151
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Molecular Mechanism of Disease-Associated Mutations in the Pre-M1 Helix of NMDA Receptors and Potential Rescue Pharmacology. PLoS Genet 2017; 13:e1006536. [PMID: 28095420 PMCID: PMC5240934 DOI: 10.1371/journal.pgen.1006536] [Citation(s) in RCA: 102] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Accepted: 12/13/2016] [Indexed: 12/31/2022] Open
Abstract
N-methyl-D-aspartate receptors (NMDARs), ligand-gated ionotropic glutamate receptors, play key roles in normal brain development and various neurological disorders. Here we use standing variation data from the human population to assess which protein domains within NMDAR GluN1, GluN2A and GluN2B subunits show the strongest signal for being depleted of missense variants. We find that this includes the GluN2 pre-M1 helix and linker between the agonist-binding domain (ABD) and first transmembrane domain (M1). We then evaluate the functional changes of multiple missense mutations in the NMDAR pre-M1 helix found in children with epilepsy and developmental delay. We find mutant GluN1/GluN2A receptors exhibit prolonged glutamate response time course for channels containing 1 or 2 GluN2A-P552R subunits, and a slow rise time only for receptors with 2 mutant subunits, suggesting rearrangement of one GluN2A pre-M1 helix is sufficient for rapid activation. GluN2A-P552R and analogous mutations in other GluN subunits increased the agonist potency and slowed response time course, suggesting a functionally conserved role for this residue. Although there is no detectable change in surface expression or open probability for GluN2A-P552R, the prolonged response time course for receptors that contained GluN2A-P552R increased charge transfer for synaptic-like activation, which should promote excitotoxic damage. Transfection of cultured neurons with GluN2A-P552R prolonged EPSPs, and triggered pronounced dendritic swelling in addition to excitotoxicity, which were both attenuated by memantine. These data implicate the pre-M1 region in gating, provide insight into how different subunits contribute to gating, and suggest that mutations in the pre-M1 helix can compromise neuronal health. Evaluation of FDA-approved NMDAR inhibitors on the mutant NMDAR-mediated current response and neuronal damage provides a potential clinical path to treat individuals harboring similar mutations in NMDARs.
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152
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Hansen KB, Yi F, Perszyk RE, Menniti FS, Traynelis SF. NMDA Receptors in the Central Nervous System. Methods Mol Biol 2017; 1677:1-80. [PMID: 28986865 DOI: 10.1007/978-1-4939-7321-7_1] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
NMDA-type glutamate receptors are ligand-gated ion channels that mediate a major component of excitatory neurotransmission in the central nervous system (CNS). They are widely distributed at all stages of development and are critically involved in normal brain functions, including neuronal development and synaptic plasticity. NMDA receptors are also implicated in the pathophysiology of numerous neurological and psychiatric disorders, such as ischemic stroke, traumatic brain injury, Alzheimer's disease, epilepsy, mood disorders, and schizophrenia. For these reasons, NMDA receptors have been intensively studied in the past several decades to elucidate their physiological roles and to advance them as therapeutic targets. Seven NMDA receptor subunits exist that assemble into a diverse array of tetrameric receptor complexes, which are differently regulated, have distinct regional and developmental expression, and possess a wide range of functional and pharmacological properties. The diversity in subunit composition creates NMDA receptor subtypes with distinct physiological roles across neuronal cell types and brain regions, and enables precise tuning of synaptic transmission. Here, we will review the relationship between NMDA receptor structure and function, the diversity and significance of NMDA receptor subtypes in the CNS, as well as principles and rules by which NMDA receptors operate in the CNS under normal and pathological conditions.
