asymmetric structures exist, and asymmetry also often forms transiently, intractable to traditional structure determination methods. Here, we explore the role of protein complex symmetry and asymmetry in cellular signalling, focusing on receptors, transcription factors and transmembrane channels, among other signalling assemblies. We highlight a recurrent tendency for asymmetry to be crucial for signalling function, often being associated with activated states. We conclude with a discussion of how consideration of protein complex symmetry and asymmetry has significant potential implications and applications for pharmacology and human disease.
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26
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Structural mechanisms of activation and desensitization in neurotransmitter-gated ion channels. Nat Struct Mol Biol 2017; 23:494-502. [PMID: 27273633 DOI: 10.1038/nsmb.3214] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Accepted: 03/29/2016] [Indexed: 12/31/2022]
Abstract
Ion channels gated by neurotransmitters are present across metazoans, in which they are essential for brain function, sensation and locomotion; closely related homologs are also found in bacteria. Structures of eukaryotic pentameric cysteine-loop (Cys-loop) receptors and tetrameric ionotropic glutamate receptors in multiple functional states have recently become available. Here, I describe how these studies relate to established ideas regarding receptor activation and how they have enabled decades' worth of functional work to be pieced together, thus allowing previously puzzling aspects of receptor activity to be understood.
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27
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Arcario MJ, Mayne CG, Tajkhorshid E. A membrane-embedded pathway delivers general anesthetics to two interacting binding sites in the Gloeobacter violaceus ion channel. J Biol Chem 2017; 292:9480-9492. [PMID: 28420728 PMCID: PMC5465477 DOI: 10.1074/jbc.m117.780197] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Revised: 04/10/2017] [Indexed: 12/30/2022] Open
Abstract
General anesthetics exert their effects on the central nervous system by acting on ion channels, most notably pentameric ligand-gated ion channels. Although numerous studies have focused on pentameric ligand-gated ion channels, the details of anesthetic binding and channel modulation are still debated. A better understanding of the anesthetic mechanism of action is necessary for the development of safer and more efficacious drugs. Herein, we present a computational study identifying two anesthetic binding sites in the transmembrane domain of the Gloeobacter violaceus ligand-gated ion channel (GLIC) channel, characterize the putative binding pathway, and observe structural changes associated with channel function. Molecular simulations of desflurane reveal a binding pathway to GLIC via a membrane-embedded tunnel using an intrasubunit protein lumen as the conduit, an observation that explains the Meyer-Overton hypothesis, or why the lipophilicity of an anesthetic and its potency are generally proportional. Moreover, employing high concentrations of ligand led to the identification of a second transmembrane site (TM2) that inhibits dissociation of anesthetic from the TM1 site and is consistent with the high concentrations of anesthetics required to achieve clinical effects. Finally, asymmetric binding patterns of anesthetic to the channel were found to promote an iris-like conformational change that constricts and dehydrates the ion pore, creating a 13.5 kcal/mol barrier to ion translocation. Together with previous studies, the simulations presented herein demonstrate a novel anesthetic binding site in GLIC that is accessed through a membrane-embedded tunnel and interacts with a previously known site, resulting in conformational changes that produce a non-conductive state of the channel.
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Affiliation(s)
- Mark J Arcario
- From the Center for Biophysics and Quantitative Biology.,Department of Biochemistry, College of Medicine, and.,Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Christopher G Mayne
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
| | - Emad Tajkhorshid
- From the Center for Biophysics and Quantitative Biology, .,Department of Biochemistry, College of Medicine, and.,Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801
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Wang J, Lindstrom J. Orthosteric and allosteric potentiation of heteromeric neuronal nicotinic acetylcholine receptors. Br J Pharmacol 2017; 175:1805-1821. [PMID: 28199738 DOI: 10.1111/bph.13745] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Revised: 01/30/2017] [Accepted: 02/06/2017] [Indexed: 12/16/2022] Open
Abstract
Heteromeric nicotinic ACh receptors (nAChRs) were thought to have two orthodox agonist-binding sites at two α/β subunit interfaces. Highly selective ligands are hard to develop by targeting orthodox agonist sites because of high sequence similarity of this binding pocket among different subunits. Recently, unorthodox ACh-binding sites have been discovered at some α/α and β/α subunit interfaces, such as α4/α4, α5/α4 and β3/α4. Targeting unorthodox sites may yield subtype-selective ligands, such as those for (α4β2)2 α5, (α4β2)2 β3 and (α6β2)2 β3 nAChRs. The unorthodox sites have unique pharmacology. Agonist binding at one unorthodox site is not sufficient to activate nAChRs, but it increases activation from the orthodox sites. NS9283, a selective agonist for the unorthodox α4/α4 site, was initially thought to be a positive allosteric modulator (PAM). NS9283 activates nAChRs with three engineered α4/α4 sites. PAMs, on the other hand, act at allosteric sites where ACh cannot bind. Known PAM sites include the ACh-homologous non-canonical site (e.g. morantel at β/α), the C-terminus (e.g. Br-PBTC and 17β-estradiol), a transmembrane domain (e.g. LY2087101) or extracellular and transmembrane domain interfaces (e.g. NS206). Some of these PAMs, such as Br-PBTC and 17β-estradiol, require only one subunit to potentiate activation of nAChRs. In this review, we will discuss differences between activation from orthosteric and allosteric sites, their selective ligands and clinical implications. These studies have advanced understanding of the structure, assembly and pharmacology of heteromeric neuronal nAChRs. 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)
- Jingyi Wang
- Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - Jon Lindstrom
- Department of Neuroscience, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
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Boffi JC, Marcovich I, Gill-Thind JK, Corradi J, Collins T, Lipovsek MM, Moglie M, Plazas PV, Craig PO, Millar NS, Bouzat C, Elgoyhen AB. Differential Contribution of Subunit Interfaces to α9α10 Nicotinic Acetylcholine Receptor Function. Mol Pharmacol 2017; 91:250-262. [PMID: 28069778 PMCID: PMC5325082 DOI: 10.1124/mol.116.107482] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 01/04/2017] [Indexed: 12/31/2022] Open
Abstract
Nicotinic acetylcholine receptors can be assembled from either homomeric or heteromeric pentameric subunit combinations. At the interface of the extracellular domains of adjacent subunits lies the acetylcholine binding site, composed of a principal component provided by one subunit and a complementary component of the adjacent subunit. Compared with neuronal nicotinic acetylcholine cholinergic receptors (nAChRs) assembled from α and β subunits, the α9α10 receptor is an atypical member of the family. It is a heteromeric receptor composed only of α subunits. Whereas mammalian α9 subunits can form functional homomeric α9 receptors, α10 subunits do not generate functional channels when expressed heterologously. Hence, it has been proposed that α10 might serve as a structural subunit, much like a β subunit of heteromeric nAChRs, providing only complementary components to the agonist binding site. Here, we have made use of site-directed mutagenesis to examine the contribution of subunit interface domains to α9α10 receptors by a combination of electrophysiological and radioligand binding studies. Characterization of receptors containing Y190T mutations revealed unexpectedly that both α9 and α10 subunits equally contribute to the principal components of the α9α10 nAChR. In addition, we have shown that the introduction of a W55T mutation impairs receptor binding and function in the rat α9 subunit but not in the α10 subunit, indicating that the contribution of α9 and α10 subunits to complementary components of the ligand-binding site is nonequivalent. We conclude that this asymmetry, which is supported by molecular docking studies, results from adaptive amino acid changes acquired only during the evolution of mammalian α10 subunits.
