1
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Zhou Y, Meng J, Xu C, Liu J. Multiple GPCR Functional Assays Based on Resonance Energy Transfer Sensors. Front Cell Dev Biol 2021; 9:611443. [PMID: 34041234 PMCID: PMC8141573 DOI: 10.3389/fcell.2021.611443] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Accepted: 02/05/2021] [Indexed: 12/19/2022] Open
Abstract
G protein-coupled receptors (GPCRs) represent one of the largest membrane protein families that participate in various physiological and pathological activities. Accumulating structural evidences have revealed how GPCR activation induces conformational changes to accommodate the downstream G protein or β-arrestin. Multiple GPCR functional assays have been developed based on Förster resonance energy transfer (FRET) and bioluminescence resonance energy transfer (BRET) sensors to monitor the conformational changes in GPCRs, GPCR/G proteins, or GPCR/β-arrestin, especially over the past two decades. Here, we will summarize how these sensors have been optimized to increase the sensitivity and compatibility for application in different GPCR classes using various labeling strategies, meanwhile provide multiple solutions in functional assays for high-throughput drug screening.
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Affiliation(s)
- Yiwei Zhou
- Cellular Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Jiyong Meng
- Cellular Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China
| | - Chanjuan Xu
- Cellular Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China.,Bioland Laboratory, Guangzhou Regenerative Medicine and Health Guangdong Laboratory, Guangzhou, China
| | - Jianfeng Liu
- Cellular Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China.,Bioland Laboratory, Guangzhou Regenerative Medicine and Health Guangdong Laboratory, Guangzhou, China
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2
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Ectopic activation of GABA B receptors inhibits neurogenesis and metamorphosis in the cnidarian Nematostella vectensis. Nat Ecol Evol 2020; 5:111-121. [PMID: 33168995 DOI: 10.1038/s41559-020-01338-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Accepted: 09/29/2020] [Indexed: 01/22/2023]
Abstract
The metabotropic gamma-aminobutyric acid B receptor (GABABR) is a G protein-coupled receptor that mediates neuronal inhibition by the neurotransmitter GABA. While GABABR-mediated signalling has been suggested to play central roles in neuronal differentiation and proliferation across evolution, it has mostly been studied in the mammalian brain. Here, we demonstrate that ectopic activation of GABABR signalling affects neurogenic functions in the sea anemone Nematostella vectensis. We identified four putative Nematostella GABABR homologues presenting conserved three-dimensional extracellular domains and residues needed for binding GABA and the GABABR agonist baclofen. Moreover, sustained activation of GABABR signalling reversibly arrests the critical metamorphosis transition from planktonic larva to sessile polyp life stage. To understand the processes that underlie the developmental arrest, we combined transcriptomic and spatial analyses of control and baclofen-treated larvae. Our findings reveal that the cnidarian neurogenic programme is arrested following the addition of baclofen to developing larvae. Specifically, neuron development and neurite extension were inhibited, resulting in an underdeveloped and less organized nervous system and downregulation of proneural factors including NvSoxB(2), NvNeuroD1 and NvElav1. Our results thus point to an evolutionarily conserved function of GABABR in neurogenesis regulation and shed light on early cnidarian development.
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3
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Mechanisms and Regulation of Neuronal GABA B Receptor-Dependent Signaling. Curr Top Behav Neurosci 2020; 52:39-79. [PMID: 32808092 DOI: 10.1007/7854_2020_129] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
γ-Aminobutyric acid B receptors (GABABRs) are broadly expressed throughout the central nervous system where they play an important role in regulating neuronal excitability and synaptic transmission. GABABRs are G protein-coupled receptors that mediate slow and sustained inhibitory actions via modulation of several downstream effector enzymes and ion channels. GABABRs are obligate heterodimers that associate with diverse arrays of proteins to form modular complexes that carry out distinct physiological functions. GABABR-dependent signaling is fine-tuned and regulated through a multitude of mechanisms that are relevant to physiological and pathophysiological states. This review summarizes the current knowledge on GABABR signal transduction and discusses key factors that influence the strength and sensitivity of GABABR-dependent signaling in neurons.
