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Ananchenko A, Hussein TOK, Mody D, Thompson MJ, Baenziger JE. Recent Insight into Lipid Binding and Lipid Modulation of Pentameric Ligand-Gated Ion Channels. Biomolecules 2022; 12:814. [PMID: 35740939 DOI: 10.3390/biom12060814] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2022] [Revised: 06/03/2022] [Accepted: 06/08/2022] [Indexed: 02/04/2023] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) play a leading role in synaptic communication, are implicated in a variety of neurological processes, and are important targets for the treatment of neurological and neuromuscular disorders. Endogenous lipids and lipophilic compounds are potent modulators of pLGIC function and may help shape synaptic communication. Increasing structural and biophysical data reveal sites for lipid binding to pLGICs. Here, we update our evolving understanding of pLGIC–lipid interactions highlighting newly identified modes of lipid binding along with the mechanistic understanding derived from the new structural data.
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2
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Koniuszewski F, Vogel FD, Bampali K, Fabjan J, Seidel T, Scholze P, Schmiedhofer PB, Langer T, Ernst M. Molecular Mingling: Multimodal Predictions of Ligand Promiscuity in Pentameric Ligand-Gated Ion Channels. Front Mol Biosci 2022; 9:860246. [PMID: 35615739 PMCID: PMC9124788 DOI: 10.3389/fmolb.2022.860246] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2022] [Accepted: 03/28/2022] [Indexed: 01/23/2023] Open
Abstract
Background: Human pentameric ligand-gated ion channels (pLGICs) comprise nicotinic acetylcholine receptors (nAChRs), 5-hydroxytryptamine type 3 receptors (5-HT3Rs), zinc-activated channels (ZAC), γ-aminobutyric acid type A receptors (GABAARs) and glycine receptors (GlyRs). They are recognized therapeutic targets of some of the most prescribed drugs like general anesthetics, anxiolytics, smoking cessation aids, antiemetics and many more. Currently, approximately 100 experimental structures of pLGICs with ligands bound exist in the protein data bank (PDB). These atomic-level 3D structures enable the generation of a comprehensive binding site inventory for the superfamily and the in silico prediction of binding site properties. Methods: A panel of high throughput in silico methods including pharmacophore screening, conformation analysis and descriptor calculation was applied to a selection of allosteric binding sites for which in vitro screens are lacking. Variant abundance near binding site forming regions and computational docking complement the approach. Results: The structural data reflects known and novel binding sites, some of which may be unique to individual receptors, while others are broadly conserved. The membrane spanning domain, comprising four highly conserved segments, contains ligand interaction sites for which in vitro assays suitable for high throughput screenings are critically lacking. This is also the case for structurally more variable novel sites in the extracellular domain. Our computational results suggest that the phytocannabinoid Δ9-tetrahydrocannabinol (Δ9-THC) can utilize multiple pockets which are likely to exist on most superfamily members. Conclusion: With this study, we explore the potential for polypharmacology among pLGICs. Our data suggest that ligands can display two forms of promiscuity to an extent greater than what has been realized: 1) Ligands can interact with homologous sites in many members of the superfamily, which bears toxicological relevance. 2) Multiple pockets in distinct localizations of individual receptor subtypes share common ligands, which counteracts efforts to develop selective agents. Moreover, conformational states need to be considered for in silico drug screening, as certain binding sites display considerable flexibility. In total, this work contributes to a better understanding of polypharmacology across pLGICs and provides a basis for improved structure guided in silico drug development and drug derisking.