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Affiliation(s)
- Juan Carlos Boffi
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Irina Marcovich
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - JasKiran K Gill-Thind
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Jeremías Corradi
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Toby Collins
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - María Marcela Lipovsek
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Marcelo Moglie
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Paola V Plazas
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Patricio O Craig
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Neil S Millar
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Cecilia Bouzat
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B)
| | - Ana Belén Elgoyhen
- Instituto de Investigaciones en Ingeniería, Genética y Biología Molecular, Dr Héctor N Torres (J.C.B., I.M., M.M. L., M.M., P.V.P., A.B.E.), Instituto de Química Biológica (P.O.C.), and Instituto de Investigaciones Bioquímicas de Bahía Blanca (J.C., C.B), Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina; Department of Neuroscience, Physiology and Pharmacology, University College London, United Kingdom (J.K.G.-T., T.C., N.S.M.); Departamento de Química Biológica Facultad de Ciencias Exactas y Naturales (P.O.C.), and Instituto de Farmacología, Facultad de Medicina (P.V.P., A.B.E.), Universidad de Buenos Aires, Buenos Aires, Argentina; and Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, Bahía Blanca, Argentina (J.C., C.B).
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Powell AD, Grafton G, Roberts A, Larkin S, O'Neill N, Palandri J, Otvos R, Cooper AJ, Ulens C, Barnes NM. Novel mechanism of modulation at a ligand-gated ion channel; action of 5-Cl-indole at the 5-HT 3 A receptor. Br J Pharmacol 2016; 173:3467-3479. [PMID: 27677804 DOI: 10.1111/bph.13638] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2016] [Revised: 09/09/2016] [Accepted: 09/16/2016] [Indexed: 01/09/2023] Open
Abstract
BACKGROUND AND PURPOSE The 5-HT3 receptor is a prototypical member of the Cys-loop ligand-gated ion channel (LGIC) superfamily and an established therapeutic target. In addition to activation via the orthosteric site, receptor function can be modulated by allosteric ligands. We have investigated the pharmacological action of Cl-indole upon the 5-HT3 A receptor and identified that this positive allosteric modulator possesses a novel mechanism of action for LGICs. EXPERIMENTAL APPROACH The impact of Cl-indole upon the 5-HT3 receptor was assessed using single cell electrophysiological recordings and [3 H]-granisetron binding in HEK293 cells stably expressing the 5-HT3 receptor. KEY RESULTS Cl-indole failed to evoke 5-HT3 A receptor-mediated responses (up to 30 μM) or display affinity for the [3 H]-granisetron binding site. However, in the presence of Cl-indole, termination of 5-HT application revealed tail currents mediated via the 5-HT3 A receptor that were independent of the preceding 5-HT concentration but were antagonized by the 5-HT3 receptor antagonist, ondansetron. These tail currents were absent in the 5-HT3 AB receptor. Furthermore, the presence of 5-HT revealed a concentration-dependent increase in the affinity of Cl-indole for the orthosteric binding site of the human 5-HT3 A receptor. CONCLUSIONS AND IMPLICATIONS Cl-indole acts as both an orthosteric agonist and an allosteric modulator, but the presence of an orthosteric agonist (e.g. 5-HT) is a prerequisite to reveal both actions. Precedent for ago-allosteric action is available, yet the essential additional presence of an orthosteric agonist is now reported for the first time. This widening of the pharmacological mechanisms to modulate LGICs may offer further therapeutic opportunities.
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Affiliation(s)
- Andrew D Powell
- Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.,School of Nursing Midwifery and Social Work, Birmingham City University, Edgbaston, UK
| | - Gillian Grafton
- Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Alexander Roberts
- Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Shannon Larkin
- Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Nathanael O'Neill
- Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Josephine Palandri
- Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Reka Otvos
- Department of Molecular and Cellular Neurobiology, VU University Amsterdam, Amsterdam, The Netherlands
| | - Alison J Cooper
- Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK
| | - Chris Ulens
- Laboratory of Structural Neurobiology, KU Leuven, Leuven, Belgium
| | - Nicholas M Barnes
- Clinical and Experimental Medicine, College of Medical and Dental Sciences, University of Birmingham, Birmingham, UK.,Department of Pharmacology and Therapeutics, School of Biomedical Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Parkville, Victoria, Australia
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31
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Fuse T, Kita T, Nakata Y, Ozoe F, Ozoe Y. Electrophysiological characterization of ivermectin triple actions on Musca chloride channels gated by l-glutamic acid and γ-aminobutyric acid. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2016; 77:78-86. [PMID: 27543424 DOI: 10.1016/j.ibmb.2016.08.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 08/14/2016] [Indexed: 06/06/2023]
Abstract
Ivermectin (IVM) is a macrocyclic lactone that exerts antifilarial, antiparasitic, and insecticidal effects on nematodes and insects by acting on l-glutamic acid-gated chloride channels (GluCls). IVM also acts as an allosteric modulator of various other ion channels. Although the IVM binding site in the Caenorhabditis elegans GluCl was identified by X-ray crystallographic analysis, the mechanism of action of IVM in insects is not well defined. We therefore examined the action of IVM on the housefly (Musca domestica) GluCl and γ-aminobutyric acid (GABA)-gated ion channel (GABACl). For both channels, IVM induced currents by itself, potentiated currents induced by low concentrations of agonists, and inhibited currents induced by high concentrations of agonists. Despite exerting common actions on both types of channels, GluCls were more susceptible to IVM actions than GABACls, indicating that GluCls are the primary target of IVM. Substitution of an amino acid residue in the third transmembrane segment (G312M in GluCls, and G333A and G333M in GABACls) resulted in significantly reduced levels or loss of activation, potentiation, and antagonism of the channels, indicating that these three actions result from the interaction of IVM with amino acid residues in the transmembrane intersubunit crevice.
