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Bourne Y, Sulzenbacher G, Chabaud L, Aráoz R, Radić Z, Conrod S, Taylor P, Guillou C, Molgó J, Marchot P. The Cyclic Imine Core Common to the Marine Macrocyclic Toxins Is Sufficient to Dictate Nicotinic Acetylcholine Receptor Antagonism. Mar Drugs 2024; 22:149. [PMID: 38667766 PMCID: PMC11050823 DOI: 10.3390/md22040149] [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: 02/13/2024] [Revised: 03/22/2024] [Accepted: 03/25/2024] [Indexed: 04/28/2024] Open
Abstract
Macrocyclic imine phycotoxins are an emerging class of chemical compounds associated with harmful algal blooms and shellfish toxicity. Earlier binding and electrophysiology experiments on nAChR subtypes and their soluble AChBP surrogates evidenced common trends for substantial antagonism, binding affinities, and receptor-subtype selectivity. Earlier, complementary crystal structures of AChBP complexes showed that common determinants within the binding nest at each subunit interface confer high-affinity toxin binding, while distinctive determinants from the flexible loop C, and either capping the nest or extending toward peripheral subsites, dictate broad versus narrow receptor subtype selectivity. From these data, small spiroimine enantiomers mimicking the functional core motif of phycotoxins were chemically synthesized and characterized. Voltage-clamp analyses involving three nAChR subtypes revealed preserved antagonism for both enantiomers, despite lower subtype specificity and binding affinities associated with faster reversibility compared with their macrocyclic relatives. Binding and structural analyses involving two AChBPs pointed to modest affinities and positional variability of the spiroimines, along with a range of AChBP loop-C conformations denoting a prevalence of antagonistic properties. These data highlight the major contribution of the spiroimine core to binding within the nAChR nest and confirm the need for an extended interaction network as established by the macrocyclic toxins to define high affinities and marked subtype specificity. This study identifies a minimal set of functional pharmacophores and binding determinants as templates for designing new antagonists targeting disease-associated nAChR subtypes.
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Affiliation(s)
- Yves Bourne
- Lab “Architecture et Fonction des Macromolécules Biologiques” (AFMB), Aix-Marseille Univ, CNRS, Faculté des Sciences Campus Luminy, 13288 Marseille cedex 09, France; (Y.B.); (G.S.)
| | - Gerlind Sulzenbacher
- Lab “Architecture et Fonction des Macromolécules Biologiques” (AFMB), Aix-Marseille Univ, CNRS, Faculté des Sciences Campus Luminy, 13288 Marseille cedex 09, France; (Y.B.); (G.S.)
| | - Laurent Chabaud
- Institut de Chimie des Substances Naturelles (ICSN), Univ Paris-Saclay, CNRS, 91198 Gif-sur-Yvette, France; (L.C.); (C.G.)
| | - Rómulo Aráoz
- Service d’Ingénierie Moléculaire pour la Santé (SIMoS) EMR CNRS 9004, Département Médicaments et Technologies pour la Santé, Institut des Sciences du Vivant Frédéric Joliot, CEA, INRAE, Université Paris-Saclay, 91191 Gif-sur-Yvette, France; (R.A.); (J.M.)
| | - Zoran Radić
- Skaggs School of Pharmacy and Pharmaceutical Sciences (SSPPS), University of California San Diego, La Jolla, CA 92093-0751, USA; (Z.R.); (P.T.)
| | - Sandrine Conrod
- Centre de Recherche en Neurobiologie et Neurophysiologie de Marseille (CRN2M), Aix Marseille Univ, CNRS, 13344 Marseille, France;
| | - Palmer Taylor
- Skaggs School of Pharmacy and Pharmaceutical Sciences (SSPPS), University of California San Diego, La Jolla, CA 92093-0751, USA; (Z.R.); (P.T.)
| | - Catherine Guillou
- Institut de Chimie des Substances Naturelles (ICSN), Univ Paris-Saclay, CNRS, 91198 Gif-sur-Yvette, France; (L.C.); (C.G.)
| | - Jordi Molgó
- Service d’Ingénierie Moléculaire pour la Santé (SIMoS) EMR CNRS 9004, Département Médicaments et Technologies pour la Santé, Institut des Sciences du Vivant Frédéric Joliot, CEA, INRAE, Université Paris-Saclay, 91191 Gif-sur-Yvette, France; (R.A.); (J.M.)
| | - Pascale Marchot
- Lab “Architecture et Fonction des Macromolécules Biologiques” (AFMB), Aix-Marseille Univ, CNRS, Faculté des Sciences Campus Luminy, 13288 Marseille cedex 09, France; (Y.B.); (G.S.)
- Centre de Recherche en Neurobiologie et Neurophysiologie de Marseille (CRN2M), Aix Marseille Univ, CNRS, 13344 Marseille, France;
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Membrane lipid organization and nicotinic acetylcholine receptor function: A two-way physiological relationship. Arch Biochem Biophys 2022; 730:109413. [DOI: 10.1016/j.abb.2022.109413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Revised: 09/07/2022] [Accepted: 09/20/2022] [Indexed: 11/21/2022]
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Activation of α7 Nicotinic Acetylcholine Receptor Upregulates HLA-DR and Macrophage Receptors: Potential Role in Adaptive Immunity and in Preventing Immunosuppression. Biomolecules 2020; 10:biom10040507. [PMID: 32230846 PMCID: PMC7225944 DOI: 10.3390/biom10040507] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2020] [Revised: 03/16/2020] [Accepted: 03/23/2020] [Indexed: 12/14/2022] Open
Abstract
Immune response during sepsis is characterized by hyper-inflammation followed by immunosuppression. The crucial role of macrophages is well-known for both septic stages, since they are involved in immune homeostasis and inflammation, their dysfunction being implicated in immunosuppression. The cholinergic anti-inflammatory pathway mediated by macrophage α7 nicotinic acetylcholine receptor (nAChR) represents possible drug target. Although α7 nAChR activation on macrophages reduces the production of proinflammatory cytokines, the role of these receptors in immunological changes at the cellular level is not fully understood. Using α7 nAChR selective agonist PNU 282,987, we investigated the influence of α7 nAChR activation on the expression of cytokines and, for the first time, of the macrophage membrane markers: cluster of differentiation 14 (CD14), human leukocyte antigen-DR (HLA-DR), CD11b, and CD54. Application of PNU 282,987 to THP-1Mϕ (THP-1 derived macrophages) cells led to inward ion currents and Ca2+ increase in cytoplasm showing the presence of functionally active α7 nAChR. Production of cytokines tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and IL-10 was estimated in classically activated macrophages (M1) and treatment with PNU 282,987 diminished IL-10 expression. α7 nAChR activation on THP-1Mϕ, THP-1M1, and monocyte-derived macrophages (MDMs) increased the expression of HLA-DR, CD54, and CD11b molecules, but decreased CD14 receptor expression, these effects being blocked by alpha (α)-bungarotoxin. Thus, PNU 282,987 enhances the macrophage-mediated immunity via α7 nAChR by regulating expression of their membrane receptors and of cytokines, both playing an important role in preventing immunosuppressive states.
