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Perozzo AM, Brown PMGE, Bowie D. Alternative Splicing of the Flip/Flop Cassette and TARP Auxiliary Subunits Engage in a Privileged Relationship That Fine-Tunes AMPA Receptor Gating. J Neurosci 2023; 43:2837-2849. [PMID: 36931708 PMCID: PMC10124957 DOI: 10.1523/jneurosci.2293-22.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Revised: 02/10/2023] [Accepted: 03/13/2023] [Indexed: 03/19/2023] Open
Abstract
Alternative splicing of AMPA-type glutamate receptors (AMPARs) and allosteric modulation by auxiliary subunits, such as transmembrane AMPAR regulatory proteins (TARPs), are two important mechanisms that regulate the time course of glutamatergic neurotransmission. Prior work has shown that alternative splicing of the flip/flop cassette profoundly regulates TARP γ2 modulation, where flip receptor gating exhibits robust sensitivity to TARPs while flop isoforms are relatively insensitive to TARP modulation. Whether this splice variant-specific regulation extends to other auxiliary subunit families, such as cornichons (CNIHs), GSG1L, or CKAMPs, remains unknown. Here, we demonstrate that CNIH-3 modulation is unaffected by AMPAR alternative splicing due to inherent differences in how CNIH-3 and TARP γ2 modify channel gating. CNIH-3 slows receptor deactivation from the outset of current decay, consistent with structural evidence showing its point of contact at the level of the pore. In contrast, TARP γ2 acts via the KGK site of the ligand-binding domain (LBD) to slow the onset of desensitization. Although GSG1L and CKAMP44 primarily slow recovery from desensitization, their effects on channel gating are unaffected by alternative splicing, further underlining that structural events leading to the onset and recovery from desensitization are separable. Together, this work establishes that alternative splicing and TARP auxiliary subunits form a unique partnership that governs fast glutamatergic signaling at central synapses. Since proteomic studies suggest that all native AMPARs co-assemble with at least two TARPs, allosteric coupling between the flip/flop cassette and TARPs may represent a common design element in all AMPAR complexes of the mammalian brain.SIGNIFICANCE STATEMENT All fast excitatory neurotransmission in the mammalian brain is mediated by AMPA-type glutamate receptors (AMPARs). The time course of AMPAR gating can be regulated by two distinct mechanisms: alternative splicing of the flip/flop cassette and association with auxiliary subunits. Although these regulatory mechanisms have been well studied individually, it is not clear whether alternative splicing impacts auxiliary protein modulation of AMPARs. Here, we compare the four main families of AMPAR auxiliary subunits, transmembrane AMPAR regulatory proteins (TARPs; γ2), cornichons (CNIH-3), GSG1L and CKAMPs (CKAMP44), and find a privileged relationship between TARPs and the flip/flop cassette that is not shared by others. The flop cassette acts as a master switch to override TARP action, and this coupling represents a way to fine-tune AMPAR signaling.