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Affiliation(s)
- Filip Koniuszewski
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Florian D. Vogel
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Konstantina Bampali
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Jure Fabjan
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Thomas Seidel
- Department of Pharmaceutical Sciences, Division of Pharmaceutical Chemistry, University of Vienna, Vienna, Austria
| | - Petra Scholze
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Philip B. Schmiedhofer
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
| | - Thierry Langer
- Department of Pharmaceutical Sciences, Division of Pharmaceutical Chemistry, University of Vienna, Vienna, Austria
| | - Margot Ernst
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University Vienna, Vienna, Austria
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3
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Zarkadas E, Pebay-Peyroula E, Thompson MJ, Schoehn G, Uchański T, Steyaert J, Chipot C, Dehez F, Baenziger JE, Nury H. Conformational transitions and ligand-binding to a muscle-type nicotinic acetylcholine receptor. Neuron 2022:S0896-6273(22)00049-6. [PMID: 35139364 DOI: 10.1016/j.neuron.2022.01.013] [Citation(s) in RCA: 34] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Revised: 11/02/2021] [Accepted: 01/10/2022] [Indexed: 12/15/2022]
Abstract
Fast synaptic communication requires receptors that respond to the presence of neurotransmitter by opening an ion channel across the post-synaptic membrane. The muscle-type nicotinic acetylcholine receptor from the electric fish, Torpedo, is the prototypic ligand-gated ion channel, yet the structural changes underlying channel activation remain undefined. Here we use cryo-EM to solve apo and agonist-bound structures of the Torpedo nicotinic receptor embedded in a lipid nanodisc. Using both a direct biochemical assay to define the conformational landscape and molecular dynamics simulations to assay flux through the pore, we correlate structures with functional states and elucidate the motions that lead to pore activation of a heteromeric nicotinic receptor. We highlight an underappreciated role for the complementary subunit in channel gating, establish the structural basis for the differential agonist affinities of α/δ versus α /γ sites, and explain why nicotine is less potent at muscle nicotinic receptors compared to neuronal ones.
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Lefebvre SN, Taly A, Menny A, Medjebeur K, Corringer PJ. Mutational analysis to explore long-range allosteric couplings involved in a pentameric channel receptor pre-activation and activation. eLife 2021; 10:60682. [PMID: 34590583 PMCID: PMC8504973 DOI: 10.7554/elife.60682] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Accepted: 09/29/2021] [Indexed: 01/23/2023] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) mediate chemical signaling through a succession of allosteric transitions that are yet not completely understood as intermediate states remain poorly characterized by structural approaches. In a previous study on the prototypic bacterial proton-gated channel GLIC, we generated several fluorescent sensors of the protein conformation that report a fast transition to a pre-active state, which precedes the slower process of activation with pore opening. Here, we explored the phenotype of a series of allosteric mutations, using simultaneous steady-state fluorescence and electrophysiological measurements over a broad pH range. Our data, fitted to a three-state Monod-Wyman-Changeux model, show that mutations at the subunit interface in the extracellular domain (ECD) principally alter pre-activation, while mutations in the lower ECD and in the transmembrane domain principally alter activation. We also show that propofol alters both transitions. Data are discussed in the framework of transition pathways generated by normal mode analysis (iModFit). It further supports that pre-activation involves major quaternary compaction of the ECD, and suggests that activation involves principally a reorganization of a ‘central gating region’ involving a contraction of the ECD β-sandwich and the tilt of the channel lining M2 helix.
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Affiliation(s)
- Solène N Lefebvre
- Institut Pasteur, Université de Paris, CNRS UMR 3571,Channel-Receptors Unit, Paris, France.,Sorbonne Université, Collège doctoral, Paris, France
| | - Antoine Taly
- Institut de Biologie Physico-chimique, Fondation Edmond de Rothschild, PSL Research University, Paris, France.,Laboratoire de Biochimie Théorique, CNRS, Université de Paris, UPR 9080, Paris, France
| | - Anaïs Menny
- Institut Pasteur, Université de Paris, CNRS UMR 3571,Channel-Receptors Unit, Paris, France.,Sorbonne Université, Collège doctoral, Paris, France
| | - Karima Medjebeur
- Institut Pasteur, Université de Paris, CNRS UMR 3571,Channel-Receptors Unit, Paris, France
| | - Pierre-Jean Corringer
- Institut Pasteur, Université de Paris, CNRS UMR 3571,Channel-Receptors Unit, Paris, France
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5
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Crnjar A, Mesoy SM, Lummis SCR, Molteni C. A Single Mutation in the Outer Lipid-Facing Helix of a Pentameric Ligand-Gated Ion Channel Affects Channel Function Through a Radially-Propagating Mechanism. Front Mol Biosci 2021; 8:644720. [PMID: 33996899 PMCID: PMC8119899 DOI: 10.3389/fmolb.2021.644720] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Accepted: 02/22/2021] [Indexed: 11/13/2022] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) mediate fast synaptic transmission and are crucial drug targets. Their gating mechanism is triggered by ligand binding in the extracellular domain that culminates in the opening of a hydrophobic gate in the transmembrane domain. This domain is made of four α-helices (M1 to M4). Recently the outer lipid-facing helix (M4) has been shown to be key to receptor function, however its role in channel opening is still poorly understood. It could act through its neighboring helices (M1/M3), or via the M4 tip interacting with the pivotal Cys-loop in the extracellular domain. Mutation of a single M4 tyrosine (Y441) to alanine renders one pLGIC-the 5-HT3A receptor-unable to function despite robust ligand binding. Using Y441A as a proxy for M4 function, we here predict likely paths of Y441 action using molecular dynamics, and test these predictions with functional assays of mutant receptors in HEK cells and Xenopus oocytes using fluorescent membrane potential sensitive dye and two-electrode voltage clamp respectively. We show that Y441 does not act via the M4 tip or Cys-loop, but instead connects radially through M1 to a residue near the ion channel hydrophobic gate on the pore-lining helix M2. This demonstrates the active role of the M4 helix in channel opening.