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Gaens D, Rummel C, Schmidt M, Hamann M, Geyer J. Suspected neurological toxicity after oral application of fluralaner (Bravecto®) in a Kooikerhondje dog. BMC Vet Res 2019; 15:283. [PMID: 31391054 PMCID: PMC6686215 DOI: 10.1186/s12917-019-2016-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Accepted: 07/18/2019] [Indexed: 11/10/2022] Open
Abstract
Background Although the new isoxazoline drug fluralaner (Bravecto®) is generally well tolerated in dogs, adverse drug reactions involving neurological dysfunction occurred in individual dogs. However, most of these cases are documented inadequately and none of them is reported and discussed in the literature. As isoxazoline drugs target neuronal chloride channels with a clear preference for invertebrates, they are considered to have a good safety profile. However, pharmacodynamic effects in the nervous system of vertebrates cannot be ruled out completely. Case presentation A seven-month-old female Kooikerhondje dog was treated with Bravecto® at the recommended dose. About 24 h after administration, the dog exhibited signs of neurological toxicity, including generalized ataxia, myoclonic jerks, tremor of head and body, muscle twitching and oral dysphagia. All symptoms were transient and the dog fully recovered without any treatment after 10 h. Conclusion This case report describes transient occurrence of neurological dysfunction after administration of Bravecto®. It may help to better classify adverse drug reactions after application of isoxazoline drugs and documents a good prognosis even after occurrence of severe neurological dysfunction in the present case. Electronic supplementary material The online version of this article (10.1186/s12917-019-2016-4) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Daniela Gaens
- Institute of Pharmacology and Toxicology, Biomedical Research Center Seltersberg, Justus Liebig University Giessen, Schubertstr. 81, 35392, Giessen, Germany
| | - Christoph Rummel
- Institute of Veterinary Physiology and Biochemistry, Justus Liebig University Giessen, Giessen, Germany
| | - Martin Schmidt
- Department of Veterinary Clinical Sciences, Clinic for Small Animal-Surgery, Faculty of Veterinary Medicine, Justus-Liebig-University Giessen, Giessen, Germany
| | - Melanie Hamann
- Institute of Pharmacology and Toxicology, Biomedical Research Center Seltersberg, Justus Liebig University Giessen, Schubertstr. 81, 35392, Giessen, Germany
| | - Joachim Geyer
- Institute of Pharmacology and Toxicology, Biomedical Research Center Seltersberg, Justus Liebig University Giessen, Schubertstr. 81, 35392, Giessen, Germany.
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5
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Malomouzh A, Ilyin V, Nikolsky E. Components of the GABAergic signaling in the peripheral cholinergic synapses of vertebrates: a review. Amino Acids 2019; 51:1093-1102. [PMID: 31236726 DOI: 10.1007/s00726-019-02754-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Accepted: 06/19/2019] [Indexed: 12/23/2022]
Abstract
Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the mammalian central nervous system. Since the 1970s, many studies have focused on the role of GABA in the mammalian peripheral nervous system, and particularly in the cholinergic synapses. In this review, we present current findings for the cholinergic neurons of vegetative ganglia as well as for the neurons innervating smooth and striated muscles. Synaptic contacts formed by these neurons contain GABA and the enzyme, glutamic acid decarboxylase, which catalyzes the synthesis of GABA from glutamate. Newly formed GABA is released in the cholinergic synapses and mostly all the peripheral cholinergic synaptic contacts contain iono- and metabotropic GABA receptors. Although the underlying molecular mechanism of the release is not well understood, still, it is speculated that GABA is released by a vesicular and/or non-vesicular way via reversal of the GABA transporter. We also review the signaling role of GABA in the peripheral cholinergic synapses by modulating acetylcholine release, but its exact physiological function remains to be elucidated.
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Affiliation(s)
- Artem Malomouzh
- Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, FRC Kazan Scientific Center of Russian Academy of Sciences, P.O. box 30, Kazan, 420111, Russia.
| | - Victor Ilyin
- Neuropharmacology Lab, Kazan Federal University, 18 Kremlyovskaya St, Kazan, 420008, Russia
| | - Evgeny Nikolsky
- Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, FRC Kazan Scientific Center of Russian Academy of Sciences, P.O. box 30, Kazan, 420111, Russia.,Neuropharmacology Lab, Kazan Federal University, 18 Kremlyovskaya St, Kazan, 420008, Russia
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6
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Yu R, Tae HS, Xu Q, Craik DJ, Adams DJ, Jiang T, Kaas Q. Molecular dynamics simulations of dihydro-β-erythroidine bound to the human α4β2 nicotinic acetylcholine receptor. Br J Pharmacol 2019; 176:2750-2763. [PMID: 31062355 DOI: 10.1111/bph.14698] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2018] [Revised: 03/20/2019] [Accepted: 04/10/2019] [Indexed: 12/27/2022] Open
Abstract
BACKGROUND AND PURPOSE The heteromeric α4β2 nicotinic acetylcholine receptor (nAChR) is abundant in the human brain and is associated with a range of CNS disorders. This nAChR subtype has been recently crystallised in a conformation that was proposed to represent a desensitised state. Here, we investigated the conformational transition mechanism of this nAChR from a desensitised to a closed/resting state. EXPERIMENTAL APPROACH The competitive antagonist dihydro-β-erythroidine (DHβE) was modelled by replacement of the agonist nicotine in the α4β2 nAChR experimental structure. DHβE is used both in vitro and in vivo for its ability to block α4β2 nAChRs. This system was studied by three molecular dynamics simulations with a combined simulation time of 2.6 μs. Electrophysiological studies of mutated receptors were performed to validate the simulation results. KEY RESULTS The relative positions of the extracellular and transmembrane domains in the models are distinct from those of the desensitised state structure and are compatible with experimental structures of Cys-loop receptors captured in a closed/resting state. CONCLUSIONS AND IMPLICATIONS Our model suggests that the side chains of α4 L257 (9') and α4 L264 (16') are the main constrictions in the transmembrane pore. The involvement of position 9' in channel gating is well established, but position 16' was only previously identified as a gate for the bacterial channels, ELIC and GLIC. L257 but not L264 was found to influence the slow component of desensitisation. The structure of the antagonist-bound state proposed here should be valuable for the development of therapeutic or insecticide compounds.
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Affiliation(s)
- Rilei Yu
- Key Laboratory of Marine Drugs, Chinese Ministry of Education, School of Medicine and Pharmacy, Ocean University of China, Qingdao, China.,Laboratory for Marine Drugs and Bioproducts, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China
| | - Han-Shen Tae
- Illawarra Health and Medical Research Institute (IHMRI), University of Wollongong, Wollongong, NSW, Australia
| | - Qingliang Xu
- Key Laboratory of Marine Drugs, Chinese Ministry of Education, School of Medicine and Pharmacy, Ocean University of China, Qingdao, China.,Laboratory for Marine Drugs and Bioproducts, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China
| | - David J Craik
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD, Australia
| | - David J Adams
- Illawarra Health and Medical Research Institute (IHMRI), University of Wollongong, Wollongong, NSW, Australia
| | - Tao Jiang
- Key Laboratory of Marine Drugs, Chinese Ministry of Education, School of Medicine and Pharmacy, Ocean University of China, Qingdao, China.,Laboratory for Marine Drugs and Bioproducts, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China
| | - Quentin Kaas
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD, Australia
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Absalom NL, Ahring PK, Liao VW, Balle T, Jiang T, Anderson LL, Arnold JC, McGregor IS, Bowen MT, Chebib M. Functional genomics of epilepsy-associated mutations in the GABA A receptor subunits reveal that one mutation impairs function and two are catastrophic. J Biol Chem 2019; 294:6157-6171. [PMID: 30728247 DOI: 10.1074/jbc.ra118.005697] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2018] [Revised: 01/30/2019] [Indexed: 12/29/2022] Open
Abstract
A number of epilepsy-causing mutations have recently been identified in the genes of the α1, β3, and γ2 subunits comprising the γ-aminobutyric acid type A (GABAA) receptor. These mutations are typically dominant, and in certain cases, such as the α1 and β3 subunits, they may lead to a mix of receptors at the cell surface that contain no mutant subunits, a single mutated subunit, or two mutated subunits. To determine the effects of mutations in a single subunit or in two subunits on receptor activation, we created a concatenated protein assembly that links all five subunits of the α1β3γ2 receptor and expresses them in the correct orientation. We created nine separate receptor variants with a single-mutant subunit and four receptors containing two subunits of the γ2R323Q, β3D120N, β3T157M, β3Y302C, and β3S254F epilepsy-causing mutations. We found that the singly mutated γ2R323Q subunit impairs GABA activation of the receptor by reducing GABA potency. A single β3D120N, β3T157M, or β3Y302C mutation also substantially impaired receptor activation, and two copies of these mutants within a receptor were catastrophic. Of note, an effect of the β3S254F mutation on GABA potency depended on the location of this mutant subunit within the receptor, possibly because of the membrane environment surrounding the transmembrane region of the receptor. Our results highlight that precise functional genomic analyses of GABAA receptor mutations using concatenated constructs can identify receptors with an intermediate phenotype that contribute to epileptic phenotypes and that are potential drug targets for precision medicine approaches.
