1
|
Nors JW, Endres Z, Goldschen-Ohm MP. GABA A receptor subunit M2-M3 linkers have asymmetric roles in pore gating and diazepam modulation. Biophys J 2024; 123:2085-2096. [PMID: 38400541 PMCID: PMC11309982 DOI: 10.1016/j.bpj.2024.02.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2023] [Revised: 01/19/2024] [Accepted: 02/20/2024] [Indexed: 02/25/2024] Open
Abstract
GABAA receptors (GABAARs) are neurotransmitter-gated ion channels critical for inhibitory synaptic transmission as well as the molecular target for benzodiazepines (BZDs), one of the most widely prescribed class of psychotropic drugs today. Despite structural insight into the conformations underlying functional channel states, the detailed molecular interactions involved in conformational transitions and the physical basis for their modulation by BZDs are not fully understood. We previously identified that alanine substitution at the central residue in the α1 subunit M2-M3 linker (V279A) enhances the efficiency of linkage between the BZD site and the pore gate. Here, we expand on this work by investigating the effect of alanine substitutions at the analogous positions in the M2-M3 linkers of β2 (I275A) and γ2 (V290A) subunits, which together with α1 comprise typical heteromeric α1β2γ2 synaptic GABAARs. We find that these mutations confer subunit-specific effects on the intrinsic pore closed-open equilibrium and its modulation by the BZD diazepam (DZ). The mutations α1(V279A) or γ2(V290A) bias the channel toward a closed conformation, whereas β2(I275A) biases the channel toward an open conformation to the extent that the channel becomes leaky and opens spontaneously in the absence of agonist. In contrast, only α1(V279A) enhances the efficiency of DZ-to-pore linkage, whereas mutations in the other two subunits have no effect. These observations show that the central residue in the M2-M3 linkers of distinct subunits in synaptic α1β2γ2 GABAARs contribute asymmetrically to the intrinsic closed-open equilibrium and its modulation by DZ.
Collapse
Affiliation(s)
- Joseph W Nors
- Department of Neuroscience, University of Texas at Austin, Austin, Texas; Department of Molecular and Cellular Physiology, Stanford University, Stanford, California
| | - Zachary Endres
- Department of Neuroscience, University of Texas at Austin, Austin, Texas
| | | |
Collapse
|
2
|
Mӓnnikkӧ R, Kullmann DM. Structure-function and pharmacologic aspects of ion channels relevant to neurologic channelopathies. HANDBOOK OF CLINICAL NEUROLOGY 2024; 203:1-23. [PMID: 39174242 DOI: 10.1016/b978-0-323-90820-7.00009-4] [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] [Indexed: 08/24/2024]
Abstract
Ion channels are membrane proteins that allow the passage of ions across the membrane. They characteristically contain a pore where the selectivity of certain ion species is determined and gates that open and close the pore are found. The pore is often connected to additional domains or subunits that regulate its function. Channels are grouped into families based on their selectivity for specific ions and the stimuli that control channel opening and closing, such as voltage or ligands. Ion channels are fundamental to the electrical properties of excitable tissues. Dysfunction of channels can lead to abnormal electrical signaling of neurons and muscle cells, accompanied by clinical manifestations, known as channelopathies. Many naturally occurring toxins target ion channels and affect excitable cells where the channels are expressed. Furthermore, ion channels, as membrane proteins and key regulators of a number of physiologic functions, are an important target for drugs in clinical use. In this chapter, we give a general overview of the classification, genetics and structure-function features of the main ion channel families, and address some pharmacologic aspects relevant to neurologic channelopathies.
Collapse
Affiliation(s)
- Roope Mӓnnikkӧ
- Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom.
| | - Dimitri M Kullmann
- Department of Clinical and Experimental Epilepsy, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom.
| |
Collapse
|
3
|
Nors JW, Gupta S, Goldschen-Ohm MP. A critical residue in the α 1M2-M3 linker regulating mammalian GABA A receptor pore gating by diazepam. eLife 2021; 10:64400. [PMID: 33591271 PMCID: PMC7899671 DOI: 10.7554/elife.64400] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Accepted: 02/15/2021] [Indexed: 01/29/2023] Open
Abstract
Benzodiazepines (BZDs) are a class of widely prescribed psychotropic drugs that modulate activity of GABAA receptors (GABAARs), neurotransmitter-gated ion channels critical for synaptic transmission. However, the physical basis of this modulation is poorly understood. We explore the role of an important gating domain, the α1M2–M3 linker, in linkage between the BZD site and pore gate. To probe energetics of this coupling without complication from bound agonist, we use a gain of function mutant (α1L9'Tβ2γ2L) directly activated by BZDs. We identify a specific residue whose mutation (α1V279A) more than doubles the energetic contribution of the BZD positive modulator diazepam (DZ) to pore opening and also enhances DZ potentiation of GABA-evoked currents in a wild-type background. In contrast, other linker mutations have little effect on DZ efficiency, but generally impair unliganded pore opening. Our observations reveal an important residue regulating BZD-pore linkage, thereby shedding new light on the molecular mechanism of these drugs.