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4
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Evenseth LSM, Gabrielsen M, Sylte I. The GABA B Receptor-Structure, Ligand Binding and Drug Development. Molecules 2020; 25:molecules25133093. [PMID: 32646032 PMCID: PMC7411975 DOI: 10.3390/molecules25133093] [Citation(s) in RCA: 55] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 07/02/2020] [Accepted: 07/06/2020] [Indexed: 11/17/2022] Open
Abstract
The γ-aminobutyric acid (GABA) type B receptor (GABAB-R) belongs to class C of the G-protein coupled receptors (GPCRs). Together with the GABAA receptor, the receptor mediates the neurotransmission of GABA, the main inhibitory neurotransmitter in the central nervous system (CNS). In recent decades, the receptor has been extensively studied with the intention being to understand pathophysiological roles, structural mechanisms and develop drugs. The dysfunction of the receptor is linked to a broad variety of disorders, including anxiety, depression, alcohol addiction, memory and cancer. Despite extensive efforts, few compounds are known to target the receptor, and only the agonist baclofen is approved for clinical use. The receptor is a mandatory heterodimer of the GABAB1 and GABAB2 subunits, and each subunit is composed of an extracellular Venus Flytrap domain (VFT) and a transmembrane domain of seven α-helices (7TM domain). In this review, we briefly present the existing knowledge about the receptor structure, activation and compounds targeting the receptor, emphasizing the role of the receptor in previous and future drug design and discovery efforts.
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Affiliation(s)
- Linn Samira Mari Evenseth
- Molecular Pharmacology and Toxicology, Department of Medical Biology, Faculty of Health Sciences, UiT The Arctic University of Norway, NO-9037 Tromsø, Norway
| | - Mari Gabrielsen
- Molecular Pharmacology and Toxicology, Department of Medical Biology, Faculty of Health Sciences, UiT The Arctic University of Norway, NO-9037 Tromsø, Norway
| | - Ingebrigt Sylte
- Molecular Pharmacology and Toxicology, Department of Medical Biology, Faculty of Health Sciences, UiT The Arctic University of Norway, NO-9037 Tromsø, Norway
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5
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Abstract
GABA (γ-aminobutyric acid) stimulation of the metabotropic GABAB receptor results in prolonged inhibition of neurotransmission that is central to brain physiology1. GABAB belongs to the Family C of G protein-coupled receptors (GPCRs), which operate as dimers to relay synaptic neurotransmitter signals into a cellular response through the binding and activation of heterotrimeric G proteins2,3. GABAB, however, is unique in its function as an obligate heterodimer in which agonist binding and G protein activation take place on distinct subunits4,5. Here we show structures of heterodimeric and homodimeric full-length GABAB receptors. Complemented by cellular signaling assays and atomistic simulations, the structures reveal an essential role for the GABAB extracellular loop 2 (ECL2) in relaying structural transitions by ordering the linker connecting the extracellular ligand-binding domain to the transmembrane region. Furthermore, the ECL2 of both GABAB subunits caps and interacts with the hydrophilic head of a phospholipid occupying the extracellular half of the transmembrane domain, thereby providing a potentially crucial link between ligand binding and the receptor core that engages G protein. These results provide a starting framework to decipher mechanistic modes of signal transduction mediated by GABAB dimers and have important implications for rational drug design targeting these receptors.
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6
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Evenseth LSM, Ocello R, Gabrielsen M, Masetti M, Recanatini M, Sylte I, Cavalli A. Exploring Conformational Dynamics of the Extracellular Venus flytrap Domain of the GABA B Receptor: A Path-Metadynamics Study. J Chem Inf Model 2020; 60:2294-2303. [PMID: 32233432 PMCID: PMC7997371 DOI: 10.1021/acs.jcim.0c00163] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2020] [Indexed: 12/21/2022]
Abstract
γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the central nervous system (CNS). Dysfunctional GABAergic neurotransmission is associated with numerous neurological and neuropsychiatric disorders. The GABAB receptor (GABAB-R) is a heterodimeric class C G protein-coupled receptor (GPCR) comprised of GABAB1a/b and GABAB2 subunits. The orthosteric binding site for GABA is located in the extracellular Venus flytrap (VFT) domain of the GABAB1a/b. Knowledge about molecular mechanisms and druggable receptor conformations associated with activation is highly important to understand the receptor function and for rational drug design. Currently, the conformational changes of the receptor upon activation are not well described. On the basis of other class C members, the VFT is proposed to fluctuate between an open/inactive and closed/active state and one of these conformations is stabilized upon ligand binding. In the present study, we investigated the dynamics of the GABAB1b-R VFT in the apo form by combining unbiased molecular dynamics with path-metadynamics. Our simulations confirmed the open/inactive and closed/active state as the main conformations adopted by the receptor. Sizeable energy barriers were found between stable minima, suggesting a relatively slow interconversion. Previously undisclosed metastable states were also identified, which might hold potential for future drug discovery efforts.
