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Abstract
Small molecules have extensive untapped potential to benefit society, but access to this potential is too often restricted by limitations inherent to the customized approach currently used to synthesize this class of chemical matter. In contrast, the "building block approach", i.e., generalized iterative assembly of interchangeable parts, has now proven to be a highly efficient and flexible way to construct things ranging all the way from skyscrapers to macromolecules to artificial intelligence algorithms. The structural redundancy found in many small molecules suggests that they possess a similar capacity for generalized building block-based construction. It is also encouraging that many customized iterative synthesis methods have been developed that improve access to specific classes of small molecules. There has also been substantial recent progress toward the iterative assembly of many different types of small molecules, including complex natural products, pharmaceuticals, biological probes, and materials, using common building blocks and coupling chemistry. Collectively, these advances suggest that a generalized building block approach for small molecule synthesis may be within reach.
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Affiliation(s)
- Jonathan W Lehmann
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Daniel J Blair
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Martin D Burke
- Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
- Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA and Carle-Illinois College of Medicine, University of Illinois at Urbana-Champaign, Champaign, IL 61820, USA
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202
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Abstract
The precise mechanism by which propofol enhances GABAergic transmission remains unclear, but much progress has been made regarding the underlying structural and dynamic mechanisms. Furthermore, it is now clear that propofol has additional molecular targets, many of which are functionally influenced at concentrations achieved clinically. Focusing primarily on molecular targets, this brief review attempts to summarize some of this recent progress while pointing out knowledge gaps and controversies. It is not intended to be comprehensive but rather to stimulate further thought, discussion, and study on the mechanisms by which propofol produces its pleiotropic effects.
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Affiliation(s)
- Pei Tang
- Department of Anesthesiology, University of Pittsburgh, 3550 Terrace Street, Pittsburgh, PA, 15261, USA
| | - Roderic Eckenhoff
- Department of Anesthesiology & Critical Care, University of Pennsylvania, 3400 Spruce St, Philadelphia, PA, 19104, USA
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203
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Shen XM, Brengman JM, Shen S, Durmus H, Preethish-Kumar V, Yuceyar N, Vengalil S, Nalini A, Deymeer F, Sine SM, Engel AG. Mutations causing congenital myasthenia reveal principal coupling pathway in the acetylcholine receptor ε-subunit. JCI Insight 2018; 3:97826. [PMID: 29367459 DOI: 10.1172/jci.insight.97826] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Accepted: 12/12/2017] [Indexed: 11/17/2022] Open
Abstract
We identify 2 homozygous mutations in the ε-subunit of the muscle acetylcholine receptor (AChR) in 3 patients with severe congenital myasthenia: εR218W in the pre-M1 region in 2 patients and εE184K in the β8-β9 linker in 1 patient. Arg218 is conserved in all eukaryotic members of the Cys-loop receptor superfamily, while Glu184 is conserved in the α-, δ-, and ε-subunits of AChRs from all species. εR218W reduces channel gating efficiency 338-fold and AChR expression on the cell surface 5-fold, whereas εE184K reduces channel gating efficiency 11-fold but does not alter AChR cell surface expression. Determinations of the effective channel gating rate constants, combined with mutant cycle analyses, demonstrate strong energetic coupling between εR218 and εE184, and between εR218 and εE45 from the β1-β2 linker, as also observed for equivalent residues in the principal coupling pathway of the α-subunit. Thus, efficient and rapid gating of the AChR channel is achieved not only by coupling between conserved residues within the principal coupling pathway of the α-subunit, but also between corresponding residues in the ε-subunit.
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Affiliation(s)
- Xin-Ming Shen
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, Minnesota, USA
| | - Joan M Brengman
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, Minnesota, USA
| | - Shelley Shen
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, Minnesota, USA
| | - Hacer Durmus
- Department of Neurology, Istanbul Faculty of Medicine, Istanbul University, Istanbul, Turkey
| | - Veeramani Preethish-Kumar
- Department of Neurology and.,Clinical Neurosciences, National Institute of Mental Health and Neurosciences, Bangalore, India
| | - Nur Yuceyar
- Department of Neurology, Ege University, Izmir, Turkey
| | | | | | - Feza Deymeer
- Department of Neurology, Istanbul Faculty of Medicine, Istanbul University, Istanbul, Turkey
| | - Steven M Sine
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, Minnesota, USA.,Departments of Physiology and Biomedical Engineering and of Pharmacology and Experimental Therapeutics, Mayo Clinic, Rochester, Minnesota, USA
| | - Andrew G Engel
- Department of Neurology and Neuromuscular Research Laboratory, Mayo Clinic, Rochester, Minnesota, USA
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204
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Theisen U, Hennig C, Ring T, Schnabel R, Köster RW. Neurotransmitter-mediated activity spatially controls neuronal migration in the zebrafish cerebellum. PLoS Biol 2018; 16:e2002226. [PMID: 29300740 PMCID: PMC5754045 DOI: 10.1371/journal.pbio.2002226] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Accepted: 11/22/2017] [Indexed: 11/27/2022] Open
Abstract
Neuronal migration during embryonic development contributes to functional brain circuitry. Many neurons migrate in morphologically distinct stages that coincide with differentiation, requiring tight spatial regulation. It had been proposed that neurotransmitter-mediated activity could exert this control. Here, we demonstrate that intracellular calcium transients occur in cerebellar neurons of zebrafish embryos during migration. We show that depolarization increases and hyperpolarization reduces the speed of tegmental hindbrain neurons using optogenetic tools and advanced track analysis optimized for in vivo migration. Finally, we introduce a compound screening assay to identify acetylcholine (ACh), glutamate, and glycine as regulators of migration, which act regionally along the neurons’ route. We summarize our findings in a model describing how different neurotransmitters spatially interact to control neuronal migration. The high evolutionary conservation of the cerebellum and hindbrain makes it likely that polarization state-driven motility constitutes an important principle in building a functional brain. Postmitotic neurons migrate from their site of origin to their final destination in the developing brain to form functional structures. These neurons typically follow defined routes through the tissue. Previous studies investigating progress along such route have identified neurotransmitters—chemicals that transmit the signals between neurons—as important regulators in neuronal migration using mostly rodent brain slice cultures and cultivated neurons. In this study, we use live zebrafish embryos to test the influence of neurotransmitters on migrating hindbrain neurons. First, we demonstrate that calcium transients can be measured in these neurons using genetically encoded reporters. Next, we use optogenetic channels to specifically de- or hyperpolarize the plasma membrane of the neurons to show that the polarization state is linked to migratory speed. Finally, we use a screening method to identify the neurotransmitter systems involved in migration progress control. We summarize these findings in a model that suggests that there are regions of influence for different neurotransmitters that act successively on the neurons to ensure their timely arrival at their destination.
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Affiliation(s)
- Ulrike Theisen
- Technische Universität Braunschweig, Zoological Institute, Cellular and Molecular Neurobiology, Braunschweig, Germany
| | - Christian Hennig
- Technische Universität Braunschweig, Institute for Genetics, Braunschweig, Germany
| | - Tobias Ring
- Technische Universität Braunschweig, Institute for Engineering Design, Vibroacoustics, Braunschweig, Germany
| | - Ralf Schnabel
- Technische Universität Braunschweig, Institute for Genetics, Braunschweig, Germany
| | - Reinhard W. Köster
- Technische Universität Braunschweig, Zoological Institute, Cellular and Molecular Neurobiology, Braunschweig, Germany
- * E-mail:
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205
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Feng HJ, Forman SA. Comparison of αβδ and αβγ GABA A receptors: Allosteric modulation and identification of subunit arrangement by site-selective general anesthetics. Pharmacol Res 2017; 133:289-300. [PMID: 29294355 DOI: 10.1016/j.phrs.2017.12.031] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/18/2017] [Revised: 12/28/2017] [Accepted: 12/29/2017] [Indexed: 12/27/2022]
Abstract
GABAA receptors play a dominant role in mediating inhibition in the mature mammalian brain, and defects of GABAergic neurotransmission contribute to the pathogenesis of a variety of neurological and psychiatric disorders. Two types of GABAergic inhibition have been described: αβγ receptors mediate phasic inhibition in response to transient high-concentrations of synaptic GABA release, and αβδ receptors produce tonic inhibitory currents activated by low-concentration extrasynaptic GABA. Both αβδ and αβγ receptors are important targets for general anesthetics, which induce apparently different changes both in GABA-dependent receptor activation and in desensitization in currents mediated by αβγ vs. αβδ receptors. Many of these differences are explained by correcting for the high agonist efficacy of GABA at most αβγ receptors vs. much lower efficacy at αβδ receptors. The stoichiometry and subunit arrangement of recombinant αβγ receptors are well established as β-α-γ-β-α, while those of αβδ receptors remain controversial. Importantly, some potent general anesthetics selectively bind in transmembrane inter-subunit pockets of αβγ receptors: etomidate acts at β+/α- interfaces, and the barbiturate R-5-allyl-1-methyl-5-(m-trifluoromethyl-diazirynylphenyl) barbituric acid (R-mTFD-MPAB) acts at α+/β- and γ+/β- interfaces. Thus, these drugs are useful as structural probes in αβδ receptors formed from free subunits or concatenated subunit assemblies designed to constrain subunit arrangement. Although a definite conclusion cannot be drawn, studies using etomidate and R-mTFD-MPAB support the idea that recombinant α1β3δ receptors may share stoichiometry and subunit arrangement with α1β3γ2 receptors.
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Affiliation(s)
- Hua-Jun Feng
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, and Department of Anesthesia, Harvard Medical School, Boston, MA 02114, USA.
| | - Stuart A Forman
- Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, and Department of Anesthesia, Harvard Medical School, Boston, MA 02114, USA.
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206
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Nemecz Á, Hu H, Fourati Z, Van Renterghem C, Delarue M, Corringer PJ. Full mutational mapping of titratable residues helps to identify proton-sensors involved in the control of channel gating in the Gloeobacter violaceus pentameric ligand-gated ion channel. PLoS Biol 2017; 15:e2004470. [PMID: 29281623 PMCID: PMC5760087 DOI: 10.1371/journal.pbio.2004470] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Revised: 01/09/2018] [Accepted: 12/04/2017] [Indexed: 11/19/2022] Open
Abstract
The Gloeobacter violaceus ligand-gated ion channel (GLIC) has been extensively studied by X-ray crystallography and other biophysical techniques. This provided key insights into the general gating mechanism of pentameric ligand-gated ion channel (pLGIC) signal transduction. However, the GLIC is activated by lowering the pH and the location of its putative proton activation site(s) still remain(s) unknown. To this end, every Asp, Glu, and His residue was mutated individually or in combination and investigated by electrophysiology. In addition to the mutational analysis, key mutations were structurally resolved to address whether particular residues contribute to proton sensing, or alternatively to GLIC-gating, independently of the side chain protonation. The data show that multiple residues located below the orthosteric site, notably E26, D32, E35, and D122 in the lower part of the extracellular domain (ECD), along with E222, H235, E243, and H277 in the transmembrane domain (TMD), alter GLIC activation. D122 and H235 were found to also alter GLIC expression. E35 is identified as a key proton-sensing residue, whereby neutralization of its side chain carboxylate stabilizes the active state. Thus, proton activation occurs allosterically to the orthosteric site, at the level of multiple loci with a key contribution of the coupling interface between the ECD and TMD. Pentameric ligand-gated ion channels are an important class of receptors that are involved in many neurological diseases. They have been extensively studied but a full understanding of their mechanism of action has yet to be achieved. In an effort to bypass obstacles in the research of human receptors, bacterial versions have been used to characterize the family’s structure-function relationship. One key bacterial receptor, known as GLIC, has lead the way in structural resolution of various mechanistic states along the gating pathway, yet its activation by protons is significantly less understood than its human counterparts. To define the site(s) involved in proton gating, we systematically mutated all titratable residues near the pH50 of activation: Asp, Glu, and His. We determined that a previously established His residue in the transmembrane domain is structurally important but likely plays little or no role in proton gating. We instead found that proton activation is a complex multiple loci mechanism, with the key contribution stemming from the coupling interface between the extracellular and transmembrane domain, with E35 acting as a key proton-sensing residue.
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Affiliation(s)
- Ákos Nemecz
- Unité Récepteurs-Canaux, Unité Mixte de Recherche 3571 du Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France
| | - Haidai Hu
- Unité de Dynamique Structurale des Macromolécules, Unité Mixte de Recherche 3528 du Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France
| | - Zaineb Fourati
- Unité de Dynamique Structurale des Macromolécules, Unité Mixte de Recherche 3528 du Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France
| | - Catherine Van Renterghem
- Unité Récepteurs-Canaux, Unité Mixte de Recherche 3571 du Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France
| | - Marc Delarue
- Unité de Dynamique Structurale des Macromolécules, Unité Mixte de Recherche 3528 du Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France
| | - Pierre-Jean Corringer
- Unité Récepteurs-Canaux, Unité Mixte de Recherche 3571 du Centre National de la Recherche Scientifique, Institut Pasteur, Paris, France
- * E-mail:
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207
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Howard RJ, Carnevale V, Delemotte L, Hellmich UA, Rothberg BS. Permeating disciplines: Overcoming barriers between molecular simulations and classical structure-function approaches in biological ion transport. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1860:927-942. [PMID: 29258839 DOI: 10.1016/j.bbamem.2017.12.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2017] [Revised: 12/08/2017] [Accepted: 12/14/2017] [Indexed: 11/20/2022]
Abstract
Ion translocation across biological barriers is a fundamental requirement for life. In many cases, controlling this process-for example with neuroactive drugs-demands an understanding of rapid and reversible structural changes in membrane-embedded proteins, including ion channels and transporters. Classical approaches to electrophysiology and structural biology have provided valuable insights into several such proteins over macroscopic, often discontinuous scales of space and time. Integrating these observations into meaningful mechanistic models now relies increasingly on computational methods, particularly molecular dynamics simulations, while surfacing important challenges in data management and conceptual alignment. Here, we seek to provide contemporary context, concrete examples, and a look to the future for bridging disciplinary gaps in biological ion transport. This article is part of a Special Issue entitled: Beyond the Structure-Function Horizon of Membrane Proteins edited by Ute Hellmich, Rupak Doshi and Benjamin McIlwain.
