1
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den Hartigh AB, Loomis WP, Anderson MJ, Frølund B, Fink SL. Muscimol inhibits plasma membrane rupture and ninjurin-1 oligomerization during pyroptosis. Commun Biol 2023; 6:1010. [PMID: 37798443 PMCID: PMC10556065 DOI: 10.1038/s42003-023-05354-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2023] [Accepted: 09/13/2023] [Indexed: 10/07/2023] Open
Abstract
Pyroptosis is a cell death process that causes inflammation and contributes to numerous diseases. Pyroptosis is mediated by caspase-1 family proteases that cleave the pore-forming protein gasdermin D, causing plasma membrane rupture and release of pathogenic cellular contents. We previously identified muscimol as a small molecule that prevents plasma membrane rupture during pyroptosis via an unidentified mechanism. Here, we show that muscimol has reversible activity to prevent cellular lysis without affecting earlier pyroptotic events. Although muscimol is a well-characterized agonist for neuronal GABAA receptors, muscimol protection is not altered by GABAA receptor antagonists or recapitulated by other GABAA agonists, suggesting that muscimol acts via a novel mechanism. We find that muscimol blocks oligomerization of ninjurin-1, which is required for plasma membrane rupture downstream of gasdermin D pore formation. Our structure-activity relationship studies reveal distinct molecular determinants defining inhibition of pyroptotic lysis compared to GABAA binding. In addition, we demonstrate that muscimol reduces lethality during LPS-induced septic shock. Together, these findings demonstrate that ninjurin-1-mediated plasma membrane rupture can be pharmacologically modulated and pave the way toward identification of therapeutic strategies for pathologic conditions associated with pyroptosis.
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Affiliation(s)
- Andreas B den Hartigh
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, USA
| | - Wendy P Loomis
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, USA
| | - Marisa J Anderson
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, USA
| | - Bente Frølund
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Susan L Fink
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, USA.
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2
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Gibbs E, Klemm E, Seiferth D, Kumar A, Ilca SL, Biggin PC, Chakrapani S. Conformational transitions and allosteric modulation in a heteromeric glycine receptor. Nat Commun 2023; 14:1363. [PMID: 36914669 PMCID: PMC10011588 DOI: 10.1038/s41467-023-37106-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Accepted: 03/02/2023] [Indexed: 03/16/2023] Open
Abstract
Glycine Receptors (GlyRs) provide inhibitory neuronal input in the spinal cord and brainstem, which is critical for muscle coordination and sensory perception. Synaptic GlyRs are a heteromeric assembly of α and β subunits. Here we present cryo-EM structures of full-length zebrafish α1βBGlyR in the presence of an antagonist (strychnine), agonist (glycine), or agonist with a positive allosteric modulator (glycine/ivermectin). Each structure shows a distinct pore conformation with varying degrees of asymmetry. Molecular dynamic simulations found the structures were in a closed (strychnine) and desensitized states (glycine and glycine/ivermectin). Ivermectin binds at all five interfaces, but in a distinct binding pose at the β-α interface. Subunit-specific features were sufficient to solve structures without a fiduciary marker and to confirm the 4α:1β stoichiometry recently observed. We also report features of the extracellular and intracellular domains. Together, our results show distinct compositional and conformational properties of α1βGlyR and provide a framework for further study of this physiologically important channel.
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Affiliation(s)
- Eric Gibbs
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, 44106-4970, USA
| | - Emily Klemm
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, 44106-4970, USA
| | - David Seiferth
- Department of Biochemistry, University of Oxford, Oxford, OX1 3QU, UK
| | - Arvind Kumar
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, 44106-4970, USA
| | - Serban L Ilca
- New York Structural Biology Center, New York, NY, 10027, USA
- Simons Electron Microscopy Center, New York, NY, 10027, USA
| | - Philip C Biggin
- Department of Biochemistry, University of Oxford, Oxford, OX1 3QU, UK
| | - Sudha Chakrapani
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, 44106-4970, USA.
- Department of Neuroscience, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106-4970, USA.
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3
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Kuhse J, Groeneweg F, Kins S, Gorgas K, Nawrotzki R, Kirsch J, Kiss E. Loss of Extrasynaptic Inhibitory Glycine Receptors in the Hippocampus of an AD Mouse Model Is Restored by Treatment with Artesunate. Int J Mol Sci 2023; 24:ijms24054623. [PMID: 36902054 PMCID: PMC10002537 DOI: 10.3390/ijms24054623] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Revised: 02/14/2023] [Accepted: 02/22/2023] [Indexed: 03/06/2023] Open
Abstract
Alzheimer's disease (AD) is characterized by synaptic failure and neuronal loss. Recently, we demonstrated that artemisinins restored the levels of key proteins of inhibitory GABAergic synapses in the hippocampus of APP/PS1 mice, a model of cerebral amyloidosis. In the present study, we analyzed the protein levels and subcellular localization of α2 and α3 subunits of GlyRs, indicated as the most abundant receptor subtypes in the mature hippocampus, in early and late stages of AD pathogenesis, and upon treatment with two different doses of artesunate (ARS). Immunofluorescence microscopy and Western blot analysis demonstrated that the protein levels of both α2 and α3 GlyRs are considerably reduced in the CA1 and the dentate gyrus of 12-month-old APP/PS1 mice when compared to WT mice. Notably, treatment with low-dose ARS affected GlyR expression in a subunit-specific way; the protein levels of α3 GlyR subunits were rescued to about WT levels, whereas that of α2 GlyRs were not affected significantly. Moreover, double labeling with a presynaptic marker indicated that the changes in GlyR α3 expression levels primarily involve extracellular GlyRs. Correspondingly, low concentrations of artesunate (≤1 µM) also increased the extrasynaptic GlyR cluster density in hAPPswe-transfected primary hippocampal neurons, whereas the number of GlyR clusters overlapping presynaptic VIAAT immunoreactivities remained unchanged. Thus, here we provide evidence that the protein levels and subcellular localization of α2 and α3 subunits of GlyRs show regional and temporal alterations in the hippocampus of APP/PS1 mice that can be modulated by the application of artesunate.
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Affiliation(s)
- Jochen Kuhse
- Institute of Anatomy and Cell Biology, University of Heidelberg, 69117 Heidelberg, Germany
| | - Femke Groeneweg
- Institute of Anatomy and Cell Biology, University of Heidelberg, 69117 Heidelberg, Germany
- Institute of Neuroanatomy, Medical Faculty Mannheim, University Heidelberg, 68167 Mannheim, Germany
| | - Stefan Kins
- Department of Human Biology and Human Genetics, University of Kaiserslautern-Landau, 67663 Kaiserslautern, Germany
| | - Karin Gorgas
- Institute of Anatomy and Cell Biology, University of Heidelberg, 69117 Heidelberg, Germany
| | - Ralph Nawrotzki
- Institute of Anatomy and Cell Biology, University of Heidelberg, 69117 Heidelberg, Germany
| | - Joachim Kirsch
- Institute of Anatomy and Cell Biology, University of Heidelberg, 69117 Heidelberg, Germany
| | - Eva Kiss
- Institute of Anatomy and Cell Biology, University of Heidelberg, 69117 Heidelberg, Germany
- Department of Cellular and Molecular Biology, George Emil Palade University of Medicine, Pharmacy, Science and Technology of Târgu Mureș, 540142 Târgu Mures, Romania
- Correspondence:
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4
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Zhu H. Structure and Mechanism of Glycine Receptor Elucidated by Cryo-Electron Microscopy. Front Pharmacol 2022; 13:925116. [PMID: 36016557 PMCID: PMC9395720 DOI: 10.3389/fphar.2022.925116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2022] [Accepted: 06/14/2022] [Indexed: 11/17/2022] Open
Abstract
Glycine receptors (GlyRs) are pentameric ion channels that mediate fast inhibitory neurotransmission. GlyRs are found in the central nervous system including the spinal cord, brain stem, and cerebellum, as well as in the retina, sperm, macrophages, hippocampus, cochlea, and liver. Due to their crucial roles in counter-balancing excitatory signals and pain signal transmission, GlyR dysfunction can lead to severe diseases, and as a result, compounds that modify GlyR activity may have tremendous therapeutic potential. Despite this potential, the development of GlyR-specific small-molecule ligands is lacking. Over the past few years, high-resolution structures of both homomeric and heteromeric GlyRs structures in various conformations have provided unprecedented details defining the pharmacology of ligand binding, subunit composition, and mechanisms of channel gating. These high-quality structures will undoubtedly help with the development of GlyR-targeted therapies.
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5
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Price KL, Lummis SCR. Characterisation of thymol effects on RDL receptors from the bee parasite Varroa destructor. PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY 2022; 183:105064. [PMID: 35430066 DOI: 10.1016/j.pestbp.2022.105064] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/22/2021] [Revised: 02/22/2022] [Accepted: 02/22/2022] [Indexed: 06/14/2023]
Abstract
A major contributor to bee colony decline is infestation with its most devastating pest, the mite Varroa destructor. To control these mites, thymol is often used, although how it achieves this is not understood. One well-documented action of thymol is to modulate GABA-activated ion channels, which includes insect RDL receptors, a known insecticidal target. Here we have cloned two Varroa RDL subunits, one of which is similar to the canonical RDL subunit, while the other has some differences in M4, and, to a lesser extent, M2 and its binding site loops. Expression of this unusual RDL receptor in Xenopus oocytes reveals GABA-activated receptors, with an EC50 of 56 μM. In contrast to canonical RDL receptors, thymol does not enhance GABA-elicited responses in this receptor, and concentration response curves reveal a decrease in GABA Imax in its presence; this decrease is not seen when similar data are obtained from Apis RDL receptors. We conclude that an M2 T6'M substitution is primarily responsible for the different thymol effects, and suggest that understanding how and where thymol acts could assist in the design of novel bee-friendly miticides.
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Affiliation(s)
- K L Price
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK
| | - S C R Lummis
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK.
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6
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Zlotos DP, Mandour YM, Jensen AA. Strychnine and its mono- and dimeric analogues: a pharmaco-chemical perspective. Nat Prod Rep 2022; 39:1910-1937. [PMID: 35380133 DOI: 10.1039/d1np00079a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Covering: up to November 2021Since its isolation in 1818, strychnine has attracted the attention of a plethora of chemists and pharmacologists who have established its structure, developed total syntheses, and examined its complex pharmacology. While numerous reviews on structure elucidation and total synthesis of strychnine are available, reports on structure-activity relationships (SARs) of this fascinating alkaloid are rare. In this review, we present and discuss structures, synthetic approaches, metabolic transformations, and the diverse pharmacological actions of strychnine and its mono- and dimeric analogues. Particular attention is given to its SARs at glycine receptors (GlyRs) in light of recently published high-resolution structures of strychnine-GlyR complexes. Other pharmacological actions of strychnine and its derivatives, such as their antagonistic properties at nicotinic acetylcholine receptors (nAChRs), allosteric modulation of muscarinic acetylcholine receptors as well as anti-cancer and anti-plasmodial effects are also critically reviewed, and possible future developments in the field are discussed.
