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Gaidin SG, Kosenkov AM. mRNA editing of kainate receptor subunits: what do we know so far? Rev Neurosci 2022; 33:641-655. [DOI: 10.1515/revneuro-2021-0144] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Accepted: 01/18/2022] [Indexed: 11/15/2022]
Abstract
Abstract
Kainate receptors (KARs) are considered one of the key modulators of synaptic activity in the mammalian central nervous system. These receptors were discovered more than 30 years ago, but their role in brain functioning remains unclear due to some peculiarities. One such feature of these receptors is the editing of pre-mRNAs encoding GluK1 and GluK2 subunits. Despite the long history of studying this phenomenon, numerous questions remain unanswered. This review summarizes the current data about the mechanism and role of pre-mRNA editing of KAR subunits in the mammalian brain and proposes a perspective of future investigations.
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Affiliation(s)
- Sergei G. Gaidin
- Institute of Cell Biophysics of the Russian Academy of Sciences , 142290 , Pushchino , Russia
| | - Artem M. Kosenkov
- Institute of Cell Biophysics of the Russian Academy of Sciences , 142290 , Pushchino , Russia
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2
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Structural Arrangement Produced by Concanavalin A Binding to Homomeric GluK2 Receptors. MEMBRANES 2021; 11:membranes11080613. [PMID: 34436376 PMCID: PMC8401665 DOI: 10.3390/membranes11080613] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Revised: 08/07/2021] [Accepted: 08/09/2021] [Indexed: 11/17/2022]
Abstract
Kainate receptors are members of the ionotropic glutamate receptor family. They form cation-specific transmembrane channels upon binding glutamate that desensitize in the continued presence of agonists. Concanavalin A (Con-A), a lectin, stabilizes the active open-channel state of the kainate receptor and reduces the extent of desensitization. In this study, we used single-molecule fluorescence resonance energy transfer (smFRET) to investigate the conformational changes underlying kainate receptor modulation by Con-A. These studies showed that Con-A binding to GluK2 homomeric kainate receptors resulted in closer proximity of the subunits at the dimer–dimer interface at the amino-terminal domain as well as between the subunits at the dimer interface at the agonist-binding domain. Additionally, the modulation of receptor functions by monovalent ions, which bind to the dimer interface at the agonist-binding domain, was not observed in the presence of Con-A. Based on these results, we conclude that Con-A modulation of kainate receptor function is mediated by a shift in the conformation of the kainate receptor toward a tightly packed extracellular domain.
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3
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Mayer ML. Structural biology of kainate receptors. Neuropharmacology 2021; 190:108511. [PMID: 33798545 DOI: 10.1016/j.neuropharm.2021.108511] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2020] [Revised: 02/16/2021] [Accepted: 02/18/2021] [Indexed: 12/31/2022]
Abstract
This review summarizes structural studies on kainate receptors that explain unique functional properties of this receptor family. A large number of structures have been solved for ligand binding domain dimer assemblies, giving insight into the subtype selective pharmacology of agonists, antagonists, and allosteric modulators. Structures and biochemical studies on the amino terminal domain reveal mechanisms that play a key role in assembly of heteromeric receptors. Surprisingly, structures of full length homomeric GluK2, GluK3 and heteromeric GluK2/GluK5, receptors reveal a novel structure for the desensitized state that is strikingly different from that for AMPA receptors.
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Affiliation(s)
- Mark L Mayer
- Porter Neuroscience Research Center, NINDS, NIH, 35A Convent Drive Room 3D 904, Bethesda, MD, 20892, USA.