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Affiliation(s)
- Rebecca J Howard
- Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, Box 1031, 17121 Solna, Sweden.
| | - Vincenzo Carnevale
- Institute for Computational Molecular Science, Department of Chemistry, Temple University, Philadelphia, PA 19122, USA.
| | - Lucie Delemotte
- Science for Life Laboratory, Department of Theoretical Physics, KTH Royal Institute of Technology, Box 1031, 17121 Solna, Sweden.
| | - Ute A Hellmich
- Johannes Gutenberg University Mainz, Institute for Pharmacy and Biochemistry, Johann-Joachim-Becherweg 30, 55128 Mainz, Germany; Centre for Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt, Max-von-Laue Str. 9, 60438 Frankfurt, Germany.
| | - Brad S Rothberg
- Department of Medical Genetics and Molecular Biochemistry, Temple University Lewis Katz School of Medicine, Philadelphia, PA 19140, USA.
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208
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Rossokhin AV. Homology modeling of the transmembrane domain of the GABAA receptor. Biophysics (Nagoya-shi) 2017. [DOI: 10.1134/s0006350917050190] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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209
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Newcombe J, Chatzidaki A, Sheppard TD, Topf M, Millar NS. Diversity of Nicotinic Acetylcholine Receptor Positive Allosteric Modulators Revealed by Mutagenesis and a Revised Structural Model. Mol Pharmacol 2017; 93:128-140. [PMID: 29196491 PMCID: PMC5767682 DOI: 10.1124/mol.117.110551] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Accepted: 11/30/2017] [Indexed: 01/26/2023] Open
Abstract
By combining electrophysiological and computational approaches we have examined a series of positive allosteric modulators (PAMs) acting on the human α7 nicotinic acetylcholine receptor (nAChR). Electrophysiological studies have focused on three α7-selective PAMs (A-867744, TBS-516, and TQS) that display similar effects on wild-type α7 nAChRs. In addition to potentiating agonist-evoked responses, all three compounds reduce receptor desensitization and, consequently, are classed as type II PAMs. Despite having similar effects on wild-type receptors, A-867744 was found to have profoundly differing effects on mutated receptors compared with TBS-516 and TQS, a finding that is consistent with previous studies indicating that A-867744 may have a different mechanism of action compare with other α7-selective type II PAMs. Due to evidence that these PAMs bind within the α7 nAChR transmembrane region, we generated and validated new structural models of α7. Importantly, we have corrected a previously identified error in the transmembrane region of the original cryo–electron microscopy Torpedo model; the only pentameric ligand-gated ion channel imaged in a native lipid membrane. Real-space refinement was used to generate closed and open conformations on which the α7 models were based. Consensus docking with an extended series of PAMs with chemical similarity to A-867744, TBS-516, and TQS suggests that all bind to a broadly similar intersubunit transmembrane site. However, differences in the predicted binding of A-867744, compared with TBS-516 and TQS, may help to explain the distinct functional effects of A-867744. Thus, our revised structural models may provide a useful tool for interpreting functional effects of PAMs.
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Affiliation(s)
- Joseph Newcombe
- Departments of Chemistry (J.N., T.D.S.) and Neuroscience, Physiology and Pharmacology (A.C., N.S.M.), University College London, London, United Kingdom; and Institute of Structural and Molecular Biology, Birkbeck, University of London, London, United Kingdom (J.N., M.T.)
| | - Anna Chatzidaki
- Departments of Chemistry (J.N., T.D.S.) and Neuroscience, Physiology and Pharmacology (A.C., N.S.M.), University College London, London, United Kingdom; and Institute of Structural and Molecular Biology, Birkbeck, University of London, London, United Kingdom (J.N., M.T.)
| | - Tom D Sheppard
- Departments of Chemistry (J.N., T.D.S.) and Neuroscience, Physiology and Pharmacology (A.C., N.S.M.), University College London, London, United Kingdom; and Institute of Structural and Molecular Biology, Birkbeck, University of London, London, United Kingdom (J.N., M.T.)
| | - Maya Topf
- Departments of Chemistry (J.N., T.D.S.) and Neuroscience, Physiology and Pharmacology (A.C., N.S.M.), University College London, London, United Kingdom; and Institute of Structural and Molecular Biology, Birkbeck, University of London, London, United Kingdom (J.N., M.T.)
| | - Neil S Millar
- Departments of Chemistry (J.N., T.D.S.) and Neuroscience, Physiology and Pharmacology (A.C., N.S.M.), University College London, London, United Kingdom; and Institute of Structural and Molecular Biology, Birkbeck, University of London, London, United Kingdom (J.N., M.T.)
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210
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Hernandez CC, Zhang Y, Hu N, Shen D, Shen W, Liu X, Kong W, Jiang Y, Macdonald RL. GABA A Receptor Coupling Junction and Pore GABRB3 Mutations are Linked to Early-Onset Epileptic Encephalopathy. Sci Rep 2017; 7:15903. [PMID: 29162865 PMCID: PMC5698489 DOI: 10.1038/s41598-017-16010-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Accepted: 10/11/2017] [Indexed: 12/17/2022] Open
Abstract
GABAA receptors are brain inhibitory chloride ion channels. Here we show functional analyses and structural simulations for three de novo missense mutations in the GABAA receptor β3 subunit gene (GABRB3) identified in patients with early-onset epileptic encephalopathy (EOEE) and profound developmental delay. We sought to obtain insights into the molecular mechanisms that might link defects in GABAA receptor biophysics and biogenesis to patients with EOEE. The mutant residues are part of conserved structural domains such as the Cys-loop (L170R) and M2-M3 loop (A305V) that form the GABA binding/channel gating coupling junction and the channel pore (T288N), which are functionally coupled during receptor activation. The mutant coupling junction residues caused rearrangements and formation of new hydrogen bonds in the open state, while the mutant pore residue reshaped the pore cavity. Whereas mutant coupling junction residues uncoupled during activation and caused gain of function, the mutant pore residue favoured low conductance receptors and differential sensitivity to diazepam and loss of function. These data reveal novel molecular mechanisms by which EOEE-linked mutations affect GABAA receptor function.
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Affiliation(s)
- Ciria C Hernandez
- Department of Neurology, Vanderbilt University, Nashville, TN., 37240-7915., USA. .,University of Michigan, Life Sciences Institute, 210 Washtenaw Ave., Room 6115, Ann Arbor, MI, 48109-2216, USA.
| | - Yujia Zhang
- Department of Pediatrics, Peking University First Hospital, Beijing, 100034, China
| | - Ningning Hu
- Department of Neurology, Vanderbilt University, Nashville, TN., 37240-7915., USA
| | - Dingding Shen
- The Graduate Program of Neuroscience, Vanderbilt University, Nashville, 37240-7915., TN, USA
| | - Wangzhen Shen
- Department of Neurology, Vanderbilt University, Nashville, TN., 37240-7915., USA
| | - Xiaoyan Liu
- Department of Pediatrics, Peking University First Hospital, Beijing, 100034, China
| | - Weijing Kong
- Department of Pediatrics, Peking University First Hospital, Beijing, 100034, China
| | - Yuwu Jiang
- Department of Pediatrics, Peking University First Hospital, Beijing, 100034, China.
| | - Robert L Macdonald
- Department of Neurology, Vanderbilt University, Nashville, TN., 37240-7915., USA.
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211
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Top-down characterization of endogenous protein complexes with native proteomics. Nat Chem Biol 2017; 14:36-41. [PMID: 29131144 PMCID: PMC5726920 DOI: 10.1038/nchembio.2515] [Citation(s) in RCA: 107] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Accepted: 10/04/2017] [Indexed: 11/08/2022]
Abstract
Protein complexes exhibit great diversity in protein membership, post-translational modifications and noncovalent cofactors, enabling them to function as the actuators of many important biological processes. The exposition of these molecular features using current methods lacks either throughput or molecular specificity, ultimately limiting the use of protein complexes as direct analytical targets in a wide range of applications. Here, we apply native proteomics, enabled by a multistage tandem MS approach, to characterize 125 intact endogenous complexes and 217 distinct proteoforms derived from mouse heart and human cancer cell lines in discovery mode. The native conditions preserved soluble protein-protein interactions, high-stoichiometry noncovalent cofactors, covalent modifications to cysteines, and, remarkably, superoxide ligands bound to the metal cofactor of superoxide dismutase 2. These data enable precise compositional analysis of protein complexes as they exist in the cell and demonstrate a new approach that uses MS as a bridge to structural biology.
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212
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Chen IS, Kubo Y. Ivermectin and its target molecules: shared and unique modulation mechanisms of ion channels and receptors by ivermectin. J Physiol 2017; 596:1833-1845. [PMID: 29063617 DOI: 10.1113/jp275236] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2017] [Accepted: 10/06/2017] [Indexed: 12/11/2022] Open
Abstract
Ivermectin (IVM) is an antiparasitic drug that is used worldwide and rescues hundreds of millions of people from onchocerciasis and lymphatic filariasis. It was discovered by Satoshi Ōmura and William C. Campbell, to whom the 2015 Nobel Prize in Physiology or Medicine was awarded. It kills parasites by activating glutamate-gated Cl- channels, and it also targets several ligand-gated ion channels and receptors, including Cys-loop receptors, P2X4 receptors and fernesoid X receptors. Recently, we found that IVM also activates a novel target, the G-protein-gated inwardly rectifying K+ channel, and also identified the structural determinant for the activation. In this review, we aim to provide an update and summary of recent progress in the identification of IVM targets, as well as their modulation mechanisms, through molecular structures, chimeras and site-directed mutagenesis, and molecular docking and modelling studies.
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Affiliation(s)
- I-Shan Chen
- Division of Biophysics and Neurobiology, Department of Molecular and Cellular Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585, Japan.,Department of Physiological Sciences, School of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Hayama, 240-0193, Japan
| | - Yoshihiro Kubo
- Division of Biophysics and Neurobiology, Department of Molecular and Cellular Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585, Japan.,Department of Physiological Sciences, School of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Hayama, 240-0193, Japan
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213
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Miller PS, Scott S, Masiulis S, De Colibus L, Pardon E, Steyaert J, Aricescu AR. Structural basis for GABA A receptor potentiation by neurosteroids. Nat Struct Mol Biol 2017; 24:986-992. [PMID: 28991263 PMCID: PMC6166781 DOI: 10.1038/nsmb.3484] [Citation(s) in RCA: 129] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Accepted: 09/13/2017] [Indexed: 12/18/2022]
Abstract
Type A γ-aminobutyric acid receptors (GABAARs) are the principal mediators of inhibitory neurotransmission in the human brain. Endogenous neurosteroids interact with GABAARs to regulate acute and chronic anxiety and are potent sedative, analgesic, anticonvulsant and anesthetic agents. Their mode of binding and mechanism of receptor potentiation, however, remain unknown. Here we report crystal structures of a chimeric GABAAR construct in apo and pregnanolone-bound states. The neurosteroid-binding site is mechanically coupled to the helices lining the ion channel pore and modulates the desensitization-gate conformation. We demonstrate that the equivalent site is responsible for physiological, heteromeric GABAAR potentiation and explain the contrasting modulatory properties of 3a versus 3b neurosteroid epimers. These results illustrate how peripheral lipid ligands can regulate the desensitization gate of GABAARs, a process of broad relevance to pentameric ligand-gated ion channels.