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Affiliation(s)
- Darius P Zlotos
- Department of Pharmaceutical Chemistry, Faculty of Pharmacy and Biotechnology, The German University in Cairo, New Cairo City, 11835 Cairo, Egypt.
| | - Yasmine M Mandour
- School of Life and Medical Sciences, University of Hertfordshire hosted by Global Academic Foundation, New Administrative Capital, Cairo, Egypt
| | - Anders A Jensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, DK-2100 Copenhagen, Denmark
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7
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Zhu H, Gouaux E. Architecture and assembly mechanism of native glycine receptors. Nature 2021; 599:513-517. [PMID: 34555840 PMCID: PMC8647860 DOI: 10.1038/s41586-021-04022-z] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2021] [Accepted: 09/15/2021] [Indexed: 02/08/2023]
Abstract
Glycine receptors (GlyRs) are pentameric, 'Cys-loop' receptors that form chloride-permeable channels and mediate fast inhibitory signalling throughout the central nervous system1,2. In the spinal cord and brainstem, GlyRs regulate locomotion and cause movement disorders when mutated2,3. However, the stoichiometry of native GlyRs and the mechanism by which they are assembled remain unclear, despite extensive investigation4-8. Here we report cryo-electron microscopy structures of native GlyRs from pig spinal cord and brainstem, revealing structural insights into heteromeric receptors and their predominant subunit stoichiometry of 4α:1β. Within the heteromeric pentamer, the β(+)-α(-) interface adopts a structure that is distinct from the α(+)-α(-) and α(+)-β(-) interfaces. Furthermore, the β-subunit contains a unique phenylalanine residue that resides within the pore and disrupts the canonical picrotoxin site. These results explain why inclusion of the β-subunit breaks receptor symmetry and alters ion channel pharmacology. We also find incomplete receptor complexes and, by elucidating their structures, reveal the architectures of partially assembled α-trimers and α-tetramers.
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Affiliation(s)
- Hongtao Zhu
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA
| | - Eric Gouaux
- Vollum Institute, Oregon Health and Science University, Portland, OR, USA.
- Howard Hughes Medical Institute, Oregon Health and Science University, Portland, OR, USA.
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8
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Han L, Shan Q. Different Behaviors of a Glycine Receptor Channel Pore Residue between Wild-Type-Mimicking and Disease-Type-Mimicking Formats. ACS Chem Neurosci 2021; 12:3397-3409. [PMID: 34460217 DOI: 10.1021/acschemneuro.1c00386] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The glycine receptor (GlyR) is a neurotransmitter-gated chloride channel that mediates fast inhibitory neurotransmission, predominantly in the spinal cord and brain stem. Mutations of the GlyR are the major cause of hereditary hyperekplexia. Site-specific cysteine substitution followed by labeling with a fluorophore has previously been used to explore the behaviors of the hyperekplexia-related 271 (19') residue of the GlyR. However, this manipulation dramatically compromises sensitivity toward the agonist glycine and alters the pharmacological effects of various agents in manners similar to those of the hyperekplexia-causing R19'Q/L mutations, raising the question whether what is reported by the substituted and modified residue faithfully reflects what actually happens to the wild-type (WT) residue. In this study, a mechanism-rescuing second-site mutation was introduced to create a WT-mimicking GlyR (with the 19' residue cysteine substitution and modification still in place), in which the sensitivity toward glycine and pharmacological effects of various agents were restored. Further experiments revealed stark differences in the behaviors upon the various pharmacological treatments and consequently the underlying mechanisms of the 19' residue between this WT-mimicking GlyR and the GlyR without the mechanism rescue, which is correspondingly defined as the disease-type (DT)-mimicking GlyR. The data presented in this study warn generally that caution is required when attempting to deduce the behaviors of a WT residue from data based on substituted or modified residues that alter protein structure and function. Extra measures, such as rescuing mechanisms via alternative means as presented in this study, are needed to mitigate this challenge.
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Affiliation(s)
- Lu Han
- Zhejiang Key Laboratory of Organ Development and Regeneration, College of Life and Environmental Sciences, Hangzhou Normal University, Hangzhou, Zhejiang 311121, China
| | - Qiang Shan
- Laboratory for Synaptic Plasticity, Shantou University Medical College, Shantou, Guangdong 515041, China
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9
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Yu H, Bai XC, Wang W. Characterization of the subunit composition and structure of adult human glycine receptors. Neuron 2021; 109:2707-2716.e6. [PMID: 34473954 DOI: 10.1016/j.neuron.2021.08.019] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Revised: 07/23/2021] [Accepted: 08/16/2021] [Indexed: 11/27/2022]
Abstract
The strychnine-sensitive pentameric glycine receptor (GlyR) mediates fast inhibitory neurotransmission in the mammalian nervous system. Only heteromeric GlyRs mediate synaptic transmission, as they contain the β subunit that permits clustering at the synapse through its interaction with scaffolding proteins. Here, we show that α2 and β subunits assemble with an unexpected 4:1 stoichiometry to produce GlyR with native electrophysiological properties. We determined structures in multiple functional states at 3.6-3.8 Å resolutions and show how 4:1 stoichiometry is consistent with the structural features of α2β GlyR. Furthermore, we show that one single β subunit in each GlyR gives rise to the characteristic electrophysiological properties of heteromeric GlyR, while more β subunits render GlyR non-conductive. A single β subunit ensures a univalent GlyR-scaffold linkage, which means the scaffold alone regulates the cluster properties.
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Affiliation(s)
- Hailong Yu
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Xiao-Chen Bai
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Weiwei Wang
- Department of Biophysics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
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10
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Tian Y, Chen S, Shan Q. Charged residues at the pore extracellular half of the glycine receptor facilitate channel gating: a potential role played by electrostatic repulsion. J Physiol 2020; 598:4643-4661. [PMID: 32844405 DOI: 10.1113/jp279288] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2019] [Accepted: 07/29/2020] [Indexed: 02/05/2023] Open
Abstract
KEY POINTS The Arg271Gln mutation of the glycine receptor (GlyR) causes hereditary hyperekplexia. This mutation dramatically compromises GlyR function; however, the underlying mechanism is not yet known. This study, by employing function and computation methods, proposes that charged residues (including the Arg residue) at the pore extracellular half from each of the five subunits of the homomeric α1 GlyR, create an electrostatic repulsive potential to widen the pore, thereby facilitating channel opening. This mechanism explains how the Arg271Gln mutation, in which the positively charged Arg residue is substituted by the neutral Gln residue, compromises GlyR function. This study furthers our understanding of the biophysical mechanism underlying the Arg271Gln mutation compromising GlyR function. ABSTRACT The R271(19')Q mutation in the α1 subunit of the glycine receptor (GlyR) chloride channel causes hereditary hyperekplexia. This mutation dramatically compromises channel function; however, the underlying mechanism is not yet known. The R271 residue is located at the extracellular half of the channel pore. In this study, an Arg-scanning mutagenesis was performed at the pore extracellular half from the 262(10') to the 272(20') position on the background of the α1 GlyR carrying the hyperekplexia-causing mutation R271(19')Q. It was found that the placement of the Arg residue rescued channel function to an extent inversely correlated with the distance between the residue and the pore central axis (perpendicular to the plane of the lipid bilayer). Accordingly, it was hypothesized that the placed Arg residues from each of the five subunits of the homomeric α1 GlyR create an electrostatic repulsive potential to widen the pore, thereby facilitating channel opening. This hypothesis was quantitatively verified by theoretical computation via exploiting basic laws of electrostatics and thermodynamics, and further supported by more experimental findings that the placement of another positively charged Lys residue or even a negatively charged Asp residue also rescued channel function in the same manner. This study provides a novel mechanism via which charged residues in the pore region facilitate channel gating, not only for the disease-causing 19'R residue in the GlyR, but also potentially for charged residues in the same region of other ion channels.
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Affiliation(s)
- Yao Tian
- Chern Institute of Mathematics, Nankai University, Tianjin, 300071, China
| | - Shijie Chen
- Laboratory for Synaptic Plasticity, Shantou University Medical College, Shantou, Guangdong, 515041, China
| | - Qiang Shan
- Laboratory for Synaptic Plasticity, Shantou University Medical College, Shantou, Guangdong, 515041, China
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11
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Mechanisms of activation and desensitization of full-length glycine receptor in lipid nanodiscs. Nat Commun 2020; 11:3752. [PMID: 32719334 PMCID: PMC7385131 DOI: 10.1038/s41467-020-17364-5] [Citation(s) in RCA: 54] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Accepted: 06/25/2020] [Indexed: 12/31/2022] Open
Abstract
Glycinergic synapses play a central role in motor control and pain processing in the central nervous system. Glycine receptors (GlyRs) are key players in mediating fast inhibitory neurotransmission at these synapses. While previous high-resolution structures have provided insights into the molecular architecture of GlyR, several mechanistic questions pertaining to channel function are still unanswered. Here, we present Cryo-EM structures of the full-length GlyR protein complex reconstituted into lipid nanodiscs that are captured in the unliganded (closed), glycine-bound (open and desensitized), and allosteric modulator-bound conformations. A comparison of these states reveals global conformational changes underlying GlyR channel gating and modulation. The functional state assignments were validated by molecular dynamics simulations, and the observed permeation events are in agreement with the anion selectivity and conductance of GlyR. These studies provide the structural basis for gating, ion selectivity, and single-channel conductance properties of GlyR in a lipid environment. Glycinergic synapses play a central role in motor control and pain processing in the central nervous system. Here, authors present cryo-EM structures of the full-length glycine receptors (GlyRs) reconstituted into lipid nanodiscs in the unliganded, glycine-bound and allosteric modulator-bound conformations and reveal global conformational changes underlying GlyR channel gating and modulation.
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12
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Identification of N-acyl amino acids that are positive allosteric modulators of glycine receptors. Biochem Pharmacol 2020; 180:114117. [PMID: 32579961 DOI: 10.1016/j.bcp.2020.114117] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Revised: 06/16/2020] [Accepted: 06/18/2020] [Indexed: 01/31/2023]
Abstract
Glycine receptors (GlyRs) mediate inhibitory neurotransmission within the spinal cord and play a crucial role in nociceptive signalling. This makes them primary targets for the development of novel chronic pain therapies. Endogenous lipids have previously been shown to modulate glycine receptors and produce analgesia in pain models, however little is known about what chemical features mediate these effects. In this study, we characterised lipid modulation of GlyRs by screening a library of N-acyl amino acids across all receptor subtypes and determined chemical features crucial for their activity. Acyl-glycine's with a C18 carbon tail were found to produce the greatest potentiation, and require a cis double bond within the central region of the carbon tail (ω6 - ω9) to be active. At 1 µM, C18 ω6,9 glycine potentiated glycine induced currents in α3 and α3β receptors by over 50%, and α1, α2, α1β and α2β receptors by over 100%. C18 ω9 glycine (N-oleoyl glycine) significantly enhance glycine induced peak currents and cause a dose-dependent shift in the glycine concentration response. In the presence of 3 µM C18 ω9 glycine, the EC5o of glycine at the α1 receptor was reduced from 17 µM to 10 µM. This study has identified several acyl-amino acids which are positive allosteric modulators of GlyRs and make promising lead compounds for the development of novel chronic pain therapies.