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Affiliation(s)
- Nathan L Absalom
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; School of Pharmacy, University of Sydney, Camperdown, New South Wales 2006, Australia
| | - Philip K Ahring
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; School of Pharmacy, University of Sydney, Camperdown, New South Wales 2006, Australia
| | - Vivian W Liao
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; School of Pharmacy, University of Sydney, Camperdown, New South Wales 2006, Australia
| | - Thomas Balle
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; School of Pharmacy, University of Sydney, Camperdown, New South Wales 2006, Australia
| | - Tian Jiang
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; School of Pharmacy, University of Sydney, Camperdown, New South Wales 2006, Australia
| | - Lyndsey L Anderson
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; Discipline of Pharmacology, Faculty of Medicine and Health, University of Sydney, Camperdown, New South Wales 2006, Australia; Lambert Initiative for Cannabinoid Therapeutics, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia
| | - Jonathon C Arnold
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; Discipline of Pharmacology, Faculty of Medicine and Health, University of Sydney, Camperdown, New South Wales 2006, Australia; Lambert Initiative for Cannabinoid Therapeutics, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia
| | - Iain S McGregor
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; Lambert Initiative for Cannabinoid Therapeutics, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; the School of Psychology, Faculty of Science, University of Sydney, Camperdown, New South Wales 2006, Australia
| | - Michael T Bowen
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; Lambert Initiative for Cannabinoid Therapeutics, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; the School of Psychology, Faculty of Science, University of Sydney, Camperdown, New South Wales 2006, Australia
| | - Mary Chebib
- From the Brain and Mind Centre, University of Sydney, 94 Mallett Street, Camperdown, New South Wales 2050, Australia; School of Pharmacy, University of Sydney, Camperdown, New South Wales 2006, Australia.
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Chiodo L, Malliavin TE, Giuffrida S, Maragliano L, Cottone G. Closed-Locked and Apo-Resting State Structures of the Human α7 Nicotinic Receptor: A Computational Study. J Chem Inf Model 2018; 58:2278-2293. [PMID: 30359518 DOI: 10.1021/acs.jcim.8b00412] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Nicotinic acetylcholine receptors, belonging to the Cys-loop superfamily of ligand-gated ion channels (LGICs), are membrane proteins present in neurons and at neuromuscular junctions. They are responsible for signal transmission, and their function is regulated by neurotransmitters, agonists, and antagonists drugs. A detailed knowledge of their conformational transition in response to ligand binding is critical to understanding the basis of ligand-receptor interaction, in view of new pharmacological approaches to control receptor activity. However, the scarcity of experimentally derived structures of human channels makes this perspective extremely challenging. To contribute overcoming this issue, we have recently reported structural models for the open and the desensitized states of the human α7 nicotinic receptor. Here, we provide all-atom structural models of the same receptor in two different nonconductive states. The first structure, built via homology modeling and relaxed with extensive Molecular Dynamics simulations, represents the receptor bound to the natural antagonist α-conotoxin ImI. After comparison with available experimental data and computational models of other eukaryotic LGICs, we deem it consistent with the "closed-locked" state. The second model, obtained with simulations from the spontaneous relaxation of the open, agonist-bound α7 structure after ligand removal, recapitulates the characteristics of the apo-resting state of the receptor. These results add to our previous work on the active and desensitized state conformations, contributing to the structural characterization of the conformational landscape of the human α7 receptor and suggesting benchmarks to discriminate among conformations found in experiments or in simulations of LGICs. In particular key interactions at the interface between the extracellular domain and the transmembrane domain are identified, that could be critical to the α7 receptor function.
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Affiliation(s)
- Letizia Chiodo
- Department of Engineering , Campus Bio-Medico University of Rome , Via Á. del Portillo 21 , 00128 Rome , Italy
| | - Thérèse E Malliavin
- Institut Pasteur and CNRS UMR 3528, Unité de Bioinformatique Structurale , 25-28 rue du Dr Roux , 75015 Paris , France.,Centre de Bioinformatique, Biostatistique et Biologie Intégrative , Institut Pasteur and CNRS USR 3756 , 25-28 rue du Dr Roux , 75015 Paris , France
| | - Sergio Giuffrida
- Department of Physics and Chemistry , University of Palermo , Viale delle Scienze Ed. 17 , 90128 Palermo , Italy
| | - Luca Maragliano
- Center for Synaptic Neuroscience and Technology (NSYN@UniGe) , Istituto Italiano di Tecnologia , Largo Rosanna Benzi, 10 , 16132 Genoa , Italy.,IRCCS Ospedale Policlinico San Martino , Largo Rosanna Benzi 10 , 16132 Genoa , Italy
| | - Grazia Cottone
- Department of Physics and Chemistry , University of Palermo , Viale delle Scienze Ed. 17 , 90128 Palermo , Italy
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Shin DJ, Germann AL, Covey DF, Steinbach JH, Akk G. Analysis of GABA A Receptor Activation by Combinations of Agonists Acting at the Same or Distinct Binding Sites. Mol Pharmacol 2018; 95:70-81. [PMID: 30337372 DOI: 10.1124/mol.118.113464] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Accepted: 10/17/2018] [Indexed: 11/22/2022] Open
Abstract
Under both physiologic and clinical conditions GABAA receptors are exposed to multiple agonists, including the transmitter GABA, endogenous or exogenous neuroactive steroids, and various GABAergic anesthetic and sedative drugs. The functional output of the receptor reflects the interplay among all active agents. We have investigated the activation of the concatemeric α1β2γ2L GABAA receptor by combinations of agonists. Simulations of receptor activity using the coagonist concerted transition model demonstrate that the response amplitude in the presence of agonist combinations is highly dependent on whether the paired agonists interact with the same or distinct sites. The experimental data for receptor activation by agonist combinations were in agreement with the established views of the overlap of binding sites for several pairs of orthosteric (GABA, β-alanine, and piperidine-4-sulfonic acid) and/or allosteric agents (propofol, pentobarbital, and several neuroactive steroids). Conversely, the degree of potentiation when two GABAergic agents are coapplied can be used to determine whether the compounds act by binding to the same or distinct sites. We show that common interaction sites mediate the actions of 5α- and 5β-reduced neuroactive steroids, and natural and enantiomeric steroids. Furthermore, the results indicate that the anesthetics propofol and pentobarbital interact with partially shared binding sites. We propose that the findings may be used to predict the efficacy of drug mixtures in combination therapy and thus have potential clinical relevance.