Collapse
Affiliation(s)
- Joseph W Nors
- University of Texas at Austin, Department of Neuroscience, Austin, United States
| | - Shipra Gupta
- University of Texas at Austin, Department of Neuroscience, Austin, United States
| | | |
Collapse
|
4
|
Ivica J, Lape R, Jazbec V, Yu J, Zhu H, Gouaux E, Gold MG, Sivilotti LG. The intracellular domain of homomeric glycine receptors modulates agonist efficacy. J Biol Chem 2021; 296:100387. [PMID: 33617876 PMCID: PMC7995613 DOI: 10.1074/jbc.ra119.012358] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Revised: 02/19/2020] [Indexed: 11/20/2022] Open
Abstract
Like other pentameric ligand-gated channels, glycine receptors (GlyRs) contain long intracellular domains (ICDs) between transmembrane helices 3 and 4. Structurally characterized GlyRs are generally engineered to have a very short ICD. We show here that for one such construct, zebrafish GlyREM, the agonists glycine, β-alanine, taurine, and GABA have high efficacy and produce maximum single-channel open probabilities greater than 0.9. In contrast, for full-length human α1 GlyR, taurine and GABA were clearly partial agonists, with maximum open probabilities of 0.46 and 0.09, respectively. We found that the elevated open probabilities in GlyREM are not due to the limited sequence differences between the human and zebrafish orthologs, but rather to replacement of the native ICD with a short tripeptide ICD. Consistent with this interpretation, shortening the ICD in the human GlyR increased the maximum open probability produced by taurine and GABA to 0.90 and 0.70, respectively, but further engineering it to resemble GlyREM (by introducing the zebrafish transmembrane helix 4 and C terminus) had no effect. Furthermore, reinstating the native ICD to GlyREM converted taurine and GABA to partial agonists, with maximum open probabilities of 0.66 and 0.40, respectively. Structural comparison of transmembrane helices 3 and 4 in short- and long-ICD GlyR subunits revealed that ICD shortening does not distort the orientation of these helices within each subunit. This suggests that the effects of shortening the ICD stem from removing a modulatory effect of the native ICD on GlyR gating, revealing a new role for the ICD in pentameric ligand-gated channels.
Collapse
Key Words
- 5-ht3, 5-hydroxytryptamine type 3
- dmem, dulbecco’s modified eagle’s medium
- ecd, extracellular domain
- glyr, glycine receptor
- icd, intracellular domain
- popen, open probability
- pdb, protein data bank
- plgic, pentameric ligand-gated ion channels
- tm, transmembrane
- zf, zebrafish
Collapse
Affiliation(s)
- Josip Ivica
- Department of Neuroscience, Physiology and Pharmacology, Division of Biosciences, University College London, London WC1E 6BT, United Kingdom
| | - Remigijus Lape
- Department of Neuroscience, Physiology and Pharmacology, Division of Biosciences, University College London, London WC1E 6BT, United Kingdom
| | - Vid Jazbec
- Department of Synthetic Biology and Immunology, National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia
| | - Jie Yu
- Vollum Institute, Oregon Health & Science University, Portland, Oregon 97239
| | - Hongtao Zhu
- Vollum Institute, Oregon Health & Science University, Portland, Oregon 97239
| | - Eric Gouaux
- Howard Hughes Medical Institute, Oregon Health & Science University, Portland, Oregon 97239
| | - Matthew G Gold
- Department of Neuroscience, Physiology and Pharmacology, Division of Biosciences, University College London, London WC1E 6BT, United Kingdom
| | - Lucia G Sivilotti
- Department of Neuroscience, Physiology and Pharmacology, Division of Biosciences, University College London, London WC1E 6BT, United Kingdom.
| |
Collapse
|
5
|
Abstract
The inhibitory glycine receptor is a member of the Cys-loop superfamily of ligand-gated ion channels. It is the principal mediator of rapid synaptic inhibition in the spinal cord and brainstem and plays an important role in the modulation of higher brain functions including vision, hearing, and pain signaling. Glycine receptor function is controlled by only a few agonists, while the number of antagonists and positive or biphasic modulators is steadily increasing. These modulators are important for the study of receptor activation and regulation and have found clinical interest as potential analgesics and anticonvulsants. High-resolution structures of the receptor have become available recently, adding to our understanding of structure-function relationships and revealing agonistic, inhibitory, and modulatory sites on the receptor protein. This Review presents an overview of compounds that activate, inhibit, or modulate glycine receptor function in vitro and in vivo.