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Affiliation(s)
- Toshinori Fuse
- Division of Bioscience and Biotechnology, The United Graduate School of Agricultural Sciences, Tottori University, Tottori 680-8553, Japan
| | - Tomo Kita
- Division of Bioscience and Biotechnology, The United Graduate School of Agricultural Sciences, Tottori University, Tottori 680-8553, Japan
| | - Yunosuke Nakata
- Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane 690-8504, Japan
| | - Fumiyo Ozoe
- Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane 690-8504, Japan
| | - Yoshihisa Ozoe
- Division of Bioscience and Biotechnology, The United Graduate School of Agricultural Sciences, Tottori University, Tottori 680-8553, Japan; Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane 690-8504, Japan.
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Corradi J, Bouzat C. Understanding the Bases of Function and Modulation of α7 Nicotinic Receptors: Implications for Drug Discovery. Mol Pharmacol 2016; 90:288-99. [PMID: 27190210 DOI: 10.1124/mol.116.104240] [Citation(s) in RCA: 131] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Accepted: 05/05/2016] [Indexed: 01/01/2023] Open
Abstract
The nicotinic acetylcholine receptor (nAChR) belongs to a superfamily of pentameric ligand-gated ion channels involved in many physiologic and pathologic processes. Among nAChRs, receptors comprising the α7 subunit are unique because of their high Ca(2+) permeability and fast desensitization. nAChR agonists elicit a transient ion flux response that is further sustained by the release of calcium from intracellular sources. Owing to the dual ionotropic/metabotropic nature of α7 receptors, signaling pathways are activated. The α7 subunit is highly expressed in the nervous system, mostly in regions implicated in cognition and memory and has therefore attracted attention as a novel drug target. Additionally, its dysfunction is associated with several neuropsychiatric and neurologic disorders, such as schizophrenia and Alzheimer's disease. α7 is also expressed in non-neuronal cells, particularly immune cells, where it plays a role in immunity, inflammation, and neuroprotection. Thus, α7 potentiation has emerged as a therapeutic strategy for several neurologic and inflammatory disorders. With unique activation properties, the receptor is a sensitive drug target carrying different potential binding sites for chemical modulators, particularly agonists and positive allosteric modulators. Although macroscopic and single-channel recordings have provided significant information about the underlying molecular mechanisms and binding sites of modulatory compounds, we know just the tip of the iceberg. Further concerted efforts are necessary to effectively exploit α7 as a drug target for each pathologic situation. In this article, we focus mainly on the molecular basis of activation and drug modulation of α7, key pillars for rational drug design.
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Affiliation(s)
- Jeremías Corradi
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Universidad Nacional del Sur, CONICET/UNS, Bahía Blanca, Argentina
| | - Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, Universidad Nacional del Sur, CONICET/UNS, Bahía Blanca, Argentina
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Yuan S, Filipek S, Vogel H. A Gating Mechanism of the Serotonin 5-HT3 Receptor. Structure 2016; 24:816-825. [PMID: 27112600 DOI: 10.1016/j.str.2016.03.019] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Revised: 01/27/2016] [Accepted: 03/06/2016] [Indexed: 11/29/2022]
Abstract
Our recently solved high-resolution structure of the serotonin 5-HT3 receptor (5-HT3R) delivered the first detailed structural insights for a mammalian pentameric ligand-gated ion channel. Based on this structure, we here performed a total of 2.8-μs all-atom molecular dynamics simulations to unravel at atomic detail how neurotransmitter binding on the extracellular domain induces sequential conformational transitions in the receptor, opening an ion channel and translating a chemical signal into electrical impulses across the membrane. We found that serotonin binding first induces distinct conformational fluctuations at the side chain of W156 in the highly conserved ligand-binding cage, followed by tilting-twisting movements of the extracellular domain which couple to the transmembrane TM2 helices, opening the hydrophobic gate at L260 and forming a continuous transmembrane water pathway. The structural transitions in the receptor's transmembrane part finally couple to the intracellular MA helix bundle, opening lateral ports for ion passage.
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Affiliation(s)
- Shuguang Yuan
- Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland.
| | - Slawomir Filipek
- Laboratory of Biomodeling, Faculty of Chemistry & Biological and Chemical Research Centre, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
| | - Horst Vogel
- Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland.
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High and low GABA sensitivity α4β2δ GABAA receptors are expressed in Xenopus laevis oocytes with divergent stoichiometries. Biochem Pharmacol 2016; 103:98-108. [DOI: 10.1016/j.bcp.2015.12.021] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2015] [Accepted: 12/29/2015] [Indexed: 12/11/2022]
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35
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Wang J, Kuryatov A, Jin Z, Norleans J, Kamenecka TM, Kenny PJ, Lindstrom J. A Novel α2/α4 Subtype-selective Positive Allosteric Modulator of Nicotinic Acetylcholine Receptors Acting from the C-tail of an α Subunit. J Biol Chem 2015; 290:28834-46. [PMID: 26432642 DOI: 10.1074/jbc.m115.676551] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Indexed: 12/30/2022] Open
Abstract
Positive allosteric modulators (PAMs) of nicotinic acetylcholine receptors (nAChR) are important therapeutic candidates as well as valuable research tools. We identified a novel type II PAM, (R)-7-bromo-N-(piperidin-3-yl)benzo[b]thiophene-2-carboxamide (Br-PBTC), which both increases activation and reactivates desensitized nAChRs. This compound increases acetylcholine-evoked responses of α2* and α4* nAChRs but is without effect on α3* or α6* nAChRs (* indicates the presence of other nAChR subunits). Br-BPTC acts from the C-terminal extracellular sequences of α4 subunits, which is also a PAM site for steroid hormone estrogens such as 17β-estradiol. Br-PBTC is much more potent than estrogens. Like 17β-estradiol, the non-steroid Br-PBTC only requires one α4 subunit to potentiate nAChR function, and its potentiation is stronger with more α4 subunits. This feature enables Br-BPTC to potentiate activation of (α4β2)(α6β2)β3 but not (α6β2)2β3 nAChRs. Therefore, this compound is potentially useful in vivo for determining functions of different α6* nAChR subtypes. Besides activation, Br-BPTC affects desensitization of nAChRs induced by sustained exposure to agonists. After minutes of exposure to agonists, Br-PBTC reactivated short term desensitized nAChRs that have at least two α4 subunits but not those with only one. Three α4 subunits were required for Br-BPTC to reactivate long term desensitized nAChRs. These data suggest that higher PAM occupancy promotes channel opening more efficiently and overcomes short and long term desensitization. This C-terminal extracellular domain could be a target for developing subtype or state-selective drugs for nAChRs.