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Affiliation(s)
- Paul S. Miller
- Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, United Kingdom
| | - Suzanne Scott
- Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, United Kingdom
- Neurobiology Division, MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom
| | - Simonas Masiulis
- Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, United Kingdom
- Neurobiology Division, MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom
| | - Luigi De Colibus
- Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, United Kingdom
| | - Els Pardon
- Structural Biology Brussels, Vrije Universiteit Brussel (VUB), Brussels, Belgium
- Structural Biology Research Center, VIB, Brussels, Belgium
| | - Jan Steyaert
- Structural Biology Brussels, Vrije Universiteit Brussel (VUB), Brussels, Belgium
- Structural Biology Research Center, VIB, Brussels, Belgium
| | - A. Radu Aricescu
- Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, United Kingdom
- Neurobiology Division, MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom
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214
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Gonzalez-Gutierrez G, Wang Y, Cymes GD, Tajkhorshid E, Grosman C. Chasing the open-state structure of pentameric ligand-gated ion channels. J Gen Physiol 2017; 149:1119-1138. [PMID: 29089419 PMCID: PMC5715906 DOI: 10.1085/jgp.201711803] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2017] [Revised: 09/14/2017] [Accepted: 10/05/2017] [Indexed: 11/25/2022] Open
Abstract
Members of the pentameric ligand-gated ion channel family have been crystallized in different conformations, including one in which the transmembrane pore is surprisingly wide. Gonzalez-Gutierrez et al. show that the open-channel conformation of animal members is more similar to the models with narrow pores. Remarkable advances have been made toward the structural characterization of ion channels in the last two decades. However, the unambiguous assignment of well-defined functional states to the obtained structural models has proved challenging. In the case of the superfamily of nicotinic-receptor channels (also referred to as pentameric ligand-gated ion channels [pLGICs]), for example, two different types of model of the open-channel conformation have been proposed on the basis of structures solved to resolutions better than 4.0 Å. At the level of the transmembrane pore, the open-state models of the proton-gated pLGIC from Gloeobacter violaceus (GLIC) and the invertebrate glutamate-gated Cl– channel (GluCl) are very similar to each other, but that of the glycine receptor (GlyR) is considerably wider. Indeed, the mean distances between the axis of ion permeation and the Cα atoms at the narrowest constriction of the pore (position −2′) differ by ∼2 Å in these two classes of model, a large difference when it comes to understanding the physicochemical bases of ion conduction and charge selectivity. Here, we take advantage of the extreme open-channel stabilizing effect of mutations at pore-facing position 9′. We find that the I9′A mutation slows down entry into desensitization of GLIC to the extent that macroscopic currents decay only slightly by the end of pH 4.5 solution applications to the extracellular side for several minutes. We crystallize (at pH 4.5) two variants of GLIC carrying this mutation and solve their structures to resolutions of 3.12 Å and 3.36 Å. Furthermore, we perform all-atom molecular dynamics simulations of ion permeation and picrotoxinin block, using the different open-channel structural models. On the basis of these results, we favor the notion that the open-channel structure of pLGICs from animals is much closer to that of the narrow models (of GLIC and GluCl) than it is to that of the GlyR.
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Affiliation(s)
| | - Yuhang Wang
- Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL.,Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL
| | - Gisela D Cymes
- Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, IL
| | - Emad Tajkhorshid
- Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL.,Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL.,Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, IL
| | - Claudio Grosman
- Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, IL .,Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL.,Neuroscience Program, University of Illinois at Urbana-Champaign, Urbana, IL
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215
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Un-gating and allosteric modulation of a pentameric ligand-gated ion channel captured by molecular dynamics. PLoS Comput Biol 2017; 13:e1005784. [PMID: 29069080 PMCID: PMC5673239 DOI: 10.1371/journal.pcbi.1005784] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Revised: 11/06/2017] [Accepted: 09/14/2017] [Indexed: 11/19/2022] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) mediate intercellular communication at synapses through the opening of an ion pore in response to the binding of a neurotransmitter. Despite the increasing availability of high-resolution structures of pLGICs, a detailed understanding of the functional isomerization from closed to open (gating) and back is currently missing. Here, we provide the first atomistic description of the transition from open to closed (un-gating) in the glutamate-gated chloride channel (GluCl) from Caenorhabditis Elegans. Starting with the active-state structure solved in complex with the neurotransmitter L-glutamate and the positive allosteric modulator (PAM) ivermectin, we analyze the spontaneous relaxation of the channel upon removal of ivermectin by explicit solvent/membrane Molecular Dynamics (MD) simulations. The μs-long trajectories support the conclusion that ion-channel deactivation is mediated by two distinct quaternary transitions, i.e. a global receptor twisting followed by the radial expansion (or blooming) of the extracellular domain. At variance with previous models, we show that pore closing is exclusively regulated by the global twisting, which controls the position of the β1-β2 loop relative to the M2-M3 loop at the EC/TM domain interface. Additional simulations with L-glutamate restrained to the crystallographic binding mode and ivermectin removed indicate that the same twisting isomerization is regulated by agonist binding at the orthosteric site. These results provide a structural model for gating in pLGICs and suggest a plausible mechanism for the pharmacological action of PAMs in this neurotransmitter receptor family. The simulated un-gating converges to the X-ray structure of GluCl resting state both globally and locally, demonstrating the predictive character of state-of-art MD simulations.
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216
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Janzen D, Schaefer N, Delto C, Schindelin H, Villmann C. The GlyR Extracellular β8-β9 Loop - A Functional Determinant of Agonist Potency. Front Mol Neurosci 2017; 10:322. [PMID: 29062270 PMCID: PMC5640878 DOI: 10.3389/fnmol.2017.00322] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2017] [Accepted: 09/22/2017] [Indexed: 01/07/2023] Open
Abstract
Ligand-binding of Cys-loop receptors results in rearrangements of extracellular loop structures which are further translated into the tilting of membrane spanning helices, and finally opening of the ion channels. The cryo-EM structure of the homopentameric α1 glycine receptor (GlyR) demonstrated an involvement of the extracellular β8–β9 loop in the transition from ligand-bound receptors to the open channel state. Recently, we identified a functional role of the β8–β9 loop in a novel startle disease mouse model shaky. The mutation of residue GlyRα1Q177 to lysine present in shaky mice resulted in reduced glycine potency, reduced synaptic expression, and a disrupted hydrogen network at the structural level around position GlyRα1Q177. Here, we investigated the role of amino acid volume, side chain length, and charge at position Q177 to get deeper insights into the functional role of the β8–β9 loop. We used a combined approach of in vitro expression analysis, functional electrophysiological recordings, and GlyR modeling to describe the role of Q177 for GlyR ion channel function. GlyRα1Q177 variants do not disturb ion channel transport to the cellular surface of transfected cells, neither in homomeric nor in heteromeric GlyR configurations. The EC50 values were increased for all GlyRα1Q177 variants in comparison to the wild type. The largest decrease in glycine potency was observed for the variant GlyRα1Q177R. Potencies of the partial agonists β-alanine and taurine were also reduced. Our data are further supported by homology modeling. The GlyRα1Q177R variant does not form hydrogen bonds with the surrounding network of residue Q177 similar to the substitution with a basic lysine present in the mouse mutant shaky. Among all investigated Q177 mutants, the neutral exchange of glutamine to asparagine as well as the introduction of the closely related amino acid glutamic acid preserve the hydrogen bond network. Introduction of amino acids with small side chains or larger volume resulted in a loss of their hydrogen bonds to neighboring residues. The β8–β9 loop is thus an important structural and functional determinant of the inhibitory GlyR.
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Affiliation(s)
- Dieter Janzen
- Institute for Clinical Neurobiology, University of Würzburg, Würzburg, Germany
| | - Natascha Schaefer
- Institute for Clinical Neurobiology, University of Würzburg, Würzburg, Germany
| | - Carolyn Delto
- Rudolf Virchow Center for Experimental Biomedicine, University of Würzburg, Würzburg, Germany
| | - Hermann Schindelin
- Rudolf Virchow Center for Experimental Biomedicine, University of Würzburg, Würzburg, Germany
| | - Carmen Villmann
- Institute for Clinical Neurobiology, University of Würzburg, Würzburg, Germany
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217
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Crystal structures of a GABA A-receptor chimera reveal new endogenous neurosteroid-binding sites. Nat Struct Mol Biol 2017; 24:977-985. [PMID: 28967882 DOI: 10.1038/nsmb.3477] [Citation(s) in RCA: 134] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Accepted: 09/01/2017] [Indexed: 12/11/2022]
Abstract
γ-Aminobutyric acid receptors (GABAARs) are vital for controlling excitability in the brain. This is emphasized by the numerous neuropsychiatric disorders that result from receptor dysfunction. A critical component of most native GABAARs is the α subunit. Its transmembrane domain is the target for many modulators, including endogenous brain neurosteroids that impact anxiety, stress and depression, and for therapeutic drugs, such as general anesthetics. Understanding the basis for the modulation of GABAAR function requires high-resolution structures. Here we present the first atomic structures of a GABAAR chimera at 2.8-Å resolution, including those bound with potentiating and inhibitory neurosteroids. These structures define new allosteric binding sites for these modulators that are associated with the α-subunit transmembrane domain. Our findings will enable the exploitation of neurosteroids for therapeutic drug design to regulate GABAARs in neurological disorders.
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218
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Atif M, Estrada-Mondragon A, Nguyen B, Lynch JW, Keramidas A. Effects of glutamate and ivermectin on single glutamate-gated chloride channels of the parasitic nematode H. contortus. PLoS Pathog 2017; 13:e1006663. [PMID: 28968469 PMCID: PMC5638611 DOI: 10.1371/journal.ppat.1006663] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Revised: 10/12/2017] [Accepted: 09/22/2017] [Indexed: 12/12/2022] Open
Abstract
Ivermectin (IVM) is a widely-used anthelmintic that works by binding to and activating glutamate-gated chloride channel receptors (GluClRs) in nematodes. The resulting chloride flux inhibits the pharyngeal muscle cells and motor neurons of nematodes, causing death by paralysis or starvation. IVM resistance is an emerging problem in many pest species, necessitating the development of novel drugs. However, drug optimisation requires a quantitative understanding of GluClR activation and modulation mechanisms. Here we investigated the biophysical properties of homomeric α (avr-14b) GluClRs from the parasitic nematode, H. contortus, in the presence of glutamate and IVM. The receptor proved to be highly responsive to low nanomolar concentrations of both compounds. Analysis of single receptor activations demonstrated that the GluClR oscillates between multiple functional states upon the binding of either ligand. The G36’A mutation in the third transmembrane domain, which was previously thought to hinder access of IVM to its binding site, was found to decrease the duration of active periods and increase receptor desensitisation. On an ensemble macropatch level the mutation gave rise to enhanced current decay and desensitisation rates. Because these responses were common to both glutamate and IVM, and were observed under conditions where agonist binding sites were likely saturated, we infer that G36’A affects the intrinsic properties of the receptor with no specific effect on IVM binding mechanisms. These unexpected results provide new insights into the activation and modulatory mechanisms of the H. contortus GluClRs and provide a mechanistic framework upon which the actions of drugs can be reliably interpreted. IVM is a gold standard anti-parasitic drug that is used extensively to control invertebrate parasites pest species. The drug targets the glutamate-gated chloride channel receptor (GluClR) found on neurons and muscle cells of these organisms, causing paralysis and death. However, IVM resistance is becoming a serious problem in human and animal health, as well as human food production. We provide the first comprehensive investigation of the functional properties of the GluClR of H. contortus, which is a major parasite in grazing animals, such as sheep and goats. We compared glutamate and IVM induced activity of the wild-type and a mutant GluClR, G36’A, that markedly reduces IVM sensitivity in wild populations of pests. Our data demonstrate that the mutation reduces IVM sensitivity by altering the functional properties of the GluClR rather than specifically affecting the binding of IVM, even though the mutation occurs at the IVM binding site. This study provides a mechanistic framework upon which the actions of new candidate anthelmintic drugs can be interpreted.
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Affiliation(s)
- Mohammed Atif
- Queensland Brain Institute, The University of Queensland, Brisbane, Australia
| | | | - Bindi Nguyen
- Queensland Brain Institute, The University of Queensland, Brisbane, Australia
| | - Joseph W. Lynch
- Queensland Brain Institute, The University of Queensland, Brisbane, Australia
- School of Biomedical Sciences, The University of Queensland, Brisbane, Australia
- * E-mail: (AK); (JL)
| | - Angelo Keramidas
- Queensland Brain Institute, The University of Queensland, Brisbane, Australia
- * E-mail: (AK); (JL)
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219
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Ghosh B, Tsao TW, Czajkowski C. A chimeric prokaryotic-eukaryotic pentameric ligand gated ion channel reveals interactions between the extracellular and transmembrane domains shape neurosteroid modulation. Neuropharmacology 2017; 125:343-352. [PMID: 28803966 PMCID: PMC5600277 DOI: 10.1016/j.neuropharm.2017.08.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Revised: 06/30/2017] [Accepted: 08/08/2017] [Indexed: 10/19/2022]
Abstract
Pentameric ligand-gated ion channels (pLGICs) are the targets of several clinical and endogenous allosteric modulators including anesthetics and neurosteroids. Molecular mechanisms underlying allosteric drug modulation are poorly understood. Here, we constructed a chimeric pLGIC by fusing the extracellular domain (ECD) of the proton-activated, cation-selective bacterial channel GLIC to the transmembrane domain (TMD) of the human ρ1 chloride-selective GABAAR, and tested the hypothesis that drug actions are regulated locally in the domain that houses its binding site. The chimeric channels were proton-gated and chloride-selective demonstrating the GLIC ECD was functionally coupled to the GABAρ TMD. Channels were blocked by picrotoxin and inhibited by pentobarbital, etomidate and propofol. The point mutation, ρ TMD W328M, conferred positive modulation and direct gating by pentobarbital. The data suggest that the structural machinery mediating general anesthetic modulation resides in the TMD. Proton-activation and neurosteroid modulation of the GLIC-ρ chimeric channels, however, did not simply mimic their respective actions on GLIC and GABAρ revealing that across domain interactions between the ECD and TMD play important roles in determining their actions. Proton-induced current responses were biphasic suggesting that the chimeric channels contain an additional proton sensor. Neurosteroid modulation of the GLIC-ρ chimeric channels by the stereoisomers, 5α-THDOC and 5β-THDOC, were swapped compared to their actions on GABAρ indicating that positive versus negative neurosteroid modulation is not encoded solely in the TMD nor by neurosteroid isomer structure but is dependent on specific interdomain connections between the ECD and TMD. Our data reveal a new mechanism for shaping neurosteroid modulation.