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Affiliation(s)
- Daniel J Shin
- Departments of Anesthesiology (D.J.S., A.L.G., J.H.S., G.A.) and Developmental Biology (D.F.C.), and the Taylor Family Institute for Innovative Psychiatric Research (D.F.C., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Allison L Germann
- Departments of Anesthesiology (D.J.S., A.L.G., J.H.S., G.A.) and Developmental Biology (D.F.C.), and the Taylor Family Institute for Innovative Psychiatric Research (D.F.C., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Douglas F Covey
- Departments of Anesthesiology (D.J.S., A.L.G., J.H.S., G.A.) and Developmental Biology (D.F.C.), and the Taylor Family Institute for Innovative Psychiatric Research (D.F.C., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Joe Henry Steinbach
- Departments of Anesthesiology (D.J.S., A.L.G., J.H.S., G.A.) and Developmental Biology (D.F.C.), and the Taylor Family Institute for Innovative Psychiatric Research (D.F.C., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Gustav Akk
- Departments of Anesthesiology (D.J.S., A.L.G., J.H.S., G.A.) and Developmental Biology (D.F.C.), and the Taylor Family Institute for Innovative Psychiatric Research (D.F.C., J.H.S., G.A.), Washington University School of Medicine, St. Louis, Missouri
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10
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Bouzat C, Mukhtasimova N. The nicotinic acetylcholine receptor as a molecular machine for neuromuscular transmission. CURRENT OPINION IN PHYSIOLOGY 2018. [DOI: 10.1016/j.cophys.2018.04.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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11
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Germann AL, Shin DJ, Kuhrau CR, Johnson AD, Evers AS, Akk G. High Constitutive Activity Accounts for the Combination of Enhanced Direct Activation and Reduced Potentiation in Mutated GABA A Receptors. Mol Pharmacol 2018; 93:468-476. [PMID: 29439087 DOI: 10.1124/mol.117.111435] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2017] [Accepted: 02/07/2018] [Indexed: 11/22/2022] Open
Abstract
GABAA receptors activated by the transmitter GABA are potentiated by several allosterically acting drugs, including the intravenous anesthetic propofol. Propofol can also directly activate the receptor, albeit at higher concentrations. Previous functional studies have identified amino acid residues whose substitution reduces potentiation of GABA-activated receptors by propofol while enhancing the ability of propofol to directly activate the receptor. One interpretation of such observations is that the mutation has specific effects on the sites or processes involved in potentiation or activation. We show here that divergent effects on potentiation and direct activation can be mediated by increased constitutive open probability in the mutant receptor without any specific effect on the interactions between the allosteric drug and the receptor. By simulating GABAA receptor activity using the concerted transition model, we demonstrate that the predicted degree of potentiation is reduced as the level of constitutive activity increases. The model further predicts that a potentiating effect of an allosteric modulator is a computable value that depends on the level of constitutive activity, the amplitude of the response to the agonist, and the amplitude of the direct activating response to the modulator. Specific predictions were confirmed by electrophysiological data from the binary α1β3 and concatemeric ternary β2α1γ2L+β2α1 GABAA receptors. The corollaries of reduced potentiation due to increased constitutive activity are isobolograms that conform to simple additivity and a loss of separation between the concentration-response relationships for direct activation and potentiation.
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Affiliation(s)
- Allison L Germann
- Department of Anesthesiology (A.L.G., D.J.S., C.R.K., A.D.J., A.S.E., G.A.) and Taylor Family Institute for Innovative Psychiatric Research (A.S.E., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Daniel J Shin
- Department of Anesthesiology (A.L.G., D.J.S., C.R.K., A.D.J., A.S.E., G.A.) and Taylor Family Institute for Innovative Psychiatric Research (A.S.E., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Christina R Kuhrau
- Department of Anesthesiology (A.L.G., D.J.S., C.R.K., A.D.J., A.S.E., G.A.) and Taylor Family Institute for Innovative Psychiatric Research (A.S.E., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Alexander D Johnson
- Department of Anesthesiology (A.L.G., D.J.S., C.R.K., A.D.J., A.S.E., G.A.) and Taylor Family Institute for Innovative Psychiatric Research (A.S.E., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Alex S Evers
- Department of Anesthesiology (A.L.G., D.J.S., C.R.K., A.D.J., A.S.E., G.A.) and Taylor Family Institute for Innovative Psychiatric Research (A.S.E., G.A.), Washington University School of Medicine, St. Louis, Missouri
| | - Gustav Akk
- Department of Anesthesiology (A.L.G., D.J.S., C.R.K., A.D.J., A.S.E., G.A.) and Taylor Family Institute for Innovative Psychiatric Research (A.S.E., G.A.), Washington University School of Medicine, St. Louis, Missouri
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12
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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: 64] [Impact Index Per Article: 9.1] [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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13
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Nemecz Á, Prevost MS, Menny A, Corringer PJ. Emerging Molecular Mechanisms of Signal Transduction in Pentameric Ligand-Gated Ion Channels. Neuron 2017; 90:452-70. [PMID: 27151638 DOI: 10.1016/j.neuron.2016.03.032] [Citation(s) in RCA: 154] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Revised: 01/07/2016] [Accepted: 03/24/2016] [Indexed: 10/21/2022]
Abstract
Nicotinic acetylcholine, serotonin type 3, γ-amminobutyric acid type A, and glycine receptors are major players of human neuronal communication. They belong to the family of pentameric ligand-gated ion channels, sharing a highly conserved modular 3D structure. Recently, high-resolution structures of both open- and closed-pore conformations have been solved for a bacterial, an invertebrate, and a vertebrate receptor in this family. These data suggest that a common gating mechanism occurs, coupling neurotransmitter binding to pore opening, but they also pinpoint significant differences among subtypes. In this Review, we summarize the structural and functional data in light of these gating models and speculate about their mechanistic consequences on ion permeation, pathological mutations, as well as functional regulation by orthosteric and allosteric effectors.
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Affiliation(s)
- Ákos Nemecz
- Channel-Receptors Unit, Institut Pasteur, 75015 Paris, France; CNRS UMR 3571, 75015 Paris, France
| | - Marie S Prevost
- Institute of Structural and Molecular Biology, University College London and Birkbeck, Malet Street, London WC1E 7HX, UK
| | - Anaïs Menny
- Channel-Receptors Unit, Institut Pasteur, 75015 Paris, France; CNRS UMR 3571, 75015 Paris, France; Université Pierre et Marie Curie (UPMC), Cellule Pasteur, 75005 Paris, France
| | - Pierre-Jean Corringer
- Channel-Receptors Unit, Institut Pasteur, 75015 Paris, France; CNRS UMR 3571, 75015 Paris, France.
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14
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Richardson JS, Videau LL, Williams CJ, Richardson DC. Broad Analysis of Vicinal Disulfides: Occurrences, Conformations with Cis or with Trans Peptides, and Functional Roles Including Sugar Binding. J Mol Biol 2017; 429:1321-1335. [PMID: 28336403 DOI: 10.1016/j.jmb.2017.03.017] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Revised: 03/12/2017] [Accepted: 03/13/2017] [Indexed: 10/19/2022]
Abstract
Vicinal disulfides between sequence-adjacent cysteine residues are very rare and rather startling structural features which play a variety of functional roles. Typically discussed as an isolated curiosity, they have never received a general treatment covering both cis and trans forms. Enabled by the growing database of high-resolution structures, required deposition of diffraction data, and improved methods for discriminating reliable from dubious cases, we identify and describe distinct protein families with reliably genuine examples of cis or trans vicinal disulfides and discuss their conformations, conservation, and functions. No cis-trans interconversions and only one case of catalytic redox function are seen. Some vicinal disulfides are essential to large, functionally coupled motions, whereas most form the centers of tightly packed internal regions. Their most widespread biological role is providing a rigid hydrophobic contact surface under the undecorated side of a sugar or multiring ligand, contributing an important aspect of binding specificity.
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Affiliation(s)
- Jane S Richardson
- Department of Biochemistry, 3711 Duke University Medical Center, Durham, NC 27710, USA.
| | - Lizbeth L Videau
- Department of Biochemistry, 3711 Duke University Medical Center, Durham, NC 27710, USA
| | | | - David C Richardson
- Department of Biochemistry, 3711 Duke University Medical Center, Durham, NC 27710, USA
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15
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Crump A. Ivermectin: enigmatic multifaceted 'wonder' drug continues to surprise and exceed expectations. J Antibiot (Tokyo) 2017; 70:495-505. [PMID: 28196978 DOI: 10.1038/ja.2017.11] [Citation(s) in RCA: 113] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Revised: 11/28/2016] [Accepted: 12/03/2016] [Indexed: 12/12/2022]
Abstract
Over the past decade, the global scientific community have begun to recognize the unmatched value of an extraordinary drug, ivermectin, that originates from a single microbe unearthed from soil in Japan. Work on ivermectin has seen its discoverer, Satoshi Ōmura, of Tokyo's prestigious Kitasato Institute, receive the 2014 Gairdner Global Health Award and the 2015 Nobel Prize in Physiology or Medicine, which he shared with a collaborating partner in the discovery and development of the drug, William Campbell of Merck & Co. Incorporated. Today, ivermectin is continuing to surprise and excite scientists, offering more and more promise to help improve global public health by treating a diverse range of diseases, with its unexpected potential as an antibacterial, antiviral and anti-cancer agent being particularly extraordinary.