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4
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Khanra N, Brown PMGE, Perozzo AM, Bowie D, Meyerson JR. Architecture and structural dynamics of the heteromeric GluK2/K5 kainate receptor. eLife 2021; 10:e66097. [PMID: 33724189 PMCID: PMC7997659 DOI: 10.7554/elife.66097] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Accepted: 03/05/2021] [Indexed: 12/15/2022] Open
Abstract
Kainate receptors (KARs) are L-glutamate-gated ion channels that regulate synaptic transmission and modulate neuronal circuits. KARs have strict assembly rules and primarily function as heteromeric receptors in the brain. A longstanding question is how KAR heteromer subunits organize and coordinate together to fulfill their signature physiological roles. Here we report structures of the GluK2/GluK5 heteromer in apo, antagonist-bound, and desensitized states. The receptor assembles with two copies of each subunit, ligand binding domains arranged as two heterodimers and GluK5 subunits proximal to the channel. Strikingly, during desensitization, GluK2, but not GluK5, subunits undergo major structural rearrangements to facilitate channel closure. We show how the large conformational differences between antagonist-bound and desensitized states are mediated by the linkers connecting the pore helices to the ligand binding domains. This work presents the first KAR heteromer structure, reveals how its subunits are organized, and resolves how the heteromer can accommodate functionally distinct closed channel structures.
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Affiliation(s)
- Nandish Khanra
- Department of Physiology and Biophysics, Weill Cornell Medical CollegeNew YorkUnited States
| | - Patricia MGE Brown
- Department of Pharmacology and Therapeutics, McGill UniversityMontréalCanada
| | - Amanda M Perozzo
- Department of Pharmacology and Therapeutics, McGill UniversityMontréalCanada
| | - Derek Bowie
- Department of Pharmacology and Therapeutics, McGill UniversityMontréalCanada
| | - Joel R Meyerson
- Department of Physiology and Biophysics, Weill Cornell Medical CollegeNew YorkUnited States
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5
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Perszyk RE, Myers SJ, Yuan H, Gibb AJ, Furukawa H, Sobolevsky AI, Traynelis SF. Hodgkin-Huxley-Katz Prize Lecture: Genetic and pharmacological control of glutamate receptor channel through a highly conserved gating motif. J Physiol 2020; 598:3071-3083. [PMID: 32468591 DOI: 10.1113/jp278086] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Accepted: 05/18/2020] [Indexed: 12/15/2022] Open
Abstract
Glutamate receptors are essential ligand-gated ion channels in the central nervous system that mediate excitatory synaptic transmission in response to the release of glutamate from presynaptic terminals. The structural and biophysical basis underlying the function of these receptors has been studied for decades by a wide range of approaches. However recent structural, pharmacological and genetic studies have provided new insight into the regions of this protein that are critical determinants of receptor function. Lack of variation in specific areas of the protein amino acid sequences in the human population has defined three regions in each receptor subunit that are under selective pressure, which has focused research efforts and driven new hypotheses. In addition, these three closely positioned elements reside near a cavity that is shown by multiple studies to be a likely site of action for allosteric modulators, one of which is currently in use as an FDA-approved anticonvulsant. These structural elements are capable of controlling gating of the pore, and appear to permit some modulators bound within the cavity to also alter permeation properties. This creates a new precedent whereby features of the channel pore can be modulated by exogenous drugs that bind outside the pore. The convergence of structural, genetic, biophysical and pharmacological approaches is a powerful means to gain insight into the complex biological processes defined by neurotransmitter receptor function.