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Affiliation(s)
- Kasper B Hansen
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, MT, USA. .,Center for Biomolecular Structure and Dynamics, University of Montana, Missoula, MT, USA.
| | - Feng Yi
- Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, MT, USA
| | - Riley E Perszyk
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA, USA
| | - Frank S Menniti
- MindImmune Therapeutics, Inc., George & Anne Ryan Institute for Neuroscience, Kingston, RI, USA
| | - Stephen F Traynelis
- Department of Pharmacology, Emory University School of Medicine, Atlanta, GA, USA
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153
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Tsitoura P, Iatrou K. Positive Allosteric Modulation of Insect Olfactory Receptor Function by ORco Agonists. Front Cell Neurosci 2016; 10:275. [PMID: 28018173 PMCID: PMC5145856 DOI: 10.3389/fncel.2016.00275] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Accepted: 11/17/2016] [Indexed: 12/25/2022] Open
Abstract
Insect olfactory receptors (ORs) are heteromeric ligand-gated cation channels composed of a common olfactory receptor subunit (ORco) and a variable subunit (ORx) of as yet unknown structures and undetermined stoichiometries. In this study, we examined the allosteric modulation exerted on Anopheles gambiae heteromeric ORx/ORco olfactory receptors in vitro by a specific class of ORco agonists (OAs) comprising ORcoRAM2 and VUAA1. High OA concentrations produced stronger functional responses in cells expressing heteromeric receptor channels relative to cells expressing ORco alone. These OA-induced responses of ORx/ORco channels were also notably much stronger than those obtained upon administration of ORx-specific ligands to the same receptors. Most importantly, small concentrations of OAs were found to act as strong potentiators of ORx/ORco function, increasing dramatically both the efficacy and potency of ORx-specific odorants. These results suggest that insect heteromeric ORs are highly dynamic complexes adopting different conformations that change in a concerted fashion as a result of the interplay between the subunits of the oligomeric assemblies, and that allosteric modulation may constitute an important element in the modulation and fining tuning of olfactory reception function.
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Affiliation(s)
| | - Kostas Iatrou
- Insect Molecular Genetics and Biotechnology Group, Institute of Biosciences and Applications, National Centre for Scientific Research “Demokritos”Athens, Greece
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154
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Romero-Hernandez A, Simorowski N, Karakas E, Furukawa H. Molecular Basis for Subtype Specificity and High-Affinity Zinc Inhibition in the GluN1-GluN2A NMDA Receptor Amino-Terminal Domain. Neuron 2016; 92:1324-1336. [PMID: 27916457 DOI: 10.1016/j.neuron.2016.11.006] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2016] [Revised: 10/05/2016] [Accepted: 11/02/2016] [Indexed: 10/20/2022]
Abstract
Zinc is vastly present in the mammalian brain and controls functions of various cell surface receptors to regulate neurotransmission. A distinctive characteristic of N-methyl-D-aspartate (NMDA) receptors containing a GluN2A subunit is that their ion channel activity is allosterically inhibited by a nano-molar concentration of zinc that binds to an extracellular domain called an amino-terminal domain (ATD). Despite physiological importance, the molecular mechanism underlying the high-affinity zinc inhibition has been incomplete because of the lack of a GluN2A ATD structure. Here we show the first crystal structures of the heterodimeric GluN1-GluN2A ATD, which provide the complete map of the high-affinity zinc-binding site and reveal distinctive features from the ATD of the GluN1-GluN2B subtype. Perturbation of hydrogen bond networks at the hinge of the GluN2A bi-lobe structure affects both zinc inhibition and open probability, supporting the general model in which the bi-lobe motion in ATD regulates the channel activity in NMDA receptors.
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Affiliation(s)
- Annabel Romero-Hernandez
- WM Keck Structural Biology Laboratory, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA; Watson School of Biological Sciences, Cold Spring Harbor, NY 11724, USA
| | - Noriko Simorowski
- WM Keck Structural Biology Laboratory, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA
| | - Erkan Karakas
- WM Keck Structural Biology Laboratory, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA
| | - Hiro Furukawa
- WM Keck Structural Biology Laboratory, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA; Watson School of Biological Sciences, Cold Spring Harbor, NY 11724, USA.