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Affiliation(s)
- Amanda M Perozzo
- Integrated Program in Neuroscience, McGill University, Montréal, Quebec H3A 2B4, Canada
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Quebec H3G 1Y6, Canada
| | - Patricia M G E Brown
- Integrated Program in Neuroscience, McGill University, Montréal, Quebec H3A 2B4, Canada
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Quebec H3G 1Y6, Canada
| | - Derek Bowie
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Quebec H3G 1Y6, Canada
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Nakane T, Kotecha A, Sente A, McMullan G, Masiulis S, Brown PMGE, Grigoras IT, Malinauskaite L, Malinauskas T, Miehling J, Uchański T, Yu L, Karia D, Pechnikova EV, de Jong E, Keizer J, Bischoff M, McCormack J, Tiemeijer P, Hardwick SW, Chirgadze DY, Murshudov G, Aricescu AR, Scheres SHW. Single-particle cryo-EM at atomic resolution. Nature 2020; 587:152-156. [PMID: 33087931 PMCID: PMC7611073 DOI: 10.1038/s41586-020-2829-0] [Citation(s) in RCA: 436] [Impact Index Per Article: 109.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2020] [Accepted: 08/27/2020] [Indexed: 12/21/2022]
Abstract
The three-dimensional positions of atoms in protein molecules define their structure and their roles in biological processes. The more precisely atomic coordinates are determined, the more chemical information can be derived and the more mechanistic insights into protein function may be inferred. Electron cryo-microscopy (cryo-EM) single-particle analysis has yielded protein structures with increasing levels of detail in recent years1,2. However, it has proved difficult to obtain cryo-EM reconstructions with sufficient resolution to visualize individual atoms in proteins. Here we use a new electron source, energy filter and camera to obtain a 1.7 Å resolution cryo-EM reconstruction for a human membrane protein, the β3 GABAA receptor homopentamer3. Such maps allow a detailed understanding of small-molecule coordination, visualization of solvent molecules and alternative conformations for multiple amino acids, and unambiguous building of ordered acidic side chains and glycans. Applied to mouse apoferritin, our strategy led to a 1.22 Å resolution reconstruction that offers a genuine atomic-resolution view of a protein molecule using single-particle cryo-EM. Moreover, the scattering potential from many hydrogen atoms can be visualized in difference maps, allowing a direct analysis of hydrogen-bonding networks. Our technological advances, combined with further approaches to accelerate data acquisition and improve sample quality, provide a route towards routine application of cryo-EM in high-throughput screening of small molecule modulators and structure-based drug discovery.
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Affiliation(s)
| | - Abhay Kotecha
- Materials and Structural Analysis Division, Thermo Fisher Scientific, Eindhoven, The Netherlands
| | | | | | - Simonas Masiulis
- MRC Laboratory of Molecular Biology, Cambridge, UK
- Materials and Structural Analysis Division, Thermo Fisher Scientific, Eindhoven, The Netherlands
| | | | - Ioana T Grigoras
- MRC Laboratory of Molecular Biology, Cambridge, UK
- Department of Physics, Imperial College London, London, UK
| | | | - Tomas Malinauskas
- Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK
| | | | - Tomasz Uchański
- Structural Biology Brussels, Vrije Universiteit Brussel, Brussels, Belgium
- VIB-VUB Center for Structural Biology, VIB, Brussels, Belgium
| | - Lingbo Yu
- Materials and Structural Analysis Division, Thermo Fisher Scientific, Eindhoven, The Netherlands
| | - Dimple Karia
- Materials and Structural Analysis Division, Thermo Fisher Scientific, Eindhoven, The Netherlands
| | - Evgeniya V Pechnikova
- Materials and Structural Analysis Division, Thermo Fisher Scientific, Eindhoven, The Netherlands
| | - Erwin de Jong
- Materials and Structural Analysis Division, Thermo Fisher Scientific, Eindhoven, The Netherlands
| | - Jeroen Keizer
- Materials and Structural Analysis Division, Thermo Fisher Scientific, Eindhoven, The Netherlands
| | - Maarten Bischoff
- Materials and Structural Analysis Division, Thermo Fisher Scientific, Eindhoven, The Netherlands
| | - Jamie McCormack
- Materials and Structural Analysis Division, Thermo Fisher Scientific, Eindhoven, The Netherlands
| | - Peter Tiemeijer
- Materials and Structural Analysis Division, Thermo Fisher Scientific, Eindhoven, The Netherlands