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Affiliation(s)
- Andy Crump
- Graduate School of Infection Control Sciences, Kitasato University, Minato-Ku, Japan
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16
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Gupta S, Chakraborty S, Vij R, Auerbach A. A mechanism for acetylcholine receptor gating based on structure, coupling, phi, and flip. J Gen Physiol 2016; 149:85-103. [PMID: 27932572 PMCID: PMC5217088 DOI: 10.1085/jgp.201611673] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Revised: 09/20/2016] [Accepted: 11/10/2016] [Indexed: 01/29/2023] Open
Abstract
Gupta et al. use single-channel electrophysiology to investigate the gating mechanism of acetylcholine receptor ion channels. They propose that channel opening starts at the M2–M3 linker and ligand-binding sites and proceeds through four brief intermediate conformations before ending with the collapse of a gate bubble. Nicotinic acetylcholine receptors are allosteric proteins that generate membrane currents by isomerizing (“gating”) between resting and active conformations under the influence of neurotransmitters. Here, to explore the mechanisms that link the transmitter-binding sites (TBSs) with the distant gate, we use mutant cycle analyses to measure coupling between residue pairs, phi value analyses to sequence domain rearrangements, and current simulations to reproduce a microsecond shut component (“flip”) apparent in single-channel recordings. Significant interactions between amino acids separated by >15 Å are rare; an exception is between the αM2–M3 linkers and the TBSs that are ∼30 Å apart. Linker residues also make significant, local interactions within and between subunits. Phi value analyses indicate that without agonists, the linker is the first region in the protein to reach the gating transition state. Together, the phi pattern and flip component suggest that a complete, resting↔active allosteric transition involves passage through four brief intermediate states, with brief shut events arising from sojourns in all or a subset. We derive energy landscapes for gating with and without agonists, and propose a structure-based model in which resting→active starts with spontaneous rearrangements of the M2–M3 linkers and TBSs. These conformational changes stabilize a twisted extracellular domain to promote transmembrane helix tilting, gate dilation, and the formation of a “bubble” that collapses to initiate ion conduction. The energy landscapes suggest that twisting is the most energetically unfavorable step in the resting→active conformational change and that the rate-limiting step in the reverse process is bubble formation.
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Affiliation(s)
- Shaweta Gupta
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
| | - Srirupa Chakraborty
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
| | - Ridhima Vij
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
| | - Anthony Auerbach
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY 14214
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17
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Zanetti SR, Ziblat A, Torres NI, Zwirner NW, Bouzat C. Expression and Functional Role of α7 Nicotinic Receptor in Human Cytokine-stimulated Natural Killer (NK) Cells. J Biol Chem 2016; 291:16541-52. [PMID: 27284006 DOI: 10.1074/jbc.m115.710574] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2015] [Indexed: 12/18/2022] Open
Abstract
The homomeric α7 nicotinic receptor (nAChR) is one of the most abundant nAChRs in the central nervous system where it contributes to cognition, attention, and working memory. α7 nAChR is also present in lymphocytes, dendritic cells (DCs), and macrophages and it is emerging as an important drug target for intervention in inflammation and sepsis. Natural killer (NK) cells display cytotoxic activity against susceptible target cells and modulate innate and adaptive immune responses through their interaction with DCs. We here show that human NK cells also express α7 nAChR. α7 nAChR mRNA is detected by RT-PCR and cell surface expression of α7 nAChR is detected by confocal microscopy and flow cytometry using α-bungarotoxin, a specific antagonist. Both mRNA and protein levels increase during NK stimulation with cytokines (IL-12, IL-18, and IL-15). Exposure of cytokine-stimulated NK cells to PNU-282987, a specific α7 nAChR agonist, increases intracellular calcium concentration ([Ca(2+)]i) mainly released from intracellular stores, indicating that α7 nAChR is functional. Moreover, its activation by PNU-282987 plus a specific positive allosteric modulator greatly enhances the Ca(2+) responses in NK cells. Stimulation of NK cells with cytokines and PNU-282987 decreases NF-κB levels and nuclear mobilization, down-regulates NKG2D receptors, and decreases NKG2D-dependent cell-mediated cytotoxicity and IFN-γ production. Also, such NK cells are less efficient to trigger DC maturation. Thus, our results demonstrate the anti-inflammatory role of α7 nAChR in NK cells and suggest that modulation of its activity in these cells may constitute a novel target for regulation of the immune response.
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Affiliation(s)
- Samanta R Zanetti
- From the Instituto de Investigaciones Bioquímicas (INIBIBB), Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 8000 Bahía Blanca
| | - Andrea Ziblat
- the Instituto de Biología y Medicina Experimental, CONICET, C1428ADN-Ciudad de Buenos Aires, and
| | - Nicolás I Torres
- the Instituto de Biología y Medicina Experimental, CONICET, C1428ADN-Ciudad de Buenos Aires, and
| | - Norberto W Zwirner
- the Instituto de Biología y Medicina Experimental, CONICET, C1428ADN-Ciudad de Buenos Aires, and the Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, C1428ADN-Ciudad de Buenos Aires, Argentina
| | - Cecilia Bouzat
- From the Instituto de Investigaciones Bioquímicas (INIBIBB), Universidad Nacional del Sur-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), 8000 Bahía Blanca,
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18
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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: 118] [Impact Index Per Article: 14.8] [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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19
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Bertrand D, Lee CHL, Flood D, Marger F, Donnelly-Roberts D. Therapeutic Potential of α7 Nicotinic Acetylcholine Receptors. Pharmacol Rev 2015; 67:1025-73. [DOI: 10.1124/pr.113.008581] [Citation(s) in RCA: 108] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
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20
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Azam L, Papakyriakou A, Zouridakis M, Giastas P, Tzartos SJ, McIntosh JM. Molecular interaction of α-conotoxin RgIA with the rat α9α10 nicotinic acetylcholine receptor. Mol Pharmacol 2015; 87:855-64. [PMID: 25740413 DOI: 10.1124/mol.114.096511] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The α9α10 nicotinic acetylcholine receptor (nAChR) was first identified in the auditory system, where it mediates synaptic transmission between efferent olivocochlear cholinergic fibers and cochlea hair cells. This receptor gained further attention due to its potential role in chronic pain and breast and lung cancers. We previously showed that α-conotoxin (α-CTx) RgIA, one of the few α9α10 selective ligands identified to date, is 300-fold less potent on human versus rat α9α10 nAChR. This species difference was conferred by only one residue in the (-), rather than (+), binding region of the α9 subunit. In light of this unexpected discovery, we sought to determine other interacting residues with α-CTx RgIA. A previous molecular modeling study, based on the structure of the homologous molluscan acetylcholine-binding protein, predicted that RgIA interacts with three residues on the α9(+) face and two residues on the α10(-) face of the α9α10 nAChR. However, mutations of these residues had little or no effect on toxin block of the α9α10 nAChR. In contrast, mutations of homologous residues in the opposing nAChR subunits (α10 Ε197, P200 and α9 T61, D121) resulted in 19- to 1700-fold loss of toxin activity. Based on the crystal structure of the extracellular domain (ECD) of human α9 nAChR, we modeled the rat α9α10 ECD and its complexes with α-CTx RgIA and acetylcholine. Our data support the interaction of α-CTx RgIA at the α10/α9 rather than the α9/α10 nAChR subunit interface, and may facilitate the development of selective ligands with therapeutic potential.