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Affiliation(s)
- Jingyi Wang
- From the Department of Neuroscience, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Alexander Kuryatov
- From the Department of Neuroscience, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Zhuang Jin
- Department of Molecular Therapeutics, Scripps Research Institute, Scripps, Florida 33458, and
| | - Jack Norleans
- From the Department of Neuroscience, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Theodore M Kamenecka
- Department of Molecular Therapeutics, Scripps Research Institute, Scripps, Florida 33458, and
| | - Paul J Kenny
- Department of Pharmacology and Systems Therapeutics, Icahn School of Medicine at Mount Sinai, New York, New York 10029
| | - Jon Lindstrom
- From the Department of Neuroscience, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104,
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Transcriptome Analysis of the Central and Peripheral Nervous Systems of the Spider Cupiennius salei Reveals Multiple Putative Cys-Loop Ligand Gated Ion Channel Subunits and an Acetylcholine Binding Protein. PLoS One 2015; 10:e0138068. [PMID: 26368804 PMCID: PMC4569296 DOI: 10.1371/journal.pone.0138068] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2015] [Accepted: 08/25/2015] [Indexed: 11/19/2022] Open
Abstract
Invertebrates possess a diverse collection of pentameric Cys-loop ligand gated ion channel (LGIC) receptors whose molecular structures, evolution and relationships to mammalian counterparts have been intensely investigated in several clinically and agriculturally important species. These receptors are targets for a variety of control agents that may also harm beneficial species. However, little is known about Cys-loop receptors in spiders, which are important natural predators of insects. We assembled de novo transcriptomes from the central and peripheral nervous systems of the Central American wandering spider Cupiennius salei, a model species for neurophysiological, behavioral and developmental studies. We found 15 Cys-loop receptor subunits that are expected to form anion or cation permeable channels, plus a putative acetylcholine binding protein (AChBP) that has only previously been reported in molluscs and one annelid. We used phylogenetic and sequence analysis to compare the spider subunits to homologous receptors in other species and predicted the 3D structures of each protein using the I-Tasser server. The quality of homology models improved with increasing sequence identity to the available high-resolution templates. We found that C. salei has orthologous γ-aminobutyric acid (GABA), GluCl, pHCl, HisCl and nAChα LGIC subunits to other arthropods, but some subgroups are specific to arachnids, or only to spiders. C. salei sequences were phylogenetically closest to gene fragments from the social spider, Stegodyphus mimosarum, indicating high conservation within the Araneomorphae suborder of spiders. C. salei sequences had similar ligand binding and transmembrane regions to other invertebrate and vertebrate LGICs. They also had motifs associated with high sensitivity to insecticides and antiparasitic agents such as fipronil, dieldrin and ivermectin. Development of truly selective control agents for pest species will require information about the molecular structure and pharmacology of Cys-loop receptors in beneficial species.
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Zoli M, Pistillo F, Gotti C. Diversity of native nicotinic receptor subtypes in mammalian brain. Neuropharmacology 2015; 96:302-11. [DOI: 10.1016/j.neuropharm.2014.11.003] [Citation(s) in RCA: 167] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Revised: 10/11/2014] [Accepted: 11/08/2014] [Indexed: 01/01/2023]
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Stoichiometry for α-bungarotoxin block of α7 acetylcholine receptors. Nat Commun 2015; 6:8057. [PMID: 26282895 PMCID: PMC4544739 DOI: 10.1038/ncomms9057] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Accepted: 07/12/2015] [Indexed: 12/21/2022] Open
Abstract
α-Bungarotoxin (α-Btx) binds to the five agonist binding sites on the homopentameric α7-acetylcholine receptor, yet the number of bound α-Btx molecules required to prevent agonist-induced channel opening remains unknown. To determine the stoichiometry for α-Btx blockade, we generate receptors comprised of wild-type and α-Btx-resistant subunits, tag one of the subunit types with conductance mutations to report subunit stoichiometry, and following incubation with α-Btx, monitor opening of individual receptor channels with defined subunit stoichiometry. We find that a single α-Btx-sensitive subunit confers nearly maximal suppression of channel opening, despite four binding sites remaining unoccupied by α-Btx and accessible to the agonist. Given structural evidence that α-Btx locks the agonist binding site in an inactive conformation, we conclude that the dominant mechanism of antagonism is non-competitive, originating from conformational arrest of the binding sites, and that the five α7 subunits are interdependent and maintain conformational symmetry in the open channel state. Since their discovery more than fifty years ago, α-neurotoxins have been used to study acetylcholine receptor-coupled ion channels. Here, daCosta et al. find that toxin binding to a single site of the pentameric α7 receptor blocks function, suggesting the five binding sites are interdependent and the toxin arrests the sites in the inactive conformation.
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Marabelli A, Lape R, Sivilotti L. Mechanism of activation of the prokaryotic channel ELIC by propylamine: a single-channel study. ACTA ACUST UNITED AC 2015; 145:23-45. [PMID: 25548135 PMCID: PMC4278187 DOI: 10.1085/jgp.201411234] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Prokaryotic channels, such as Erwinia chrysanthemi ligand-gated ion channel (ELIC) and Gloeobacter violaceus ligand-gated ion channel, give key structural information for the pentameric ligand-gated ion channel family, which includes nicotinic acetylcholine receptors. ELIC, a cationic channel from E. chrysanthemi, is particularly suitable for single-channel recording because of its high conductance. Here, we report on the kinetic properties of ELIC channels expressed in human embryonic kidney 293 cells. Single-channel currents elicited by the full agonist propylamine (0.5-50 mM) in outside-out patches at -60 mV were analyzed by direct maximum likelihood fitting of kinetic schemes to the idealized data. Several mechanisms were tested, and their adequacy was judged by comparing the predictions of the best fit obtained with the observable features of the experimental data. These included open-/shut-time distributions and the time course of macroscopic propylamine-activated currents elicited by fast theta-tube applications (50-600 ms, 1-50 mM, -100 mV). Related eukaryotic channels, such as glycine and nicotinic receptors, when fully liganded open with high efficacy to a single open state, reached via a preopening intermediate. The simplest adequate description of their activation, the "Flip" model, assumes a concerted transition to a single intermediate state at high agonist concentration. In contrast, ELIC open-time distributions at saturating propylamine showed multiple components. Thus, more than one open state must be accessible to the fully liganded channel. The "Primed" model allows opening from multiple fully liganded intermediates. The best fits of this type of model showed that ELIC maximum open probability (99%) is reached when at least two and probably three molecules of agonist have bound to the channel. The overall efficacy with which the fully liganded channel opens was ∼ 102 (∼ 20 for α1β glycine channels). The microscopic affinity for the agonist increased as the channel activated, from 7 mM for the resting state to 0.15 mM for the partially activated intermediate state.