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13
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Atif M, Lynch JW, Keramidas A. The effects of insecticides on two splice variants of the glutamate-gated chloride channel receptor of the major malaria vector, Anopheles gambiae. Br J Pharmacol 2019; 177:175-187. [PMID: 31479507 DOI: 10.1111/bph.14855] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2019] [Revised: 08/18/2019] [Accepted: 08/27/2019] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND AND PURPOSE Between half to 1 million people die annually from malaria. Anopheles gambiae mosquitoes are major malaria vectors. Unfortunately, resistance has emerged to the agents currently used to control A. gambiae, creating a demand for novel control measures. The pentameric glutamate-gated chloride channel (GluCl) expressed in the muscle and nerve cells of these organisms are a potentially important biological target for malaria control. The pharmacological properties of Anophiline GluCl receptors are, however, largely unknown. Accordingly, we compared the efficacy of four insecticides (lindane, fipronil, picrotoxin, and ivermectin) on two A. gambiae GluCl receptor splice variants with the aim of providing a molecular basis for designing novel anti-malaria treatments. EXPERIMENTAL APPROACH The A. gambiae GluCl receptor b1 and c splice variants were expressed homomerically in Xenopus laevis oocytes and studied with electrophysiological techniques, using two-electrode voltage-clamp. KEY RESULTS The b1 and c GluCl receptors were activated with similar potencies by glutamate and ivermectin. Fipronil was more potent than picrotoxin and lindane at inhibiting glutamate- and ivermectin-gated currents. Importantly, b1 GluCl receptors exhibited reduced sensitivity to picrotoxin and lindane. They also recovered from these effects to a greater extent than c GluCl receptors CONCLUSIONS AND IMPLICATIONS: The two splice variant subunits exhibited differential sensitivities to multiple, structurally divergent insecticides, without accompanying changes in the sensitivity to the endogenous neurotransmitter, glutamate, implying that drug resistance may be caused by alterations in relative subunit expression levels, without affecting physiological function. Our results strongly suggest that it should be feasible to develop novel subunit-specific pharmacological agents.
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Affiliation(s)
- Mohammed Atif
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
| | - Joseph W Lynch
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
| | - Angelo Keramidas
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
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14
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A loss-of-function mutation of an inhibitory zinc- and proton-binding site reduces channel blocker potency in the glycine receptor. Neuropharmacology 2019; 153:121-133. [PMID: 31063738 DOI: 10.1016/j.neuropharm.2019.05.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Revised: 04/16/2019] [Accepted: 05/02/2019] [Indexed: 02/05/2023]
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15
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McLaughlin C, Clements J, Oprişoreanu AM, Sylantyev S. The role of tonic glycinergic conductance in cerebellar granule cell signalling and the effect of gain-of-function mutation. J Physiol 2019; 597:2457-2481. [PMID: 30875431 DOI: 10.1113/jp277626] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Accepted: 03/14/2019] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS A T258F mutation of the glycine receptor increases the receptor affinity to endogenous agonists, modifies single-channel conductance and shapes response decay kinetics. Glycine receptors of cerebellar granule cells play their functional role not continuously, but when the granule cell layer starts receiving a high amount of excitatory inputs. Despite their relative scarcity, tonically active glycine receptors of cerebellar granule cells make a significant impact on action potential generation and inter-neuronal crosstalk, and modulate synaptic plasticity in neural networks; extracellular glycine increases probability of postsynaptic response occurrence acting at NMDA receptors and decreases this probability acting at glycine receptors. Tonic conductance through glycine receptors of cerebellar granule cells is a yet undiscovered element of the biphasic mechanism that regulates processing of sensory inputs in the cerebellum. A T258F point mutation disrupts this biphasic mechanism, thus illustrating the possible role of the gain-of-function mutations of the glycine receptor in development of neural pathologies. ABSTRACT Functional glycine receptors (GlyRs) have been repeatedly detected in cerebellar granule cells (CGCs), where they deliver exclusively tonic inhibitory signals. The functional role of this signalling, however, remains unclear. Apart from that, there is accumulating evidence of the important role of GlyRs in cerebellar structures in development of neural pathologies such as hyperekplexia, which can be triggered by GlyR gain-of-function mutations. In this research we initially tested functional properties of GlyRs, carrying the yet understudied T258F gain-of-function mutation, and found that this mutation makes significant modifications in GlyR response to endogenous agonists. Next, we clarified the role of tonic GlyR conductance in neuronal signalling generated by single CGCs and by neural networks in cell cultures and in living cerebellar tissue of C57Bl-6J mice. We found that GlyRs of CGCs deliver a significant amount of tonic inhibition not continuously, but when the cerebellar granule layer starts receiving substantial excitatory input. Under these conditions tonically active GlyRs become a part of neural signalling machinery allowing generation of action potential (AP) bursts of limited length in response to sensory-evoked signals. GlyRs of CGCs support a biphasic modulatory mechanism which enhances AP firing when excitatory input intensity is low, but suppresses it when excitatory input rises to a certain critical level. This enables one of the key functions of the CGC layer: formation of sensory representations and their translation into motor output. Finally, we have demonstrated that the T258F mutation in CGC GlyRs modifies single-cell and neural network signalling, and breaks a biphasic modulation of the AP-generating machinery.
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Affiliation(s)
- Catherine McLaughlin
- Gene Therapy Group, The Roslin Institute, University of Edinburgh, Easter Bush, Midlothian, EH25 9RG, UK
| | - John Clements
- The John Curtin School of Medical Research, Australian National University, 131 Garran Road, Canberra, ACT 2601, Australia
| | - Ana-Maria Oprişoreanu
- Center for Discovery Brain Sciences, University of Edinburgh, 49 Little France Crescent, Edinburgh, EH16 4SB, UK
| | - Sergiy Sylantyev
- Center for Clinical Brain Sciences, University of Edinburgh, 49 Little France Crescent, Edinburgh, EH16 4SB, UK
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16
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Low SE, Ito D, Hirata H. Characterization of the Zebrafish Glycine Receptor Family Reveals Insights Into Glycine Receptor Structure Function and Stoichiometry. Front Mol Neurosci 2018; 11:286. [PMID: 30323738 PMCID: PMC6130310 DOI: 10.3389/fnmol.2018.00286] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Accepted: 07/30/2018] [Indexed: 11/28/2022] Open
Abstract
To study characterization of zebrafish glycine receptors (zGlyRs), we assessed expression and function of five α- and two ß-subunit encoding GlyR in zebrafish. Our qPCR analysis revealed variable expression during development, while in situ hybridizations uncovered expression in the hindbrain and spinal cord; a finding consistent with the reported expression of GlyR subunits in these tissues from other organisms. Electrophysiological recordings using Xenopus oocytes revealed that all five α subunits form homomeric receptors activated by glycine, and inhibited by strychnine and picrotoxin. In contrast, ß subunits only formed functional heteromeric receptors when co-expressed with α subunits. Curiously, the second transmembranes of both ß subunits were found to lack a phenylalanine at the sixth position that is commonly associated with conferring picrotoxin resistance to heteromeric receptors. Consistent with the absence of phenylalanines at the sixth position, heteromeric zGlyRs often lacked significant picrotoxin resistance. Subsequent efforts revealed that resistance to picrotoxin in both zebrafish and human heteromeric GlyRs involves known residues within transmembrane 2, as well as previously unknown residues within transmembrane 3. We also found that a dominant mutation in human GlyRα1 that gives rise to hyperekplexia, and recessive mutations in zebrafish GlyRßb that underlie the bandoneon family of motor mutants, result in reduced receptor function. Lastly, through the use of a concatenated construct we demonstrate that zebrafish heteromeric receptors assemble with a stoichiometry of 3α:2ß. Collectively, our findings have furthered our knowledge regarding the assembly of heteromeric receptors, and the molecular basis of ß subunit-conferred picrotoxin resistance. These results should aid in future investigations of glycinergic signaling in zebrafish and mammals.
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Affiliation(s)
- Sean Eric Low
- Department of Chemistry and Biological Science, Aoyama Gakuin University, Sagamihara, Japan
| | - Daishi Ito
- Department of Chemistry and Biological Science, Aoyama Gakuin University, Sagamihara, Japan
| | - Hiromi Hirata
- Department of Chemistry and Biological Science, Aoyama Gakuin University, Sagamihara, Japan
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17
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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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18
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Naffaa MM, Hung S, Chebib M, Johnston GAR, Hanrahan JR. GABA-ρ receptors: distinctive functions and molecular pharmacology. Br J Pharmacol 2017; 174:1881-1894. [PMID: 28258627 DOI: 10.1111/bph.13768] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Revised: 02/26/2017] [Accepted: 03/01/2017] [Indexed: 01/14/2023] Open
Abstract
The homomeric GABA-ρ ligand-gated ion channels (also known as GABAC or GABAA -ρ receptors) are similar to heteromeric GABAA receptors in structure, function and mechanism of action. However, their distinctive pharmacological properties and distribution make them of special interest. This review focuses on GABA-ρ ion channel structure, ligand selectivity toward ρ receptors over heteromeric GABAA receptor sub-types and selectivity between different homomeric ρ sub-type receptors. Several GABA analogues show selectivity at homomeric GABA-ρ receptors over heteromeric GABAA receptors. More recently, some synthetic ligands have been found to show selectivity at receptors formed from one ρ subtype over others. The unique pharmacological profiles of these agents are discussed in this review. The classical binding site of GABA within the orthosteric site of GABA-ρ homomeric receptors is discussed in detail regarding the loops and residues that constitute the binding site. The ligand-residue interactions in this classical binding and those of mutant receptors are discussed. The structure and conformations of GABA are discussed in regard to its flexibility and molecular properties. Although the binding mode of GABA is difficult to predict, several interactions between GABA and the receptor assist in predicting its potential conformation and mode of action. The structure-activity relationships of GABA and structurally key ligands at ρ receptors are described and discussed.