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Affiliation(s)
- Layla Azam
- Departments of Biology (L.A., J.M.M.) and Psychiatry (J.M.M.), University of Utah, Salt Lake City, Utah; George E. Wahlen Veterans Affair Medical Center, Salt Lake City, Utah (J.M.M.); National Center for Scientific Research "Demokritos," Athens, Greece (A.P.); and Department of Neurobiology, Hellenic Pasteur Institute, Athens, Greece (M.Z., P.G., S.J.T.)
| | - Athanasios Papakyriakou
- Departments of Biology (L.A., J.M.M.) and Psychiatry (J.M.M.), University of Utah, Salt Lake City, Utah; George E. Wahlen Veterans Affair Medical Center, Salt Lake City, Utah (J.M.M.); National Center for Scientific Research "Demokritos," Athens, Greece (A.P.); and Department of Neurobiology, Hellenic Pasteur Institute, Athens, Greece (M.Z., P.G., S.J.T.)
| | - Marios Zouridakis
- Departments of Biology (L.A., J.M.M.) and Psychiatry (J.M.M.), University of Utah, Salt Lake City, Utah; George E. Wahlen Veterans Affair Medical Center, Salt Lake City, Utah (J.M.M.); National Center for Scientific Research "Demokritos," Athens, Greece (A.P.); and Department of Neurobiology, Hellenic Pasteur Institute, Athens, Greece (M.Z., P.G., S.J.T.)
| | - Petros Giastas
- Departments of Biology (L.A., J.M.M.) and Psychiatry (J.M.M.), University of Utah, Salt Lake City, Utah; George E. Wahlen Veterans Affair Medical Center, Salt Lake City, Utah (J.M.M.); National Center for Scientific Research "Demokritos," Athens, Greece (A.P.); and Department of Neurobiology, Hellenic Pasteur Institute, Athens, Greece (M.Z., P.G., S.J.T.)
| | - Socrates J Tzartos
- Departments of Biology (L.A., J.M.M.) and Psychiatry (J.M.M.), University of Utah, Salt Lake City, Utah; George E. Wahlen Veterans Affair Medical Center, Salt Lake City, Utah (J.M.M.); National Center for Scientific Research "Demokritos," Athens, Greece (A.P.); and Department of Neurobiology, Hellenic Pasteur Institute, Athens, Greece (M.Z., P.G., S.J.T.)
| | - J Michael McIntosh
- Departments of Biology (L.A., J.M.M.) and Psychiatry (J.M.M.), University of Utah, Salt Lake City, Utah; George E. Wahlen Veterans Affair Medical Center, Salt Lake City, Utah (J.M.M.); National Center for Scientific Research "Demokritos," Athens, Greece (A.P.); and Department of Neurobiology, Hellenic Pasteur Institute, Athens, Greece (M.Z., P.G., S.J.T.)
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21
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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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22
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The evolution of pentameric ligand-gated ion-channels and the changing family of anthelmintic drug targets. Parasitology 2014; 142:303-17. [PMID: 25354656 DOI: 10.1017/s003118201400170x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
SUMMARY Pentameric ligand-gated ion-channels rapidly transduce synaptic neurotransmitter signals to an electrical response in post-synaptic neuronal or muscle cells and control the neuromusculature of a majority of multicellular animals. A wide range of pharmaceuticals target these receptors including ethanol, nicotine, anti-depressants and other mood regulating drugs, compounds that control pain and mobility and are targeted by a majority of anthelmintic drugs used to control parasitic infection of humans and livestock. Major advances have been made in recent years to our understanding of the structure, function, activity and the profile of compounds that can activate specific receptors. It is becoming clear that these anthelmintic drug targets are not fixed, but differ in significant details from one nematode species to another. Here we review what is known about the evolution of the pentameric ligand-gated ion-channels, paying particular attention to the nematodes, how we can infer the origins of such receptors and understand the factors that determine how they change both over time and from one species to another. Using this knowledge provides a biological framework in which to understand these important drug targets and avenues to identify new receptors and aid the search for new anthelmintic drugs.
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23
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Ulens C, Spurny R, Thompson A, Alqazzaz M, Debaveye S, Han L, Price K, Villalgordo J, Tresadern G, Lynch J, Lummis S. The Prokaryote Ligand-Gated Ion Channel ELIC Captured in a Pore Blocker-Bound Conformation by the Alzheimer’s Disease Drug Memantine. Structure 2014; 22:1399-407. [DOI: 10.1016/j.str.2014.07.013] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2014] [Revised: 07/24/2014] [Accepted: 07/25/2014] [Indexed: 01/05/2023]
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24
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Tillman TS, Seyoum E, Mowrey DD, Xu Y, Tang P. ELIC-α7 Nicotinic acetylcholine receptor (α7nAChR) chimeras reveal a prominent role of the extracellular-transmembrane domain interface in allosteric modulation. J Biol Chem 2014; 289:13851-7. [PMID: 24695730 PMCID: PMC4022858 DOI: 10.1074/jbc.m113.524611] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2013] [Revised: 03/10/2014] [Indexed: 01/08/2023] Open
Abstract
The native α7 nicotinic acetylcholine receptor (α7nAChR) is a homopentameric ligand-gated ion channel mediating fast synaptic transmission and is of pharmaceutical interest for treatment of numerous disorders. The transmembrane domain (TMD) of α7nAChR has been identified as a target for positive allosteric modulators (PAMs), but it is unclear whether modulation occurs through changes entirely within the TMD or changes involving both the TMD and the extracellular domain (ECD)-TMD interface. In this study, we constructed multiple chimeras using the TMD of human α7nAChR and the ECD of a prokaryotic homolog, ELIC, which is not sensitive to these modulators, and for which a high resolution structure has been solved. Functional ELIC-α7nAChR (EA) chimeras were obtained when their ECD-TMD interfaces were modified to resemble either the ELIC interface (EAELIC) or α7nAChR interface (EAα7). Both EAα7 and EAELIC show similar activation response and desensitization characteristics, but only EAα7 retained the unique pharmacology of α7nAChR evoked by PAMs, including potentiation by ivermectin, PNU-120596, and TQS, as well as activation by 4BP-TQS. This study suggests that PAM modulation through the TMD has a more stringent requirement at the ECD-TMD interface than agonist activation.
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Affiliation(s)
| | | | - David D Mowrey
- From the Departments of Anesthesiology, Computational and Systems Biology, and
| | - Yan Xu
- From the Departments of Anesthesiology, Pharmacology and Chemical Biology, Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15260
| | - Pei Tang
- From the Departments of Anesthesiology, Computational and Systems Biology, and Pharmacology and Chemical Biology,
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25
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α1F64 Residue at GABA(A) receptor binding site is involved in gating by influencing the receptor flipping transitions. J Neurosci 2014; 34:3193-209. [PMID: 24573278 DOI: 10.1523/jneurosci.2533-13.2014] [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: 11/21/2022] Open
Abstract
GABA receptors (GABAARs) mediate inhibition in the adult brain. These channels are heteropentamers and their ligand binding sites are localized at the β+ / α- interfaces. As expected, mutations of binding-site residues affect binding kinetics but accumulating evidence indicates that gating is also altered, although the underlying mechanisms are unclear. We investigated the impact of the hydrophobic box residue localized at α1(-), F64 (α1F64), on the binding and gating of rat recombinant α1β1γ2 receptors. The analysis of current responses to rapid agonist applications confirmed a marked effect of α1F64 mutations on agonist binding and revealed surprisingly strong effects on gating, including the disappearance of rapid desensitization, the slowing of current onset, and accelerated deactivation. Moreover, nonstationary variance analysis revealed that the α1F64C mutation dramatically reduced the maximum open probability without altering channel conductance. Interestingly, for wild-type receptors, responses to saturating concentration of a partial agonist, P4S, showed no rapid desensitization, similar to GABA-evoked responses mediated by α1F64C mutants. For the α1F64L mutation, the application of the high-affinity agonist muscimol partially rescued rapid desensitization compared with responses evoked by GABA. These findings suggest that α1F64 mutations do not disrupt desensitization mechanisms but rather affect other gating features that obscure it. Model simulations indicated that all of our observations related to α1F64 mutations could be properly reproduced by altering the flipped state transitions that occurred after agonist binding but preceded opening. In conclusion, we propose that the α1F64 residue may participate in linking binding and gating by influencing flipping kinetics.