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Brown PMGE, McGuire H, Bowie D. Stargazin and cornichon-3 relieve polyamine block of AMPA receptors by enhancing blocker permeation. J Gen Physiol 2017; 150:67-82. [PMID: 29222130 PMCID: PMC5749116 DOI: 10.1085/jgp.201711895] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Revised: 10/06/2017] [Accepted: 11/06/2017] [Indexed: 01/12/2023] Open
Abstract
Polyamine block of AMPA-type ionotropic glutamate receptors is attenuated by auxiliary proteins stargazin and cornichon-3. Brown et al. show that relief from block is due to enhanced blocker permeation and present a modified model of permeant channel block to account for their experimental findings. Most ligand- and voltage-gated ion channels assemble as signaling complexes consisting of pore-forming and auxiliary subunits. In the mammalian brain, AMPA-type ionotropic glutamate receptors (AMPARs) coassemble with several families of auxiliary subunits that regulate channel gating as well as ion channel block and permeation. Previous work has shown that auxiliary proteins stargazin (or γ2) and cornichon-3 (CNIH-3) attenuate the cytoplasmic polyamine channel block of AMPARs, although the underlying mechanism has yet to be established. Here, we show that γ2 and CNIH-3 relieve channel block by enhancing the rate of blocker permeation. Surprisingly, the relative permeability of the polyamine spermine (Spm) through the pore of the AMPAR-γ2 or -CNIH-3 complexes is considerably more than AMPARs expressed alone. Spm permeability is comparable to that of Na+ for the GluA2-γ2 complex and four times greater than Na+ with GluA2 + CNIH-3. A modified model of permeant channel block fully accounts for both the voltage- and time-dependent nature of Spm block. Estimates of block rate constants reveal that auxiliary subunits do not attenuate block by shifting the location of the block site within the membrane electric field, and they do not affect the blocker’s ability to reach it. Instead, γ2 and CNIH-3 relieve channel block by facilitating the blocker’s exit rates from the open channel. From a physiological perspective, the relief of channel block exerted by γ2 and CNIH-3 ensures that there is unfettered signaling by AMPARs at glutamatergic synapses. Moreover, the pronounced ability of AMPARs to transport polyamines may have an unexpected role in regulating cellular polyamine levels.
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Affiliation(s)
- Patricia M G E Brown
- Integrated Program in Neurosciences, McGill University, Montréal, Québec, Canada.,Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada
| | - Hugo McGuire
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada
| | - Derek Bowie
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada
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Paramo T, Brown PMGE, Musgaard M, Bowie D, Biggin PC. Functional Validation of Heteromeric Kainate Receptor Models. Biophys J 2017; 113:2173-2177. [PMID: 28935133 PMCID: PMC5700254 DOI: 10.1016/j.bpj.2017.08.047] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2017] [Revised: 08/30/2017] [Accepted: 08/31/2017] [Indexed: 01/31/2023] Open
Abstract
Kainate receptors require the presence of external ions for gating. Most work thus far has been performed on homomeric GluK2 but, in vivo, kainate receptors are likely heterotetramers. Agonists bind to the ligand-binding domain (LBD) which is arranged as a dimer of dimers as exemplified in homomeric structures, but no high-resolution structure currently exists of heteromeric kainate receptors. In a full-length heterotetramer, the LBDs could potentially be arranged either as a GluK2 homomer alongside a GluK5 homomer or as two GluK2/K5 heterodimers. We have constructed models of the LBD dimers based on the GluK2 LBD crystal structures and investigated their stability with molecular dynamics simulations. We have then used the models to make predictions about the functional behavior of the full-length GluK2/K5 receptor, which we confirmed via electrophysiological recordings. A key prediction and observation is that lithium ions bind to the dimer interface of GluK2/K5 heteromers and slow their desensitization.
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Affiliation(s)
- Teresa Paramo
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Patricia M G E Brown
- Integrated Program in Neurosciences, McGill University, Montréal, Québec, Canada
| | - Maria Musgaard
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom
| | - Derek Bowie
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada
| | - Philip C Biggin
- Department of Biochemistry, University of Oxford, Oxford, United Kingdom.