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Affiliation(s)
- Alessandro Marabelli
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, England, UK
| | - Remigijus Lape
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, England, UK
| | - Lucia Sivilotti
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, England, UK
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Corradi J, Thompson AJ, McGonigle I, Price KL, Bouzat C, Lummis SCR. 5-HT3 Receptor Brain-Type B-Subunits are Differentially Expressed in Heterologous Systems. ACS Chem Neurosci 2015; 6:1158-64. [PMID: 25951416 PMCID: PMC4505687 DOI: 10.1021/acschemneuro.5b00080] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
![]()
Genes for five different
5-HT3 receptor subunits have
been identified. Most of the subunits have multiple isoforms, but
two isoforms of the B subunits, brain-type 1 (Br1) and brain-type
2 (Br2) are of particular interest as they appear to be abundantly
expressed in human brain, where 5-HT3B subunit RNA consists of approximately
75% 5-HT3Br2, 24% 5-HT3Br1, and <1% 5-HT3B. Here we use two-electrode
voltage-clamp, radioligand binding, fluorescence, whole cell, and
single channel patch-clamp studies to characterize the roles of 5-HT3Br1
and 5-HT3Br2 subunits on function and pharmacology in heterologously
expressed 5-HT3 receptors. The data show that the 5-HT3Br1
transcriptional variant, when coexpressed with 5-HT3A subunits, alters
the EC50, nH, and single channel
conductance of the 5-HT3 receptor, but has no effect on
the potency of competitive antagonists; thus, 5-HT3ABr1
receptors have the same characteristics as 5-HT3AB receptors.
There were some differences in the shapes of 5-HT3AB and
5-HT3ABr1 receptor responses, which were likely due to
a greater proportion of homomeric 5-HT3A versus heteromeric
5-HT3ABr1 receptors in the latter, as expression of the
5-HT3Br1 compared to the 5-HT3B subunit is less efficient. Conversely,
the 5-HT3Br2 subunit does not appear to form functional channels with
the 5-HT3A subunit in either oocytes or HEK293 cells, and the role
of this subunit is yet to be determined.
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Affiliation(s)
- Jeremias Corradi
- INIBIBB, UNS/CONICET, Camino La Carrindanga Km 7, 8000 Bahía Blanca, Argentina
| | - Andrew J. Thompson
- Department
of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom
| | - Ian McGonigle
- Department
of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom
| | - Kerry. L. Price
- Department
of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom
| | - Cecilia Bouzat
- INIBIBB, UNS/CONICET, Camino La Carrindanga Km 7, 8000 Bahía Blanca, Argentina
| | - Sarah C. R. Lummis
- Department
of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom
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The coupling interface and pore domain codetermine the single-channel activity of the α7 nicotinic receptor. Neuropharmacology 2015; 95:448-58. [PMID: 25908400 DOI: 10.1016/j.neuropharm.2015.04.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Revised: 03/26/2015] [Accepted: 04/09/2015] [Indexed: 11/22/2022]
Abstract
Ligand-gated ion channels play a role in mediating fast synaptic transmission for communication between neurons. However, the structural basis for the functional coupling of the binding and pore domains, resulting in channel opening, remains a topic of intense investigation. Here, a series of α7 nicotinic receptor mutants were constructed for expression in cultured mammalian cells, and their single-channel properties were examined using the patch-clamp technique combined with radio ligand binding and the fluorescence staining technique. We demonstrated that the replacement of the four pore-lining residues in the channel domain of the α7 nicotinic receptor with the hydrophilic residue serine prolongs the open-channel lifetime, although the conductance of these mutants decreases. At the coupling interface between the extracellular and transmembrane domains, when the VRW residues in the Cys-loop were substituted with the corresponding residues (i.e., IYN) in the 5-HT3A receptor, the single-channel activity elicited by acetylcholine is impaired. This effect occurred despite the expression of the mutant receptors on the cell surface and despite the fact that the apparent Kd values were much lower than those of the wild-type α7 receptor. When we further lowered the channel-gating barrier of this chimera to enhance the open-channel probability, the loss of function was rescued. Overall, we explored the microscopic mechanisms underlying the interplay between the channel domains and the coupling interface that affect the channel activity, and we generated an allosteric gating model for the α7 receptor. This model shows that the gating machinery and coupling assembly codetermine the single-channel gating kinetics. These results likely apply to all channels in the Cys-loop receptor family.
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Wang J, Kuryatov A, Sriram A, Jin Z, Kamenecka TM, Kenny PJ, Lindstrom J. An Accessory Agonist Binding Site Promotes Activation of α4β2* Nicotinic Acetylcholine Receptors. J Biol Chem 2015; 290:13907-18. [PMID: 25869137 DOI: 10.1074/jbc.m115.646786] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Indexed: 11/06/2022] Open
Abstract
Neuronal nicotinic acetylcholine receptors containing α4, β2, and sometimes other subunits (α4β2* nAChRs) regulate addictive and other behavioral effects of nicotine. These nAChRs exist in several stoichiometries, typically with two high affinity acetylcholine (ACh) binding sites at the interface of α4 and β2 subunits and a fifth accessory subunit. A third low affinity ACh binding site is formed when this accessory subunit is α4 but not if it is β2. Agonists selective for the accessory ACh site, such as 3-[3-(3-pyridyl)-1,2,4-oxadiazol-5-yl]benzonitrile (NS9283), cannot alone activate a nAChR but can facilitate more efficient activation in combination with agonists at the canonical α4β2 sites. We therefore suggest categorizing agonists according to their site selectivity. NS9283 binds to the accessory ACh binding site; thus it is termed an accessory site-selective agonist. We expressed (α4β2)2 concatamers in Xenopus oocytes with free accessory subunits to obtain defined nAChR stoichiometries and α4/accessory subunit interfaces. We show that α2, α3, α4, and α6 accessory subunits can form binding sites for ACh and NS9283 at interfaces with α4 subunits, but β2 and β4 accessory subunits cannot. To permit selective blockage of the accessory site, α4 threonine 126 located on the minus side of α4 that contributes to the accessory site, but not the α4β2 sites, was mutated to cysteine. Alkylation of this cysteine with a thioreactive reagent blocked activity of ACh and NS9283 at the accessory site. Accessory agonist binding sites are promising drug targets.