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Affiliation(s)
- Linn S. M. Evenseth
- Molecular
Pharmacology and Toxicology, Department of Medical Biology, Faculty
of Health Sciences, UiT—The Arctic
University of Norway, NO-9037Tromsø, Norway
| | - Riccardo Ocello
- Department
of Pharmacy and Biotechnology, Alma Mater
Studiorum—Università di Bologna, Via Belmeloro 6, I-40126 Bologna, Italy
- CompuNet, Istituto Italiano
di Tecnologia, Via Morego
30, I-16163 Genova, Italy
| | - Mari Gabrielsen
- Molecular
Pharmacology and Toxicology, Department of Medical Biology, Faculty
of Health Sciences, UiT—The Arctic
University of Norway, NO-9037Tromsø, Norway
| | - Matteo Masetti
- Department
of Pharmacy and Biotechnology, Alma Mater
Studiorum—Università di Bologna, Via Belmeloro 6, I-40126 Bologna, Italy
| | - Maurizio Recanatini
- Department
of Pharmacy and Biotechnology, Alma Mater
Studiorum—Università di Bologna, Via Belmeloro 6, I-40126 Bologna, Italy
| | - Ingebrigt Sylte
- Molecular
Pharmacology and Toxicology, Department of Medical Biology, Faculty
of Health Sciences, UiT—The Arctic
University of Norway, NO-9037Tromsø, Norway
| | - Andrea Cavalli
- Department
of Pharmacy and Biotechnology, Alma Mater
Studiorum—Università di Bologna, Via Belmeloro 6, I-40126 Bologna, Italy
- CompuNet, Istituto Italiano
di Tecnologia, Via Morego
30, I-16163 Genova, Italy
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7
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Kniazeff J. The different aspects of the GABAB receptor allosteric modulation. FROM STRUCTURE TO CLINICAL DEVELOPMENT: ALLOSTERIC MODULATION OF G PROTEIN-COUPLED RECEPTORS 2020; 88:83-113. [DOI: 10.1016/bs.apha.2020.02.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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8
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Li X, Slesinger PA. GABA B Receptors and Drug Addiction: Psychostimulants and Other Drugs of Abuse. Curr Top Behav Neurosci 2020; 52:119-155. [PMID: 33442842 DOI: 10.1007/7854_2020_187] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Metabotropic GABAB receptors (GABABRs) mediate slow inhibition and modulate synaptic plasticity throughout the brain. Dysfunction of GABABRs has been associated with psychiatric illnesses and addiction. Drugs of abuse alter GABAB receptor (GABABR) signaling in multiple brain regions, which partly contributes to the development of drug addiction. Recently, GABABR ligands and positive allosteric modulators (PAMs) have been shown to attenuate the initial rewarding effect of addictive substances, inhibit seeking and taking of these drugs, and in some cases, ameliorate drug withdrawal symptoms. The majority of the anti-addiction effects seen with GABABR modulation can be localized to ventral tegmental area (VTA) dopamine neurons, which receive complex inhibitory and excitatory inputs that are modified by drugs of abuse. Preclinical research suggests that GABABR PAMs are emerging as promising candidates for the treatment of drug addiction. Clinical studies on drug dependence have shown positive results with GABABR ligands but more are needed, and compounds with better pharmacokinetics and fewer side effects are critically needed.
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Affiliation(s)
- Xiaofan Li
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, USA.
| | - Paul A Slesinger
- Nash Family Department of Neuroscience, Icahn School of Medicine at Mount Sinai, New York, NY, USA.
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9
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Molecular Docking of Phenylethylamine and CGP54626 to an Extracellular Domain of the GABAB-Receptor. NEUROPHYSIOLOGY+ 2018. [DOI: 10.1007/s11062-018-9743-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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10
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Frangaj A, Fan QR. Structural biology of GABA B receptor. Neuropharmacology 2018; 136:68-79. [PMID: 29031577 PMCID: PMC5897222 DOI: 10.1016/j.neuropharm.2017.10.011] [Citation(s) in RCA: 58] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2017] [Revised: 10/09/2017] [Accepted: 10/11/2017] [Indexed: 11/17/2022]
Abstract
Metabotropic GABAB receptor is a G protein-coupled receptor (GPCR) that mediates slow and prolonged inhibitory neurotransmission in the brain. It functions as a constitutive heterodimer composed of the GABAB1 and GABAB2 subunits. Each subunit contains three domains; the extracellular Venus flytrap module, seven-helix transmembrane region and cytoplasmic tail. In recent years, the three-dimensional structures of GABAB receptor extracellular and intracellular domains have been elucidated. These structures reveal the molecular basis of ligand recognition, receptor heterodimerization and receptor activation. Here we provide a brief review of the GABAB receptor structures, with an emphasis on describing the different ligand-bound states of the receptor. We will also compare these with the known structures of related GPCRs to shed light on the molecular mechanisms of activation and regulation in the GABAB system, as well as GPCR dimers in general. This article is part of the "Special Issue Dedicated to Norman G. Bowery".
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Affiliation(s)
- Aurel Frangaj
- Department of Pharmacology, Columbia University, New York, NY 10032, USA
| | - Qing R Fan
- Department of Pharmacology, Columbia University, New York, NY 10032, USA; Department of Pathology & Cell Biology, Columbia University, New York, NY 10032, USA.