Collapse
Affiliation(s)
- Ulrike Breitinger
- Department of Biochemistry, German University in Cairo, New Cairo 11835, Egypt
| | | |
Collapse
|
6
|
Chemogenetics a robust approach to pharmacology and gene therapy. Biochem Pharmacol 2020; 175:113889. [DOI: 10.1016/j.bcp.2020.113889] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2020] [Accepted: 02/26/2020] [Indexed: 12/20/2022]
|
7
|
Oliveira ASF, Edsall CJ, Woods CJ, Bates P, Nunez GV, Wonnacott S, Bermudez I, Ciccotti G, Gallagher T, Sessions RB, Mulholland AJ. A General Mechanism for Signal Propagation in the Nicotinic Acetylcholine Receptor Family. J Am Chem Soc 2019; 141:19953-19958. [PMID: 31805762 DOI: 10.1021/jacs.9b09055] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Nicotinic acetylcholine receptors (nAChRs) modulate synaptic activity in the central nervous system. The α7 subtype, in particular, has attracted considerable interest in drug discovery as a target for several conditions, including Alzheimer's disease and schizophrenia. Identifying agonist-induced structural changes underlying nAChR activation is fundamentally important for understanding biological function and rational drug design. Here, extensive equilibrium and nonequilibrium molecular dynamics simulations, enabled by cloud-based high-performance computing, reveal the molecular mechanism by which structural changes induced by agonist unbinding are transmitted within the human α7 nAChR. The simulations reveal the sequence of coupled structural changes involved in driving conformational change responsible for biological function. Comparison with simulations of the α4β2 nAChR subtype identifies features of the dynamical architecture common to both receptors, suggesting a general structural mechanism for signal propagation in this important family of receptors.
Collapse
Affiliation(s)
- Ana Sofia F Oliveira
- School of Biochemistry , University of Bristol , Bristol BS8 1DT , United Kingdom
- Centre for Computational Chemistry, School of Chemistry , University of Bristol , Bristol BS8 1TS , United Kingdom
| | - Christopher J Edsall
- Research Software Engineering, Advanced Computing Research Centre , University of Bristol , Bristol BS1 5QD , United Kingdom
| | - Christopher J Woods
- Centre for Computational Chemistry, School of Chemistry , University of Bristol , Bristol BS8 1TS , United Kingdom
- Research Software Engineering, Advanced Computing Research Centre , University of Bristol , Bristol BS1 5QD , United Kingdom
| | - Phil Bates
- Department of Computer Science, Faculty of Engineering , University of Bristol , Bristol BS8 1TR , United Kingdom
- Oracle Corporation, Oracle Cloud Development Centre , Bristol BS2 2JJ , United Kingdom
| | - Gerardo Viedma Nunez
- Oracle Corporation, Oracle Cloud Development Centre , Bristol BS2 2JJ , United Kingdom
| | - Susan Wonnacott
- Department of Biology and Biochemistry , University of Bath , Bath BA2 7AY , United Kingdom
| | - Isabel Bermudez
- Department of Biological and Medical Sciences , Oxford Brookes University , Oxford OX30BP , United Kingdom
| | - Giovanni Ciccotti
- Institute for Applied Computing "Mauro Picone" (IAC), CNR , Via dei Taurini 19 , 00185 Rome , Italy
- School of Physics , University College of Dublin UCD-Belfield , Dublin 4, Ireland
- Università di Roma La Sapienza , Ple. A. Moro 5 , 00185 Roma , Italy
| | - Timothy Gallagher
- Centre for Computational Chemistry, School of Chemistry , University of Bristol , Bristol BS8 1TS , United Kingdom
| | - Richard B Sessions
- School of Biochemistry , University of Bristol , Bristol BS8 1DT , United Kingdom
| | - Adrian J Mulholland
- Centre for Computational Chemistry, School of Chemistry , University of Bristol , Bristol BS8 1TS , United Kingdom
| |
Collapse
|
8
|
Oliveira ASF, Shoemark DK, Campello HR, Wonnacott S, Gallagher T, Sessions RB, Mulholland AJ. Identification of the Initial Steps in Signal Transduction in the α4β2 Nicotinic Receptor: Insights from Equilibrium and Nonequilibrium Simulations. Structure 2019; 27:1171-1183.e3. [PMID: 31130483 DOI: 10.1016/j.str.2019.04.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2018] [Revised: 01/28/2019] [Accepted: 04/10/2019] [Indexed: 02/02/2023]
Abstract
Nicotinic acetylcholine receptors (nAChRs) modulate synaptic transmission in the nervous system. These receptors have emerged as therapeutic targets in drug discovery for treating several conditions, including Alzheimer's disease, pain, and nicotine addiction. In this in silico study, we use a combination of equilibrium and nonequilibrium molecular dynamics simulations to map dynamic and structural changes induced by nicotine in the human α4β2 nAChR. They reveal a striking pattern of communication between the extracellular binding pockets and the transmembrane domains (TMDs) and show the sequence of conformational changes associated with the initial steps in this process. We propose a general mechanism for signal transduction for Cys-loop receptors: the mechanistic steps for communication proceed firstly through loop C in the principal subunit, and are subsequently transmitted, gradually and cumulatively, to loop F of the complementary subunit, and then to the TMDs through the M2-M3 linker.
Collapse
Affiliation(s)
- A Sofia F Oliveira
- School of Biochemistry, University of Bristol, Bristol BS8 1DT, UK; Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
| | | | - Hugo Rego Campello
- Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
| | - Susan Wonnacott
- Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, UK
| | - Timothy Gallagher
- Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS, UK
| | | | - Adrian J Mulholland
- Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS, UK.
| |
Collapse
|