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Affiliation(s)
- Borna Ghosh
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin - Madison, 1111 Highland Ave, Madison, WI 53705, USA; Eli Lilly and Company, 1220 W Morris St, Indianapolis, IN 46221, USA
| | - Tzu-Wei Tsao
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin - Madison, 1111 Highland Ave, Madison, WI 53705, USA; Physiology Training Program, University of Wisconsin - Madison, 1111 Highland Ave, Madison, WI 53705, USA
| | - Cynthia Czajkowski
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin - Madison, 1111 Highland Ave, Madison, WI 53705, USA.
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220
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Cioffi CL. Modulation of Glycine-Mediated Spinal Neurotransmission for the Treatment of Chronic Pain. J Med Chem 2017; 61:2652-2679. [PMID: 28876062 DOI: 10.1021/acs.jmedchem.7b00956] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Chronic pain constitutes a significant and expanding worldwide health crisis. Currently available analgesics poorly serve individuals suffering from chronic pain, and new therapeutic agents that are more effective, safer, and devoid of abuse liabilities are desperately needed. Among the myriad of cellular and molecular processes contributing to chronic pain, spinal disinhibition of pain signaling to higher cortical centers plays a critical role. Accumulating evidence shows that glycinergic inhibitory neurotransmission in the spinal cord dorsal horn gates nociceptive signaling, is essential in maintaining physiological pain sensitivity, and is diminished in pathological pain states. Thus, it is hypothesized that agents capable of enhancing glycinergic tone within the dorsal horn could obtund nociceptor signaling to the brain and serve as analgesics for persistent pain. This Perspective highlights the potential that pharmacotherapies capable of increasing inhibitory spinal glycinergic neurotransmission hold in providing new and transformative analgesic therapies for the treatment of chronic pain.
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Affiliation(s)
- Christopher L Cioffi
- Departments of Basic and Clinical Sciences and Pharmaceutical Sciences , Albany College of Pharmacy and Health Sciences , 106 New Scotland Avenue , Albany , New York 12208 United States
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221
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Hawken NM, Zaika EI, Nakagawa T. Engineering defined membrane-embedded elements of AMPA receptor induces opposing gating modulation by cornichon 3 and stargazin. J Physiol 2017; 595:6517-6539. [PMID: 28815591 DOI: 10.1113/jp274897] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2017] [Accepted: 08/04/2017] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The AMPA-type ionotropic glutamate receptors (AMPARs) mediate the majority of excitatory synaptic transmission and their function impacts learning, cognition and behaviour. The gating of AMPARs occurs in milliseconds, precisely controlled by a variety of auxiliary subunits that are expressed differentially in the brain, but the difference in mechanisms underlying AMPAR gating modulation by auxiliary subunits remains elusive and is investigated. The elements of the AMPAR that are functionally recruited by auxiliary subunits, stargazin and cornichon 3, are located not only in the extracellular domains but also in the lipid-accessible surface of the AMPAR. We reveal that the two auxiliary subunits require a shared surface on the transmembrane domain of the AMPAR for their function, but the gating is influenced by this surface in opposing directions for each auxiliary subunit. Our results provide new insights into the mechanistic difference of AMPAR modulation by auxiliary subunits and a conceptual framework for functional engineering of the complex. ABSTRACT During excitatory synaptic transmission, various structurally unrelated transmembrane auxiliary subunits control the function of AMPA receptors (AMPARs), but the underlying mechanisms remain unclear. We identified lipid-exposed residues in the transmembrane domain (TMD) of the GluA2 subunit of AMPARs that are critical for the function of AMPAR auxiliary subunits, stargazin (Stg) and cornichon 3 (CNIH3). These residues are essential for stabilizing the AMPAR-CNIH3 complex in detergents and overlap with the contacts made between GluA2 TMD and Stg in the cryoEM structures. Mutating these residues had opposite effects on gating modulation and complex stability when Stg- and CNIH3-bound AMPARs were compared. Specifically, in detergent the GluA2-A793F formed an unstable complex with CNIIH3 but in the membrane the GluA2-A793F-CNIH3 complex expressed a gain of function. In contrast, the GluA2-A793F-Stg complex was stable, but had diminished gating modulation. GluA2-C528L destabilized the AMPAR-CNIH3 complex but stabilized the AMPAR-Stg complex, with overall loss of function in gating modulation. Furthermore, loss-of-function mutations in this TMD region cancelled the effects of a gain-of-function Stg carrying mutation in its extracellular loop, demonstrating that both the extracellular and the TMD elements contribute independently to gating modulation. The elements of AMPAR functionally recruited by auxiliary subunits are, therefore, located not only in the extracellular domains but also in the lipid accessible surface of the AMPAR. The TMD surface we defined is a potential target for auxiliary subunit-specific compounds, because engineering of this hotspot induces opposing functional outcomes by Stg and CNIH3. The collection of mutant-phenotype mapping provides a framework for engineering AMPAR gating using auxiliary subunits.
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Affiliation(s)
- Natalie M Hawken
- Department of Molecular Physiology and Biophysics, Vanderbilt University, School of Medicine, Nashville, TN, 37232, USA
| | - Elena I Zaika
- Department of Molecular Physiology and Biophysics, Vanderbilt University, School of Medicine, Nashville, TN, 37232, USA
| | - Terunaga Nakagawa
- Department of Molecular Physiology and Biophysics, Vanderbilt University, School of Medicine, Nashville, TN, 37232, USA.,Center for Structural Biology, Vanderbilt University, School of Medicine, Nashville, TN, 37232, USA.,Vanderbilt Brain Institute, Vanderbilt University, School of Medicine, Nashville, TN, 37232, USA
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222
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Alpha subunit-dependent glycine receptor clustering and regulation of synaptic receptor numbers. Sci Rep 2017; 7:10899. [PMID: 28883437 PMCID: PMC5589798 DOI: 10.1038/s41598-017-11264-3] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Accepted: 08/21/2017] [Indexed: 02/08/2023] Open
Abstract
Accumulation of glycine receptors at synapses requires the interaction between the beta subunit of the receptor and the scaffold protein gephyrin. Here, we questioned whether different alpha subunits could modulate the receptors' diffusion and propensity to cluster at spinal cord synapses. Using quantitative photoactivated localisation microscopy we found that alpha-1 and alpha-3 containing glycine receptors display the same α3:β2 stoichiometry and gephyrin binding. Despite these similarities, alpha-3 containing receptors are less mobile and cluster at higher density compared to alpha-1, with 1500 versus 1100 complexes µm-2, respectively. Furthermore, we identified a subunit-specific regulation of glycine receptor copy numbers at synapses: when challenged with interleukin 1β, the synaptic occupancy of alpha-1 but not alpha-3 receptors was reduced. This mechanism may play a role in the cell-type dependent regulation of glycinergic currents in response to interleukin 1β and highlights the capacity of the alpha subunits to affect receptor-gephyrin binding at synapses.
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223
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Changeux JP, Christopoulos A. Allosteric modulation as a unifying mechanism for receptor function and regulation. Diabetes Obes Metab 2017; 19 Suppl 1:4-21. [PMID: 28880476 DOI: 10.1111/dom.12959] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Four major receptor families enable cells to respond to chemical and physical signals from their proximal environment. The ligand- and voltage-gated ion channels, G-protein-coupled receptors, nuclear hormone receptors and receptor tyrosine kinases are all allosteric proteins that carry multiple, spatially distinct, yet conformationally linked ligand-binding sites. Recent studies point to common mechanisms governing the allosteric transitions of these receptors, including the impact of oligomerization, pre-existing and functionally distinct conformational ensembles, intrinsically disordered regions, and the occurrence of allosteric modulatory sites. Importantly, synthetic allosteric modulators are being discovered for these receptors, providing an enriched, yet challenging, landscape for novel therapeutics.
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MESH Headings
- Allosteric Regulation/drug effects
- Allosteric Site/drug effects
- Animals
- Binding Sites/drug effects
- Dimerization
- Drug Discovery/trends
- Drugs, Investigational/chemistry
- Drugs, Investigational/pharmacology
- Humans
- Ligand-Gated Ion Channels/agonists
- Ligand-Gated Ion Channels/antagonists & inhibitors
- Ligand-Gated Ion Channels/chemistry
- Ligand-Gated Ion Channels/metabolism
- Ligands
- Models, Molecular
- Protein Conformation/drug effects
- Protein Multimerization/drug effects
- Receptor Protein-Tyrosine Kinases/agonists
- Receptor Protein-Tyrosine Kinases/antagonists & inhibitors
- Receptor Protein-Tyrosine Kinases/chemistry
- Receptor Protein-Tyrosine Kinases/metabolism
- Receptors, Cytoplasmic and Nuclear/agonists
- Receptors, Cytoplasmic and Nuclear/antagonists & inhibitors
- Receptors, Cytoplasmic and Nuclear/chemistry
- Receptors, Cytoplasmic and Nuclear/metabolism
- Receptors, G-Protein-Coupled/agonists
- Receptors, G-Protein-Coupled/antagonists & inhibitors
- Receptors, G-Protein-Coupled/chemistry
- Receptors, G-Protein-Coupled/metabolism
- Voltage-Gated Sodium Channels/chemistry
- Voltage-Gated Sodium Channels/metabolism
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Affiliation(s)
| | - Arthur Christopoulos
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, VIC 3052 Parkville, Australia
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224
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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: 159] [Impact Index Per Article: 22.7] [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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225
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Schaefer N, Berger A, van Brederode J, Zheng F, Zhang Y, Leacock S, Littau L, Jablonka S, Malhotra S, Topf M, Winter F, Davydova D, Lynch JW, Paige CJ, Alzheimer C, Harvey RJ, Villmann C. Disruption of a Structurally Important Extracellular Element in the Glycine Receptor Leads to Decreased Synaptic Integration and Signaling Resulting in Severe Startle Disease. J Neurosci 2017; 37:7948-7961. [PMID: 28724750 PMCID: PMC5559766 DOI: 10.1523/jneurosci.0009-17.2017] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2017] [Revised: 06/15/2017] [Accepted: 06/24/2017] [Indexed: 01/09/2023] Open
Abstract
Functional impairments or trafficking defects of inhibitory glycine receptors (GlyRs) have been linked to human hyperekplexia/startle disease and autism spectrum disorders. We found that a lack of synaptic integration of GlyRs, together with disrupted receptor function, is responsible for a lethal startle phenotype in a novel spontaneous mouse mutant shaky, caused by a missense mutation, Q177K, located in the extracellular β8-β9 loop of the GlyR α1 subunit. Recently, structural data provided evidence that the flexibility of the β8-β9 loop is crucial for conformational transitions during opening and closing of the ion channel and represents a novel allosteric binding site in Cys-loop receptors. We identified the underlying neuropathological mechanisms in male and female shaky mice through a combination of protein biochemistry, immunocytochemistry, and both in vivo and in vitro electrophysiology. Increased expression of the mutant GlyR α1Q177K subunit in vivo was not sufficient to compensate for a decrease in synaptic integration of α1Q177Kβ GlyRs. The remaining synaptic heteromeric α1Q177Kβ GlyRs had decreased current amplitudes with significantly faster decay times. This functional disruption reveals an important role for the GlyR α1 subunit β8-β9 loop in initiating rearrangements within the extracellular-transmembrane GlyR interface and that this structural element is vital for inhibitory GlyR function, signaling, and synaptic clustering.SIGNIFICANCE STATEMENT GlyR dysfunction underlies neuromotor deficits in startle disease and autism spectrum disorders. We describe an extracellular GlyR α1 subunit mutation (Q177K) in a novel mouse startle disease mutant shaky Structural data suggest that during signal transduction, large transitions of the β8-β9 loop occur in response to neurotransmitter binding. Disruption of the β8-β9 loop by the Q177K mutation results in a disruption of hydrogen bonds between Q177 and the ligand-binding residue R65. Functionally, the Q177K change resulted in decreased current amplitudes, altered desensitization decay time constants, and reduced GlyR clustering and synaptic strength. The GlyR β8-β9 loop is therefore an essential regulator of conformational rearrangements during ion channel opening and closing.