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Affiliation(s)
- Moawiah M Naffaa
- Faculty of Pharmacy, University of Sydney, Sydney, NSW, Australia
| | - Sandy Hung
- Faculty of Pharmacy, University of Sydney, Sydney, NSW, Australia
| | - Mary Chebib
- Faculty of Pharmacy, University of Sydney, Sydney, NSW, Australia
| | | | - Jane R Hanrahan
- Faculty of Pharmacy, University of Sydney, Sydney, NSW, Australia
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19
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The binding mode of picrotoxinin in GABA A-ρ receptors: Insight into the subunit's selectivity in the transmembrane domain. Comput Biol Chem 2016; 64:202-209. [PMID: 27423910 DOI: 10.1016/j.compbiolchem.2016.07.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Revised: 05/10/2016] [Accepted: 07/01/2016] [Indexed: 11/24/2022]
Abstract
The channel blocker picrotoxinin has been studied with GABAA-ρ1 and GABAA-ρ2 homology models based on the GluCl crystal structure. Picrotoxinin is tenfold more potent for GABAA-ρ2 than for GABAA-ρ1 homomeric channels. This intra-subunit selectivity arises from the unconserved residues at the 2' sites, which are the essential molecular basis for both the binding and potency of picrotoxinin. The serine residues at the 2' positions of the ρ2 channel are predicted to form multiple hydrogen bonds and hydrophobic interactions with picrotoxinin, whereas the proline residues in the 2' positions of ρ1 channels are predicted to form only hydrophobic contacts with picrotoxinin. However, although the studied ρ1 P2'G, A, and V models form no hydrogen bonds with picrotoxinin, they may participate in several hydrophobic interactions, and the ligand may have distinctive binding modes with GABAA-ρ mutant channels. Picrotoxinin has a lower Emodel value with ρ2 than ρ1 homomeric models (-47Kcal/mol and -36Kcal/mol, respectively), suggesting that picrotoxin blocks the pores of the ρ2 channels more effectively.
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20
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Lara CO, Murath P, Muñoz B, Marileo AM, Martín LS, San Martín VP, Burgos CF, Mariqueo TA, Aguayo LG, Fuentealba J, Godoy P, Guzman L, Yévenes GE. Functional modulation of glycine receptors by the alkaloid gelsemine. Br J Pharmacol 2016; 173:2263-77. [PMID: 27128379 DOI: 10.1111/bph.13507] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Revised: 04/12/2016] [Accepted: 04/18/2016] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND AND PURPOSE Gelsemine is one of the principal alkaloids produced by the Gelsemium genus of plants belonging to the Loganiaceae family. The extracts of these plants have been used for many years, for a variety of medicinal purposes. Coincidentally, recent studies have shown that gelsemine exerts anxiolytic and analgesic effects on behavioural models. Several lines of evidence have suggested that these beneficial actions were dependent on glycine receptors, which are inhibitory neurotransmitter-gated ion channels of the CNS. However, it is currently unknown whether gelsemine can directly modulate the function of glycine receptors. EXPERIMENTAL APPROACH We examined the functional effects of gelsemine on glycine receptors expressed in transfected HEK293 cells and in cultured spinal neurons by electrophysiological techniques. KEY RESULTS Gelsemine directly modulated recombinant and native glycine receptors and exerted conformation-specific and subunit-selective effects. Gelsemine modulation was voltage-independent and was associated with differential changes in the apparent affinity for glycine and in the open probability of the ion channel. In addition, the alkaloid preferentially targeted glycine receptors in spinal neurons and showed only minor effects on GABAA and AMPA receptors. Furthermore, gelsemine significantly diminished the frequency of glycinergic and glutamatergic synaptic events without altering the amplitude. CONCLUSIONS AND IMPLICATIONS Our results provide a pharmacological basis to explain, at least in part, the glycine receptor-dependent, beneficial and toxic effects of gelsemine in animals and humans. In addition, the pharmacological profile of gelsemine may open new approaches to the development of subunit-selective modulators of glycine receptors.
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Affiliation(s)
- Cesar O Lara
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Chile
| | - Pablo Murath
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Chile
| | - Braulio Muñoz
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Chile
| | - Ana M Marileo
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Chile
| | - Loreto San Martín
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Chile
| | - Victoria P San Martín
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Chile
| | - Carlos F Burgos
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Chile
| | | | - Luis G Aguayo
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Chile
| | - Jorge Fuentealba
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Chile
| | - Patricio Godoy
- IfADo-Leibniz Research Centre for Working Environment and Human Factors at the Technical University Dortmund, Dortmund, Germany
| | - Leonardo Guzman
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Chile
| | - Gonzalo E Yévenes
- Department of Physiology, Faculty of Biological Sciences, University of Concepcion, Chile
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21
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Transcriptome Analysis of the Central and Peripheral Nervous Systems of the Spider Cupiennius salei Reveals Multiple Putative Cys-Loop Ligand Gated Ion Channel Subunits and an Acetylcholine Binding Protein. PLoS One 2015; 10:e0138068. [PMID: 26368804 PMCID: PMC4569296 DOI: 10.1371/journal.pone.0138068] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2015] [Accepted: 08/25/2015] [Indexed: 11/19/2022] Open
Abstract
Invertebrates possess a diverse collection of pentameric Cys-loop ligand gated ion channel (LGIC) receptors whose molecular structures, evolution and relationships to mammalian counterparts have been intensely investigated in several clinically and agriculturally important species. These receptors are targets for a variety of control agents that may also harm beneficial species. However, little is known about Cys-loop receptors in spiders, which are important natural predators of insects. We assembled de novo transcriptomes from the central and peripheral nervous systems of the Central American wandering spider Cupiennius salei, a model species for neurophysiological, behavioral and developmental studies. We found 15 Cys-loop receptor subunits that are expected to form anion or cation permeable channels, plus a putative acetylcholine binding protein (AChBP) that has only previously been reported in molluscs and one annelid. We used phylogenetic and sequence analysis to compare the spider subunits to homologous receptors in other species and predicted the 3D structures of each protein using the I-Tasser server. The quality of homology models improved with increasing sequence identity to the available high-resolution templates. We found that C. salei has orthologous γ-aminobutyric acid (GABA), GluCl, pHCl, HisCl and nAChα LGIC subunits to other arthropods, but some subgroups are specific to arachnids, or only to spiders. C. salei sequences were phylogenetically closest to gene fragments from the social spider, Stegodyphus mimosarum, indicating high conservation within the Araneomorphae suborder of spiders. C. salei sequences had similar ligand binding and transmembrane regions to other invertebrate and vertebrate LGICs. They also had motifs associated with high sensitivity to insecticides and antiparasitic agents such as fipronil, dieldrin and ivermectin. Development of truly selective control agents for pest species will require information about the molecular structure and pharmacology of Cys-loop receptors in beneficial species.
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22
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Burgos CF, Muñoz B, Guzman L, Aguayo LG. Ethanol effects on glycinergic transmission: From molecular pharmacology to behavior responses. Pharmacol Res 2015; 101:18-29. [PMID: 26158502 DOI: 10.1016/j.phrs.2015.07.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2015] [Revised: 07/01/2015] [Accepted: 07/01/2015] [Indexed: 10/23/2022]
Abstract
It is well accepted that ethanol is able to produce major health and economic problems associated to its abuse. Because of its intoxicating and addictive properties, it is necessary to analyze its effect in the central nervous system. However, we are only now learning about the mechanisms controlling the modification of important membrane proteins such as ligand-activated ion channels by ethanol. Furthermore, only recently are these effects being correlated to behavioral changes. Current studies show that the glycine receptor (GlyR) is a susceptible target for low concentrations of ethanol (5-40mM). GlyRs are relevant for the effects of ethanol because they are found in the spinal cord and brain stem where they primarily express the α1 subunit. More recently, the presence of GlyRs was described in higher regions, such as the hippocampus and nucleus accumbens, with a prevalence of α2/α3 subunits. Here, we review data on the following aspects of ethanol effects on GlyRs: (1) direct interaction of ethanol with amino acids in the extracellular or transmembrane domains, and indirect mechanisms through the activation of signal transduction pathways; (2) analysis of α2 and α3 subunits having different sensitivities to ethanol which allows the identification of structural requirements for ethanol modulation present in the intracellular domain and C-terminal region; (3) Genetically modified knock-in mice for α1 GlyRs that have an impaired interaction with G protein and demonstrate reduced ethanol sensitivity without changes in glycinergic transmission; and (4) GlyRs as potential therapeutic targets.
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Affiliation(s)
- Carlos F Burgos
- Laboratory of Neurophysiology, Department of Physiology, University of Concepción, Chile
| | - Braulio Muñoz
- Laboratory of Neurophysiology, Department of Physiology, University of Concepción, Chile
| | - Leonardo Guzman
- Laboratory of Molecular Neurobiology, Department of Physiology, University of Concepción, Chile
| | - Luis G Aguayo
- Laboratory of Neurophysiology, Department of Physiology, University of Concepción, Chile.
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23
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Price KL, Lummis SCR. An atypical residue in the pore of Varroa destructor GABA-activated RDL receptors affects picrotoxin block and thymol modulation. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2014; 55:19-25. [PMID: 25460510 PMCID: PMC4261083 DOI: 10.1016/j.ibmb.2014.10.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2014] [Revised: 10/08/2014] [Accepted: 10/10/2014] [Indexed: 05/16/2023]
Abstract
GABA-activated RDL receptors are the insect equivalent of mammalian GABAA receptors, and play a vital role in neurotransmission and insecticide action. Here we clone the pore lining M2 region of the Varroa mite RDL receptor and show that it has 4 atypical residues when compared to M2 regions of most other insects, including bees, which are the major host of Varroa mites. We create mutant Drosophila RDL receptors containing these substitutions and characterise their effects on function. Using two electrode voltage clamp electrophysiology we show that one substitution (T6'M) ablates picrotoxin inhibition and increases the potency of GABA. This mutation also alters the effect of thymol, which enhances both insect and mammalian GABA responses, and is widely used as a miticide. Thymol decreases the GABA EC50 of WT receptors, enhancing responses, but in T6'M-containing receptors it is inhibitory. The other 3 atypical residues have no major effects on either the GABA EC50, the picrotoxin potency or the effect of thymol. In conclusion we show that the RDL 6' residue is important for channel block, activation and modulation, and understanding its function also has the potential to prove useful in the design of Varroa-specific insecticidal agents.
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Affiliation(s)
- Kerry L Price
- Department of Biochemistry, University of Cambridge, Cambridge, CB2 1QW, UK
| | - Sarah C R Lummis
- Department of Biochemistry, University of Cambridge, Cambridge, CB2 1QW, UK.
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24
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Flores-Fernández JM, Gutiérrez-Ortega A, Padilla-Camberos E, Rosario-Cruz R, Hernández-Gutiérrez R, Martínez-Velázquez M. Molecular cloning and characterization of a glycine-like receptor gene from the cattle tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae). Parasite 2014; 21:43. [PMID: 25174962 PMCID: PMC4150426 DOI: 10.1051/parasite/2014047] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Accepted: 08/15/2014] [Indexed: 11/18/2022] Open
Abstract
The cattle tick Rhipicephalus (Boophilus) microplus is the most economically important ectoparasite affecting the cattle industry in tropical and subtropical areas around the world. The principal method of tick control has relied mainly on the use of chemical acaricides, including ivermectin; however, cattle tick populations resistant to ivermectin have recently been reported in Brazil, Mexico, and Uruguay. Currently, the molecular basis for ivermectin susceptibility and resistance are not well understood in R. microplus. This prompted us to search for potential molecular targets for ivermectin. Here, we report the cloning and molecular characterization of a R. microplus glycine-like receptor (RmGlyR) gene. The characterized mRNA encodes for a 464-amino acid polypeptide, which contains features common to ligand-gated ion channels, such as a large N-terminal extracellular domain, four transmembrane domains, a large intracellular loop and a short C-terminal extracellular domain. The deduced amino acid sequence showed around 30% identity to GlyRs from some invertebrate and vertebrate organisms. The polypeptide also contains the PAR motif, which is important for forming anion channels, and a conserved glycine residue at the third transmembrane domain, which is essential for high ivermectin sensitivity. PCR analyses showed that RmGlyR is expressed at egg, larval and adult developmental stages. Our findings suggest that the deduced receptor is an additional molecular target to ivermectin and it might be involved in ivermectin resistance in R. microplus.