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Krogsgaard-Larsen N, Delgar CG, Koch K, Brown PMGE, Møller C, Han L, Huynh THV, Hansen SW, Nielsen B, Bowie D, Pickering DS, Kastrup JS, Frydenvang K, Bunch L. Design and Synthesis of a Series of l-trans-4-Substituted Prolines as Selective Antagonists for the Ionotropic Glutamate Receptors Including Functional and X-ray Crystallographic Studies of New Subtype Selective Kainic Acid Receptor Subtype 1 (GluK1) Antagonist (2S,4R)-4-(2-Carboxyphenoxy)pyrrolidine-2-carboxylic Acid. J Med Chem 2016; 60:441-457. [PMID: 28005385 DOI: 10.1021/acs.jmedchem.6b01516] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Ionotropic glutamate receptor antagonists are valuable tool compounds for studies of neurological pathways in the central nervous system. On the basis of rational ligand design, a new class of selective antagonists, represented by (2S,4R)-4-(2-carboxyphenoxy)pyrrolidine-2-carboxylic acid (1b), for cloned homomeric kainic acid receptors subtype 1 (GluK1) was attained (Ki = 4 μM). In a functional assay, 1b displayed full antagonist activity with IC50 = 6 ± 2 μM. A crystal structure was obtained of 1b when bound in the ligand binding domain of GluK1. A domain opening of 13-14° was seen compared to the structure with glutamate, consistent with 1b being an antagonist. A structure-activity relationship study showed that the chemical nature of the tethering atom (C, O, or S) linking the pyrrolidine ring and the phenyl ring plays a key role in the receptor selectivity profile and that substituents on the phenyl ring are well accommodated by the GluK1 receptor.
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Affiliation(s)
| | | | | | - Patricia M G E Brown
- Bowie Lab, Department of Pharmacology & Therapeutics, Faculty of Medicine, McGill University , Montreal, Quebec H3G 0B1, Canada
| | | | | | | | | | | | - Derek Bowie
- Bowie Lab, Department of Pharmacology & Therapeutics, Faculty of Medicine, McGill University , Montreal, Quebec H3G 0B1, Canada
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Brown PMGE, Aurousseau MRP, Musgaard M, Biggin PC, Bowie D. Kainate receptor pore-forming and auxiliary subunits regulate channel block by a novel mechanism. J Physiol 2016; 594:1821-40. [PMID: 26682513 PMCID: PMC4818602 DOI: 10.1113/jp271690] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2015] [Accepted: 12/07/2015] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Kainate receptor heteromerization and auxiliary subunits, Neto1 and Neto2, attenuate polyamine ion-channel block by facilitating blocker permeation. Relief of polyamine block in GluK2/GluK5 heteromers results from a key proline residue that produces architectural changes in the channel pore α-helical region. Auxiliary subunits exert an additive effect to heteromerization, and thus relief of polyamine block is due to a different mechanism. Our findings have broad implications for work on polyamine block of other cation-selective ion channels. ABSTRACT Channel block and permeation by cytoplasmic polyamines is a common feature of many cation-selective ion channels. Although the channel block mechanism has been studied extensively, polyamine permeation has been considered less significant as it occurs at extreme positive membrane potentials. Here, we show that kainate receptor (KAR) heteromerization and association with auxiliary proteins, Neto1 and Neto2, attenuate polyamine block by enhancing blocker permeation. Consequently, polyamine permeation and unblock occur at more negative and physiologically relevant membrane potentials. In GluK2/GluK5 heteromers, enhanced permeation is due to a single proline residue in GluK5 that alters the dynamics of the α-helical region of the selectivity filter. The effect of auxiliary proteins is additive, and therefore the structural basis of polyamine permeation and unblock is through a different mechanism. As native receptors are thought to assemble as heteromers in complex with auxiliary proteins, our data identify an unappreciated impact of polyamine permeation in shaping the signalling properties of neuronal KARs and point to a structural mechanism that may be shared amongst other cation-selective ion channels.