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11
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Lecat-Guillet N, Monnier C, Rovira X, Kniazeff J, Lamarque L, Zwier JM, Trinquet E, Pin JP, Rondard P. FRET-Based Sensors Unravel Activation and Allosteric Modulation of the GABA B Receptor. Cell Chem Biol 2017; 24:360-370. [PMID: 28286129 DOI: 10.1016/j.chembiol.2017.02.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2016] [Revised: 11/21/2016] [Accepted: 02/10/2017] [Indexed: 01/11/2023]
Abstract
The main inhibitory neurotransmitter, γ-aminobutyric acid (GABA), modulates many synapses by activating the G protein-coupled receptor GABAB, which is a target for various therapeutic applications. It is an obligatory heterodimer made of GB1 and GB2 that can be regulated by positive allosteric modulators (PAMs). The molecular mechanism of activation of the GABAB receptor remains poorly understood. Here, we have developed FRET-based conformational GABAB sensors compatible with high-throughput screening. We identified conformational changes occurring within the extracellular and transmembrane domains upon receptor activation, which are smaller than those observed in the related metabotropic glutamate receptors. These sensors also allow discrimination between agonists of different efficacies and between PAMs that have different modes of action, which has not always been possible using conventional functional assays. Our study brings important new information on the activation mechanism of the GABAB receptor and should facilitate the screening and identification of new chemicals targeting this receptor.
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Affiliation(s)
- Nathalie Lecat-Guillet
- Institut de Génomique Fonctionnelle (IGF), CNRS, INSERM, University of Montpellier, 141 rue de la Cardonille, 34094 Montpellier, France
| | - Carine Monnier
- Institut de Génomique Fonctionnelle (IGF), CNRS, INSERM, University of Montpellier, 141 rue de la Cardonille, 34094 Montpellier, France
| | - Xavier Rovira
- Institut de Génomique Fonctionnelle (IGF), CNRS, INSERM, University of Montpellier, 141 rue de la Cardonille, 34094 Montpellier, France
| | - Julie Kniazeff
- Institut de Génomique Fonctionnelle (IGF), CNRS, INSERM, University of Montpellier, 141 rue de la Cardonille, 34094 Montpellier, France
| | | | | | | | - Jean-Philippe Pin
- Institut de Génomique Fonctionnelle (IGF), CNRS, INSERM, University of Montpellier, 141 rue de la Cardonille, 34094 Montpellier, France
| | - Philippe Rondard
- Institut de Génomique Fonctionnelle (IGF), CNRS, INSERM, University of Montpellier, 141 rue de la Cardonille, 34094 Montpellier, France.
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12
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Fu P, Wu Q, Hu J, Li T, Gao F. Baclofen Protects Primary Rat Retinal Ganglion Cells from Chemical Hypoxia-Induced Apoptosis Through the Akt and PERK Pathways. Front Cell Neurosci 2016; 10:255. [PMID: 27867349 PMCID: PMC5095369 DOI: 10.3389/fncel.2016.00255] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2016] [Accepted: 10/18/2016] [Indexed: 12/26/2022] Open
Abstract
Retinal ganglion cells (RGCs) consume large quantities of energy to convert light information into a neuronal signal, which makes them highly susceptible to hypoxic injury. This study aimed to investigate the potential protection by baclofen, a GABAB receptor agonist of RGCs against hypoxia-induced apoptosis. Cobalt chloride (CoCl2) was applied to mimic hypoxia. Primary rat RGCs were subjected to CoCl2 with or without baclofen treatment, and RNA interference techniques were used to knock down the GABAB2 gene in the primary RGCs. The viability and apoptosis of RGCs were assessed using cell viability and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assays, Hoechst staining, and flow cytometry. The expression of cleaved caspase-3, bcl-2, bax, Akt, phospho-Akt, protein kinase RNA (PKR)-like ER kinase (PERK), phospho-PERK, eIF2α, phospho-eIF2α, ATF-4 and CCAAT/enhancer-binding protein homologous protein (CHOP) were measured using western blotting. GABAB2 mRNA expression was determined using quantitative real-time polymerase chain reaction (qRT-PCR) analysis. Our study revealed that CoCl2 significantly induced RGC apoptosis and that baclofen reversed these effects. CoCl2-induced reduction of Akt activity was also reversed by baclofen. Baclofen prevented the activation of the PERK pathway and the increase in CHOP expression induced by CoCl2. Knockdown of GABAB2 and the inactivation of the Akt pathway by inhibitors reduced the protective effect of baclofen on CoCl2-treated RGCs. Taken together, these results demonstrate that baclofen protects RGCs from CoCl2-induced apoptosis by increasing Akt activity and by suppressing the PERK pathway and CHOP activation.