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Affiliation(s)
- José Miguel Flores-Fernández
- Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, AC, Av. Normalistas 800, Col. Colinas de la Normal, 44270 Guadalajara, Jalisco, México
| | - Abel Gutiérrez-Ortega
- Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, AC, Av. Normalistas 800, Col. Colinas de la Normal, 44270 Guadalajara, Jalisco, México
| | - Eduardo Padilla-Camberos
- Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, AC, Av. Normalistas 800, Col. Colinas de la Normal, 44270 Guadalajara, Jalisco, México
| | - Rodrigo Rosario-Cruz
- Centro Nacional de Investigaciones en Parasitología Veterinaria-INIFAP, Carretera Federal Cuernavaca Cuautla No. 8534, Colonia Progreso, 62550 Jiutepec, Morelos, México
| | - Rodolfo Hernández-Gutiérrez
- Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, AC, Av. Normalistas 800, Col. Colinas de la Normal, 44270 Guadalajara, Jalisco, México
| | - Moisés Martínez-Velázquez
- Centro de Investigación y Asistencia en Tecnología y Diseño del Estado de Jalisco, AC, Av. Normalistas 800, Col. Colinas de la Normal, 44270 Guadalajara, Jalisco, México
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25
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Schaefer N, Langlhofer G, Kluck CJ, Villmann C. Glycine receptor mouse mutants: model systems for human hyperekplexia. Br J Pharmacol 2014; 170:933-52. [PMID: 23941355 DOI: 10.1111/bph.12335] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Revised: 07/19/2013] [Accepted: 08/02/2013] [Indexed: 11/30/2022] Open
Abstract
Human hyperekplexia is a neuromotor disorder caused by disturbances in inhibitory glycine-mediated neurotransmission. Mutations in genes encoding for glycine receptor subunits or associated proteins, such as GLRA1, GLRB, GPHN and ARHGEF9, have been detected in patients suffering from hyperekplexia. Classical symptoms are exaggerated startle attacks upon unexpected acoustic or tactile stimuli, massive tremor, loss of postural control during startle and apnoea. Usually patients are treated with clonazepam, this helps to dampen the severe symptoms most probably by up-regulating GABAergic responses. However, the mechanism is not completely understood. Similar neuromotor phenotypes have been observed in mouse models that carry glycine receptor mutations. These mouse models serve as excellent tools for analysing the underlying pathomechanisms. Yet, studies in mutant mice looking for postsynaptic compensation of glycinergic dysfunction via an up-regulation in GABAA receptor numbers have failed, as expression levels were similar to those in wild-type mice. However, presynaptic adaptation mechanisms with an unusual switch from mixed GABA/glycinergic to GABAergic presynaptic terminals have been observed. Whether this presynaptic adaptation explains the improvement in symptoms or other compensation mechanisms exist is still under investigation. With the help of spontaneous glycine receptor mouse mutants, knock-in and knock-out studies, it is possible to associate behavioural changes with pharmacological differences in glycinergic inhibition. This review focuses on the structural and functional characteristics of the various mouse models used to elucidate the underlying signal transduction pathways and adaptation processes and describes a novel route that uses gene-therapeutic modulation of mutated receptors to overcome loss of function mutations.
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Affiliation(s)
- Natascha Schaefer
- Institute for Clinical Neurobiology, Julius-Maximilians-University of Würzburg, Würzburg, Germany
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26
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Abstract
Picrotoxin is a pore blocker that can differentiate ligand-gated inhibitory chloride channels. Even within one receptor type, such as the glycine receptor, picrotoxin block differs between subunits. The effect of subunit gating properties on block of the inhibitory glycine receptor (GlyR) was explored using heteromeric α subunit expression in voltage-clamped HEK293 cells. The α2 GlyR is more sensitive to picrotin block than the α1 GlyR, and this difference was used to explore whether mutations that interfered with gating of the α2 subunit would also interfere with picrotin block. Two mutations were used: one that decreased the glycine sensitivity of α2 by almost two log units and the other that was unresponsive to glycine. In both cases, the sensitivity to picrotin was essentially unaltered. The results indicated that α2 subunits can determine the picrotin sensitivity of α1α2-heteromeric receptors and that direct gating of the α2 subunit is not required for this picrotin inhibition.
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27
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Lemoine D, Jiang R, Taly A, Chataigneau T, Specht A, Grutter T. Ligand-gated ion channels: new insights into neurological disorders and ligand recognition. Chem Rev 2012; 112:6285-318. [PMID: 22988962 DOI: 10.1021/cr3000829] [Citation(s) in RCA: 115] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Damien Lemoine
- Laboratoire de Biophysicochimie des Récepteurs Canaux, UMR 7199 CNRS, Conception et Application de Molécules Bioactives, Faculté de Pharmacie, Université de Strasbourg , 67400 Illkirch, France
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Islam R, Lynch JW. Mechanism of action of the insecticides, lindane and fipronil, on glycine receptor chloride channels. Br J Pharmacol 2012; 165:2707-20. [PMID: 22035056 DOI: 10.1111/j.1476-5381.2011.01722.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND AND PURPOSE Docking studies predict that the insecticides, lindane and fipronil, block GABA(A) receptors by binding to 6' pore-lining residues. However, this has never been tested at any Cys-loop receptor. The neurotoxic effects of these insecticides are also thought to be mediated by GABA(A) receptors, although a recent morphological study suggested glycine receptors mediated fipronil toxicity in zebrafish. Here we investigated whether human α1, α1β, α2 and α3 glycine receptors were sufficiently sensitive to block by either compound as to represent possible neurotoxicity targets. We also investigated the mechanisms by which lindane and fipronil inhibit α1 glycine receptors. EXPERIMENTAL APPROACH Glycine receptors were recombinantly expressed in HEK293 cells and insecticide effects were studied using patch-clamp electrophysiology. KEY RESULTS Both compounds completely inhibited all tested glycine receptor subtypes with IC(50) values ranging from 0.2-2 µM, similar to their potencies at vertebrate GABA(A) receptors. Consistent with molecular docking predictions, both lindane and fipronil interacted with 6' threonine residues via hydrophobic interactions and hydrogen bonds. In contrast with predictions, we found no evidence for lindane interacting at the 2' level. We present evidence for fipronil binding in a non-blocking mode in the anaesthetic binding pocket, and for lindane as an excellent pharmacological tool for identifying the presence of β subunits in αβ heteromeric glycine receptors. CONCLUSIONS AND IMPLICATIONS This study implicates glycine receptors as novel vertebrate toxicity targets for fipronil and lindane. Furthermore, lindane interacted with pore-lining 6' threonine residues, whereas fipronil may have both pore and non-pore binding sites.
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Affiliation(s)
- Robiul Islam
- Queensland Brain Institute, The University of Queensland, Brisbane, Queensland, Australia
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Shan Q, Han L, Lynch JW. Function of hyperekplexia-causing α1R271Q/L glycine receptors is restored by shifting the affected residue out of the allosteric signalling pathway. Br J Pharmacol 2012; 165:2113-23. [PMID: 21955162 DOI: 10.1111/j.1476-5381.2011.01701.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND AND PURPOSE Glycine receptor α1 subunit R271Q and R271L (α1R271Q/L) mutations cause the neuromotor disorder, hereditary hyperekplexia. Studies suggest that the 271 residue is located within the allosteric signalling pathway linking the agonist binding site to the channel gate. The present study aimed to investigate a possible mechanism for restoring the function of the α1R271Q/L glycine receptor. EXPERIMENTAL APPROACH A 12-amino-acid segment incorporating the 271 residue on the glycine receptor α1271Q/L subunit was replaced by the homologous segment from the glycine receptor β subunit (α1(Ch) 271Q/L). The function of the α1(Ch) 271Q/L glycine receptor was examined by whole-cell patch-clamp recording and voltage-clamp fluorometry techniques. KEY RESULTS The function of the α1(Ch) 271Q/L glycine receptor was restored to the level of the wild-type (WT) α1 glycine receptor. Moreover, in the α1(Ch) glycine receptor, in contrast to the α1 glycine receptor, the channel function was not sensitive to various substitutions of the 271 residue, and the conformational change in the vicinity of the 271 residue was uncoupled from the channel gating. CONCLUSIONS AND IMPLICATIONS The 271 residue is shifted out of the allosteric signalling pathway in the α1(Ch) glycine receptor. We propose that this mechanism provides a novel drug design strategy not only for glycine receptor α1R271Q/L-caused hereditary hyperekplexia, but also for any pathological condition that is caused by missense mutation- or covalent modification-induced disorders involving residues in allosteric signalling pathways. Such a strategy makes it possible to design an ideal drug, which only corrects the function of the mutant or modified protein without affecting the WT or naive protein.
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Affiliation(s)
- Qiang Shan
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia.
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Shan Q, Han L, Lynch JW. Distinct properties of glycine receptor β+/α- interface: unambiguously characterizing heteromeric interface reconstituted in homomeric protein. J Biol Chem 2012; 287:21244-52. [PMID: 22535951 DOI: 10.1074/jbc.m111.337741] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The glycine receptor (GlyR) exists either in homomeric α or heteromeric αβ forms. Its agonists bind at extracellular subunit interfaces. Unlike subunit interfaces from the homomeric α GlyR, subunit interfaces from the heteromeric αβ GlyR have not been characterized unambiguously because of the existence of multiple types of interface within single receptors. Here, we report that, by reconstituting β+/α- interfaces in a homomeric GlyR (αChb+a- GlyR), we were able to functionally characterize the αβ GlyR β+/α- interfaces. We found that the β+/α- interface had a higher agonist sensitivity than that of the α+/α- interface. This high sensitivity was contributed primarily by loop A. We also found that the β+/α- interface differentially modulates the agonist properties of glycine and taurine. Using voltage clamp fluorometry, we found that the conformational changes induced by glycine binding to the β+/α- interface were different from those induced by glycine binding to the α+/α- interface in the α GlyR. Moreover, the distinct conformational changes found at the β+/α- interface in the αChb+a- GlyR were also found in the heteromeric αβ GlyR, which suggests that the αChb+a- GlyR reconstitutes structural components and recapitulates functional properties, of the β+/α- interface in the heteromeric αβ GlyR. Our investigation not only provides structural and functional information about the GlyR β+/α- interface, which could direct GlyR β+/α- interface-specific drug design, but also provides a general methodology for unambiguously characterizing properties of specific protein interfaces from heteromeric proteins.