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Affiliation(s)
- Jingyi Wang
- From the Department of Neuroscience, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Alexander Kuryatov
- From the Department of Neuroscience, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Aarati Sriram
- From the Department of Neuroscience, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Zhuang Jin
- Department of Molecular Therapeutics at the Scripps Research Institute, Scripps, Florida 33458, and
| | - Theodore M Kamenecka
- Department of Molecular Therapeutics at the Scripps Research Institute, Scripps, Florida 33458, and
| | - Paul J Kenny
- Department of Pharmacology and Systems Therapeutics, Icahn School of Medicine at Mount Sinai, New York, New York 10029
| | - Jon Lindstrom
- From the Department of Neuroscience, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104,
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Dionisio L, Bergé I, Bravo M, Esandi MDC, Bouzat C. Neurotransmitter GABA Activates Muscle but Not α7 Nicotinic Receptors. Mol Pharmacol 2014; 87:391-400. [DOI: 10.1124/mol.114.095539] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Arias HR, Feuerbach D, Targowska-Duda K, Kaczor AA, Poso A, Jozwiak K. Pharmacological and molecular studies on the interaction of varenicline with different nicotinic acetylcholine receptor subtypes. Potential mechanism underlying partial agonism at human α4β2 and α3β4 subtypes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1848:731-41. [PMID: 25475645 DOI: 10.1016/j.bbamem.2014.11.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2014] [Revised: 10/29/2014] [Accepted: 11/06/2014] [Indexed: 02/06/2023]
Abstract
To determine the structural components underlying differences in affinity, potency, and selectivity of varenicline for several human (h) nicotinic acetylcholine receptors (nAChRs), functional and structural experiments were performed. The Ca2+ influx results established that: (a) varenicline activates (μM range) nAChR subtypes with the following rank sequence: hα7>hα4β4>hα4β2>hα3β4>>>hα1β1γδ; (b) varenicline binds to nAChR subtypes with the following affinity order (nM range): hα4β2~hα4β4>hα3β4>hα7>>>Torpedo α1β1γδ. The molecular docking results indicating that more hydrogen bond interactions are apparent for α4-containing nAChRs in comparison to other nAChRs may explain the observed higher affinity; and that (c) varenicline is a full agonist at hα7 (101%) and hα4β4 (93%), and a partial agonist at hα4β2 (20%) and hα3β4 (45%), relative to (±)-epibatidine. The allosteric sites found at the extracellular domain (EXD) of hα3β4 and hα4β2 nAChRs could explain the partial agonistic activity of varenicline on these nAChR subtypes. Molecular dynamics simulations show that the interaction of varenicline to each allosteric site decreases the capping of Loop C at the hα4β2 nAChR, suggesting that these allosteric interactions limit the initial step in the gating process. In conclusion, we propose that in addition to hα4β2 nAChRs, hα4β4 nAChRs can be considered as potential targets for the clinical activity of varenicline, and that the allosteric interactions at the hα3β4- and hα4β2-EXDs are alternative mechanisms underlying partial agonism at these nAChRs.
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Affiliation(s)
- Hugo R Arias
- Department of Medical Education, California Northstate University College of Medicine, Elk Grove, CA, USA.
| | - Dominik Feuerbach
- Neuroscience Research, Novartis Institutes for Biomedical Research, Basel, Switzerland
| | - Katarzyna Targowska-Duda
- Department of Chemistry, Laboratory of Medicinal Chemistry and Neuroengineering, Medical University of Lublin, Lublin, Poland
| | - Agnieszka A Kaczor
- Department of Synthesis and Chemical Technology of Pharmaceutical Substances with Computer Modeling Lab, Medical University of Lublin, Lublin, Poland
| | - Antti Poso
- School of Pharmacy, University of Eastern Finland, Kuopio, Finland
| | - Krzysztof Jozwiak
- Department of Chemistry, Laboratory of Medicinal Chemistry and Neuroengineering, Medical University of Lublin, Lublin, Poland
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Benallegue N, Mazzaferro S, Alcaino C, Bermudez I. The additional ACh binding site at the α4(+)/α4(-) interface of the (α4β2)2α4 nicotinic ACh receptor contributes to desensitization. Br J Pharmacol 2014; 170:304-16. [PMID: 23742319 DOI: 10.1111/bph.12268] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2012] [Revised: 05/16/2013] [Accepted: 05/23/2013] [Indexed: 12/01/2022] Open
Abstract
BACKGROUND AND PURPOSE Nicotinic ACh (α4β2)2α4 receptors are highly prone to desensitization by prolonged exposure to low concentrations of agonist. Here, we report on the sensitivity of the three agonist sites of the (α4β2)2α4 to desensitization induced by prolonged exposure to ACh. We present electrophysiological data that show that the agonist sites of the (α4β2)2α4 receptor have different sensitivity to desensitization and that full receptor occupation decreases sensitivity to desensitization. EXPERIMENTAL APPROACH Two-electrode voltage-clamp electrophysiology was used to study the desensitization of concatenated (α4β2)2α4 receptors expressed heterologously in Xenopus oocytes. Desensitization was assessed by measuring the degree of functional inhibition caused by prolonged exposure to ACh, as measured under equilibrium conditions. We used the single-point mutation α4W182A to measure the contribution of individual agonist sites to desensitization. KEY RESULTS (α4β2)2α4 receptors are less sensitive to activation and desensitization by ACh than (α4β2)2β2 receptors. Incorporation of α4W182A into any of the agonist sites of concatenated (α4β2)2α4 receptors decreased sensitivity to activation and desensitization but the effects were more pronounced when the mutation was introduced into the α4(+)/α4(-) interface. CONCLUSIONS AND IMPLICATIONS The findings suggest that the agonist sites in (α4β2)2α4 receptors are not functionally equivalent. The agonist site at the α4(+)/α4(-) interface defines the sensitivity of (α4β2)2α4 receptors to agonist-induced activation and desensitization. Functional differences between (α4β2)2α4 and (α4β2)2β2 receptors might shape the physiological and behavioural responses to nicotinic ligands when the receptors are exposed to nicotinic ligands for prolonged periods of times.