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Affiliation(s)
- Riley E Perszyk
- Department of Pharmacology and Chemical Biology, Emory University School of Medicine, Atlanta, GA, 30322, USA
| | - Scott J Myers
- Department of Pharmacology and Chemical Biology, Emory University School of Medicine, Atlanta, GA, 30322, USA.,Center for Functional Evaluation of Rare Variants (CFERV), Emory University School of Medicine, Atlanta, GA, 30322, USA
| | - Hongjie Yuan
- Department of Pharmacology and Chemical Biology, Emory University School of Medicine, Atlanta, GA, 30322, USA.,Center for Functional Evaluation of Rare Variants (CFERV), Emory University School of Medicine, Atlanta, GA, 30322, USA
| | - Alasdair J Gibb
- Department of Neuroscience, Physiology & Pharmacology, University College London, London, UK
| | - Hiro Furukawa
- WM Keck Structural Biology Laboratory, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, NY, 11724, USA
| | - Alexander I Sobolevsky
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, 10032, USA
| | - Stephen F Traynelis
- Department of Pharmacology and Chemical Biology, Emory University School of Medicine, Atlanta, GA, 30322, USA.,Center for Functional Evaluation of Rare Variants (CFERV), Emory University School of Medicine, Atlanta, GA, 30322, USA
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6
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Kumari J, Bendre AD, Bhosale S, Vinnakota R, Burada AP, Tria G, Ravelli RBG, Peters PJ, Joshi M, Kumar J. Structural dynamics of the GluK3-kainate receptor neurotransmitter binding domains revealed by cryo-EM. Int J Biol Macromol 2020; 149:1051-1058. [PMID: 32006583 DOI: 10.1016/j.ijbiomac.2020.01.282] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 01/28/2020] [Accepted: 01/28/2020] [Indexed: 12/19/2022]
Abstract
Kainate receptors belong to the ionotropic glutamate receptor family and play critical roles in the regulation of synaptic networks. The kainate receptor subunit GluK3 has unique functional properties and contributes to presynaptic facilitation at the hippocampal mossy fiber synapses along with roles at the post-synapses. To gain structural insights into the unique functional properties and dynamics of GluK3 receptor, we imaged them via electron microscopy in the apo-state and in complex with either agonist kainate or antagonist UBP301. Our analysis of all the GluK3 full-length structures not only provides insights into the receptor transitions between desensitized and closed states but also reveals a "non-classical" conformation of neurotransmitter binding domain in the closed-state distinct from that observed in AMPA and other kainate receptor structures. We show by molecular dynamics simulations that Asp759 influences the stability of the LBD dimers and hence could be responsible for the observed conformational variability and dynamics of the GluK3 via electron microscopy. Lower dimer stability could explain faster desensitization and low agonist sensitivity of GluK3. In overview, our work helps to associate biochemistry and physiology of GluK3 receptors with their structural biology and offers structural insights into the unique functional properties of these atypical receptors.
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Affiliation(s)
- Jyoti Kumari
- Laboratory of Membrane Protein Biology, National Centre for Cell Science, NCCS Complex, S. P. Pune University, Pune, Maharashtra 411007, India
| | - Ameya D Bendre
- Laboratory of Membrane Protein Biology, National Centre for Cell Science, NCCS Complex, S. P. Pune University, Pune, Maharashtra 411007, India
| | - Sumedha Bhosale
- Bioinformatics Centre, S. P. Pune University, Pune, Maharashtra 411007, India
| | - Rajesh Vinnakota
- Laboratory of Membrane Protein Biology, National Centre for Cell Science, NCCS Complex, S. P. Pune University, Pune, Maharashtra 411007, India
| | - Ananth P Burada
- Laboratory of Membrane Protein Biology, National Centre for Cell Science, NCCS Complex, S. P. Pune University, Pune, Maharashtra 411007, India
| | - Giancarlo Tria
- The Maastricht Multimodal Molecular Imaging Institute (M4I), Division of Nanoscopy, Maastricht University, PO Box 616, 6200 MD Maastricht, the Netherlands
| | - Raimond B G Ravelli
- The Maastricht Multimodal Molecular Imaging Institute (M4I), Division of Nanoscopy, Maastricht University, PO Box 616, 6200 MD Maastricht, the Netherlands
| | - Peter J Peters
- The Maastricht Multimodal Molecular Imaging Institute (M4I), Division of Nanoscopy, Maastricht University, PO Box 616, 6200 MD Maastricht, the Netherlands
| | - Manali Joshi
- Bioinformatics Centre, S. P. Pune University, Pune, Maharashtra 411007, India
| | - Janesh Kumar
- Laboratory of Membrane Protein Biology, National Centre for Cell Science, NCCS Complex, S. P. Pune University, Pune, Maharashtra 411007, India.