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Affiliation(s)
- Patricia M G E Brown
- Integrated Program in Neurosciences, McGill University, Montréal, Québec, Canada, H3G 0B1
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada, H3G 0B1
| | - Mark R P Aurousseau
- Graduate Program in Pharmacology, McGill University, Montréal, Québec, Canada, H3G 0B1
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada, H3G 0B1
| | - Maria Musgaard
- Department of Biochemistry, University of Oxford, Oxford, OX1 3QU, UK
| | - Philip C Biggin
- Department of Biochemistry, University of Oxford, Oxford, OX1 3QU, UK
| | - Derek Bowie
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada, H3G 0B1
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Accardi MV, Daniels BA, Brown PMGE, Fritschy JM, Tyagarajan SK, Bowie D. Mitochondrial reactive oxygen species regulate the strength of inhibitory GABA-mediated synaptic transmission. Nat Commun 2016; 5:3168. [PMID: 24430741 PMCID: PMC4977183 DOI: 10.1038/ncomms4168] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Accepted: 12/20/2013] [Indexed: 01/08/2023] Open
Abstract
Neuronal communication imposes a heavy metabolic burden in maintaining ionic gradients essential for action potential firing and synaptic signaling. Although cellular metabolism is known to regulate excitatory neurotransmission, it is still unclear whether the brain’s energy supply affects inhibitory signaling. Here we show that mitochondrial-derived reactive oxygen species (mROS) regulate the strength of postsynaptic GABAA receptors at inhibitory synapses of cerebellar stellate cells. Inhibition is strengthened through a mechanism that selectively recruits α3-containing GABAA receptors into synapses with no discernible effect on resident α1-containing receptors. Since mROS promotes the emergence of postsynaptic events with unique kinetic properties, we conclude that newly-recruited α3-containing GABAA receptors are activated by neurotransmitter released onto discrete postsynaptic sites. Although traditionally associated with oxidative stress in neurodegenerative disease, our data identifies mROS as a putative homeostatic signaling molecule coupling cellular metabolism to the strength of inhibitory transmission.
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Affiliation(s)
- Michael V Accardi
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada H3B 0B1
| | - Bryan A Daniels
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada H3B 0B1
| | - Patricia M G E Brown
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada H3B 0B1
| | - Jean-Marc Fritschy
- Institute of Pharmacology and Toxicology, University of Zurich, CH-8057, Zurich, Switzerland
| | - Shiva K Tyagarajan
- Institute of Pharmacology and Toxicology, University of Zurich, CH-8057, Zurich, Switzerland
| | - Derek Bowie
- Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, Canada H3B 0B1
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Demmer CS, Møller C, Brown PMGE, Han L, Pickering DS, Nielsen B, Bowie D, Frydenvang K, Kastrup JS, Bunch L. Binding mode of an α-amino acid-linked quinoxaline-2,3-dione analogue at glutamate receptor subtype GluK1. ACS Chem Neurosci 2015; 6:845-54. [PMID: 25856736 DOI: 10.1021/acschemneuro.5b00038] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Two α-amino acid-functionalized quinoxalines, 1a (CNG-10301) and 1b (CNG-10300), of a quinoxaline moiety coupled to an amino acid moiety were designed, synthesized, and characterized pharmacologically. While 1a displayed low affinity at native AMPA, KA, and NMDA receptors, and at homomeric GluK1,3 receptors, the affinity for GluK2 was in the midmicromolar range (Ki = 136 μM), 1b displayed low to midmicromolar range binding affinity at all the iGluRs (Ki = 9-126 μM). In functional experiments (outside-out patches excised from transfected HEK293T cells), 100 μM 1a partially blocked GluK1 (33% peak response), while GluK2 was unaffected (96% peak response). Furthermore, 1a was shown not to be an agonist at GluK1 and GluK2 at 100 μM. On the other hand, 100 μM 1b fully antagonized GluK1 (8% peak response) but only partially blocked GluK2 (33% peak response). An X-ray structure at 2.3 Å resolution of 1b in the GluK1-LBD (ligand-binding domain) disclosed an unexpected binding mode compared to the predictions made during the design phase; the quinoxaline moiety remains to act as an amino acid bioisostere, but the amino acid moiety is oriented into a new area within the GluK1 receptor. The structure of the GluK1-LBD with 1b showed a large variation in domain openings of the three molecules from 25° to 49°, demonstrating that the GluK1-LBD is capable of undergoing major domain movements.
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