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Affiliation(s)
- N Benallegue
- Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, UK
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46
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Moretti M, Zoli M, George AA, Lukas RJ, Pistillo F, Maskos U, Whiteaker P, Gotti C. The novel α7β2-nicotinic acetylcholine receptor subtype is expressed in mouse and human basal forebrain: biochemical and pharmacological characterization. Mol Pharmacol 2014; 86:306-17. [PMID: 25002271 DOI: 10.1124/mol.114.093377] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We examined α7β2-nicotinic acetylcholine receptor (α7β2-nAChR) expression in mammalian brain and compared pharmacological profiles of homomeric α7-nAChRs and α7β2-nAChRs. α-Bungarotoxin affinity purification or immunoprecipitation with anti-α7 subunit antibodies (Abs) was used to isolate nAChRs containing α7 subunits from mouse or human brain samples. α7β2-nAChRs were detected in forebrain, but not other tested regions, from both species, based on Western blot analysis of isolates using β2 subunit-specific Abs. Ab specificity was confirmed in control studies using subunit-null mutant mice or cell lines heterologously expressing specific human nAChR subtypes and subunits. Functional expression in Xenopus oocytes of concatenated pentameric (α7)5-, (α7)4(β2)1-, and (α7)3(β2)2-nAChRs was confirmed using two-electrode voltage clamp recording of responses to nicotinic ligands. Importantly, pharmacological profiles were indistinguishable for concatenated (α7)5-nAChRs or for homomeric α7-nAChRs constituted from unlinked α7 subunits. Pharmacological profiles were similar for (α7)5-, (α7)4(β2)1-, and (α7)3(β2)2-nAChRs except for diminished efficacy of nicotine (normalized to acetylcholine efficacy) at α7β2- versus α7-nAChRs. This study represents the first direct confirmation of α7β2-nAChR expression in human and mouse forebrain, supporting previous mouse studies that suggested relevance of α7β2-nAChRs in Alzheimer disease etiopathogenesis. These data also indicate that α7β2-nAChR subunit isoforms with different α7/β2 subunit ratios have similar pharmacological profiles to each other and to α7 homopentameric nAChRs. This supports the hypothesis that α7β2-nAChR agonist activation predominantly or entirely reflects binding to α7/α7 subunit interface sites.
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Affiliation(s)
- Milena Moretti
- CNR Institute of Neuroscience, Biometra University of Milan, Milan, Italy (M.M., F.P., C.G.); Section of Physiology and Neurosciences, Department of Biomedical, Metabolic, and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy (M.Z.); Division of Neurobiology, Barrow Neurologic Institute, Phoenix, Arizona (A.A.G., R.J.L., P.W.); and Centre National de la Recherche Scientifique, Unité Neurobiologie Intégrative des Systèmes Cholinergiques, Institut Pasteur, Paris, France (U.M.)
| | - Michele Zoli
- CNR Institute of Neuroscience, Biometra University of Milan, Milan, Italy (M.M., F.P., C.G.); Section of Physiology and Neurosciences, Department of Biomedical, Metabolic, and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy (M.Z.); Division of Neurobiology, Barrow Neurologic Institute, Phoenix, Arizona (A.A.G., R.J.L., P.W.); and Centre National de la Recherche Scientifique, Unité Neurobiologie Intégrative des Systèmes Cholinergiques, Institut Pasteur, Paris, France (U.M.)
| | - Andrew A George
- CNR Institute of Neuroscience, Biometra University of Milan, Milan, Italy (M.M., F.P., C.G.); Section of Physiology and Neurosciences, Department of Biomedical, Metabolic, and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy (M.Z.); Division of Neurobiology, Barrow Neurologic Institute, Phoenix, Arizona (A.A.G., R.J.L., P.W.); and Centre National de la Recherche Scientifique, Unité Neurobiologie Intégrative des Systèmes Cholinergiques, Institut Pasteur, Paris, France (U.M.)
| | - Ronald J Lukas
- CNR Institute of Neuroscience, Biometra University of Milan, Milan, Italy (M.M., F.P., C.G.); Section of Physiology and Neurosciences, Department of Biomedical, Metabolic, and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy (M.Z.); Division of Neurobiology, Barrow Neurologic Institute, Phoenix, Arizona (A.A.G., R.J.L., P.W.); and Centre National de la Recherche Scientifique, Unité Neurobiologie Intégrative des Systèmes Cholinergiques, Institut Pasteur, Paris, France (U.M.)
| | - Francesco Pistillo
- CNR Institute of Neuroscience, Biometra University of Milan, Milan, Italy (M.M., F.P., C.G.); Section of Physiology and Neurosciences, Department of Biomedical, Metabolic, and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy (M.Z.); Division of Neurobiology, Barrow Neurologic Institute, Phoenix, Arizona (A.A.G., R.J.L., P.W.); and Centre National de la Recherche Scientifique, Unité Neurobiologie Intégrative des Systèmes Cholinergiques, Institut Pasteur, Paris, France (U.M.)
| | - Uwe Maskos
- CNR Institute of Neuroscience, Biometra University of Milan, Milan, Italy (M.M., F.P., C.G.); Section of Physiology and Neurosciences, Department of Biomedical, Metabolic, and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy (M.Z.); Division of Neurobiology, Barrow Neurologic Institute, Phoenix, Arizona (A.A.G., R.J.L., P.W.); and Centre National de la Recherche Scientifique, Unité Neurobiologie Intégrative des Systèmes Cholinergiques, Institut Pasteur, Paris, France (U.M.)
| | - Paul Whiteaker
- CNR Institute of Neuroscience, Biometra University of Milan, Milan, Italy (M.M., F.P., C.G.); Section of Physiology and Neurosciences, Department of Biomedical, Metabolic, and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy (M.Z.); Division of Neurobiology, Barrow Neurologic Institute, Phoenix, Arizona (A.A.G., R.J.L., P.W.); and Centre National de la Recherche Scientifique, Unité Neurobiologie Intégrative des Systèmes Cholinergiques, Institut Pasteur, Paris, France (U.M.)
| | - Cecilia Gotti
- CNR Institute of Neuroscience, Biometra University of Milan, Milan, Italy (M.M., F.P., C.G.); Section of Physiology and Neurosciences, Department of Biomedical, Metabolic, and Neural Sciences, University of Modena and Reggio Emilia, Modena, Italy (M.Z.); Division of Neurobiology, Barrow Neurologic Institute, Phoenix, Arizona (A.A.G., R.J.L., P.W.); and Centre National de la Recherche Scientifique, Unité Neurobiologie Intégrative des Systèmes Cholinergiques, Institut Pasteur, Paris, France (U.M.)