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Affiliation(s)
| | - Susanne M. Mesoy
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Sarah C. R. Lummis
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Carla Molteni
- Physics Department, King's College London, London, United Kingdom
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6
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Cerdan AH, Cecchini M. On the Functional Annotation of Open-Channel Structures in the Glycine Receptor. Structure 2021; 28:690-693.e3. [PMID: 32492413 DOI: 10.1016/j.str.2020.05.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Revised: 03/06/2020] [Accepted: 05/07/2020] [Indexed: 11/25/2022]
Abstract
The glycine receptor (GlyR) is by far the best-characterized pentameric ligand-gated ion channel, with several high-resolution structures from X-ray crystallography, cryoelectron microscopy (cryo-EM), and modeling. Nonetheless, the significance of the currently available open-pore conformations is debated due to their diversity in the pore geometry. Here, we discuss the physiological significance of existing models of the GlyR active state based on conductance and selectivity measurements by computational electrophysiology. The results support the conclusion that the original cryo-EM reconstruction of the active state obtained in detergents as well as its subsequent refinement by molecular dynamics simulations are likely to be non-physiological as they feature artificially dilated ion pores. In addition, the calculations indicate that a physiologically relevant open pore should be constricted within a radius of 2.5 and 2.8 Å, which is consistent with previous modeling, electrophysiology measurements, and the most recent cryo-EM structures obtained in a native lipid membrane environment.
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Affiliation(s)
- Adrien Henri Cerdan
- Institut de Chimie de Strasbourg, UMR 7177, CNRS, Université de Strasbourg, Strasbourg Cedex 67083, France; Channel-Receptors Unit, UMR 3571, CNRS, Institut Pasteur, Paris 75015, France
| | - Marco Cecchini
- Institut de Chimie de Strasbourg, UMR 7177, CNRS, Université de Strasbourg, Strasbourg Cedex 67083, France.
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Cymes GD, Grosman C. Signal transduction through Cys-loop receptors is mediated by the nonspecific bumping of closely apposed domains. Proc Natl Acad Sci U S A 2021; 118:e2021016118. [PMID: 33785596 DOI: 10.1073/pnas.2021016118] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
One of the most fundamental questions in the field of Cys-loop receptors (pentameric ligand-gated ion channels, pLGICs) is how the affinity for neurotransmitters and the conductive/nonconductive state of the transmembrane pore are correlated despite the ∼60-Å distance between the corresponding domains. Proposed mechanisms differ, but they all converge into the idea that interactions between wild-type side chains across the extracellular-transmembrane-domain (ECD-TMD) interface are crucial for this phenomenon. Indeed, the successful design of fully functional chimeras that combine intact ECD and TMD modules from different wild-type pLGICs has commonly been ascribed to the residual conservation of sequence that exists at the level of the interfacial loops even between evolutionarily distant parent channels. Here, using mutagenesis, patch-clamp electrophysiology, and radiolabeled-ligand binding experiments, we studied the effect of eliminating this residual conservation of sequence on ion-channel function and cell-surface expression. From our results, we conclude that proper state interconversion ("gating") does not require conservation of sequence-or even physicochemical properties-across the ECD-TMD interface. Wild-type ECD and TMD side chains undoubtedly interact with their surroundings, but the interactions between them-straddling the interface-do not seem to be more important for gating than those occurring elsewhere in the protein. We propose that gating of pLGICs requires, instead, that the overall structure of the interfacial loops be conserved, and that their relative orientation and distance be the appropriate ones for changes in one side to result in changes in the other, in a phenomenon akin to the nonspecific "bumping" of closely apposed domains.