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Affiliation(s)
- Natascha Schaefer
- Institute of Clinical Neurobiology, Julius-Maximilians-University of Würzburg, 97078 Würzburg, Germany
| | - Alexandra Berger
- Princess Margaret Cancer Centre, University Health Network, University of Toronto, Toronto, Ontario M5G 2M9, Canada
| | | | - Fang Zheng
- Institute of Physiology and Pathophysiology, and
| | - Yan Zhang
- Queensland Brain Institute, University of Queensland, Brisbane 4072, Australia
| | - Sophie Leacock
- Department of Pharmacology, UCL School of Pharmacy, London WC1N 1AX, United Kingdom
| | - Laura Littau
- Institute of Clinical Neurobiology, Julius-Maximilians-University of Würzburg, 97078 Würzburg, Germany
| | - Sibylle Jablonka
- Institute of Clinical Neurobiology, Julius-Maximilians-University of Würzburg, 97078 Würzburg, Germany
| | - Sony Malhotra
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom, and
| | - Maya Topf
- Institute of Structural and Molecular Biology, UCL Birkbeck College, London WC1E 7HX, United Kingdom
| | - Friederike Winter
- Institute of Biochemistry, Friedrich-Alexander-University Erlangen-Nürnberg, 91054 Erlangen-Nürnberg, Germany
| | - Daria Davydova
- Institute of Clinical Neurobiology, Julius-Maximilians-University of Würzburg, 97078 Würzburg, Germany
| | - Joseph W Lynch
- Queensland Brain Institute, University of Queensland, Brisbane 4072, Australia
| | - Christopher J Paige
- Princess Margaret Cancer Centre, University Health Network, University of Toronto, Toronto, Ontario M5G 2M9, Canada
| | | | - Robert J Harvey
- Department of Pharmacology, UCL School of Pharmacy, London WC1N 1AX, United Kingdom
| | - Carmen Villmann
- Institute of Clinical Neurobiology, Julius-Maximilians-University of Würzburg, 97078 Würzburg, Germany,
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226
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Acetylcholine nicotinic receptor subtypes in chromaffin cells. Pflugers Arch 2017; 470:13-20. [DOI: 10.1007/s00424-017-2050-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Revised: 07/26/2017] [Accepted: 07/27/2017] [Indexed: 02/08/2023]
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227
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Chen IS, Tateyama M, Fukata Y, Uesugi M, Kubo Y. Ivermectin activates GIRK channels in a PIP 2 -dependent, G βγ -independent manner and an amino acid residue at the slide helix governs the activation. J Physiol 2017; 595:5895-5912. [PMID: 28715108 DOI: 10.1113/jp274871] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2017] [Accepted: 07/13/2017] [Indexed: 01/19/2023] Open
Abstract
KEY POINTS Ivermectin (IVM) is a widely used antiparasitic drug in humans and pets which activates glutamate-gated Cl- channel in parasites. It is known that IVM binds to the transmembrane domains (TMs) of several ligand-gated channels, such as Cys-loop receptors and P2X receptors. We found that the G-protein-gated inwardly rectifying K+ (GIRK) channel, especially GIRK2, is activated by IVM directly in a Gβγ -independent manner, but the activation is dependent on phosphatidylinositol-4,5-biphosphate (PIP2 ). We identified a critical amino acid residue of GIRK2 for activation by IVM, Ile82, located in the slide helix between the TM1 and the N-terminal cytoplasmic tail domain (CTD). The results demonstrate that the TM-CTD interface in GIRK channel, rather than the TMs, governs IVM-mediated activation and provide us with novel insights on the mode of action of IVM in ion channels. ABSTRACT Ivermectin (IVM) is a widely used antiparasitic drug in humans and pets which activates glutamate-gated Cl- channel in parasites. It is also known that IVM binds to the transmembrane domains (TMs) of several ligand-gated channels, such as Cys-loop receptors and P2X receptors. In this study, we found that the G-protein-gated inwardly rectifying K+ (GIRK) channel is activated by IVM directly. Electrophysiological recordings in Xenopus oocytes revealed that IVM activates GIRK channel in a phosphatidylinositol-4,5-biphosphate (PIP2 )-dependent manner, and that the IVM-mediated GIRK activation is independent of Gβγ subunits. We found that IVM activates GIRK2 more efficiently than GIRK4. In cultured hippocampal neurons, we also observed that IVM activates native GIRK current. Chimeric and mutagenesis analyses identified an amino acid residue unique to GIRK2 among the GIRK family, Ile82, located in the slide helix between the TM1 and the N-terminal cytoplasmic tail domain (CTD), which is critical for the activation. The results demonstrate that the TM-CTD interface in GIRK channels, rather than the TMs, governs IVM-mediated activation. These findings provide us with novel insights on the mode of action of IVM in ion channels that could lead to identification of new pharmacophores which activate the GIRK channel.
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Affiliation(s)
- I-Shan Chen
- Division of Biophysics and Neurobiology, Department of Molecular and Cellular Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585, Japan.,Department of Physiological Sciences, School of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Hayama, 240-0193, Japan
| | - Michihiro Tateyama
- Division of Biophysics and Neurobiology, Department of Molecular and Cellular Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585, Japan.,Department of Physiological Sciences, School of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Hayama, 240-0193, Japan
| | - Yuko Fukata
- Division of Membrane Physiology, Department of Molecular and Cellular Physiology, National Institute for Physiological Sciences, Okazaki, 444-8787, Japan.,Department of Physiological Sciences, School of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Hayama, 240-0193, Japan
| | - Motonari Uesugi
- Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Uji, Kyoto, 611-0011, Japan.,Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011, Japan
| | - Yoshihiro Kubo
- Division of Biophysics and Neurobiology, Department of Molecular and Cellular Physiology, National Institute for Physiological Sciences, Okazaki, 444-8585, Japan.,Department of Physiological Sciences, School of Life Science, SOKENDAI (The Graduate University for Advanced Studies), Hayama, 240-0193, Japan
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228
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Unwin N. Segregation of lipids near acetylcholine-receptor channels imaged by cryo-EM. IUCRJ 2017; 4:393-399. [PMID: 28875026 PMCID: PMC5571802 DOI: 10.1107/s2052252517005243] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Accepted: 04/06/2017] [Indexed: 05/23/2023]
Abstract
Rapid communication at the chemical synapse depends on the action of ion channels residing in the postsynaptic membrane. The channels open transiently upon the binding of a neurotransmitter released from the presynaptic nerve terminal, eliciting an electrical response. Membrane lipids also play a vital but poorly understood role in this process of synaptic transmission. The present study examines the lipid distribution around nicotinic acetylcholine (ACh) receptors in tubular vesicles made from postsynaptic membranes of the Torpedo ray, taking advantage of the recent advances in cryo-EM. A segregated distribution of lipid molecules is found in the outer leaflet of the bilayer. Apparent cholesterol-rich patches are located in specific annular regions next to the transmembrane helices and also in a more extended 'microdomain' between the apposed δ subunits of neighbouring receptors. The particular lipid distribution can be interpreted straightforwardly in relation to the gating movements revealed by an earlier time-resolved cryo-EM study, in which the membranes were exposed briefly to ACh. The results suggest that in addition to stabilizing the protein, cholesterol may play a mechanical role by conferring local rigidity to the membrane so that there is productive coupling between the extracellular and membrane domains, leading to opening of the channel.
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Affiliation(s)
- Nigel Unwin
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0QH, England
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229
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Musgaard M, Paramo T, Domicevica L, Andersen OJ, Biggin PC. Insights into channel dysfunction from modelling and molecular dynamics simulations. Neuropharmacology 2017; 132:20-30. [PMID: 28669899 DOI: 10.1016/j.neuropharm.2017.06.030] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Revised: 06/06/2017] [Accepted: 06/28/2017] [Indexed: 11/20/2022]
Abstract
Developments in structural biology mean that the number of different ion channel structures has increased significantly in recent years. Structures of ion channels enable us to rationalize how mutations may lead to channelopathies. However, determining the structures of ion channels is still not trivial, especially as they necessarily exist in many distinct functional states. Therefore, the use of computational modelling can provide complementary information that can refine working hypotheses of both wild type and mutant ion channels. The simplest but still powerful tool is homology modelling. Many structures are available now that can provide suitable templates for many different types of ion channels, allowing a full three-dimensional interpretation of mutational effects. These structural models, and indeed the structures themselves obtained by X-ray crystallography, and more recently cryo-electron microscopy, can be subjected to molecular dynamics simulations, either as a tool to help explore the conformational dynamics in detail or simply as a means to refine the models further. Here we review how these approaches have been used to improve our understanding of how diseases might be linked to specific mutations in ion channel proteins. This article is part of the Special Issue entitled 'Channelopathies.'
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Affiliation(s)
- Maria Musgaard
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, United Kingdom
| | - Teresa Paramo
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, United Kingdom
| | - Laura Domicevica
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, United Kingdom
| | - Ole Juul Andersen
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, United Kingdom
| | - Philip C Biggin
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford, OX1 3QU, United Kingdom.
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230
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Giastas P, Zouridakis M, Tzartos SJ. Understanding structure-function relationships of the human neuronal acetylcholine receptor: insights from the first crystal structures of neuronal subunits. Br J Pharmacol 2017; 175:1880-1891. [PMID: 28452148 DOI: 10.1111/bph.13838] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Revised: 04/13/2017] [Accepted: 04/20/2017] [Indexed: 01/27/2023] Open
Abstract
Nicotinic ACh receptors (nAChRs) are the best studied members of the superfamily of pentameric ligand-gated ion channels (pLGICs). Neuronal nAChRs regulate neuronal excitability and neurotransmitter release in the nervous system and form either homo- or hetero-pentameric complexes with various combinations of the 11 neuronal nAChR subunits (α2-7, α9, α10 and β2-4) known to exist in humans. In addition to their wide distribution in the nervous system, neuronal nAChRs have been also found in immune cells and many peripheral tissues. These nAChRs are important drug targets for neurological and neuropsychiatric diseases (e.g. Alzheimer's, schizophrenia) and substance addiction (e.g. nicotine), as well as in a variety of diseases such as chronic pain, auditory disorders and some cancers. To decipher the functional mechanisms of human nAChRs and develop efficient and specific therapeutic drugs, elucidation of their high-resolution structures is needed. Recent studies, including the X-ray crystal structures of the near-intact α4β2 nAChR and of the ligand-binding domains of the α9 and α2 subunits, have advanced our knowledge on the detailed structure of the ligand-binding sites formed between the same and different subunits and revealed many other functionally important interactions. The aim of this review is to highlight some of the structural and functional findings of these studies and to compare them with recent breakthrough findings on other pLGIC members and earlier data from their homologous ACh-binding proteins. LINKED ARTICLES This article is part of a themed section on Nicotinic Acetylcholine Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.11/issuetoc.
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Affiliation(s)
- Petros Giastas
- Department of Neurobiology, Hellenic Pasteur Institute, Athens, Greece
| | - Marios Zouridakis
- Department of Neurobiology, Hellenic Pasteur Institute, Athens, Greece
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231
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Li Y, Kahraman O, Haselwandter CA. Stochastic lattice model of synaptic membrane protein domains. Phys Rev E 2017; 95:052406. [PMID: 28618626 DOI: 10.1103/physreve.95.052406] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2017] [Indexed: 11/07/2022]
Abstract
Neurotransmitter receptor molecules, concentrated in synaptic membrane domains along with scaffolds and other kinds of proteins, are crucial for signal transmission across chemical synapses. In common with other membrane protein domains, synaptic domains are characterized by low protein copy numbers and protein crowding, with rapid stochastic turnover of individual molecules. We study here in detail a stochastic lattice model of the receptor-scaffold reaction-diffusion dynamics at synaptic domains that was found previously to capture, at the mean-field level, the self-assembly, stability, and characteristic size of synaptic domains observed in experiments. We show that our stochastic lattice model yields quantitative agreement with mean-field models of nonlinear diffusion in crowded membranes. Through a combination of analytic and numerical solutions of the master equation governing the reaction dynamics at synaptic domains, together with kinetic Monte Carlo simulations, we find substantial discrepancies between mean-field and stochastic models for the reaction dynamics at synaptic domains. Based on the reaction and diffusion properties of synaptic receptors and scaffolds suggested by previous experiments and mean-field calculations, we show that the stochastic reaction-diffusion dynamics of synaptic receptors and scaffolds provide a simple physical mechanism for collective fluctuations in synaptic domains, the molecular turnover observed at synaptic domains, key features of the observed single-molecule trajectories, and spatial heterogeneity in the effective rates at which receptors and scaffolds are recycled at the cell membrane. Our work sheds light on the physical mechanisms and principles linking the collective properties of membrane protein domains to the stochastic dynamics that rule their molecular components.
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Affiliation(s)
- Yiwei Li
- Department of Physics & Astronomy and Molecular and Computational Biology Program, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089, USA
| | - Osman Kahraman
- Department of Physics & Astronomy and Molecular and Computational Biology Program, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089, USA
| | - Christoph A Haselwandter
- Department of Physics & Astronomy and Molecular and Computational Biology Program, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089, USA
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232
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Structural mechanisms of activation and desensitization in neurotransmitter-gated ion channels. Nat Struct Mol Biol 2017; 23:494-502. [PMID: 27273633 DOI: 10.1038/nsmb.3214] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Accepted: 03/29/2016] [Indexed: 12/31/2022]
Abstract
Ion channels gated by neurotransmitters are present across metazoans, in which they are essential for brain function, sensation and locomotion; closely related homologs are also found in bacteria. Structures of eukaryotic pentameric cysteine-loop (Cys-loop) receptors and tetrameric ionotropic glutamate receptors in multiple functional states have recently become available. Here, I describe how these studies relate to established ideas regarding receptor activation and how they have enabled decades' worth of functional work to be pieced together, thus allowing previously puzzling aspects of receptor activity to be understood.
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233
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Lev B, Murail S, Poitevin F, Cromer BA, Baaden M, Delarue M, Allen TW. String method solution of the gating pathways for a pentameric ligand-gated ion channel. Proc Natl Acad Sci U S A 2017; 114:E4158-E4167. [PMID: 28487483 PMCID: PMC5448215 DOI: 10.1073/pnas.1617567114] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Pentameric ligand-gated ion channels control synaptic neurotransmission by converting chemical signals into electrical signals. Agonist binding leads to rapid signal transduction via an allosteric mechanism, where global protein conformational changes open a pore across the nerve cell membrane. We use all-atom molecular dynamics with a swarm-based string method to solve for the minimum free-energy gating pathways of the proton-activated bacterial GLIC channel. We describe stable wetted/open and dewetted/closed states, and uncover conformational changes in the agonist-binding extracellular domain, ion-conducting transmembrane domain, and gating interface that control communication between these domains. Transition analysis is used to compute free-energy surfaces that suggest allosteric pathways; stabilization with pH; and intermediates, including states that facilitate channel closing in the presence of an agonist. We describe a switching mechanism that senses proton binding by marked reorganization of subunit interface, altering the packing of β-sheets to induce changes that lead to asynchronous pore-lining M2 helix movements. These results provide molecular details of GLIC gating and insight into the allosteric mechanisms for the superfamily of pentameric ligand-gated channels.