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Olsen JA, Ahring PK, Kastrup JS, Gajhede M, Balle T. Structural and functional studies of the modulator NS9283 reveal agonist-like mechanism of action at α4β2 nicotinic acetylcholine receptors. J Biol Chem 2014; 289:24911-21. [PMID: 24982426 DOI: 10.1074/jbc.m114.568097] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Modulation of Cys loop receptor ion channels is a proven drug discovery strategy, but many underlying mechanisms of the mode of action are poorly understood. We report the x-ray structure of the acetylcholine-binding protein from Lymnaea stagnalis with NS9283, a stoichiometry selective positive modulator that targets the α4-α4 interface of α4β2 nicotinic acetylcholine receptors (nAChRs). Together with homology modeling, mutational data, quantum mechanical calculations, and pharmacological studies on α4β2 nAChRs, the structure reveals a modulator binding mode that overlaps the α4-α4 interface agonist (acetylcholine)-binding site. Analysis of contacts to residues known to govern agonist binding and function suggests that modulation occurs by an agonist-like mechanism. Selectivity for α4-α4 over α4-β2 interfaces is determined mainly by steric restrictions from Val-136 on the β2-subunit and favorable interactions between NS9283 and His-142 at the complementary side of α4. In the concentration ranges where modulation is observed, its selectivity prevents NS9283 from directly activating nAChRs because activation requires coordinated action from more than one interface. However, we demonstrate that in a mutant receptor with one natural and two engineered α4-α4 interfaces, NS9283 is an agonist. Modulation via extracellular binding sites is well known for benzodiazepines acting at γ-aminobutyric acid type A receptors. Like NS9283, benzodiazepines increase the apparent agonist potency with a minimal effect on efficacy. The shared modulatory profile along with a binding site located in an extracellular subunit interface suggest that modulation via an agonist-like mechanism may be a common mechanism of action that potentially could apply to Cys loop receptors beyond the α4β2 nAChRs.
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Affiliation(s)
- Jeppe A Olsen
- From NeuroSearch A/S, Pederstrupvej 93, 2750 Ballerup, Denmark, the Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark, the Faculty of Pharmacy, The University of Sydney, Sydney, New South Wales 2006, Australia, and
| | - Philip K Ahring
- the Faculty of Pharmacy, The University of Sydney, Sydney, New South Wales 2006, Australia, and Saniona AB, Baltorpvej 54, 2750 Ballerup, Denmark
| | - Jette S Kastrup
- the Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Michael Gajhede
- the Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Thomas Balle
- the Faculty of Pharmacy, The University of Sydney, Sydney, New South Wales 2006, Australia, and
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48
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Lynagh T, Pless SA. Principles of agonist recognition in Cys-loop receptors. Front Physiol 2014; 5:160. [PMID: 24795655 PMCID: PMC4006026 DOI: 10.3389/fphys.2014.00160] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2014] [Accepted: 04/04/2014] [Indexed: 12/22/2022] Open
Abstract
Cys-loop receptors are ligand-gated ion channels that are activated by a structurally diverse array of neurotransmitters, including acetylcholine, serotonin, glycine, and GABA. After the term "chemoreceptor" emerged over 100 years ago, there was some wait until affinity labeling, molecular cloning, functional studies, and X-ray crystallography experiments identified the extracellular interface of adjacent subunits as the principal site of agonist binding. The question of how subtle differences at and around agonist-binding sites of different Cys-loop receptors can accommodate transmitters as chemically diverse as glycine and serotonin has been subject to intense research over the last three decades. This review outlines the functional diversity and current structural understanding of agonist-binding sites, including those of invertebrate Cys-loop receptors. Together, this provides a framework to understand the atomic determinants involved in how these valuable therapeutic targets recognize and bind their ligands.
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Affiliation(s)
| | - Stephan A. Pless
- Department of Drug Design and Pharmacology, Center for Biopharmaceuticals, University of CopenhagenCopenhagen, Denmark
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Asymmetric perturbations of signalling oligomers. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2014; 114:153-69. [PMID: 24650570 DOI: 10.1016/j.pbiomolbio.2014.03.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Revised: 02/26/2014] [Accepted: 03/04/2014] [Indexed: 01/06/2023]
Abstract
This review focuses on rapid and reversible noncovalent interactions for symmetric oligomers of signalling proteins. Symmetry mismatch, transient symmetry breaking and asymmetric perturbations via chemical (ligand binding) and physical (electric or mechanic) effects can initiate the signalling events. Advanced biophysical methods can reveal not only structural symmetries of stable membrane-bound signalling proteins but also asymmetric functional transition states. Relevant techniques amenable to distinguish between symmetric and asymmetric architectures are discussed including those with the capability of capturing low-populated transient conformational states. Typical examples of signalling proteins are overviewed for symmetry breaking in dimers (GPCRs, growth factor receptors, transcription factors); trimers (acid-sensing ion channels); tetramers (voltage-gated cation channels, ionotropic glutamate receptor, CNG and CHN channels); pentameric ligand-gated and mechanosensitive channels; higher order oligomers (gap junction channel, chaperonins, proteasome, virus capsid); as well as primary and secondary transporters. In conclusion, asymmetric perturbations seem to play important functional roles in a broad range of communicating networks.
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50
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daCosta CJB, Baenziger JE. Gating of pentameric ligand-gated ion channels: structural insights and ambiguities. Structure 2014; 21:1271-83. [PMID: 23931140 DOI: 10.1016/j.str.2013.06.019] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Revised: 05/31/2013] [Accepted: 06/26/2013] [Indexed: 01/09/2023]
Abstract
Pentameric ligand-gated ion channels (pLGICs) mediate fast synaptic communication by converting chemical signals into an electrical response. Recently solved agonist-bound and agonist-free structures greatly extend our understanding of these complex molecular machines. A key challenge to a full description of function, however, is the ability to unequivocally relate determined structures to the canonical resting, open, and desensitized states. Here, we review current understanding of pLGIC structure, with a focus on the conformational changes underlying channel gating. We compare available structural information and review the evidence supporting the assignment of each structure to a particular conformational state. We discuss multiple factors that may complicate the interpretation of crystal structures, highlighting the potential influence of lipids and detergents. We contend that further advances in the structural biology of pLGICs will require deeper insight into the nature of pLGIC-lipid interactions.
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Affiliation(s)
- Corrie J B daCosta
- Receptor Biology Laboratory, Departments of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905, USA
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