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Affiliation(s)
- Pingping Fu
- Department of Ophthalmology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital Shanghai, China
| | - Qiang Wu
- Department of Ophthalmology, Shanghai Jiao Tong University Affiliated Sixth People's HospitalShanghai, China; Shanghai Key Laboratory of Diabetes Mellitus, Shanghai Jiao Tong University Affiliated Sixth People's HospitalShanghai, China
| | - Jianyan Hu
- Department of Ophthalmology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital Shanghai, China
| | - Tingting Li
- Department of Ophthalmology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital Shanghai, China
| | - Fengjuan Gao
- Department of Ophthalmology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital Shanghai, China
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13
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GABAB receptor upregulates fragile X mental retardation protein expression in neurons. Sci Rep 2015; 5:10468. [PMID: 26020477 PMCID: PMC4447080 DOI: 10.1038/srep10468] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Accepted: 04/15/2015] [Indexed: 12/17/2022] Open
Abstract
Fragile X mental retardation protein (FMRP) is an RNA-binding protein important for the control of translation and synaptic function. The mutation or silencing of FMRP causes Fragile X syndrome (FXS), which leads to intellectual disability and social impairment. γ-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter of the mammalian central nervous system, and its metabotropic GABAB receptor has been implicated in various mental disorders. The GABAB receptor agonist baclofen has been shown to improve FXS symptoms in a mouse model and in human patients, but the signaling events linking the GABAB receptor and FMRP are unknown. In this study, we found that GABAB receptor activation upregulated cAMP response element binding protein-dependent Fmrp expression in cultured mouse cerebellar granule neurons via two distinct mechanisms: the transactivation of insulin-like growth factor-1 receptor and activation of protein kinase C. In addition, a positive allosteric modulator of the GABAB receptor, CGP7930, stimulated Fmrp expression in neurons. These results suggest a role for GABAB receptor in Fmrp regulation and a potential interest of GABAB receptor signaling in FXS improvement.
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14
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Nørskov-Lauritsen L, Jørgensen S, Bräuner-Osborne H. N-glycosylation and disulfide bonding affects GPRC6A receptor expression, function, and dimerization. FEBS Lett 2015; 589:588-97. [PMID: 25617829 DOI: 10.1016/j.febslet.2015.01.019] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Revised: 12/28/2014] [Accepted: 01/14/2015] [Indexed: 12/20/2022]
Abstract
Investigation of post-translational modifications of receptor proteins is important for our understanding of receptor pharmacology and disease physiology. However, our knowledge about post-translational modifications of class C G protein-coupled receptors and how these modifications regulate expression and function is very limited. Herein, we show that the nutrient-sensing class C G protein-coupled receptor GPRC6A carries seven N-glycans and that one of these sites modulates surface expression whereas mutation of another site affects receptor function. GPRC6A has been speculated to form covalently linked dimers through cysteine disulfide linkage in the extracellular amino-terminal domain and here we show that GPRC6A indeed is a homodimer and that a disulfide bridge between the C131 residues is formed.
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Affiliation(s)
- Lenea Nørskov-Lauritsen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Stine Jørgensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark
| | - Hans Bräuner-Osborne
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Denmark.
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15
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Adelfinger L, Turecek R, Ivankova K, Jensen AA, Moss SJ, Gassmann M, Bettler B. GABAB receptor phosphorylation regulates KCTD12-induced K⁺ current desensitization. Biochem Pharmacol 2014; 91:369-79. [PMID: 25065880 PMCID: PMC4402209 DOI: 10.1016/j.bcp.2014.07.013] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Revised: 07/14/2014] [Accepted: 07/15/2014] [Indexed: 01/08/2023]
Abstract
GABAB receptors assemble from GABAB1 and GABAB2 subunits. GABAB2 additionally associates with auxiliary KCTD subunits (named after their K(+) channel tetramerization-domain). GABAB receptors couple to heterotrimeric G-proteins and activate inwardly-rectifying K(+) channels through the βγ subunits released from the G-protein. Receptor-activated K(+) currents desensitize in the sustained presence of agonist to avoid excessive effects on neuronal activity. Desensitization of K(+) currents integrates distinct mechanistic underpinnings. GABAB receptor activity reduces protein kinase-A activity, which reduces phosphorylation of serine-892 in GABAB2 and promotes receptor degradation. This form of desensitization operates on the time scale of several minutes to hours. A faster form of desensitization is induced by the auxiliary subunit KCTD12, which interferes with channel activation by binding to the G-protein βγ subunits. Here we show that the two mechanisms of desensitization influence each other. Serine-892 phosphorylation in heterologous cells rearranges KCTD12 at the receptor and slows KCTD12-induced desensitization. Likewise, protein kinase-A activation in hippocampal neurons slows fast desensitization of GABAB receptor-activated K(+) currents while protein kinase-A inhibition accelerates fast desensitization. Protein kinase-A fails to regulate fast desensitization in KCTD12 knock-out mice or knock-in mice with a serine-892 to alanine mutation, thus demonstrating that serine-892 phosphorylation regulates KCTD12-induced desensitization in vivo. Fast current desensitization is accelerated in hippocampal neurons carrying the serine-892 to alanine mutation, showing that tonic serine-892 phosphorylation normally limits KCTD12-induced desensitization. Tonic serine-892 phosphorylation is in turn promoted by assembly of receptors with KCTD12. This cross-regulation of serine-892 phosphorylation and KCTD12 activity sharpens the response during repeated receptor activation.