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Salari R, Murlidaran S, Brannigan G. Pentameric Ligand-gated Ion Channels : Insights from Computation. MOLECULAR SIMULATION 2014; 40:821-829. [PMID: 25931676 PMCID: PMC4412168 DOI: 10.1080/08927022.2014.896462] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Pentameric ligand-gated ion channels (pLGICs) conduct upon the binding of an agonist and are fundamental to neurotransmission. New insights into the complex mechanisms underlying pLGIC gating, ion selectivity, and modulation have recently been gained via a series of crystal structures in prokaryotes and C .elegans, as well as computational studies relying on these structures. Here we review contributions from a variety of computational approaches, including normal mode analysis, automated docking, and fully atomistic molecular dynamics simulation. Examples from our own research, particularly concerning interactions with general anesthetics and lipids, are used to illustrate predictive results complementary to crystallographic studies.
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Affiliation(s)
- Reza Salari
- Center for Computational and Integrative Biology, Rutgers University, Camden, NJ
- Department of Physics, Rutgers University, Camden, NJ
| | - Sruthi Murlidaran
- Center for Computational and Integrative Biology, Rutgers University, Camden, NJ
| | - Grace Brannigan
- Center for Computational and Integrative Biology, Rutgers University, Camden, NJ
- Department of Physics, Rutgers University, Camden, NJ
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27
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Hernando G, Bouzat C. Caenorhabditis elegans neuromuscular junction: GABA receptors and ivermectin action. PLoS One 2014; 9:e95072. [PMID: 24743647 PMCID: PMC3990606 DOI: 10.1371/journal.pone.0095072] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Accepted: 03/23/2014] [Indexed: 11/25/2022] Open
Abstract
The prevalence of human and animal helminth infections remains staggeringly high, thus urging the need for concerted efforts towards this area of research. GABA receptors, encoded by the unc-49 gene, mediate body muscle inhibition in Caenorhabditis elegans and parasitic nematodes and are targets of anthelmintic drugs. Thus, the characterization of nematode GABA receptors provides a foundation for rational anti-parasitic drug design. We therefore explored UNC-49 channels from C. elegans muscle cultured cells of the first larval stage at the electrophysiological and behavioral levels. Whole-cell recordings reveal that GABA, muscimol and the anthelmintic piperazine elicit macroscopic currents from UNC-49 receptors that decay in their sustained presence, indicating full desensitization. Single-channel recordings show that all drugs elicit openings of ∼2.5 pA (+100 mV), which appear either as brief isolated events or in short bursts. The comparison of the lowest concentration required for detectable channel opening, the frequency of openings and the amplitude of macroscopic currents suggest that piperazine is the least efficacious of the three drugs. Macroscopic and single-channel GABA-activated currents are profoundly and apparently irreversibly inhibited by ivermectin. To gain further insight into ivermectin action at C. elegans muscle, we analyzed its effect on single-channel activity of the levamisol-sensitive nicotinic receptor (L-AChR), the excitatory receptor involved in neuromuscular transmission. Ivermectin produces a profound inhibition of the frequency of channel opening without significant changes in channel properties. By revealing that ivermectin inhibits C. elegans muscle GABA and L-AChR receptors, our study adds two receptors to the already known ivermectin targets, thus contributing to the elucidation of its pleiotropic effects. Behavioral assays in worms show that ivermectin potentiates piperazine-induced paralysis, thus suggesting that their combination is a good strategy to overcome the increasing resistance of parasites, an issue of global concern for human and animal health.
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Affiliation(s)
- Guillermina Hernando
- Instituto de Investigaciones Bioquímicas de Bahía Blanca-Universidad Nacional del Sur, Consejo Nacional de Investigaciones Científicas y Técnicas, Bahía Blanca, Buenos Aires, Argentina
| | - Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca-Universidad Nacional del Sur, Consejo Nacional de Investigaciones Científicas y Técnicas, Bahía Blanca, Buenos Aires, Argentina
- * E-mail:
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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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Abstract
Neuronal α7 nicotinic receptors elicit rapid cation influx in response to acetylcholine (ACh) or its hydrolysis product choline. They contribute to cognition, synaptic plasticity, and neuroprotection and have been implicated in neurodegenerative and neuropsychiatric disorders. α7, however, often localizes distal to sites of nerve-released ACh and binds ACh with low affinity, and thus elicits its biological response with low agonist occupancy. To assess the function of α7 when ACh occupies fewer than five of its identical binding sites, we measured the open-channel lifetime of individual receptors in which four of the five ACh binding sites were disabled. To improve the time resolution of the inherently brief α7 channel openings, background mutations or a potentiator was used to increase open duration. We find that, in receptors with only one intact binding site, the open-channel lifetime is indistinguishable from receptors with five intact binding sites, counter to expectations from prototypical neurotransmitter-gated ion channels where the open-channel lifetime increases with the number of binding sites occupied by agonist. Replacing the membrane-embedded domain of α7 by that of the related 5-HT3A receptor increases the number of sites that need to be occupied to achieve the maximal open-channel lifetime, thus revealing a unique interdependence between the detector and actuator domains of these receptors. The distinctive ability of a single occupancy to elicit a full biological response adapts α7 to volume transmission, a prevalent mechanism of ACh-mediated signaling in the nervous system and nonneuronal cells.
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Arias HR, De Rosa MJ, Bergé I, Feuerbach D, Bouzat C. Differential Pharmacological Activity of JN403 between α7 and Muscle Nicotinic Acetylcholine Receptors. Biochemistry 2013; 52:8480-8. [DOI: 10.1021/bi4012572] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Hugo R. Arias
- Department
of Medical Education, California Northstate University College of Medicine, Elk Grove, California 95757, United States
| | - Maria Jose De Rosa
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, UNS-CONICET, 8000 Bahia Blanca, Argentina
| | - Ignacio Bergé
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, UNS-CONICET, 8000 Bahia Blanca, Argentina
| | - Dominik Feuerbach
- Novartis Institutes for Biomedical Research, CH-4002 Basel, Switzerland
| | - Cecilia Bouzat
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, UNS-CONICET, 8000 Bahia Blanca, Argentina
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31
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Dionisio L, Arias V, Bouzat C, Esandi MDC. GABAA receptor plasticity in Jurkat T cells. Biochimie 2013; 95:2376-84. [PMID: 24012548 DOI: 10.1016/j.biochi.2013.08.023] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Accepted: 08/25/2013] [Indexed: 11/16/2022]
Abstract
GABAA receptors (GABAAR) mediate inhibitory neurotransmission in the human brain. Neurons modify subunit expression, cellular distribution and function of GABAAR in response to different stimuli, a process named plasticity. Human lymphocytes have a functional neuronal-like GABAergic system with GABAAR acting as inhibitors of proliferation. We here explore if receptor plasticity occurs in lymphocytes. To this end, we analyzed human T lymphocyte Jurkat cells exposed to different physiological stimuli shown to mediate plasticity in neurons: GABA, progesterone and insulin. The exposure to 100 μM GABA differently affected the expression of GABAAR subunits measured at both the mRNA and protein level, showing an increase of α1, β3, and γ2 subunits but no changes in δ subunit. Exposure of Jurkat cells to different stimuli produced different changes in subunit expression: 0.1 μM progesterone decreased δ and 0.5 μM insulin increased β3 subunits. To identify the mechanisms underlying plasticity, we evaluated the Akt pathway, which is involved in the phosphorylation of β subunits and receptor translocation to the membrane. A significant increase of phosphorylated Akt and on the expression of β3 subunit in membrane occurred in cells exposed 15 h to GABA. To determine if plastic changes are translated into functional changes, we performed whole cell recordings. After 15 h GABA-exposure, a significantly higher percentage of cells responded to GABA application when compared to 0 and 40 h exposure, thus indicating that the detected plastic changes may have a role in GABA-modulated lymphocyte function. Our results reveal that lymphocyte GABAAR are modified by different stimuli similarly and by similar mechanisms to those in neurons. This property is of significance for the development of future therapies involving pharmacological modulation of the immune response.