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Affiliation(s)
- Qiang Shan
- Brain and Mind Research Institute, University of Sydney, Sydney, New South Wales 2050, Australia.
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Shan Q, Lynch JW. Incompatibility between a pair of residues from the pre-M1 linker and Cys-loop blocks surface expression of the glycine receptor. J Biol Chem 2012; 287:7535-42. [PMID: 22267740 DOI: 10.1074/jbc.m111.325126] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Regulation of cell membrane excitability can be achieved either by modulating the functional properties of cell membrane-expressed single channels or by varying the number of expressed channels. Whereas the structural basis underlying single channel properties has been intensively studied, the structural basis contributing to surface expression is less well characterized. Here we demonstrate that homologous substitution of the pre-M1 linker from the β subunit prevents surface expression of the α1 glycine receptor chloride channel. By investigating a series of chimeras comprising α1 and β subunits, we hypothesized that this effect was due to incompatibility between a pair of positively charged residues, which lie in close proximity to each other in the tertiary structure, from the pre-M1 linker and Cys-loop. Abolishing either positive charge restored surface expression. We propose that incompatibility (electrostatic repulsion) between this pair of residues misfolds the glycine receptor, and in consequence, the protein is retained in the cytoplasm and prevented from surface expression by the quality control machinery. This hypothesis suggests a novel mechanism, i.e. residue incompatibility, for explaining the mutation-induced reduction in channel surface expression, often present in the cases of hereditary hyperekplexia.
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Affiliation(s)
- Qiang Shan
- Brain and Mind Research Institute, University of Sydney, Sydney, New South Wales, 2050 Australia.
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Shan Q, Han L, Lynch JW. β Subunit M2-M3 loop conformational changes are uncoupled from α1 β glycine receptor channel gating: implications for human hereditary hyperekplexia. PLoS One 2011; 6:e28105. [PMID: 22132222 PMCID: PMC3222680 DOI: 10.1371/journal.pone.0028105] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Accepted: 11/01/2011] [Indexed: 01/30/2023] Open
Abstract
Hereditary hyperekplexia, or startle disease, is a neuromotor disorder caused mainly by mutations that either prevent the surface expression of, or modify the function of, the human heteromeric α1 β glycine receptor (GlyR) chloride channel. There is as yet no explanation as to why hyperekplexia mutations that modify channel function are almost exclusively located in the α1 to the exclusion of β subunit. The majority of these mutations are identified in the M2–M3 loop of the α1 subunit. Here we demonstrate that α1 β GlyR channel function is less sensitive to hyperekplexia-mimicking mutations introduced into the M2–M3 loop of the β than into the α1 subunit. This suggests that the M2–M3 loop of the α subunit dominates the β subunit in gating the α1 β GlyR channel. A further attempt to determine the possible mechanism underlying this phenomenon by using the voltage-clamp fluorometry technique revealed that agonist-induced conformational changes in the β subunit M2–M3 loop were uncoupled from α1 β GlyR channel gating. This is in contrast to the α subunit, where the M2–M3 loop conformational changes were shown to be directly coupled to α1 β GlyR channel gating. Finally, based on analysis of α1 β chimeric receptors, we demonstrate that the structural components responsible for this are distributed throughout the β subunit, implying that the β subunit has evolved without the functional constraint of a normal gating pathway within it. Our study provides a possible explanation of why hereditary hyperekplexia-causing mutations that modify α1 β GlyR channel function are almost exclusively located in the α1 to the exclusion of the β subunit.
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Affiliation(s)
- Qiang Shan
- Queensland Brain Institute, University of Queensland, Brisbane, Queensland, Australia.
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Thompson AJ, Duke RK, Lummis SCR. Binding sites for bilobalide, diltiazem, ginkgolide, and picrotoxinin at the 5-HT3 receptor. Mol Pharmacol 2011; 80:183-90. [PMID: 21505038 PMCID: PMC3127528 DOI: 10.1124/mol.111.071415] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2011] [Accepted: 04/18/2011] [Indexed: 11/22/2022] Open
Abstract
Bilobalide (BB), ginkgolide B (GB), diltiazem (DTZ), and picrotoxinin (PXN) are 5-hydroxytryptamine type 3 (5-HT(3)) receptor antagonists in which the principal sites of action are in the channel. To probe their exact binding locations, 5-HT(3) receptors with substitutions in their pore lining residues were constructed (N-4'Q, E-1'D, S2'A, T6'S, L7'T, L9'V, S12'A, I16'V, D20'E), expressed in Xenopus laevis oocytes, and the effects of the compounds on 5-HT-induced currents were examined. EC(50) values at mutant receptors were less than 6-fold different from those of wild type, indicating that the mutations were well tolerated. BB, GB, DTZ, and PXN had pIC(50) values of 3.33, 3.14, 4.67, and 4.97, respectively. Inhibition by BB and GB was abolished in mutant receptors containing T6'S and S12'A substitutions, but their potencies were enhanced (42- and 125-fold, respectively) in S2'A mutant receptors. S2'A substitution also caused GB ligand trap. PXN potency was modestly enhanced (5-fold) in S2'A, abolished in T6'S, and reduced in L9'V (40-fold) and S12'A (7-fold) receptors. DTZ potency was reduced in L7'T and S12'A receptors (5-fold), and DTZ also displaced [(3)H]granisetron binding, indicating mixed competitive/noncompetitive inhibition. We conclude that regions close to the hydrophobic gate of M2 are important for the inhibitory effects of BB, GB, DTZ, and PXN at the 5-HT(3) receptor; for BB, GB, and PXN, the data show that the 6' channel lining residue is their major site of action, with minor roles for 2', 9', and 12' residues, whereas for DTZ, the 7' and 12' sites are important.
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Affiliation(s)
- A J Thompson
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
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Abstract
Cys-loop receptors are membrane-spanning neurotransmitter-gated ion channels that are responsible for fast excitatory and inhibitory transmission in the peripheral and central nervous systems. The best studied members of the Cys-loop family are nACh, 5-HT3, GABAA and glycine receptors. All these receptors share a common structure of five subunits, pseudo-symmetrically arranged to form a rosette with a central ion-conducting pore. Some are cation selective (e.g. nACh and 5-HT3) and some are anion selective (e.g. GABAA and glycine). Each receptor has an extracellular domain (ECD) that contains the ligand-binding sites, a transmembrane domain (TMD) that allows ions to pass across the membrane, and an intracellular domain (ICD) that plays a role in channel conductance and receptor modulation. Cys-loop receptors are the targets for many currently used clinically relevant drugs (e.g. benzodiazepines and anaesthetics). Understanding the molecular mechanisms of these receptors could therefore provide the catalyst for further development in this field, as well as promoting the development of experimental techniques for other areas of neuroscience.In this review, we present our current understanding of Cys-loop receptor structure and function. The ECD has been extensively studied. Research in this area has been stimulated in recent years by the publication of high-resolution structures of nACh receptors and related proteins, which have permitted the creation of many Cys loop receptor homology models of this region. Here, using the 5-HT3 receptor as a typical member of the family, we describe how homology modelling and ligand docking can provide useful but not definitive information about ligand interactions. We briefly consider some of the many Cys-loop receptors modulators. We discuss the current understanding of the structure of the TMD, and how this links to the ECD to allow channel gating, and consider the roles of the ICD, whose structure is poorly understood. We also describe some of the current methods that are beginning to reveal the differences between different receptor states, and may ultimately show structural details of transitions between them.
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Abstract
Hyperekplexia is a rare, but potentially fatal, neuromotor disorder characterized by exaggerated startle reflexes and hypertonia in response to sudden, unexpected auditory or tactile stimuli. This disorder is primarily caused by inherited mutations in the genes encoding the glycine receptor (GlyR) alpha1 subunit (GLRA1) and the presynaptic glycine transporter GlyT2 (SLC6A5). In this study, systematic DNA sequencing of GLRA1 in 88 new unrelated human hyperekplexia patients revealed 19 sequence variants in 30 index cases, of which 21 cases were inherited in recessive or compound heterozygote modes. This indicates that recessive hyperekplexia is far more prevalent than previous estimates. From the 19 GLRA1 sequence variants, we have investigated the functional effects of 11 novel and 2 recurrent mutations. The expression levels and functional properties of these hyperekplexia mutants were analyzed using a high-content imaging system and patch-clamp electrophysiology. When expressed in HEK293 cells, either as homomeric alpha1 or heteromeric alpha1beta GlyRs, subcellular localization defects were the major mechanism underlying recessive mutations. However, mutants without trafficking defects typically showed alterations in the glycine sensitivity suggestive of disrupted receptor function. This study also reports the first hyperekplexia mutation associated with a GlyR leak conductance, suggesting tonic channel opening as a new mechanism in neuronal ligand-gated ion channels.
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36
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Jensen AA, Bergmann ML, Sander T, Balle T. Ginkgolide X is a potent antagonist of anionic Cys-loop receptors with a unique selectivity profile at glycine receptors. J Biol Chem 2010; 285:10141-10153. [PMID: 20106969 DOI: 10.1074/jbc.m109.079319] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The novel ginkgolide analog ginkgolide X was characterized functionally at human glycine and gamma-aminobutyric acid type A receptors (GlyRs and GABA(A)Rs, respectively) in the fluorescence-based FLIPR(TM) Membrane Potential assay. The compound inhibited the signaling of all GABA(A)R subtypes included in the study with high nanomolar/low micromolar IC(50) values, except the rho 1 receptor at which it was a significantly weaker antagonist. Ginkgolide X also displayed high nanomolar/low micromolar IC(50) values at the homomeric alpha1 and alpha2 GlyRs, whereas it was inactive at the heteromeric alpha 1 beta and alpha 2 beta subtypes at concentrations up to 300 microm. Thus, the functional properties of the compound were significantly different from those of the naturally occurring ginkgolides A, B, C, J, and M but similar to those of picrotoxin. In a mutagenesis study the 6' M2 residues in the GlyR ion channel were identified as the primary molecular determinant of the selectivity profile of ginkgolide X, and a 6' M2 ring consisting of five Thr residues was found to be of key importance for its activity at the GABA(A)R. Conformational analysis and docking of low-energy conformations of the native ginkgolide A and ginkgolide X into a alpha1 GlyR homology model revealed two distinct putative binding sites formed by the 6' M2 residues together with the 2' residues and the 10' and 13' residues, respectively. Thus, we propose that the distinct functionalities of ginkgolide X compared with the other ginkgolides could arise from different flexibility and thus different binding modes to the ion channel of the anionic Cys-loop receptor.