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Affiliation(s)
- Lisa Adelfinger
- Department of Biomedicine, University of Basel, 4056 Basel, Switzerland
| | - Rostislav Turecek
- Department of Biomedicine, University of Basel, 4056 Basel, Switzerland; Institute of Experimental Medicine, ASCR, Videnska 1083, 14220 Prague 4-Krc, Czech Republic
| | - Klara Ivankova
- Department of Biomedicine, University of Basel, 4056 Basel, Switzerland
| | - Anders A Jensen
- Department of Biomedicine, University of Basel, 4056 Basel, Switzerland
| | - Stephen J Moss
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, United States
| | - Martin Gassmann
- Department of Biomedicine, University of Basel, 4056 Basel, Switzerland
| | - Bernhard Bettler
- Department of Biomedicine, University of Basel, 4056 Basel, Switzerland.
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16
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Chen LH, Sun B, Zhang Y, Xu TJ, Xia ZX, Liu JF, Nan FJ. Discovery of a Negative Allosteric Modulator of GABAB Receptors. ACS Med Chem Lett 2014; 5:742-7. [PMID: 25050158 PMCID: PMC4094264 DOI: 10.1021/ml500162z] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2013] [Accepted: 05/27/2014] [Indexed: 12/11/2022] Open
Abstract
Initialized from the scaffold of CGP7930, an allosteric agonist of GABAB receptors, a series of noncompetitive antagonists were discovered. Among these compounds, compounds 3, 6, and 14 decreased agonist GABA-induced maximal effect of IP3 production in HEK293 cells overexpressing GABAB receptors and Gqi9 proteins without changing the EC50. Compounds 3, 6, and 14 not only inhibited agonist baclofen-induced ERK1/2 phosphorylation but also blocked CGP7930-induced ERK1/2 phosphorylation in HEK293 cells overexpressing GABAB receptors. The results suggested that compounds 3, 6, and 14 are negative allosteric modulators of GABAB receptors. The representative compound 14 decreased GABA-induced IP3 production with IC50 of 37.9 μM and had no effect on other GPCR Class C members such as mGluR1, mGluR2, and mGluR5. Finally, we showed that compound 14 did not bind to the orthosteric binding sites of GABAB receptors, demonstrating that compound 14 negatively modulated GABAB receptors activity as a negative allosteric modulator.
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Affiliation(s)
- Lin-Hai Chen
- National
Center for Drug Screening, State Key Laboratory of Drug Research,
Shanghai Institute of Materia Medica, Chinese
Academy of Sciences, Shanghai, China
| | - Bing Sun
- Cellular
Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry
of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Yang Zhang
- Cellular
Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry
of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Tong-Jie Xu
- Cellular
Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry
of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Zhi-Xiong Xia
- Cellular
Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry
of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Jian-Feng Liu
- Cellular
Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry
of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Fa-Jun Nan
- National
Center for Drug Screening, State Key Laboratory of Drug Research,
Shanghai Institute of Materia Medica, Chinese
Academy of Sciences, Shanghai, China
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17
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Sbai O, Monnier C, Dodé C, Pin JP, Hardelin JP, Rondard P. Biased signaling through G-protein-coupled PROKR2 receptors harboring missense mutations. FASEB J 2014; 28:3734-44. [PMID: 24830383 DOI: 10.1096/fj.13-243402] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Various missense mutations in the gene coding for prokineticin receptor 2 (PROKR2), a G-protein-coupled receptor, have been identified in patients with Kallmann syndrome. However, the functional consequences of these mutations on the different signaling pathways of this receptor have not been studied. We first showed that the wild-type PROKR2 can activate different G-protein subtypes (Gq, Gs, and Gi/o) and recruit β-arrestins in transfected HEK-293 cells. We then examined, for each of these signaling pathways, the effects of 9 mutations that did not significantly impair cell surface targeting or ligand binding of the receptor. Four mutant receptors showing defective Gq signaling (R85C, R85H, R164Q, and V331M) could still recruit β-arrestins on ligand activation, which may cause biased signaling in vivo. Conversely, the R80C receptor could activate the 3 types of G proteins but could not recruit β-arrestins. Finally, the R268C receptor could recruit β-arrestins and activate the Gq and Gs signaling pathways but could not activate the Gi/o signaling pathway. Our results validate the concept that mutations in the genes encoding membrane receptors can bias downstream signaling in various ways, possibly leading to pathogenic and, perhaps in some cases, protective (e.g., R268C) effects.