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8
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Lara CO, Burgos CF, Moraga-Cid G, Carrasco MA, Yévenes GE. Pentameric Ligand-Gated Ion Channels as Pharmacological Targets Against Chronic Pain. Front Pharmacol 2020; 11:167. [PMID: 32218730 PMCID: PMC7079299 DOI: 10.3389/fphar.2020.00167] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2019] [Accepted: 02/07/2020] [Indexed: 12/31/2022] Open
Abstract
Chronic pain is a common detrimental condition that affects around 20% of the world population. The current drugs to treat chronic pain states, especially neuropathic pain, have a limited clinical efficiency and present significant adverse effects that complicates their regular use. Recent studies have proposed new therapeutic strategies focused on the pharmacological modulation of G-protein-coupled receptors, transporters, enzymes, and ion channels expressed on the nociceptive pathways. The present work intends to summarize recent advances on the pharmacological modulation of pentameric ligand-gated ion channels, which plays a key role in pain processing. Experimental data have shown that novel allosteric modulators targeting the excitatory nicotinic acetylcholine receptor, as well as the inhibitory GABAA and glycine receptors, reverse chronic pain-related behaviors in preclinical assays. Collectively, these evidences strongly suggest the pharmacological modulation of pentameric ligand-gated ion channels is a promising strategy towards the development of novel therapeutics to treat chronic pain states in humans.
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Affiliation(s)
- César O Lara
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Concepcion, Chile
| | - Carlos F Burgos
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Concepcion, Chile
| | - Gustavo Moraga-Cid
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Concepcion, Chile
| | - Mónica A Carrasco
- Department of Biomedical Sciences, Faculty of Health Sciences, University of Talca, Talca, Chile
| | - Gonzalo E Yévenes
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Concepcion, Chile
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9
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Crnjar A, Comitani F, Melis C, Molteni C. Mutagenesis computer experiments in pentameric ligand-gated ion channels: the role of simulation tools with different resolution. Interface Focus 2019; 9:20180067. [PMID: 31065340 PMCID: PMC6501341 DOI: 10.1098/rsfs.2018.0067] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/26/2019] [Indexed: 12/21/2022] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) are an important class of widely expressed membrane neuroreceptors, which play a crucial role in fast synaptic communications and are involved in several neurological conditions. They are activated by the binding of neurotransmitters, which trigger the transmission of an electrical signal via facilitated ion flux. They can also be activated, inhibited or modulated by a number of drugs. Mutagenesis electrophysiology experiments, with natural or unnatural amino acids, have provided a large body of functional data that, together with emerging structural information from X-ray spectroscopy and cryo-electron microscopy, are helping unravel the complex working mechanisms of these neuroreceptors. Computer simulations are complementing these mutagenesis experiments, with insights at various levels of accuracy and resolution. Here, we review how a selection of computational tools, including first principles methods, classical molecular dynamics and enhanced sampling techniques, are contributing to construct a picture of how pLGICs function and can be pharmacologically targeted to treat the disorders they are responsible for.