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7
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Litwin DB, Paudyal N, Carrillo E, Berka V, Jayaraman V. The structural arrangement and dynamics of the heteromeric GluK2/GluK5 kainate receptor as determined by smFRET. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2020; 1862:183001. [PMID: 31194959 PMCID: PMC6899175 DOI: 10.1016/j.bbamem.2019.05.023] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Revised: 05/14/2019] [Accepted: 05/31/2019] [Indexed: 01/08/2023]
Abstract
Kainate receptors, which are glutamate activated excitatory neurotransmitter receptors, predominantly exist as heteromers of GluK2 and GluK5 subunits in the mammalian central nervous system. There are currently no structures of the full-length heteromeric kainate receptors. Here, we have used single molecule FRET to determine the specific arrangement of the GluK2 and GluK5 subunits within the dimer of dimers configuration in a full-length receptor. Additionally, we have also studied the dynamics and conformational heterogeneity of the amino-terminal and agonist-binding domain interfaces associated with the resting and desensitized states of the full-length heteromeric kainate receptor using FRET-based methods. The smFRET data are compared to similar experiments performed on the homomeric kainate receptor to provide insight into the differences in conformational dynamics that distinguish the two functionally. This article is part of a Special Issue entitled: Molecular biophysics of membranes and membrane proteins.
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Affiliation(s)
- Douglas B Litwin
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA; MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Nabina Paudyal
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA; MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Elisa Carrillo
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Vladimir Berka
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA
| | - Vasanthi Jayaraman
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, TX 77030, USA.
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8
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Damaging coding variants within kainate receptor channel genes are enriched in individuals with schizophrenia, autism and intellectual disabilities. Sci Rep 2019; 9:19215. [PMID: 31844109 PMCID: PMC6915710 DOI: 10.1038/s41598-019-55635-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2019] [Accepted: 11/23/2019] [Indexed: 01/13/2023] Open
Abstract
Schizophrenia (Scz), autism spectrum disorder (ASD) and intellectual disability are common complex neurodevelopmental disorders. Kainate receptors (KARs) are ionotropic glutamate ion channels involved in synaptic plasticity which are modulated by auxiliary NETO proteins. Using UK10K exome sequencing data, we interrogated the coding regions of KAR and NETO genes in individuals with Scz, ASD or intellectual disability and population controls; performed follow-up genetic replication studies; and, conducted in silico and in vitro functional studies. We found an excess of Loss-of-Function and missense variants in individuals with Scz compared with control individuals (p = 1.8 × 10−10), and identified a significant burden of functional variants for Scz (p < 1.6 × 10−11) and ASD (p = 6.9 × 10−18). Single allele associations for 6 damaging missense variants were significantly replicated (p < 5.0 × 10−15) and confirmed GRIK3 S310A as a protective genetic factor. Functional studies demonstrated that three missense variants located within GluK2 and GluK4, GluK2 (K525E) and GluK4 (Y555N, L825W), affect agonist sensitivity and current decay rates. These findings establish that genetic variation in KAR receptor ion channels confers risk for schizophrenia, autism and intellectual disability and provide new genetic and pharmacogenetic biomarkers for neurodevelopmental disease.
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9
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Litwin DB, Carrillo E, Shaikh SA, Berka V, Jayaraman V. The structural arrangement at intersubunit interfaces in homomeric kainate receptors. Sci Rep 2019; 9:6969. [PMID: 31061516 PMCID: PMC6502836 DOI: 10.1038/s41598-019-43360-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Accepted: 04/23/2019] [Indexed: 02/02/2023] Open
Abstract
Kainate receptors are glutamate-gated cation-selective channels involved in excitatory synaptic signaling and are known to be modulated by ions. Prior functional and structural studies suggest that the dimer interface at the agonist-binding domain plays a key role in activation, desensitization, and ion modulation in kainate receptors. Here we have used fluorescence-based methods to investigate the changes and conformational heterogeneity at these interfaces associated with the resting, antagonist-bound, active, desensitized, and ion-modulated states of the receptor. These studies show that in the presence of Na+ ions the interfaces exist primarily in the coupled state in the apo, antagonist-bound and activated (open channel) states. Under desensitizing conditions, the largely decoupled dimer interface at the agonist-binding domain as seen in the cryo-EM structure is one of the states observed. However, in addition to this state there are several additional states with lower levels of decoupling. Replacing Na+ with Cs+ does not alter the FRET efficiencies of the states significantly, but shifts the population to the more decoupled states in both resting and desensitized states, which can be correlated with the lower activation seen in the presence of Cs+.