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Affiliation(s)
- Anders A Jensen
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
| | - Marianne L Bergmann
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
| | - Tommy Sander
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
| | - Thomas Balle
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
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37
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Hernandes MS, Troncone LRP. Glycine as a neurotransmitter in the forebrain: a short review. J Neural Transm (Vienna) 2009; 116:1551-60. [DOI: 10.1007/s00702-009-0326-6] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2009] [Accepted: 09/20/2009] [Indexed: 11/30/2022]
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38
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Pore Structure of the Cys-loop Ligand-gated Ion Channels. Neurochem Res 2009; 34:1805-15. [DOI: 10.1007/s11064-009-9971-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2009] [Accepted: 04/03/2009] [Indexed: 11/26/2022]
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Chen X, Cromer B, Webb TI, Yang Z, Hantke J, Harvey RJ, Parker MW, Lynch JW. Dihydropyridine inhibition of the glycine receptor: subunit selectivity and a molecular determinant of inhibition. Neuropharmacology 2008; 56:318-27. [PMID: 18657556 DOI: 10.1016/j.neuropharm.2008.07.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2008] [Revised: 06/24/2008] [Accepted: 07/01/2008] [Indexed: 01/29/2023]
Abstract
The dihydropyridines (DHPs), nifedipine and nicardipine, modulate native glycine receptors (GlyRs) at micromolar concentrations. Nicardipine has a biphasic potentiating and inhibitory effect, whereas nifedipine causes inhibition only. The present study sought to investigate (1) the molecular mechanism by which these compounds inhibit recombinant GlyRs, and (2) their potential utility as subunit-selective inhibitors of alpha1, alpha1beta, alpha3 and alpha3beta GlyRs. The rate of onset of inhibition in the open state was accelerated by pre-application of DHP in the closed state, with the degree of acceleration proportional to the concentration of pre-applied DHP. This implies a non-inhibitory binding site close to the DHP inhibitory site. DHP inhibition was use-dependent and independent of glycine concentration, consistent with a pore-blocking mode of action. DHP sensitivity was abolished by the G2'A mutation, providing a strong case for a DHP binding site in the pore. Nifedipine exhibited an approximately 10-fold higher inhibitory potency at alpha1-containing relative to alpha3-containing receptors, whereas nicardipine was only weakly selective for alpha1-containing GlyRs. The differential sensitivities of nifedipine and nicardipine for different GlyR isoforms suggest that DHPs may be a useful resource to screen as pharmacological tools for selectively inhibiting different synaptic GlyR isoforms.
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Affiliation(s)
- Xuebin Chen
- School of Biomedical Sciences and Queensland Brain Institute, University of Queensland, Brisbane, QLD 4072, Australia
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40
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Erkkila BE, Sedelnikova AV, Weiss DS. Stoichiometric pore mutations of the GABAAR reveal a pattern of hydrogen bonding with picrotoxin. Biophys J 2008; 94:4299-306. [PMID: 18310243 PMCID: PMC2480680 DOI: 10.1529/biophysj.107.118455] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2007] [Accepted: 01/22/2008] [Indexed: 11/18/2022] Open
Abstract
Picrotoxin (PTX) is a noncompetitive antagonist of many ligand-gated ion channels, with a site of action believed to be within the ion-conducting pore. In the A-type gamma-aminobutyric acid receptor, a threonine residue in the second transmembrane domain is of particular importance for the binding of, and ultimate inhibition by, PTX. To better understand the relationship between this residue and the PTX molecule, we mutated this threonine residue to serine, valine, and tyrosine to change the structural and biochemical characteristics at this location. The known subunit stoichiometry of the A-type gamma-aminobutyric acid receptor allowed us to create receptors with anywhere from zero to five mutations. With an increasing number of mutated subunits, each amino acid substitution revealed a unique pattern of changes in PTX sensitivity, ultimately encompassing sensitivity shifts over several orders of magnitude. The electrophysiological data on PTX-mediated block, and supporting modeling and docking studies, provide evidence that an interaction between the PTX molecule and three adjacent uncharged polar amino acids at this position of the pore are crucial for PTX-mediated inhibition.
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Affiliation(s)
- Brian E Erkkila
- Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA
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Li P, Slaughter M. Glycine receptor subunit composition alters the action of GABA antagonists. Vis Neurosci 2007; 24:513-21. [PMID: 17659095 DOI: 10.1017/s0952523807070368] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2007] [Accepted: 04/11/2007] [Indexed: 11/07/2022]
Abstract
GABA receptor antagonists produce an unexpectedly significant inhibition of native glycine receptors in retina and in alpha1 or alpha2 homomeric glycine receptors (GlyRs) expressed in HEK 293 cells. In this study we evaluate this phenomenon in heteromeric glycine receptors, formed by mixing alpha1, alpha2, and beta subunits. Picrotoxinin, picrotin, SR95531, and bicuculline are all more effective antagonists at GlyRs containing alpha2 subunits than alpha1 subunits. Inclusion of beta subunits reduces the inhibitory potency of picrotoxinin and picrotin but increases the potency of SR95531 and bicuculline. As a result of these two factors, bicuculline is particularly poor at discriminating GABA and glycine receptors. Picrotin, which has been reported to be inactive at GABA receptors, blocks glycine currents in retina and in HEK293 cells, suggesting its utility as a selective glycine antagonist. However, picrotin is a more potent inhibitor of GABA than glycine in retinal neurons. We also tested if GABA and glycine receptor subunits can combine to form functional receptors. If GABAAR gamma2S subunits are co-expressed with GlyR alpha subunits, the mixed receptor is glycine-sensitive and GABA-insensitive. But the mixed receptor exhibits a non-competitive picrotoxinin inhibition that is not observed in the homomeric GlyRs. This suggests that glycine and GABA subunits can co-assemble to form functional glycine receptors.
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Affiliation(s)
- Ping Li
- Department of Physiology and Biophysics, University at Buffalo, Buffalo, New York 14214, USA
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Yang Z, Cromer BA, Harvey RJ, Parker MW, Lynch JW. A proposed structural basis for picrotoxinin and picrotin binding in the glycine receptor pore. J Neurochem 2007; 103:580-9. [PMID: 17714449 DOI: 10.1111/j.1471-4159.2007.04850.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Picrotoxin, an antagonist of structurally-rated GABA(A) receptors (GABA(A)Rs) and glycine receptors (GlyRs), is an equimolar mixture of picrotoxinin (PTXININ) and picrotin (PTN). These compounds share a common structure except that PTN contains a slightly larger dimethylmethanol in place of the PTXININ isopropenyl group. Although the homomeric alpha1 GlyR is equally sensitive to both compounds, we show here that homomeric alpha2 and alpha3 GlyRs, like most GABA(A)Rs, are selectively inhibited by PTXININ. As conservative mutations to pore-lining 6' threonines equally affect the sensitivity of the alpha1 GlyR to both compounds, we conclude that PTXININ and PTN bind to 6' threonines by hydrogen bonding with exocyclic oxygens common to both molecules. In contrast, substitution of the 2' pore-lining glycine by serine selectively reduces PTN sensitivity, whereas the introduction of 2' alanines selectively increases PTXININ sensitivity. These results define the orientation of PTXININ and PTN binding in the alpha1 GlyR pore and allow us to conclude that the relatively reduced sensitivity of PTN at GABA(A)Rs and alpha2 and alpha3 GlyRs is due predominantly to its larger size and reduced ability to form hydrophobic interactions with 2' alanines.
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MESH Headings
- DNA, Complementary/biosynthesis
- DNA, Complementary/genetics
- Data Interpretation, Statistical
- Electrophysiology
- Glycine/pharmacology
- Humans
- Hydrogen Bonding
- Models, Molecular
- Mutagenesis
- Neurons, Afferent/drug effects
- Pain/physiopathology
- Patch-Clamp Techniques
- Picrotoxin/analogs & derivatives
- Picrotoxin/chemistry
- Picrotoxin/metabolism
- Receptors, GABA-A/chemistry
- Receptors, GABA-A/drug effects
- Receptors, GABA-A/metabolism
- Receptors, Glycine/chemistry
- Receptors, Glycine/genetics
- Receptors, Glycine/metabolism
- Sesterterpenes
- Synapses/drug effects
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Affiliation(s)
- Zhe Yang
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia
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43
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Hisano K, Ozoe F, Huang J, Kong X, Ozoe Y. The channel-lining 6' amino acid in the second membrane-spanning region of ionotropic GABA receptors has more profound effects on 4'-ethynyl-4-n-propylbicycloorthobenzoate binding than the 2' amino acid. INVERTEBRATE NEUROSCIENCE 2007; 7:39-46. [PMID: 17205299 DOI: 10.1007/s10158-006-0035-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2006] [Accepted: 12/12/2006] [Indexed: 10/23/2022]
Abstract
The noncompetitive antagonist of ionotropic gamma-aminobutyric acid (GABA) receptors 4'-ethynyl-4-n-propylbicycloorthobenzoate (EBOB) is a useful tool to probe the antagonist-binding site. In the present study, four mutants of the human GABA(A) receptor beta3 subunit were stably expressed in S2 cells and examined for their abilities to bind [(3)H]EBOB to identify the binding site of EBOB. The homo-oligomeric beta3 GABA receptor was used as a housefly GABA receptor model, as the beta3 subunit has a high sequence similarity with the housefly Rdl subunit in the second membrane-spanning (M2) region. The A274S mutation at the -1' position in the M2 region had no effect on [(3)H]EBOB binding. The A277S mutation at the 2' position led to a decrease in the affinity of EBOB for the GABA receptor. The T281V mutant at the 6' position and the A277S/T281V double mutant completely abolished the binding ability. A beta3 GABA receptor homology model predicts these interactions between the receptor and EBOB. These results suggest that EBOB interacts with threonine 281 and alanine 277, and that threonine 281 plays a more critical role in interacting with EBOB than alanine 277.
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Affiliation(s)
- Kazutoshi Hisano
- Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane, 690-8504, Japan
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Kalueff AV. Mapping convulsants' binding to the GABA-A receptor chloride ionophore: a proposed model for channel binding sites. Neurochem Int 2007; 50:61-8. [PMID: 16959376 PMCID: PMC1939818 DOI: 10.1016/j.neuint.2006.07.004] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2006] [Revised: 07/05/2006] [Accepted: 07/07/2006] [Indexed: 02/01/2023]
Abstract
Gamma-aminobutyric acid (GABA) type A receptors play a key role in brain inhibitory neurotransmission, and are ligand-activated chloride channels blocked by numerous convulsant ligands. Here we summarize data on binding of picrotoxin, tetrazoles, beta-lactams, bicyclophosphates, butyrolactones and neurotoxic pesticides to GABA-A ionophore, and discuss functional and structural overlapping of their binding sites. The paper reviews data on convulsants' binding sensitivity to different point mutations in ionophore-lining second trans-membrane domains of GABA-A subunits, and maps possible location of convulsants' sites within the chloride ionophore. We also discuss data on inhibition of glycine, glutamate, serotonin (5-HT3) and N-acetylcholine receptors by GABA-A channel blockers, and examine the applicability of this model to other homologous ionotropic receptors. Positioning various convulsant-binding sites within ionophore of GABA-A receptors, this model enables a better understanding of complex architectonics of ionotropic receptors, and may be used for developing new channel-modulating drugs.