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Affiliation(s)
- Alessandro Crnjar
- King’s College London, Department of Physics, Strand, London WC2R 2LS, UK
| | - Federico Comitani
- Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, Ontario, Canada
| | - Claudio Melis
- Universitá degli Studi di Cagliari, Complesso Universitario di Monserrato, Dipartimento di Fisica, S.P. Monserrato-Sestu Km 0,700, Monserrato (CA) 09042, Italy
| | - Carla Molteni
- King’s College London, Department of Physics, Strand, London WC2R 2LS, UK
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10
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Baptista-Hon DT, Gulbinaite S, Hales TG. Loop G in the GABA A receptor α1 subunit influences gating efficacy. J Physiol 2017; 595:1725-1741. [PMID: 27981574 DOI: 10.1113/jp273752] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2016] [Accepted: 12/01/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The functional importance of residues in loop G of the GABAA receptor has not been investigated. D43 and T47 in the α1 subunit are of particular significance as their structural modification inhibits activation by GABA. While the T47C substitution had no significant effect, non-conservative substitution of either residue (D43C or T47R) reduced the apparent potency of GABA. Propofol potentiated maximal GABA-evoked currents mediated by α1(D43C)β2γ2 and α1(T47R)β2γ2 receptors. Non-stationary variance analysis revealed a reduction in maximal GABA-evoked Popen , suggesting impaired agonist efficacy. Further analysis of α1(T47R)β2γ2 receptors revealed that the efficacy of the partial agonist THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-3-ol) relative to GABA was impaired. GABA-, THIP- and propofol-evoked currents mediated by α1(T47R)β2γ2 receptors deactivated faster than those mediated by α1β2γ2 receptors, indicating that the mutation impairs agonist-evoked gating. Spontaneous gating caused by the β2(L285R) mutation was also reduced in α1(T47R)β2(L285R)γ2 compared to α1β2(L285R)γ2 receptors, confirming that α1(T47R) impairs gating independently of agonist activation. ABSTRACT The modification of cysteine residues (substituted for D43 and T47) by 2-aminoethyl methanethiosulfonate in the GABAA α1 subunit loop G is known to impair activation of α1β2γ2 receptors by GABA and propofol. While the T47C substitution had no significant effect, non-conservative substitution of either residue (D43C or T47R) reduced the apparent potency of GABA. Propofol (1 μm), which potentiates sub-maximal but not maximal GABA-evoked currents mediated by α1β2γ2 receptors, also potentiated maximal currents mediated by α1(D43C)β2γ2 and α1(T47R)β2γ2 receptors. Furthermore, the peak open probabilities of α1(D43C)β2γ2 and α1(T47R)β2γ2 receptors were reduced. The kinetics of macroscopic currents mediated by α1(D43C)β2γ2 and α1(T47R)β2γ2 receptors were characterised by slower desensitisation and faster deactivation. Similar changes in macroscopic current kinetics, together with a slower activation rate, were observed with the loop D α1(F64C) substitution, known to impair both efficacy and agonist binding, and when the partial agonist THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-3-ol) was used to activate WT or α1(T47R)β2γ2 receptors. Propofol-evoked currents mediated by α1(T47R)β2γ2 and α1(F64C)β2γ2 receptors also exhibited faster deactivation than their WT counterparts, revealing that these substitutions impair gating through a mechanism independent of orthosteric binding. Spontaneous gating caused by the introduction of the β2(L285R) mutation was also reduced in α1(T47R)β2(L285R)γ2 compared to α1β2(L285R)γ2 receptors, confirming that α1(T47R) impairs gating independently of activation by any agonist. These findings implicate movement of the GABAA receptor α1 subunit's β1 strand during agonist-dependent and spontaneous gating. Immobilisation of the β1 strand may provide a mechanism for the inhibition of gating by inverse agonists such as bicuculline.
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Affiliation(s)
- Daniel T Baptista-Hon
- The Institute of Academic Anaesthesia, Division of Neuroscience, School of Medicine, Ninewells Hospital, University of Dundee, Dundee, UK
| | - Simona Gulbinaite
- The Institute of Academic Anaesthesia, Division of Neuroscience, School of Medicine, Ninewells Hospital, University of Dundee, Dundee, UK
| | - Tim G Hales
- The Institute of Academic Anaesthesia, Division of Neuroscience, School of Medicine, Ninewells Hospital, University of Dundee, Dundee, UK
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Chen Q, Wells MM, Tillman TS, Kinde MN, Cohen A, Xu Y, Tang P. Structural Basis of Alcohol Inhibition of the Pentameric Ligand-Gated Ion Channel ELIC. Structure 2016; 25:180-187. [PMID: 27916519 DOI: 10.1016/j.str.2016.11.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2016] [Revised: 09/30/2016] [Accepted: 11/07/2016] [Indexed: 11/18/2022]
Abstract
The structural basis for alcohol modulation of neuronal pentameric ligand-gated ion channels (pLGICs) remains elusive. We determined an inhibitory mechanism of alcohol on the pLGIC Erwinia chrysanthemi (ELIC) through direct binding to the pore. X-ray structures of ELIC co-crystallized with 2-bromoethanol, in both the absence and presence of agonist, reveal 2-bromoethanol binding in the pore near T237(6') and the extracellular domain (ECD) of each subunit at three different locations. Binding to the ECD does not appear to contribute to the inhibitory action of 2-bromoethanol and ethanol as indicated by the same functional responses of wild-type ELIC and mutants. In contrast, the ELIC-α1β3GABAAR chimera, replacing the ELIC transmembrane domain (TMD) with the TMD of α1β3GABAAR, is potentiated by 2-bromoethanol and ethanol. The results suggest a dominant role of the TMD in modulating alcohol effects. The X-ray structures and functional measurements support a pore-blocking mechanism for inhibitory action of short-chain alcohols.