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Affiliation(s)
- Oualid Sbai
- Centre National de la Recherche Scientifique (CNRS) Unité Mixte de Recherche (UMR) 5203, Institut de Génomique Fonctionnelle, Montpellier, France; Institut National de la Santé et de la Recherche Médicale (INSERM) U661, Montpellier, France; Université Montpellier 1 and 2, Montpellier, France
| | - Carine Monnier
- Centre National de la Recherche Scientifique (CNRS) Unité Mixte de Recherche (UMR) 5203, Institut de Génomique Fonctionnelle, Montpellier, France; Institut National de la Santé et de la Recherche Médicale (INSERM) U661, Montpellier, France; Université Montpellier 1 and 2, Montpellier, France
| | - Catherine Dodé
- EA7331, Faculté des Sciences Pharmaceutiques et Biologiques, Université Paris-Descartes, Paris, France; and
| | - Jean-Philippe Pin
- Centre National de la Recherche Scientifique (CNRS) Unité Mixte de Recherche (UMR) 5203, Institut de Génomique Fonctionnelle, Montpellier, France; Institut National de la Santé et de la Recherche Médicale (INSERM) U661, Montpellier, France; Université Montpellier 1 and 2, Montpellier, France
| | - Jean-Pierre Hardelin
- INSERM Unité Mixte de Recherche en Santé (UMRS) 1120, Département Neuroscience, Institut Pasteur, Paris, France
| | - Philippe Rondard
- Centre National de la Recherche Scientifique (CNRS) Unité Mixte de Recherche (UMR) 5203, Institut de Génomique Fonctionnelle, Montpellier, France; Institut National de la Santé et de la Recherche Médicale (INSERM) U661, Montpellier, France; Université Montpellier 1 and 2, Montpellier, France;
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18
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Xu C, Zhang W, Rondard P, Pin JP, Liu J. Complex GABAB receptor complexes: how to generate multiple functionally distinct units from a single receptor. Front Pharmacol 2014; 5:12. [PMID: 24575041 PMCID: PMC3920572 DOI: 10.3389/fphar.2014.00012] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Accepted: 01/22/2014] [Indexed: 01/05/2023] Open
Abstract
The main inhibitory neurotransmitter, GABA, acts on both ligand-gated and G protein-coupled receptors, the GABAA/C and GABAB receptors, respectively. The later play important roles in modulating many synapses, both at the pre- and post-synaptic levels, and are then still considered as interesting targets to treat a number of brain diseases, including addiction. For many years, several subtypes of GABAB receptors were expected, but cloning revealed only two genes that work in concert to generate a single type of GABAB receptor composed of two subunits. Here we will show that the signaling complexity of this unit receptor type can be largely increased through various ways, including receptor stoichiometry, subunit isoforms, cell-surface expression and localization, crosstalk with other receptors, or interacting proteins. These recent data revealed how complexity of a receptor unit can be increased, observation that certainly are not unique to the GABAB receptor.
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Affiliation(s)
- Chanjuan Xu
- Cellular Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology Wuhan, China
| | - Wenhua Zhang
- Cellular Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology Wuhan, China
| | - Philippe Rondard
- Institut de Génomique Fonctionnelle, CNRS UMR5203, INSERM U661, Universités de Montpellier I & II Montpellier, France
| | - Jean-Philippe Pin
- Institut de Génomique Fonctionnelle, CNRS UMR5203, INSERM U661, Universités de Montpellier I & II Montpellier, France
| | - Jianfeng Liu
- Cellular Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology Wuhan, China
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19
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Geng Y, Bush M, Mosyak L, Wang F, Fan QR. Structural mechanism of ligand activation in human GABA(B) receptor. Nature 2013; 504:254-9. [PMID: 24305054 PMCID: PMC3865065 DOI: 10.1038/nature12725] [Citation(s) in RCA: 135] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2013] [Accepted: 09/30/2013] [Indexed: 01/02/2023]
Abstract
Human GABA(B) (γ-aminobutyric acid class B) receptor is a G-protein-coupled receptor central to inhibitory neurotransmission in the brain. It functions as an obligatory heterodimer of the subunits GBR1 and GBR2. Here we present the crystal structures of a heterodimeric complex between the extracellular domains of GBR1 and GBR2 in the apo, agonist-bound and antagonist-bound forms. The apo and antagonist-bound structures represent the resting state of the receptor; the agonist-bound complex corresponds to the active state. Both subunits adopt an open conformation at rest, and only GBR1 closes on agonist-induced receptor activation. The agonists and antagonists are anchored in the interdomain crevice of GBR1 by an overlapping set of residues. An antagonist confines GBR1 to the open conformation of the inactive state, whereas an agonist induces its domain closure for activation. Our data reveal a unique activation mechanism for GABA(B) receptor that involves the formation of a novel heterodimer interface between subunits.