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Affiliation(s)
- A V Kalueff
- Laboratory of Clinical Science, Building 10, Room 3D41, National Institute of Mental Health (NIMH), NIH, 10 Center Dr. MSC 1264, Bethesda, MD 20892-1264, USA.
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45
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Oertel J, Villmann C, Kettenmann H, Kirchhoff F, Becker CM. A novel glycine receptor beta subunit splice variant predicts an unorthodox transmembrane topology. Assembly into heteromeric receptor complexes. J Biol Chem 2006; 282:2798-807. [PMID: 17145751 DOI: 10.1074/jbc.m608941200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The inhibitory glycine receptor is a ligand-gated ion channel with a pentameric assembly from ligand binding alpha and structural beta subunits. In addition to alpha subunit gene variants (alpha1-alpha4) and developmental alterations in subunit composition of the receptor protein complex, alternative splicing of alpha subunits has been found to contribute to glycine receptor heterogeneity. Here, we describe a novel splice variant of the glycine receptor beta subunit from mouse central nervous system, prevailing in macroglial cells, predominantly in astrocytes and extraneural tissues. As predicted by its cDNA sequence, the novel subunit betaDelta7 lacks amino acid positions 251-302 encoded by exon 7 of the Glrb gene. Transcripts and antigen of betaDelta7 were detected in cerebral cortex, liver, and heart. Lack of exon 7 results in a profoundly altered prediction of transmembrane topology as betaDelta7 lacks TM1 and TM2 present in the full-length variant. Despite these topological alterations, in vitro studies showed that the betaDelta7 polypeptide integrates into the plasma membrane, forming receptor complexes with the alpha1 subunit and gephyrin. Our data demonstrate that a topology deviating from the classical four transmembrane-fold is compatible with formation of glycine receptor protein complexes. However, co-expression of alpha1 with betaDelta7 subunits did not change glycine receptor channel properties. Rather, the high level of expression in non-neuronal cells having intimate contact with synaptic regions may account for a yet unknown function of this splice variant betaDelta7 in glycinergic neurotransmission.
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Affiliation(s)
- Jana Oertel
- Institut für Biochemie, Emil-Fischer-Zentrum, Universität Erlangen-Nürnberg, Fahrstrasse 17, 91054 Erlangen, Germany
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46
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Sedelnikova A, Erkkila BE, Harris H, Zakharkin SO, Weiss DS. Stoichiometry of a pore mutation that abolishes picrotoxin-mediated antagonism of the GABAA receptor. J Physiol 2006; 577:569-77. [PMID: 16990398 PMCID: PMC1890441 DOI: 10.1113/jphysiol.2006.120287] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Picrotoxin, a potent antagonist of the inhibitory central nervous system GABAA and glycine receptors, is believed to interact with residues that line the central ion pore. These pore-lining residues are in the second transmembrane domain (TM2) of each of the five constituent subunits. One of these amino acids, a threonine at the 6' location, when mutated to phenylalanine, abolishes picrotoxin sensitivity. It has been suggested that this threonine, via hydrogen bonding, directly interacts with the picrotoxin molecule. We previously demonstrated that this mutation, in the alpha, beta or gamma subunit, can impart picrotoxin resistance to the GABA receptor. Since the functional pentameric GABA receptor contains two alpha subunits, two beta subunits and one gamma subunit, it is not clear how many alpha and beta subunits must carry this mutation to impart the resistant phenotype. In this study, by coexpression of mutant alpha or beta subunits with their wild-type counterparts in various defined ratios, we demonstrate that any single subunit carrying the 6' mutation imparts picrotoxin resistance. Implications of this finding in terms of the mechanism of antagonism are considered.
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Affiliation(s)
- Anna Sedelnikova
- Department of Physiology, UTHSCSA, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA
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47
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Hawthorne R, Cromer BA, Ng HL, Parker MW, Lynch JW. Molecular determinants of ginkgolide binding in the glycine receptor pore. J Neurochem 2006; 98:395-407. [PMID: 16805834 DOI: 10.1111/j.1471-4159.2006.03875.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Ginkgolides are potent blockers of the glycine receptor Cl- channel (GlyR) pore. We sought to identify their binding sites by comparing the effects of ginkgolides A, B and C and bilobalide on alpha1, alpha2, alpha1beta and alpha2beta GlyRs. Bilobalide sensitivity was drastically reduced by incorporation of the beta subunit. In contrast, the sensitivities to ginkgolides B and C were enhanced by beta subunit expression. However, ginkgolide A sensitivity was increased in the alpha2beta GlyR relative to the alpha2 GlyR but not in the alpha1beta GlyR relative to the alpha1 GlyR. We hypothesised that the subunit-specific differences were mediated by residue differences at the second transmembrane domain 2' and 6' pore-lining positions. The increased ginkgolide A sensitivity of the alpha2beta GlyR was transferred to the alpha1beta GlyR by the G2'A (alpha1 to alpha2 subunit) substitution. In addition, the alpha1 subunit T6'F mutation abolished inhibition by all ginkgolides. As the ginkgolides share closely related structures, their molecular interactions with pore-lining residues were amenable to mutant cycle analysis. This identified an interaction between the variable R2 position of the ginkgolides and the 2' residues of both alpha1 and beta subunits. These findings provide strong evidence for ginkgolides binding at the 2' pore-lining position.
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Affiliation(s)
- Rebecca Hawthorne
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, Australia
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48
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Wang DS, Mangin JM, Moonen G, Rigo JM, Legendre P. Mechanisms for picrotoxin block of alpha2 homomeric glycine receptors. J Biol Chem 2005; 281:3841-55. [PMID: 16344549 DOI: 10.1074/jbc.m511022200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
It is well known that the convulsant alkaloid picrotoxin (PTX) can inhibit neuronal gamma-aminobutyric acid (GABA) and homomeric glycine receptors (GlyR). However, the mechanism for PTX block of alpha(2) homomeric GlyR is still unclear compared with that of alpha(1) homomeric GlyR, GABA(A), and GABA(C) receptors. Furthermore, PTX effects on GlyR kinetics have been poorly explored at the single-channel level. Hence, we used the patch-clamp technique in the outside-out configuration to investigate the mechanism of PTX suppression of currents carried by alpha(2) homomeric GlyRs stably transfected into Chinese hamster ovary cells. PTX inhibited the alpha(2) homomeric GlyR current elicited by glycine in a concentration-dependent and voltage-independent manner. Both competitive and noncompetitive mechanisms were observed. PTX decreased the mean open time of the GlyR channel in a concentration-dependent manner, suggesting that PTX can block channel openings and bind to the receptor in the open channel conformation. When PTX and glycine were co-applied, a small rebound current was observed during drug washout. Application of PTX during the deactivation phase of glycine-induced currents eliminated the rebound current and accelerated the deactivation time course in a concentration-dependent manner. PTX could not bind to the unbound conformation of GlyR, but could be trapped at its binding site when the channel closed during glycine dissociation. Based on these observations, we propose a kinetic Markov model in which PTX binds to the alpha(2) homomeric GlyR in both the open channel state and the fully liganded closed state. Our data suggest a new allosteric mechanism for PTX inhibition of wild-type homomeric alpha(2) GlyR.
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Affiliation(s)
- Dian-Shi Wang
- Unité Mixte de Recherche, CNRS 7102, Neurobiologie des Processus Adaptatifs, Université Pierre et Marie Curie, Paris, France
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49
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Hawthorne R, Lynch JW. A Picrotoxin-specific Conformational Change in the Glycine Receptor M2–M3 Loop. J Biol Chem 2005; 280:35836-43. [PMID: 16109711 DOI: 10.1074/jbc.m506645200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The external loop linking the M2 and M3 transmembrane domains is crucial for coupling agonist binding to channel gating in the glycine receptor chloride channel (GlyR). A substituted cysteine accessibility scan previously showed that glycine activation increased the surface accessibility of 6 contiguous residues (Arg271-Lys276) toward the N-terminal end of the homomeric alpha1 GlyR M2-M3 loop. In the present study we used a similar approach to determine whether the allosteric antagonist, picrotoxin, could impose conformational changes to this domain that cannot be induced by varying agonist concentrations alone. Picrotoxin slowed the reaction rate of a sulfhydryl-containing compound (MTSET) with A272C, S273C, and L274C. Before interpreting this as a picrotoxin-specific conformational change, it was necessary to eliminate the possibility of steric competition between picrotoxin and MTSET. Accordingly, we showed that picrotoxin and the structurally unrelated blocker, bilobalide, were both trapped in the R271C GlyR in the closed state and that a point mutation to the pore-lining Thr6' residue abolished inhibition by both compounds. We also demonstrated that the picrotoxin dissociation rate was linearly related to the channel open probability. These observations constitute a strong case for picrotoxin binding in the pore. We thus conclude that the picrotoxin-specific effects on the M2-M3 loop are mediated allosterically. This suggests that the M2-M3 loop responds differently to the occupation of different binding sites.
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Affiliation(s)
- Rebecca Hawthorne
- School of Biomedical Sciences, University of Queensland, Brisbane, Queensland 4072, Australia
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Kondratskaya EL, Betz H, Krishtal OA, Laube B. The beta subunit increases the ginkgolide B sensitivity of inhibitory glycine receptors. Neuropharmacology 2005; 49:945-51. [PMID: 16125206 DOI: 10.1016/j.neuropharm.2005.07.001] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2005] [Accepted: 07/05/2005] [Indexed: 11/30/2022]
Abstract
We investigated the effect of ginkgolide B (GB), a component of the extract from the leaves of the Ginkgo biloba tree, on recombinant glycine receptors (GlyRs) expressed in Xenopus oocytes by using voltage-clamp recording. GB (0.01-10 microM) inhibited glycine-induced currents of homo-oligomeric alpha1, alpha2 and alpha 3 GlyRs, with the highest potency being found at the alpha1 GlyR (IC(50) value=0.61+/-0.1 microM). Coexpression of the alpha subunits with the beta subunit resulted in a shift of the IC(50) value of GB to nanomolar values, indicating selectivity of GB for beta subunit containing GlyRs. We also analyzed the mechanism of GB inhibition and the effect of point mutations introduced into the alpha1 subunit. Our results are consistent with a channel blocking effect, since (i) GB inhibited glycine currents non-competitively, and (ii) a point mutation in the pore forming M2 domain reduced GB potency. In conclusion, GB is a potent blocker of beta subunit containing GlyR channels and hence can be used to discriminate homo- from hetero-oligomeric GlyRs. As hetero-oligomeric GlyRs are known to be synaptically localized, GB represents a channel blocker that may be employed to separate extrasynaptic from synaptic glycine currents.
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Affiliation(s)
- Elena L Kondratskaya
- Department of Neurochemistry, Max-Planck-Institute for Brain Research, Deutschordenstrasse 46, 60528 Frankfurt, Germany
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