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Affiliation(s)
- Douglas B Litwin
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, Texas, 77030, USA
- MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, University of Texas Health Science Center at Houston, Houston, Texas, 77030, USA
| | - Elisa Carrillo
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, Texas, 77030, USA
| | - Sana A Shaikh
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, Texas, 77030, USA
| | - Vladimir Berka
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, Texas, 77030, USA
| | - Vasanthi Jayaraman
- Center for Membrane Biology, Department of Biochemistry and Molecular Biology, University of Texas Health Science Center at Houston, Houston, Texas, 77030, USA.
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10
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Lau AY. Enhanced sampling of glutamate receptor ligand-binding domains. Neurosci Lett 2019; 700:17-21. [DOI: 10.1016/j.neulet.2018.04.018] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Revised: 04/08/2018] [Accepted: 04/10/2018] [Indexed: 01/23/2023]
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11
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Scholefield CL, Atlason PT, Jane DE, Molnár E. Assembly and Trafficking of Homomeric and Heteromeric Kainate Receptors with Impaired Ligand Binding Sites. Neurochem Res 2018; 44:585-599. [PMID: 30302614 PMCID: PMC6420462 DOI: 10.1007/s11064-018-2654-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2018] [Revised: 09/27/2018] [Accepted: 10/01/2018] [Indexed: 10/28/2022]
Abstract
Kainate receptors (KARs) are a subfamily of ionotropic glutamate receptors (iGluRs) mediating excitatory synaptic transmission. Cell surface expressed KARs modulate the excitability of neuronal networks. The transfer of iGluRs from the endoplasmic reticulum (ER) to the cell surface requires occupation of the agonist binding sites. Here we used molecular modelling to produce a range of ligand binding domain (LBD) point mutants of GluK1-3 KAR subunits with and without altered agonist efficacy to further investigate the role of glutamate binding in surface trafficking and activation of homomeric and heteromeric KARs using endoglycosidase digestion, cell surface biotinylation and imaging of changes in intracellular Ca2+ concentration [Ca2+]i. Mutations of conserved amino acid residues in the LBD that disrupt agonist binding to GluK1-3 (GluK1-T675V, GluK2-A487L, GluK2-T659V and GluK3-T661V) reduced both the total expression levels and cell surface delivery of all of these mutant subunits compared to the corresponding wild type in transiently transfected human embryonic kidney 293 (HEK293) cells. In contrast, the exchange of non-conserved residues in the LBD that convert antagonist selectivity of GluK1-3 (GluK1-T503A, GluK2-A487T, GluK3-T489A, GluK1-N705S/S706N, GluK2-S689N/N690S, GluK3-N691S) did not alter the biosynthesis and trafficking of subunit proteins. Co-assembly of mutant GluK2 with an impaired LBD and wild type GluK5 subunits enables the cell surface expression of both subunits. However, [Ca2+]i imaging indicates that the occupancy of both GluK2 and GluK5 LBDs is required for the full activation of GluK2/GluK5 heteromeric KAR channels.
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Affiliation(s)
- Caroline L Scholefield
- Centre for Synaptic Plasticity, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, BS8 1TD, UK
| | - Palmi T Atlason
- Centre for Synaptic Plasticity, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, BS8 1TD, UK
| | - David E Jane
- Centre for Synaptic Plasticity, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, BS8 1TD, UK
| | - Elek Molnár
- Centre for Synaptic Plasticity, School of Physiology, Pharmacology and Neuroscience, University of Bristol, Biomedical Sciences Building, University Walk, Bristol, BS8 1TD, UK.