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155
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Tian M, Ye S. Allosteric regulation in NMDA receptors revealed by the genetically encoded photo-cross-linkers. Sci Rep 2016; 6:34751. [PMID: 27713495 PMCID: PMC5054432 DOI: 10.1038/srep34751] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Accepted: 09/16/2016] [Indexed: 11/09/2022] Open
Abstract
Allostery is essential to neuronal receptor function, but its transient nature poses a challenge for characterization. The N-terminal domains (NTDs) distinct from ligand binding domains are a major locus for allosteric regulation of NMDA receptors (NMDARs), where different modulatory binding sites have been observed. The inhibitor ifenprodil, and related phenylethanoamine compounds specifically targeting GluN1/GluN2B NMDARs have neuroprotective activity. However, whether they use differential structural pathways than the endogenous inhibitor Zn2+ for regulation is unknown. We applied genetically encoded unnatural amino acids (Uaas) and monitored the functional changes in living cells with photo-cross-linkers specifically incorporated at the ifenprodil binding interface between GluN1 and GluN2B subunits. We report constraining the NTD domain movement, by a light induced crosslinking bond that introduces minimal perturbation to the ligand binding, specifically impedes the transduction of ifenprodil but not Zn2+ inhibition. Subtle distance changes reveal interfacial flexibility and NTD rearrangements in the presence of modulators. Our results present a much richer dynamic picture of allostery than conventional approaches targeting the same interface, and highlight key residues that determine functional and subtype specificity of NMDARs. The light-sensitive mutant neuronal receptors provide complementary tools to the photo-switchable ligands for opto-neuropharmacology.
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Affiliation(s)
- Meilin Tian
- Shanghai Key Laboratory of Brain Functional Genomics, East China Normal University, Shanghai, China.,Ecole Normale Supérieure, Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Paris, France.,Institut National de la Santé et de la Recherche Médicale, U1024, Paris, France.,Centre National de la Recherche Scientifique, UMR 8197, Paris, France
| | - Shixin Ye
- Ecole Normale Supérieure, Institut de Biologie de l'Ecole Normale Supérieure (IBENS), Paris, France.,Institut National de la Santé et de la Recherche Médicale, U1024, Paris, France.,Centre National de la Recherche Scientifique, UMR 8197, Paris, France
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156
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Unravelling biological macromolecules with cryo-electron microscopy. Nature 2016; 537:339-46. [PMID: 27629640 DOI: 10.1038/nature19948] [Citation(s) in RCA: 262] [Impact Index Per Article: 32.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Accepted: 07/15/2016] [Indexed: 12/11/2022]
Abstract
Knowledge of the three-dimensional structures of proteins and other biological macromolecules often aids understanding of how they perform complicated tasks in the cell. Because many such tasks involve the cleavage or formation of chemical bonds, structural characterization at the atomic level is most useful. Developments in the electron microscopy of frozen hydrated samples (cryo-electron microscopy) are providing unprecedented opportunities for the structural characterization of biological macromolecules. This is resulting in a wave of information about processes in the cell that were impossible to characterize with existing techniques in structural biology.
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157
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Zhu S, Gouaux E. Structure and symmetry inform gating principles of ionotropic glutamate receptors. Neuropharmacology 2016; 112:11-15. [PMID: 27663701 DOI: 10.1016/j.neuropharm.2016.08.034] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Accepted: 08/24/2016] [Indexed: 12/29/2022]
Abstract
Ionotropic glutamate receptors (iGluRs) transduce signals derived from release of the excitatory neurotransmitter glutamate from pre-synaptic neurons into excitation of post-synaptic neurons on a millisecond time-scale. In recent years, the elucidation of full-length iGluR structures of NMDA, AMPA and kainate receptors by X-ray crystallography and single particle cryo-electron microscopy has greatly enhanced our understanding of the interrelationships between receptor architecture and gating mechanism. Here we briefly review full-length iGluR structures and discuss the similarities and differences between NMDA receptors and non-NMDA iGluRs. We focus on distinct conformations, including ligand-free, agonist-bound active, agonist-bound desensitized and antagonist-bound conformations as well as modulator and auxiliary protein-bound states. These findings provide insights into structure-based mechanisms of iGluR gating and modulation which together shape the amplitude and time course of the excitatory postsynaptic potential. This article is part of the Special Issue entitled 'Ionotropic glutamate receptors'.