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Affiliation(s)
- Leonardo Dionisio
- Instituto de Investigaciones Bioquímicas de Bahía Blanca, UNS-CONICET, Camino La Carrindanga Km7, 8000 Bahía Blanca, Argentina
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Approaching the 5-HT₃ receptor heterogeneity by computational studies of the transmembrane and intracellular domains. J Comput Aided Mol Des 2013; 27:491-509. [PMID: 23771549 DOI: 10.1007/s10822-013-9658-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2012] [Accepted: 06/11/2013] [Indexed: 10/26/2022]
Abstract
5-hydroxytryptamine type-3 receptor (5-HT₃), an important target of many neuroactive drugs, is a cation selective transmembrane pentamer whose functional stoichiometries and subunit arrangements are still debated, due to the extreme complexity of the system. The three dimensional structure of the 5-HT₃R subunits has not been solved so far. Moreover, most of the available structural and functional data is related to the extracellular ligand-binding domain, whereas the transmembrane and the intracellular receptor domains are far less characterised, although they are crucial for receptor function. Here, for the first time, 3D homology models of the transmembrane and the intracellular receptor domains of all the known human 5-HT₃ subunits have been built and assembled into homopentameric (5-HT(3A)R, 5-HT(3B)R, 5-HT(3C)R, 5-HT(3D)R and 5-HT(3E)R) and heteropentameric receptors (5-HT(3AB), 5-HT(3AC), 5-HT(3AD) and 5-HT(3AE)), on the basis of the known three-dimensional structures of the nicotinic-acetylcholine receptor and of the ligand gated channel from Erwinia chrysanthemi. The comparative analyses of sequences, modelled structures, and computed electrostatic properties of the single subunits and of the assembled pentamers shed new light both on the stoichiometric composition and on the physicochemical requirements of the functional receptors. In particular, it emerges that a favourable environment for the crossing of the pore at the transmembrane and intracellular C terminus domain levels by Ca²⁺ ions is granted by the maximum presence of two B subunits in the 5-HT₃ pentamer.
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Engle SE, Broderick HJ, Drenan RM. Local application of drugs to study nicotinic acetylcholine receptor function in mouse brain slices. J Vis Exp 2012:e50034. [PMID: 23128482 DOI: 10.3791/50034] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
Tobacco use leads to numerous health problems, including cancer, heart disease, emphysema, and stroke. Addiction to cigarette smoking is a prevalent neuropsychiatric disorder that stems from the biophysical and cellular actions of nicotine on nicotinic acetylcholine receptors (nAChRs) throughout the central nervous system. Understanding the various nAChR subtypes that exist in brain areas relevant to nicotine addiction is a major priority. Experiments that employ electrophysiology techniques such as whole-cell patch clamp or two-electrode voltage clamp recordings are useful for pharmacological characterization of nAChRs of interest. Cells expressing nAChRs, such as mammalian tissue culture cells or Xenopus laevis oocytes, are physically isolated and are therefore easily studied using the tools of modern pharmacology. Much progress has been made using these techniques, particularly when the target receptor was already known and ectopic expression was easily achieved. Often, however, it is necessary to study nAChRs in their native environment: in neurons within brain slices acutely harvested from laboratory mice or rats. For example, mice expressing "hypersensitive" nAChR subunits such as α4 L9'A mice (1) and α6 L9'S mice (2), allow for unambiguous identification of neurons based on their functional expression of a specific nAChR subunit. Although whole-cell patch clamp recordings from neurons in brain slices is routinely done by the skilled electrophysiologist, it is challenging to locally apply drugs such as acetylcholine or nicotine to the recorded cell within a brain slice. Dilution of drugs into the superfusate (bath application) is not rapidly reversible, and U-tube systems are not easily adapted to work with brain slices. In this paper, we describe a method for rapidly applying nAChR-activating drugs to neurons recorded in adult mouse brain slices. Standard whole-cell recordings are made from neurons in slices, and a second micropipette filled with a drug of interest is maneuvered into position near the recorded cell. An injection of pressurized air or inert nitrogen into the drug-filled pipette causes a small amount of drug solution to be ejected from the pipette onto the recorded cell. Using this method, nAChR-mediated currents are able to be resolved with millisecond accuracy. Drug application times can easily be varied, and the drug-filled pipette can be retracted and replaced with a new pipette, allowing for concentration-response curves to be created for a single neuron. Although described in the context of nAChR neurobiology, this technique should be useful for studying many types of ligand-gated ion channels or receptors in neurons from brain slices.
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Affiliation(s)
- Staci E Engle
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, USA
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Criado M, Valor LM, Mulet J, Gerber S, Sala S, Sala F. Expression and functional properties of α7 acetylcholine nicotinic receptors are modified in the presence of other receptor subunits. J Neurochem 2012; 123:504-14. [DOI: 10.1111/j.1471-4159.2012.07931.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Revised: 07/30/2012] [Accepted: 08/20/2012] [Indexed: 01/03/2023]
Affiliation(s)
- Manuel Criado
- Instituto de Neurociencias; Universidad Miguel Hernández-CSIC; Alicante Spain
| | - Luis M. Valor
- Instituto de Neurociencias; Universidad Miguel Hernández-CSIC; Alicante Spain
| | - José Mulet
- Instituto de Neurociencias; Universidad Miguel Hernández-CSIC; Alicante Spain
| | - Susana Gerber
- Instituto de Neurociencias; Universidad Miguel Hernández-CSIC; Alicante Spain
| | - Salvador Sala
- Instituto de Neurociencias; Universidad Miguel Hernández-CSIC; Alicante Spain
| | - Francisco Sala
- Instituto de Neurociencias; Universidad Miguel Hernández-CSIC; Alicante Spain
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Hernando G, Bergé I, Rayes D, Bouzat C. Contribution of Subunits to Caenorhabditis elegans Levamisole-Sensitive Nicotinic Receptor Function. Mol Pharmacol 2012; 82:550-60. [DOI: 10.1124/mol.112.079962] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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36
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Pandhare A, Hamouda AK, Staggs B, Aggarwal S, Duddempudi PK, Lever JR, Lapinsky DJ, Jansen M, Cohen JB, Blanton MP. Bupropion binds to two sites in the Torpedo nicotinic acetylcholine receptor transmembrane domain: a photoaffinity labeling study with the bupropion analogue [(125)I]-SADU-3-72. Biochemistry 2012; 51:2425-35. [PMID: 22394379 DOI: 10.1021/bi300101r] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bupropion, a clinically used antidepressant and smoking-cessation drug, acts as a noncompetitive antagonist of nicotinic acetylcholine receptors (nAChRs). To identify its binding site(s) in nAChRs, we developed a photoreactive bupropion analogue, (±)-2-(N-tert-butylamino)-3'-[(125)I]-iodo-4'-azidopropiophenone (SADU-3-72). Based on inhibition of [(125)I]SADU-3-72 binding, SADU-3-72 binds with high affinity (IC(50) = 0.8 μM) to the Torpedo nAChR in the resting (closed channel) state and in the agonist-induced desensitized state, and bupropion binds to that site with 3-fold higher affinity in the desensitized (IC(50) = 1.2 μM) than in the resting state. Photolabeling of Torpedo nAChRs with [(125)I]SADU-3-72 followed by limited in-gel digestion of nAChR subunits with endoproteinase Glu-C established the presence of [(125)I]SADU-3-72 photoincorporation within nAChR subunit fragments containing M1-M2-M3 helices (αV8-20K, βV8-22/23K, and γV8-24K) or M1-M2 helices (δV8-14). Photolabeling within βV8-22/23K, γV8-24K, and δV8-14 was reduced in the desensitized state and inhibited by ion channel blockers selective for the resting (tetracaine) or desensitized (thienycyclohexylpiperidine (TCP)) state, and this pharmacologically specific photolabeling was localized to the M2-9 leucine ring (δLeu(265), βLeu(257)) within the ion channel. In contrast, photolabeling within the αV8-20K was enhanced in the desensitized state and not inhibited by TCP but was inhibited by bupropion. This agonist-enhanced photolabeling was localized to αTyr(213) in αM1. These results establish the presence of two distinct bupropion binding sites within the Torpedo nAChR transmembrane domain: a high affinity site at the middle (M2-9) of the ion channel and a second site near the extracellular end of αM1 within a previously described halothane (general anesthetic) binding pocket.
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Affiliation(s)
- Akash Pandhare
- Department of Pharmacology and Neuroscience and the Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, United States
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