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Affiliation(s)
- Bogdan Lev
- School of Science, RMIT University, Melbourne, VIC 3001, Australia
| | - Samuel Murail
- Laboratoire de Biochimie Théorique, CNRS, UPR9080, Université Paris Diderot, Sorbonne Paris Cité, F-75005 Paris, France
| | - Frédéric Poitevin
- Department of Structural Biology, Stanford University, Stanford, CA 94305
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, CA 94025
| | - Brett A Cromer
- School of Science, RMIT University, Melbourne, VIC 3001, Australia
- School of Health and Biomedical Sciences, RMIT University, Bundoora, VIC 3083, Australia
| | - Marc Baaden
- Laboratoire de Biochimie Théorique, CNRS, UPR9080, Université Paris Diderot, Sorbonne Paris Cité, F-75005 Paris, France
| | - Marc Delarue
- Department of Structural Biology and Chemistry, Institut Pasteur and UMR 3528 du CNRS, F-75015 Paris, France
| | - Toby W Allen
- School of Science, RMIT University, Melbourne, VIC 3001, Australia;
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234
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235
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Langlhofer G, Villmann C. The role of charged residues in independent glycine receptor folding domains for intermolecular interactions and ion channel function. J Neurochem 2017; 142:41-55. [PMID: 28429370 DOI: 10.1111/jnc.14049] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2016] [Revised: 03/18/2017] [Accepted: 04/12/2017] [Indexed: 01/03/2023]
Abstract
Glycine receptor (GlyR) truncations in the intracellular TM3-4 loop, documented in patients suffering from hyperekplexia and in the mouse mutant oscillator, lead to non-functionality of GlyRs. The missing part that contains the TM3-4 loop, TM4 and C-terminal sequences is essential for pentameric receptor arrangements. In vitro co-expressions of GlyRα1-truncated N-domains and C-domains were able to restore ion channel function. An ionic interaction between both domains was hypothesized as the underlying mechanism. Here, we analysed the proposed ionic interaction between GlyR N- and C-domains using C-terminal constructs with either positively or negatively charged N-termini. Charged residues at the N-terminus of the C-domain did interfere with receptor surface expression and ion channel function. In particular, presence of negatively charged residues at the N-terminus led to significantly decreased ion channel function. Presence of positive charges resulted in reduced maximal currents possibly as a result of repulsion of both domains. If the C-domain was tagged by a myc-epitope, low maximal current amplitudes were detected. Intrinsic charges of the myc-epitope and charged N-terminal ends of the C-domain most probably induce intramolecular interactions. These interactions might hinder the close proximity of C-domains and N-domains, which is a prerequisite for functional ion channel configurations. The remaining basic subdomains close to TM3 and 4 were sufficient for domain complementation and functional ion channel formation. Thus, these basic subdomains forming α-helical elements or an intracellular portal represent attractants for incoming negatively charged chloride ions and interact with the phospholipids thereby stabilizing the GlyR in a conformation that allows ion channel opening.
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Affiliation(s)
- Georg Langlhofer
- Institute for Clinical Neurobiology, Julius-Maximilians-University of Würzburg, Würzburg, Germany
| | - Carmen Villmann
- Institute for Clinical Neurobiology, Julius-Maximilians-University of Würzburg, Würzburg, Germany
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236
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Maleeva G, Peiretti F, Zhorov BS, Bregestovski P. Voltage-Dependent Inhibition of Glycine Receptor Channels by Niflumic Acid. Front Mol Neurosci 2017; 10:125. [PMID: 28559795 PMCID: PMC5432571 DOI: 10.3389/fnmol.2017.00125] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2017] [Accepted: 04/12/2017] [Indexed: 01/11/2023] Open
Abstract
Niflumic acid (NFA) is a member of the fenamate class of nonsteroidal anti-inflammatory drugs. This compound and its derivatives are used worldwide clinically for the relief of chronic and acute pain. NFA is also a commonly used blocker of voltage-gated chloride channels. Here we present evidence that NFA is an efficient blocker of chloride-permeable glycine receptors (GlyRs) with subunit heterogeneity of action. Using the whole-cell configuration of patch-clamp recordings and molecular modeling, we analyzed the action of NFA on homomeric α1ΔIns, α2B, α3L, and heteromeric α1β and α2β GlyRs expressed in CHO cells. NFA inhibited glycine-induced currents in a voltage-dependent manner and its blocking potency in α2 and α3 GlyRs was higher than that in α1 GlyR. The Woodhull analysis suggests that NFA blocks α1 and α2 GlyRs at the fractional electrical distances of 0.16 and 0.65 from the external membrane surface, respectively. Thus, NFA binding site in α1 GlyR is closer to the external part of the membrane, while in α2 GlyR it is significantly deeper in the pore. Mutation G254A at the cytoplasmic part of the α1 GlyR pore-lining TM2 helix (level 2') increased the NFA blocking potency, while incorporation of the β subunit did not have a significant effect. The Hill plot analysis suggests that α1 and α2 GlyRs are preferably blocked by two and one NFA molecules, respectively. Molecular modeling using Monte Carlo energy minimizations provides the structural rationale for the experimental data and proposes more than one interaction site along the pore where NFA can suppress the ion permeation.
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Affiliation(s)
- Galyna Maleeva
- INSERM, INS, Institut de Neurosciences des Systèmes, Aix-Marseille UniversityMarseille, France.,Department of Cytology, Bogomoletz Institute of PhysiologyKyiv, Ukraine
| | - Franck Peiretti
- INSERM 1062, INRA 1260, NORT, Aix-Marseille UniversityMarseille, France
| | - Boris S Zhorov
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of SciencesSt. Petersburg, Russia.,Department of Biochemistry and Biomedical Sciences, McMaster UniversityHamilton, ON, Canada
| | - Piotr Bregestovski
- INSERM, INS, Institut de Neurosciences des Systèmes, Aix-Marseille UniversityMarseille, France.,Department of Physiology, Kazan State Medical UniversityKazan, Russia
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237
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Chakka N, Andrews KL, Berry LM, Bregman H, Gunaydin H, Huang L, Guzman-Perez A, Plant MH, Simard JR, Gingras J, DiMauro EF. Applications of parallel synthetic lead hopping and pharmacophore-based virtual screening in the discovery of efficient glycine receptor potentiators. Eur J Med Chem 2017; 137:63-75. [PMID: 28575722 DOI: 10.1016/j.ejmech.2017.05.036] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2017] [Revised: 05/09/2017] [Accepted: 05/11/2017] [Indexed: 12/24/2022]
Abstract
Glycine receptors (GlyRs) are pentameric glycine-gated chloride ion channels that are enriched in the brainstem and spinal cord where they have been demonstrated to play a role in central nervous system (CNS) inhibition. Herein we describe two novel classes of glycine receptor potentiators that have been developed using similarity- and property-guided scaffold hopping enabled by parallel synthesis and pharmacophore-based virtual screening strategies. This effort resulted in the identification of novel, efficient and modular leads having favorable in vitro ADME profiles and high CNS multi-parameter optimization (MPO) scores, exemplified by azetidine sulfonamide 19 and aminothiazole sulfone (ent2)-20.
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Affiliation(s)
- Nagasree Chakka
- Department of Medicinal Chemistry, Amgen Inc., 360 Binney Street, Cambridge, MA 02142, USA
| | - Kristin L Andrews
- Department of Molecular Engineering, Amgen Inc., 360 Binney Street, Cambridge, MA 02142, USA
| | - Loren M Berry
- Department of Pharmacokinetics, Amgen Inc., 360 Binney Street, Cambridge, MA 02142, USA
| | - Howard Bregman
- Department of Medicinal Chemistry, Amgen Inc., 360 Binney Street, Cambridge, MA 02142, USA
| | - Hakan Gunaydin
- Department of Molecular Engineering, Amgen Inc., 360 Binney Street, Cambridge, MA 02142, USA
| | - Liyue Huang
- Department of Pharmacokinetics, Amgen Inc., 360 Binney Street, Cambridge, MA 02142, USA
| | - Angel Guzman-Perez
- Department of Medicinal Chemistry, Amgen Inc., 360 Binney Street, Cambridge, MA 02142, USA
| | - Matthew H Plant
- Department of Discovery Attribute Sciences, Amgen Inc., 360 Binney Street, Cambridge, MA 02142, USA
| | - Jeffrey R Simard
- Department of Neuroscience, Amgen Inc., 360 Binney Street, Cambridge, MA 02142, USA
| | - Jacinthe Gingras
- Department of Neuroscience, Amgen Inc., 360 Binney Street, Cambridge, MA 02142, USA
| | - Erin F DiMauro
- Department of Medicinal Chemistry, Amgen Inc., 360 Binney Street, Cambridge, MA 02142, USA.
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Huang X, Chen H, Shaffer PL. Crystal Structures of Human GlyRα3 Bound to Ivermectin. Structure 2017; 25:945-950.e2. [PMID: 28479061 DOI: 10.1016/j.str.2017.04.007] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 01/31/2017] [Accepted: 04/14/2017] [Indexed: 11/30/2022]
Abstract
Ivermectin acts as a positive allosteric modulator of several Cys-loop receptors including the glutamate-gated chloride channels (GluCls), γ-aminobutyric acid receptors (GABAARs), glycine receptors (GlyRs), and neuronal α7-nicotinic receptors (α7 nAChRs). The crystal structure of Caenorhabditis elegans GluCl complexed with ivermectin revealed the details of its ivermectin binding site. Although the electron microscopy structure of zebrafish GlyRα1 complexed with ivermectin demonstrated a similar binding orientation, detailed structural information on the ivermectin binding and pore opening for Cys-loop receptors in vertebrates has been elusive. Here we present the crystal structures of human GlyRα3 in complex with ivermectin at 2.85 and 3.08 Å resolution. Our structures allow us to explore in detail the molecular recognition of ivermectin by GlyRs, GABAARs, and α7 nAChRs. Comparisons with previous structures reveal how the ivermectin binding expands the ion channel pore. Our results hold promise in structure-based design of GlyR modulators for the treatment of neuropathic pain.
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Affiliation(s)
- Xin Huang
- Department of Molecular Structure and Characterization, Amgen Inc., 360 Binney Street, Cambridge, MA 02142, USA.
| | - Hao Chen
- Department of Protein Technologies, Amgen Inc., 360 Binney Street, Cambridge, MA 02142, USA
| | - Paul L Shaffer
- Department of Molecular Structure and Characterization, Amgen Inc., 360 Binney Street, Cambridge, MA 02142, USA.
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239
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Therien JPD, Baenziger JE. Pentameric ligand-gated ion channels exhibit distinct transmembrane domain archetypes for folding/expression and function. Sci Rep 2017; 7:450. [PMID: 28348412 PMCID: PMC5428567 DOI: 10.1038/s41598-017-00573-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Accepted: 03/03/2017] [Indexed: 11/17/2022] Open
Abstract
Although transmembrane helix-helix interactions must be strong enough to drive folding, they must still permit the inter-helix movements associated with conformational change. Interactions between the outermost M4 and adjacent M1 and M3 α-helices of pentameric ligand-gated ion channels have been implicated in folding and function. Here, we evaluate the role of different physical interactions at this interface in the function of two prokaryotic homologs, GLIC and ELIC. Strikingly, disruption of most interactions in GLIC lead to either a reduction or a complete loss of expression and/or function, while analogous disruptions in ELIC often lead to gains in function. Structural comparisons suggest that GLIC and ELIC represent distinct transmembrane domain archetypes. One archetype, exemplified by GLIC, the glycine and GABA receptors and the glutamate activated chloride channel, has extensive aromatic contacts that govern M4-M1/M3 interactions and that are essential for expression and function. The other archetype, exemplified by ELIC and both the nicotinic acetylcholine and serotonin receptors, has relatively few aromatic contacts that are detrimental to function. These archetypes likely have evolved different mechanisms to balance the need for strong M4 "binding" to M1/M3 to promote folding/expression, and the need for weaker interactions that allow for greater conformational flexibility.
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Affiliation(s)
- J P Daniel Therien
- Department of Biochemistry, Microbiology, and Immunology University of Ottawa, Ottawa, ON, K1H 8M5, Canada
| | - John E Baenziger
- Department of Biochemistry, Microbiology, and Immunology University of Ottawa, Ottawa, ON, K1H 8M5, Canada.