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Affiliation(s)
- Qiang Chen
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Marta M Wells
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA; Department of Computational and System Biology, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Tommy S Tillman
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Monica N Kinde
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Aina Cohen
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
| | - Yan Xu
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA; Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA 15260, USA; Department of Structural Biology, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Pei Tang
- Department of Anesthesiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA; Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA 15260, USA; Department of Computational and System Biology, University of Pittsburgh, Pittsburgh, PA 15260, USA.
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12
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Tillman TS, Alvarez FJD, Reinert NJ, Liu C, Wang D, Xu Y, Xiao K, Zhang P, Tang P. Functional Human α7 Nicotinic Acetylcholine Receptor (nAChR) Generated from Escherichia coli. J Biol Chem 2016; 291:18276-82. [PMID: 27385587 DOI: 10.1074/jbc.m116.729970] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2016] [Indexed: 11/06/2022] Open
Abstract
Human Cys-loop receptors are important therapeutic targets. High-resolution structures are essential for rational drug design, but only a few are available due to difficulties in obtaining sufficient quantities of protein suitable for structural studies. Although expression of proteins in E. coli offers advantages of high yield, low cost, and fast turnover, this approach has not been thoroughly explored for full-length human Cys-loop receptors because of the conventional wisdom that E. coli lacks the specific chaperones and post-translational modifications potentially required for expression of human Cys-loop receptors. Here we report the successful production of full-length wild type human α7nAChR from E. coli Chemically induced chaperones promote high expression levels of well-folded proteins. The choice of detergents, lipids, and ligands during purification determines the final protein quality. The purified α7nAChR not only forms pentamers as imaged by negative-stain electron microscopy, but also retains pharmacological characteristics of native α7nAChR, including binding to bungarotoxin and positive allosteric modulators specific to α7nAChR. Moreover, the purified α7nAChR injected into Xenopus oocytes can be activated by acetylcholine, choline, and nicotine, inhibited by the channel blockers QX-222 and phencyclidine, and potentiated by the α7nAChR specific modulators PNU-120596 and TQS. The successful generation of functional human α7nAChR from E. coli opens a new avenue for producing mammalian Cys-loop receptors to facilitate structure-based rational drug design.