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Affiliation(s)
- Shujia Zhu
- Vollum Institute, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland OR 97239, USA
| | - Eric Gouaux
- Vollum Institute, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland OR 97239, USA; Howard Hughes Medical Institute, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland OR 97239, USA.
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158
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Tovar KR, Westbrook GL. Modulating synaptic NMDA receptors. Neuropharmacology 2016; 112:29-33. [PMID: 27565459 DOI: 10.1016/j.neuropharm.2016.08.023] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Accepted: 08/17/2016] [Indexed: 12/14/2022]
Abstract
Recent structural information on ligand-gated glutamate receptors and newly-discovered clinical uses for NMDA receptor antagonists has renewed interest in understanding the mechanisms of drug action at these receptors. Although the voltage-dependence and calcium permeability of NMDA receptors are well-studied, the mechanisms affecting the time course of synaptic NMDA receptor activation may be of more therapeutic value by serving as a rheostat for the total synaptic response. The NMDA receptor-mediated EPSC time course has been thought of as a fixed parameter based simply on receptor subunit composition as variably constrained by anatomical and developmental expression patterns, albeit subject to modification by kinetic behaviors such as modal gating. However, the EPSC time course also can be manipulated by endogenous and exogenous ligands. In this commentary we discuss insights into the in situ composition and kinetic behavior of synaptic NMDA receptors and propose new opportunities to target modulatory sites on NMDA receptors and to develop useful therapeutics. The emerging data on the atomic structure of NMDA receptors and knowledge of the kinetics of native receptors in neurons provide a roadmap in this regard. This article is part of the Special Issue entitled 'Ionotropic glutamate receptors'.
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Affiliation(s)
- Kenneth R Tovar
- Vollum Institute, Oregon Health & Science University, Portland, OR 97239, United States.
| | - Gary L Westbrook
- Vollum Institute, Oregon Health & Science University, Portland, OR 97239, United States.
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159
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Subramaniam S, Earl LA, Falconieri V, Milne JL, Egelman EH. Resolution advances in cryo-EM enable application to drug discovery. Curr Opin Struct Biol 2016; 41:194-202. [PMID: 27552081 DOI: 10.1016/j.sbi.2016.07.009] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2016] [Accepted: 07/13/2016] [Indexed: 12/23/2022]
Abstract
The prospect that the structures of protein assemblies, small and large, can be determined using cryo-electron microscopy (cryo-EM) is beginning to transform the landscape of structural biology and cell biology. Great progress is being made in determining 3D structures of biological assemblies ranging from icosahedral viruses and helical arrays to small membrane proteins and protein complexes. Here, we review recent advances in this field, focusing especially on the emerging use of cryo-EM in mapping the binding of drugs and inhibitors to protein targets, an application that requires structure determination at the highest possible resolutions. We discuss methods used to evaluate the information contained in cryo-EM density maps and consider strengths and weaknesses of approaches currently used to measure map resolution.
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Affiliation(s)
- Sriram Subramaniam
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Lesley A Earl
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Veronica Falconieri
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Jacqueline Ls Milne
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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160
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Structural biology of glutamate receptor ion channel complexes. Curr Opin Struct Biol 2016; 41:119-127. [PMID: 27454049 DOI: 10.1016/j.sbi.2016.07.002] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Revised: 06/28/2016] [Accepted: 07/01/2016] [Indexed: 12/23/2022]
Abstract
Chemical transmission at excitatory synapses in the brain is mediated by a diverse family of glutamate receptor ion channels (iGluRs), tetrameric membrane protein assemblies of molecular weight 400-600kDa. Until recently, structural information for intact iGluRs was limited to biochemically tractable homomeric receptors trapped in different conformational states. These provided key insights into the mechanisms of iGluR activation and desensitization. Structures of heteromeric AMPA and NMDA receptors, the major iGluR families in the brain, together with long awaited cryo-EM structures of an AMPA receptor TARP complex, expand this picture and reveal surprising conformational diversity, raising many fundamental and controversial questions.
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