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240
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Wang J, Lindstrom J. Orthosteric and allosteric potentiation of heteromeric neuronal nicotinic acetylcholine receptors. Br J Pharmacol 2017; 175:1805-1821. [PMID: 28199738 DOI: 10.1111/bph.13745] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Revised: 01/30/2017] [Accepted: 02/06/2017] [Indexed: 12/16/2022] Open
Abstract
Heteromeric nicotinic ACh receptors (nAChRs) were thought to have two orthodox agonist-binding sites at two α/β subunit interfaces. Highly selective ligands are hard to develop by targeting orthodox agonist sites because of high sequence similarity of this binding pocket among different subunits. Recently, unorthodox ACh-binding sites have been discovered at some α/α and β/α subunit interfaces, such as α4/α4, α5/α4 and β3/α4. Targeting unorthodox sites may yield subtype-selective ligands, such as those for (α4β2)2 α5, (α4β2)2 β3 and (α6β2)2 β3 nAChRs. The unorthodox sites have unique pharmacology. Agonist binding at one unorthodox site is not sufficient to activate nAChRs, but it increases activation from the orthodox sites. NS9283, a selective agonist for the unorthodox α4/α4 site, was initially thought to be a positive allosteric modulator (PAM). NS9283 activates nAChRs with three engineered α4/α4 sites. PAMs, on the other hand, act at allosteric sites where ACh cannot bind. Known PAM sites include the ACh-homologous non-canonical site (e.g. morantel at β/α), the C-terminus (e.g. Br-PBTC and 17β-estradiol), a transmembrane domain (e.g. LY2087101) or extracellular and transmembrane domain interfaces (e.g. NS206). Some of these PAMs, such as Br-PBTC and 17β-estradiol, require only one subunit to potentiate activation of nAChRs. In this review, we will discuss differences between activation from orthosteric and allosteric sites, their selective ligands and clinical implications. These studies have advanced understanding of the structure, assembly and pharmacology of heteromeric neuronal nAChRs. LINKED ARTICLES This article is part of a themed section on Nicotinic Acetylcholine Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.11/issuetoc.
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Affiliation(s)
- Jingyi Wang
- Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - Jon Lindstrom
- Department of Neuroscience, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
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241
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Soh MS, Estrada-Mondragon A, Durisic N, Keramidas A, Lynch JW. Probing the Structural Mechanism of Partial Agonism in Glycine Receptors Using the Fluorescent Artificial Amino Acid, ANAP. ACS Chem Biol 2017; 12:805-813. [PMID: 28121133 DOI: 10.1021/acschembio.6b00926] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The efficacy of an agonist at a pentameric ligand-gated ion channel is determined by the rate at which it induces a conformational change from the resting closed state to a preopen ("flip") state. If the ability of an agonist to promote this isomerization is sufficiently low, then it becomes a partial agonist. As partial agonists at pentameric ligand-gated ion channels show considerable promise as therapeutics, understanding the structural basis of the resting-flip-state isomerization may provide insight into therapeutic design. Accordingly, we sought to identify structural correlates of the resting-flip conformational change in the glycine receptor chloride channel. We used nonsense suppression to introduce the small, fluorescent amino acid, 3-(6-acetylnaphthalen-2-ylamino)-2-aminopropanoic acid (ANAP), into specific sites in the extracellular and transmembrane domains. Then, under voltage-clamp conditions in Xenopus oocytes, we simultaneously quantified current and fluorescence responses induced by structurally similar agonists with high, medium, and low efficacies (glycine, β-alanine, and taurine, respectively). Analyzing results from nine ANAP-incorporated sites, we show that glycine receptor activation by agonists with graded efficacies manifests structurally as correspondingly graded movements of the β1-β2 loop, the β8-β9 loop, and the Cys-loop from the extracellular domain and the TM2-TM3 linker in the transmembrane domain. We infer that the resting-flip transition involves an efficacy-dependent molecular reorganization at the extracellular-transmembrane domain interface that primes receptors for efficacious opening.
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Affiliation(s)
- Ming S. Soh
- Queensland Brain
Institute, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Argel Estrada-Mondragon
- Queensland Brain
Institute, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Nela Durisic
- Queensland Brain
Institute, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Angelo Keramidas
- Queensland Brain
Institute, The University of Queensland, Brisbane, Queensland 4072, Australia
| | - Joseph W. Lynch
- Queensland Brain
Institute, The University of Queensland, Brisbane, Queensland 4072, Australia
- School
of Biomedical Sciences, The University of Queensland, Brisbane, Queensland 4072, Australia
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242
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Menny A, Lefebvre SN, Schmidpeter PA, Drège E, Fourati Z, Delarue M, Edelstein SJ, Nimigean CM, Joseph D, Corringer PJ. Identification of a pre-active conformation of a pentameric channel receptor. eLife 2017; 6. [PMID: 28294942 PMCID: PMC5398890 DOI: 10.7554/elife.23955] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Accepted: 03/14/2017] [Indexed: 11/26/2022] Open
Abstract
Pentameric ligand-gated ion channels (pLGICs) mediate fast chemical signaling through global allosteric transitions. Despite the existence of several high-resolution structures of pLGICs, their dynamical properties remain elusive. Using the proton-gated channel GLIC, we engineered multiple fluorescent reporters, each incorporating a bimane and a tryptophan/tyrosine, whose close distance causes fluorescence quenching. We show that proton application causes a global compaction of the extracellular subunit interface, coupled to an outward motion of the M2-M3 loop near the channel gate. These movements are highly similar in lipid vesicles and detergent micelles. These reorganizations are essentially completed within 2 ms and occur without channel opening at low proton concentration, indicating that they report a pre-active intermediate state in the transition pathway toward activation. This provides a template to investigate the gating of eukaryotic neurotransmitter receptors, for which intermediate states also participate in activation. DOI:http://dx.doi.org/10.7554/eLife.23955.001 In the nervous system, proteins of the pLGIC family are found in the membrane that surrounds each neuron. These proteins have channels that can allow ions to pass through the membrane and are responsible for transmitting electrical signals from one neuron to the next. Small molecules called neurotransmitters interact with the pLGICs to open or close the ion channel. If the ability of the pLGIC channels to open is altered, it can lead to behavioral changes like addiction, or diseases such as schizophrenia or epilepsy. For a pLGIC channel to switch between the “open” and “closed” states, specific parts of the protein need to move in relation to each other. However, to study these transitions researchers have previously relied on comparing the three-dimensional structures of open and closed pLGICs extracted out of the cell membrane. Different techniques are needed to directly follow these movements within membranes. Bacteria also have proteins belonging to the pLGIC family, and Menny et al. have now investigated one such bacterial protein to understand how pLGICs open. First, a small fluorescent molecule that glows differently if the environment around it changes was attached to various parts of the bacterial channel. These fluorescent markers revealed how several parts of the protein move and they also made it possible to measure how quickly these movements take place. Some of these movements happen before the channel opens, suggesting that the activation of this pLGIC protein happens in stages and involves the protein adopting a temporary intermediate state. The next step will be to better understand the structure of the intermediate state, which could help us to understand how pLGICs work in the nervous systems of animals. In future this may aid the design of new drugs that can modify the activity of these channels in patients with neurological conditions or addictions. DOI:http://dx.doi.org/10.7554/eLife.23955.002
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Affiliation(s)
- Anaïs Menny
- Channel Receptors Unit, Institut Pasteur, Paris, France.,Unité Mixte de Recherche 3571, Centre National de la Recherche Scientifique, Paris, France.,Université Pierre et Marie Curie, Cellule Pasteur, Paris, France
| | - Solène N Lefebvre
- Channel Receptors Unit, Institut Pasteur, Paris, France.,Unité Mixte de Recherche 3571, Centre National de la Recherche Scientifique, Paris, France.,Université Pierre et Marie Curie, Cellule Pasteur, Paris, France
| | - Philipp Am Schmidpeter
- Departments of Anesthesiology, Physiology and Biophysics, Biochemistry, Weill Cornell Medicine, New York, United States
| | - Emmanuelle Drège
- BioCIS, Université Paris-Sud, CNRS, Université Paris-Saclay, Châtenay-Malabry, France
| | - Zaineb Fourati
- Unité de Dynamique Structurale des Macromolécules, Institut Pasteur, Paris, France.,Unité Mixte de Recherche 3528, Centre National de la Recherche Scientifique, Paris, France
| | - Marc Delarue
- Unité de Dynamique Structurale des Macromolécules, Institut Pasteur, Paris, France.,Unité Mixte de Recherche 3528, Centre National de la Recherche Scientifique, Paris, France
| | - Stuart J Edelstein
- Biologie Cellulaire de la Synapse, Institute of Biology, Ecole Normale Supérieure, Paris, France
| | - Crina M Nimigean
- Departments of Anesthesiology, Physiology and Biophysics, Biochemistry, Weill Cornell Medicine, New York, United States
| | - Delphine Joseph
- BioCIS, Université Paris-Sud, CNRS, Université Paris-Saclay, Châtenay-Malabry, France
| | - Pierre-Jean Corringer
- Channel Receptors Unit, Institut Pasteur, Paris, France.,Unité Mixte de Recherche 3571, Centre National de la Recherche Scientifique, Paris, France
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243
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Feng X, Fu Z, Kaledhonkar S, Jia Y, Shah B, Jin A, Liu Z, Sun M, Chen B, Grassucci RA, Ren Y, Jiang H, Frank J, Lin Q. A Fast and Effective Microfluidic Spraying-Plunging Method for High-Resolution Single-Particle Cryo-EM. Structure 2017; 25:663-670.e3. [PMID: 28286002 DOI: 10.1016/j.str.2017.02.005] [Citation(s) in RCA: 82] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Revised: 01/10/2017] [Accepted: 02/10/2017] [Indexed: 11/17/2022]
Abstract
We describe a spraying-plunging method for preparing cryoelectron microscopy (cryo-EM) grids with vitreous ice of controllable, highly consistent thickness using a microfluidic device. The new polydimethylsiloxane (PDMS)-based sprayer was tested with apoferritin. We demonstrate that the structure can be solved to high resolution with this method of sample preparation. Besides replacing the conventional pipetting-blotting-plunging method, one of many potential applications of the new sprayer is in time-resolved cryo-EM, as part of a PDMS-based microfluidic reaction channel to study short-lived intermediates on the timescale of 10-1,000 ms.
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Affiliation(s)
- Xiangsong Feng
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA; School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China
| | - Ziao Fu
- Integrated Program in Cellular, Molecular, and Biophysical Studies, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA
| | - Sandip Kaledhonkar
- Department of Biochemistry and Molecular Biophysics, Columbia University New York, NY 10027, USA
| | - Yuan Jia
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA
| | - Binita Shah
- Department of Biological Sciences, Barnard College, New York, NY 10027, USA
| | - Amy Jin
- Department of Biochemistry and Molecular Biophysics, Columbia University New York, NY 10027, USA
| | - Zheng Liu
- Department of Biochemistry and Molecular Biophysics, Columbia University New York, NY 10027, USA
| | - Ming Sun
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
| | - Bo Chen
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
| | - Robert A Grassucci
- Department of Biochemistry and Molecular Biophysics, Columbia University New York, NY 10027, USA; Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA
| | - Yukun Ren
- School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China
| | - Hongyuan Jiang
- School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China
| | - Joachim Frank
- Department of Biochemistry and Molecular Biophysics, Columbia University New York, NY 10027, USA; Department of Biological Sciences, Columbia University, New York, NY 10027, USA; Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA.
| | - Qiao Lin
- Department of Mechanical Engineering, Columbia University, New York, NY 10027, USA.
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244
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Elberson BW, Whisenant TE, Cortes DM, Cuello LG. A cost-effective protocol for the over-expression and purification of fully-functional and more stable Erwinia chrysanthemi ligand-gated ion channel. Protein Expr Purif 2017; 133:177-186. [PMID: 28279818 DOI: 10.1016/j.pep.2017.03.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Revised: 02/21/2017] [Accepted: 03/04/2017] [Indexed: 10/20/2022]
Abstract
The Erwinia chrysanthemi ligand-gated ion channel, ELIC, is considered an excellent structural and functional surrogate for the whole pentameric ligand-gated ion channel family. Despite its simplicity, ELIC is structurally capable of undergoing ligand-dependent activation and a concomitant desensitization process. To determine at the molecular level the structural changes underlying ELIC's function, it is desirable to produce large quantities of protein. This protein should be properly folded, fully-functional and amenable to structural determinations. In the current paper, we report a completely new protocol for the expression and purification of milligram quantities of fully-functional, more stable and crystallizable ELIC. The use of an autoinduction media and inexpensive detergents during ELIC extraction, in addition to the high-quality and large quantity of the purified channel, are the highlights of this improved biochemical protocol.
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Affiliation(s)
- Benjamin W Elberson
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, 3601 4th Street STOP 6551, Lubbock, TX 79430, USA
| | - Ty E Whisenant
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, 3601 4th Street STOP 6551, Lubbock, TX 79430, USA
| | - D Marien Cortes
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, 3601 4th Street STOP 6551, Lubbock, TX 79430, USA
| | - Luis G Cuello
- Department of Cell Physiology and Molecular Biophysics and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, 3601 4th Street STOP 6551, Lubbock, TX 79430, USA.