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12
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Gibb AJ, Ogden KK, McDaniel MJ, Vance KM, Kell SA, Butch C, Burger P, Liotta DC, Traynelis SF. A structurally derived model of subunit-dependent NMDA receptor function. J Physiol 2018; 596:4057-4089. [PMID: 29917241 PMCID: PMC6117563 DOI: 10.1113/jp276093] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2018] [Accepted: 06/11/2018] [Indexed: 12/14/2022] Open
Abstract
Key points The kinetics of NMDA receptor (NMDAR) signalling are a critical aspect of the physiology of excitatory synaptic transmission in the brain. Here we develop a mechanistic description of NMDAR function based on the receptor tetrameric structure and the principle that each agonist‐bound subunit must undergo some rate‐limiting conformational change after agonist binding, prior to channel opening. By fitting this mechanism to single channel data using a new MATLAB‐based software implementation of maximum likelihood fitting with correction for limited time resolution, rate constants were derived for this mechanism that reflect distinct structural changes and predict the properties of macroscopic and synaptic NMDAR currents. The principles applied here to develop a mechanistic description of the heterotetrameric NMDAR, and the software used in this analysis, can be equally applied to other heterotetrameric glutamate receptors, providing a unifying mechanistic framework to understanding the physiology of glutamate receptor signalling in the brain.
Abstract NMDA receptors (NMDARs) are tetrameric complexes comprising two glycine‐binding GluN1 and two glutamate‐binding GluN2 subunits. Four GluN2 subunits encoded by different genes can produce up to 10 different di‐ and triheteromeric receptors. In addition, some neurological patients contain a de novo mutation or inherited rare variant in only one subunit. There is currently no mechanistic framework to describe tetrameric receptor function that can be extended to receptors with two different GluN1 or GluN2 subunits. Here we use the structural features of glutamate receptors to develop a mechanism describing both single channel and macroscopic NMDAR currents. We propose that each agonist‐bound subunit undergoes some rate‐limiting conformational change after agonist binding, prior to channel opening. We hypothesize that this conformational change occurs within a triad of interactions between a short helix preceding the M1 transmembrane helix, the highly conserved M3 motif encoded by the residues SYTANLAAF, and the linker preceding the M4 transmembrane helix of the adjacent subunit. Molecular dynamics simulations suggest that pre‐M1 helix motion is uncorrelated between subunits, which we interpret to suggest independent subunit‐specific conformational changes may influence these pre‐gating steps. According to this interpretation, these conformational changes are the main determinants of the key kinetic properties of NMDA receptor activation following agonist binding, and so these steps sculpt their physiological role. We show that this structurally derived tetrameric model describes both single channel and macroscopic data, giving a new approach to interpreting functional properties of synaptic NMDARs that provides a logical framework to understanding receptors with non‐identical subunits. The kinetics of NMDA receptor (NMDAR) signalling are a critical aspect of the physiology of excitatory synaptic transmission in the brain. Here we develop a mechanistic description of NMDAR function based on the receptor tetrameric structure and the principle that each agonist‐bound subunit must undergo some rate‐limiting conformational change after agonist binding, prior to channel opening. By fitting this mechanism to single channel data using a new MATLAB‐based software implementation of maximum likelihood fitting with correction for limited time resolution, rate constants were derived for this mechanism that reflect distinct structural changes and predict the properties of macroscopic and synaptic NMDAR currents. The principles applied here to develop a mechanistic description of the heterotetrameric NMDAR, and the software used in this analysis, can be equally applied to other heterotetrameric glutamate receptors, providing a unifying mechanistic framework to understanding the physiology of glutamate receptor signalling in the brain.