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Affiliation(s)
| | | | | | | | | | - Yan Xu
- From the Departments of Anesthesiology, Structural Biology, Pharmacology and Chemical Biology, and
| | | | | | - Pei Tang
- From the Departments of Anesthesiology, Pharmacology and Chemical Biology, and Computational & Systems Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15260
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Nishtala SN, Mnatsakanyan N, Pandhare A, Leung C, Jansen M. Direct interaction of the resistance to inhibitors of cholinesterase type 3 protein with the serotonin receptor type 3A intracellular domain. J Neurochem 2016; 137:528-38. [PMID: 26875553 PMCID: PMC4860158 DOI: 10.1111/jnc.13578] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Revised: 02/01/2016] [Accepted: 02/02/2016] [Indexed: 10/22/2022]
Abstract
Pentameric ligand-gated ion channels (pLGIC) are expressed in both excitable and non-excitable cells that are targeted by numerous clinically used drugs. Assembly from five identical or homologous subunits yields homo- or heteromeric pentamers, respectively. The protein known as Resistance to Inhibitors of Cholinesterase (RIC-3) was identified to interfere with assembly and functional maturation of pLGICs. We have shown previously for serotonin type 3A homopentamers (5-HT3A ) that the interaction with RIC-3 requires the intracellular domain (ICD) of this pLGIC. After expression in Xenopus laevis oocytes RIC-3 attenuated serotonin-induced currents in 5-HT3A wild-type channels, but not in functional 5-HT3A glvM3M4 channels that have the 115-amino acid ICD replaced by a heptapeptide. In complementary experiments we have shown that engineering the Gloeobacter violaceus ligand-gated ion channel (GLIC) to contain the 5-HT3A -ICD confers sensitivity to RIC-3 in oocytes to otherwise insensitive GLIC. In this study, we identify endogenous RIC-3 protein expression in X. laevis oocytes. We purified RIC-3 to homogeneity after expression in Echericia coli. By using heterologously over-expressed and purified RIC-3 and the chimera consisting of the 5-HT3A -ICD and the extracellular and transmembrane domains of GLIC in pull-down experiments, we demonstrate a direct and specific interaction between the two proteins. This result further underlines that the domain within 5-HT3 A R that mediates the interaction with RIC-3 is the ICD. Importantly, this is the first experimental evidence that the interaction between 5-HT3 A R-ICD and RIC-3 does not require other proteins. In addition, we demonstrate that the pentameric assembly of the GLIC-5-HT3A -ICD chimera interacts with RIC-3. We hypothesized that pentameric ligand-gated ion channels (pLGICs) associate directly with the chaperone protein RIC-3 (resistance to inhibitors of cholinesterase type 3), and that the interaction does not require other protein factors. We found that the two proteins indeed interact directly, that the pLGIC intracellular domain is required for the effect, and that pLGICs in their pentameric form associate with RIC-3. These results provide the basis for future studies aimed at investigating which motifs provide the interaction surfaces, and at delineating the mechanism(s) of RIC-3 modulation of functional pLGIC surface expression.
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Affiliation(s)
- Sita Nirupama Nishtala
- Department of Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
- Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
| | - Nelli Mnatsakanyan
- Department of Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
- Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
| | - Akash Pandhare
- Department of Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
- Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
| | - Chun Leung
- Department of Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
- Medical Student Summer Research Program, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
- Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
| | - Michaela Jansen
- Department of Cell Physiology and Molecular Biophysics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
- Center for Membrane Protein Research, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, Texas 79430
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Hénault CM, Juranka PF, Baenziger JE. The M4 Transmembrane α-Helix Contributes Differently to Both the Maturation and Function of Two Prokaryotic Pentameric Ligand-gated Ion Channels. J Biol Chem 2015; 290:25118-28. [PMID: 26318456 DOI: 10.1074/jbc.m115.676833] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2015] [Indexed: 01/22/2023] Open
Abstract
The role of the outermost transmembrane α-helix in both the maturation and function of the prokaryotic pentameric ligand-gated ion channels, GLIC and ELIC, was examined by Ala scanning mutagenesis, deletion mutations, and mutant cycle analyses. Ala mutations at the M4-M1/M3 interface lead to loss-of-function phenotypes in GLIC, with the largest negative effects occurring near the M4 C terminus. In particular, two aromatic residues at the M4 C terminus form a network of π-π and/or cation-π interactions with residues on M3 and the β6-β7 loop that is essential for both maturation and function. M4-M1/M3 interactions appear to be optimized in GLIC with even subtle structural changes at this interface leading to detrimental effects. In contrast, mutations along the M4-M1/M3 interface of ELIC typically lead to gain-of-function phenotypes, suggesting that these interactions in ELIC are not optimized for channel function. In addition, no cluster of interacting residues involving the M4 C terminus, M3, and the β6-β7 loop was found, suggesting that the M4 C terminus plays little role in ELIC maturation or function. This study shows that M4 makes distinct contributions to the maturation and gating of these two closely related homologs, suggesting that GLIC and ELIC exhibit divergent features of channel function.
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Affiliation(s)
- Camille M Hénault
- From the Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - Peter F Juranka
- From the Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - John E Baenziger
- From the Department of Biochemistry, Microbiology, and Immunology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
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