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245
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Basak S, Schmandt N, Gicheru Y, Chakrapani S. Crystal structure and dynamics of a lipid-induced potential desensitized-state of a pentameric ligand-gated channel. eLife 2017; 6:23886. [PMID: 28262093 PMCID: PMC5378477 DOI: 10.7554/elife.23886] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Accepted: 03/04/2017] [Indexed: 12/14/2022] Open
Abstract
Desensitization in pentameric ligand-gated ion channels plays an important role in regulating neuronal excitability. Here, we show that docosahexaenoic acid (DHA), a key ω−3 polyunsaturated fatty acid in synaptic membranes, enhances the agonist-induced transition to the desensitized state in the prokaryotic channel GLIC. We determined a 3.25 Å crystal structure of the GLIC-DHA complex in a potentially desensitized conformation. The DHA molecule is bound at the channel-periphery near the M4 helix and exerts a long-range allosteric effect on the pore across domain-interfaces. In this previously unobserved conformation, the extracellular-half of the pore-lining M2 is splayed open, reminiscent of the open conformation, while the intracellular-half is constricted, leading to a loss of both water and permeant ions. These findings, in combination with spin-labeling/EPR spectroscopic measurements in reconstituted-membranes, provide novel mechanistic details of desensitization in pentameric channels. DOI:http://dx.doi.org/10.7554/eLife.23886.001 The nerve cells (or neurons) in the brain communicate with each other by releasing chemicals called neurotransmitters that bind to ion channels on neighboring neurons. This ultimately causes ions to flow in or out of the receiving neuron through these ion channels; this ion flow determines how the neuron responds. One family of ion channels that is found at the junction between neurons, and between neurons and muscle fibers, is known as the pentameric ligand-gated ion channels (or pLGICs). These channels act as ‘gates’ that open to allow ions through them when a neurotransmitter binds to the channel. In addition to the open ‘active’ state, the channels can take on two different ‘inactive’ states that do not allow ions to pass through the channel: a closed (resting) state and a desensitized state (that is still bound to the neurotransmitter). Understanding how channels switch between these states is important for designing drugs that correct problems that cause the channels to work incorrectly. Problems that affect the desensitized state have been linked to neurological disorders such as epilepsy. Medically important molecules such as anesthetics and alcohols are thought to affect desensitization, and drugs that target desensitized ion channels may present ways of treating neurological disorders with fewer side effects. Docosahexaenoic acid (DHA) is an abundant lipid molecule that is present in the membranes of neurons. It is one of the key ingredients in fish oil supplements and is thought to enhance learning and memory. DHA affects the desensitization of pLGICs but it is not clear exactly how it does so. Basak et al. now show that DHA affects a bacterial pLGIC in the same way as it affects human channels – by enhancing desensitization. Using a technique called X-ray crystallography to analyze the channel while bound to DHA revealed a previously unobserved channel structure. The DHA molecule binds to a site at the edge of the channel and causes a change in its structure that leaves the upper part of the channel open while the lower part is constricted. Basak et al. predict that molecules such as anesthetics target this desensitized state. The next step will be to obtain the structures of bacterial and human pLGIC channels in a natural membrane environment. This will allow us to better understand the changes in structure that the channels go through as they transmit signals between neurons, and so help in the development of new treatments for neurological disorders. DOI:http://dx.doi.org/10.7554/eLife.23886.002
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Affiliation(s)
- Sandip Basak
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, United States
| | - Nicolaus Schmandt
- Department of Neuroscience, School of Medicine, Case Western Reserve University, Cleveland, United States
| | - Yvonne Gicheru
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, United States
| | - Sudha Chakrapani
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, United States
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246
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Degani-Katzav N, Klein M, Har-Even M, Gortler R, Tobi R, Paas Y. Trapping of ivermectin by a pentameric ligand-gated ion channel upon open-to-closed isomerization. Sci Rep 2017; 7:42481. [PMID: 28218274 PMCID: PMC5317004 DOI: 10.1038/srep42481] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Accepted: 01/11/2017] [Indexed: 11/09/2022] Open
Abstract
Ivermectin (IVM) is a broad-spectrum anthelmintic drug used to treat human parasitic diseases like river blindness and lymphatic filariasis. By activating invertebrate pentameric glutamate-gated chloride channels (GluCl receptors; GluClRs), IVM induces sustained chloride influx and long-lasting membrane hyperpolarization that inhibit neural excitation in nematodes. Although IVM activates the C. elegans heteromeric GluClα/β receptor, it cannot activate a homomeric receptor composed of the C. elegans GluClβ subunits. To understand this incapability, we generated a homopentameric α7-GluClβ chimeric receptor that consists of an extracellular ligand-binding domain of an α7 nicotinic acetylcholine receptor known to be potentiated by IVM, and a chloride-selective channel domain assembled from GluClβ subunits. Application of IVM prior to acetylcholine inhibited the responses of the chimeric α7-GluClβR. Adding IVM to activated α7-GluClβRs, considerably accelerated the decline of ACh-elicited currents and stabilized the receptors in a non-conducting state. Determination of IVM association and dissociation rate constants and recovery experiments suggest that, following initial IVM binding to open α7-GluClβRs, the drug induces a conformational change and locks the ion channel in a closed state for a long duration. We further found that IVM also inhibits the activation by glutamate of a homomeric receptor assembled from the C. elegans full-length GluClβ subunits.
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Affiliation(s)
- Nurit Degani-Katzav
- Laboratory of Ion Channels, The Mina and Everard Goodman Faculty of Life Sciences and The Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan 52900, Israel
| | - Moshe Klein
- Laboratory of Ion Channels, The Mina and Everard Goodman Faculty of Life Sciences and The Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan 52900, Israel
| | - Moran Har-Even
- Laboratory of Ion Channels, The Mina and Everard Goodman Faculty of Life Sciences and The Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan 52900, Israel
| | - Revital Gortler
- Laboratory of Ion Channels, The Mina and Everard Goodman Faculty of Life Sciences and The Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan 52900, Israel
| | - Ruthi Tobi
- Laboratory of Ion Channels, The Mina and Everard Goodman Faculty of Life Sciences and The Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan 52900, Israel
| | - Yoav Paas
- Laboratory of Ion Channels, The Mina and Everard Goodman Faculty of Life Sciences and The Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat Gan 52900, Israel
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247
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Welsh BT, Todorovic J, Kirson D, Allen HM, Bayly MD, Mihic SJ. Disruption of a putative intersubunit electrostatic bond enhances agonist efficacy at the human α1 glycine receptor. Brain Res 2017; 1657:148-155. [PMID: 27923639 DOI: 10.1016/j.brainres.2016.11.024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Revised: 11/17/2016] [Accepted: 11/21/2016] [Indexed: 10/20/2022]
Abstract
Partial agonists have lower efficacies than compounds considered 'full agonists', eliciting submaximal responses even at saturating concentrations. Taurine is a partial agonist at the glycine receptor (GlyR), a member of the cys-loop ligand-gated ion channel superfamily. The molecular mechanisms responsible for agonism are not fully understood but evidence suggests that efficacy at these receptors is determined by conformational changes that occur early in the process of receptor activation. We previously identified a residue located near the human α1 glycine binding site (aspartate-97; D97) that, when mutated to arginine (D97R), results in GlyR channels opening spontaneously with a high open probability, mimicking the effects of saturating glycine concentrations on wildtype GlyR. This D97 residue is hypothesized to form an electrostatic interaction with arginine-119 on an adjacent subunit, stabilizing the channel in a shut state. Here we demonstrate that the disruption of this putative bond increases the efficacy of partial agonists including taurine, as well as two other β-amino acid partial agonists, β-aminobutyric acid (β-ABA) and β-aminoisobutyric acid (β-AIBA). Even the subtle charge-conserving mutation of D97 to glutamate (D97E) markedly affects partial agonist efficacy. Mutation to the neutral alanine residue in the D97A mutant mimics the effects seen with D97R, indicating that charge repulsion does not significantly affect these findings. Our findings suggest that the determination of efficacy following ligand binding to the glycine receptor may involve the disruption of an intersubunit electrostatic interaction occurring near the agonist binding site.
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Affiliation(s)
- Brian T Welsh
- Institute for Neuroscience, University of Texas at Austin, Austin, TX 78712, United States
| | - Jelena Todorovic
- Waggoner Center for Alcohol & Addiction Research, Austin, TX 78712, United States
| | - Dean Kirson
- Institute for Neuroscience, University of Texas at Austin, Austin, TX 78712, United States
| | - Hunter M Allen
- Waggoner Center for Alcohol & Addiction Research, Austin, TX 78712, United States
| | - Michelle D Bayly
- Institute for Neuroscience, University of Texas at Austin, Austin, TX 78712, United States
| | - S John Mihic
- Department of Neuroscience, University of Texas at Austin, Austin, TX 78712, United States; Division of Pharmacology and Toxicology, University of Texas at Austin, Austin, TX 78712, United States; Waggoner Center for Alcohol & Addiction Research, Austin, TX 78712, United States; Institute for Neuroscience, University of Texas at Austin, Austin, TX 78712, United States; Institute for Cell & Molecular Biology, University of Texas at Austin, Austin, TX 78712, United States.
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Altered Channel Conductance States and Gating of GABA A Receptors by a Pore Mutation Linked to Dravet Syndrome. eNeuro 2017; 4:eN-NWR-0251-16. [PMID: 28197552 PMCID: PMC5301078 DOI: 10.1523/eneuro.0251-16.2017] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Revised: 01/19/2017] [Accepted: 01/19/2017] [Indexed: 11/21/2022] Open
Abstract
We identified a de novo missense mutation, P302L, in the γ-aminobutyric acid type A (GABAA) receptor γ2 subunit gene GABRG2 in a patient with Dravet syndrome using targeted next-generation sequencing. The mutation was in the cytoplasmic portion of the transmembrane segment M2 of the γ2 subunit that faces the pore lumen. GABAA receptor α1 and β3 subunits were coexpressed with wild-type (wt) γ2L or mutant γ2L(P302L) subunits in HEK 293T cells and cultured mouse cortical neurons. We measured currents using whole-cell and single-channel patch clamp techniques, surface and total expression levels using surface biotinylation and Western blotting, and potential structural perturbations in mutant GABAA receptors using structural modeling. The γ2(P302L) subunit mutation produced an ∼90% reduction of whole-cell current by increasing macroscopic desensitization and reducing GABA potency, which resulted in a profound reduction of GABAA receptor-mediated miniature IPSCs (mIPSCs). The conductance of the receptor channel was reduced to 24% of control conductance by shifting the relative contribution of the conductance states from high- to low-conductance levels with only slight changes in receptor surface expression. Structural modeling of the GABAA receptor in the closed, open, and desensitized states showed that the mutation was positioned to slow activation, enhance desensitization, and shift channels to a low-conductance state by reshaping the hour-glass-like pore cavity during transitions between closed, open, and desensitized states. Our study revealed a novel γ2 subunit missense mutation (P302L) that has a novel pathogenic mechanism to cause defects in the conductance and gating of GABAA receptors, which results in hyperexcitability and contributes to the pathogenesis of the genetic epilepsy Dravet syndrome.
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Safar F, Hurdiss E, Erotocritou M, Greiner T, Lape R, Irvine MW, Fang G, Jane D, Yu R, Dämgen MA, Biggin PC, Sivilotti LG. The Startle Disease Mutation E103K Impairs Activation of Human Homomeric α1 Glycine Receptors by Disrupting an Intersubunit Salt Bridge across the Agonist Binding Site. J Biol Chem 2017; 292:5031-5042. [PMID: 28174298 PMCID: PMC5377815 DOI: 10.1074/jbc.m116.767616] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Revised: 01/25/2017] [Indexed: 11/25/2022] Open
Abstract
Glycine receptors (GlyR) belong to the pentameric ligand-gated ion channel (pLGIC) superfamily and mediate fast inhibitory transmission in the vertebrate CNS. Disruption of glycinergic transmission by inherited mutations produces startle disease in man. Many startle mutations are in GlyRs and provide useful clues to the function of the channel domains. E103K is one of few startle mutations found in the extracellular agonist binding site of the channel, in loop A of the principal side of the subunit interface. Homology modeling shows that the side chain of Glu-103 is close to that of Arg-131, in loop E of the complementary side of the binding site, and may form a salt bridge at the back of the binding site, constraining its size. We investigated this hypothesis in recombinant human α1 GlyR by site-directed mutagenesis and functional measurements of agonist efficacy and potency by whole cell patch clamp and single channel recording. Despite its position near the binding site, E103K causes hyperekplexia by impairing the efficacy of glycine, its ability to gate the channel once bound, which is very high in wild type GlyR. Mutating Glu-103 and Arg-131 caused various degrees of loss-of-function in the action of glycine, whereas mutations in Arg-131 enhanced the efficacy of the slightly bigger partial agonist sarcosine (N-methylglycine). The effects of the single charge-swapping mutations of these two residues were largely rescued in the double mutant, supporting the possibility that they interact via a salt bridge that normally constrains the efficacy of larger agonist molecules.
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Affiliation(s)
- Fatemah Safar
- From the Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Elliot Hurdiss
- From the Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Marios Erotocritou
- From the Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Timo Greiner
- From the Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Remigijus Lape
- From the Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Mark W Irvine
- the School of Physiology and Pharmacology, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom, and
| | - Guangyu Fang
- the School of Physiology and Pharmacology, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom, and
| | - David Jane
- the School of Physiology and Pharmacology, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom, and
| | - Rilei Yu
- the Department of Biochemistry, Structural Bioinformatics and Computational Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom.,the Key Laboratory of Marine Drugs, Chinese Ministry of Education, School of Medicine and Pharmacy, Ocean University of China, Qingdao 266003, China
| | - Marc A Dämgen
- the Department of Biochemistry, Structural Bioinformatics and Computational Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
| | - Philip C Biggin
- the Department of Biochemistry, Structural Bioinformatics and Computational Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
| | - Lucia G Sivilotti
- From the Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom,
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250
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Merino F, Raunser S. Kryo-Elektronenmikroskopie als Methode für die strukturbasierte Wirkstoffentwicklung. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201608432] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Felipe Merino
- Strukturelle Biochemie; Max-Planck-Institut für Molekulare Physiologie; 44227 Dortmund Deutschland
| | - Stefan Raunser
- Strukturelle Biochemie; Max-Planck-Institut für Molekulare Physiologie; 44227 Dortmund Deutschland
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