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Affiliation(s)
- Alasdair J Gibb
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
| | - Kevin K Ogden
- Department of Pharmacology, Emory University School of Medicine, Rollins Research Center, 1510 Clifton Road, Atlanta, GA, 30322, USA
| | - Miranda J McDaniel
- Department of Pharmacology, Emory University School of Medicine, Rollins Research Center, 1510 Clifton Road, Atlanta, GA, 30322, USA
| | - Katie M Vance
- Department of Pharmacology, Emory University School of Medicine, Rollins Research Center, 1510 Clifton Road, Atlanta, GA, 30322, USA
| | - Steven A Kell
- Department of Chemistry, Emory University School, 1515 Dickey Drive, Atlanta, GA, 30322, USA
| | - Chris Butch
- Department of Chemistry, Emory University School, 1515 Dickey Drive, Atlanta, GA, 30322, USA
| | - Pieter Burger
- Department of Chemistry, Emory University School, 1515 Dickey Drive, Atlanta, GA, 30322, USA
| | - Dennis C Liotta
- Department of Chemistry, Emory University School, 1515 Dickey Drive, Atlanta, GA, 30322, USA
| | - Stephen F Traynelis
- Department of Pharmacology, Emory University School of Medicine, Rollins Research Center, 1510 Clifton Road, Atlanta, GA, 30322, USA
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13
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Dudev T, Mazmanian K, Lim C. Competition between Li + and Na + in sodium transporters and receptors: Which Na +-Binding sites are "therapeutic" Li + targets? Chem Sci 2018; 9:4093-4103. [PMID: 29780538 PMCID: PMC5944251 DOI: 10.1039/c7sc05284g] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2017] [Accepted: 04/02/2018] [Indexed: 11/21/2022] Open
Abstract
Li+ (turquoise), the better charge acceptor, can displace Na+ (purple) bound by only one or two aa residues in buried sites. Thus, Li+ can displace Na+ bound by Asp– and Ser in the A2AAR/β1AR receptor and enhance the metal site's stability, thus prohibiting structural distortions induced by agonist binding, leading to lower cytosolic levels of activated G-proteins, which are hyperactive in bipolar disorder patients.
Sodium (Na+) acts as an indispensable allosteric regulator of the activities of biologically important neurotransmitter transporters and G-protein coupled receptors (GPCRs), which comprise well-known drug targets for psychiatric disorders and addictive behavior. How selective these allosteric Na+-binding sites are for the cognate cation over abiogenic Li+, a first-line drug to treat bipolar disorder, is unclear. Here, we reveal how properties of the host protein and its binding cavity affect the outcome of the competition between Li+ and Na+ for allosteric binding sites in sodium transporters and receptors. We show that rigid Na+-sites that are crowded with multiple protein ligands are well-protected against Li+ attack, but their flexible counterparts or buried Na+-sites containing only one or two protein ligands are vulnerable to Li+ substitution. These findings suggest a novel possible mode of Li+ therapeutic action: By displacing Na+ bound by ≤2 protein ligands in buried GPCR sites and stabilizing the receptor's inactive state, Li+ could prohibit conformational changes to an active state, leading to lower cytosolic levels of activated guanine nucleotide-binding proteins, which are hyperactive/overexpressed in bipolar disorder patients.
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Affiliation(s)
- Todor Dudev
- Faculty of Chemistry and Pharmacy , Sofia University , Sofia 1164 , Bulgaria .
| | - Karine Mazmanian
- Institute of Biomedical Sciences , Academia Sinica , Taipei 11529 , Taiwan . .,Chemical Biology and Molecular Biophysics Program , Taiwan International Graduate Program , Academia Sinica , Taipei 11529 , Taiwan
| | - Carmay Lim
- Institute of Biomedical Sciences , Academia Sinica , Taipei 11529 , Taiwan . .,Department of Chemistry , National Tsing Hua University , Hsinchu 300 , Taiwan
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Biophysics of the Brain: From Molecules to Networks. Biophys J 2017; 113:E1. [PMID: 29079011 DOI: 10.1016/j.bpj.2017.10.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2017] [Accepted: 10/18/2017] [Indexed: 11/22/2022] Open
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