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Affiliation(s)
- Yong Geng
- Department of Pharmacology, Columbia University, New York, New York 10032, USA
| | - Martin Bush
- Department of Pharmacology, Columbia University, New York, New York 10032, USA
| | - Lidia Mosyak
- Department of Pharmacology, Columbia University, New York, New York 10032, USA
| | - Feng Wang
- Department of Pharmacology, Columbia University, New York, New York 10032, USA
| | - Qing R Fan
- 1] Department of Pharmacology, Columbia University, New York, New York 10032, USA [2] Department of Pathology & Cell Biology, Columbia University, New York, New York 10032, USA
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20
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Benke D. GABAB receptor trafficking and interacting proteins: Targets for the development of highly specific therapeutic strategies to treat neurological disorders? Biochem Pharmacol 2013; 86:1525-30. [DOI: 10.1016/j.bcp.2013.09.016] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2013] [Revised: 09/20/2013] [Accepted: 09/20/2013] [Indexed: 10/26/2022]
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21
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Illuminating the activation mechanisms and allosteric properties of metabotropic glutamate receptors. Proc Natl Acad Sci U S A 2013; 110:E1416-25. [PMID: 23487753 DOI: 10.1073/pnas.1215615110] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In multimeric cell-surface receptors, the conformational changes of the extracellular ligand-binding domains (ECDs) associated with receptor activation remain largely unknown. This is the case for the dimeric metabotropic glutamate receptors even though a number of ECD structures have been solved. Here, using an innovative approach based on cell-surface labeling and FRET, we demonstrate that a reorientation of the ECDs is associated with receptor and G-protein activation. Our approach helps identify partial agonists and highlights allosteric interactions between the effector and binding domains. Any approach expected to stabilize the active conformation of the effector domain increased the agonist potency in stabilizing the active ECDs conformation. These data provide key information on the structural dynamics and drug action at metabotropic glutamate receptors and validate an approach for tackling such analysis on other receptors.
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22
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Masharina A, Reymond L, Maurel D, Umezawa K, Johnsson K. A Fluorescent Sensor for GABA and Synthetic GABAB Receptor Ligands. J Am Chem Soc 2012; 134:19026-34. [DOI: 10.1021/ja306320s] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- Anastasiya Masharina
- Institute of Chemical
Sciences and Engineering (ISIC),
Institute of Bioengineering, NCCR in Chemical Biology, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Luc Reymond
- Institute of Chemical
Sciences and Engineering (ISIC),
Institute of Bioengineering, NCCR in Chemical Biology, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Damien Maurel
- Institute of Chemical
Sciences and Engineering (ISIC),
Institute of Bioengineering, NCCR in Chemical Biology, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Keitaro Umezawa
- Institute of Chemical
Sciences and Engineering (ISIC),
Institute of Bioengineering, NCCR in Chemical Biology, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
| | - Kai Johnsson
- Institute of Chemical
Sciences and Engineering (ISIC),
Institute of Bioengineering, NCCR in Chemical Biology, Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
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23
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Forrest M, Chapman RM, Doyle AM, Tinsley CL, Waite A, Blake DJ. Functional analysis of TCF4 missense mutations that cause Pitt-Hopkins syndrome. Hum Mutat 2012; 33:1676-86. [PMID: 22777675 DOI: 10.1002/humu.22160] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2012] [Accepted: 06/19/2012] [Indexed: 12/16/2022]
Abstract
Pitt-Hopkins syndrome (PTHS) is a rare developmental disorder associated with severe mental retardation, facial abnormalities, and intermittent hyperventilation. Autosomal dominant PTHS is caused by mutations in the transcription factor 4 (TCF4) gene, whereas NRXN1 and CNTNAP2 mutations are associated with autosomal recessive PTHS. To determine the impact of missense mutations on TCF4 function, we tested a panel of PTHS-associated mutations using a range of quantitative techniques. Mutations in the basic helix-loop-helix (bHLH) domain of TCF4 alter the subnuclear localization of the mutant protein and can attenuate homo- and heterodimer formation in homogenous time-resolved fluorescence (HTRF) assays. By contrast, mutations proximal to the bHLH domain do not alter the location of TCF4 or impair heterodimer formation. In addition, we show that TCF4 can transactivate the NRXN1β and CNTNAP2 promoters in luciferase assays. Here we find variable, context-specific deficits in the ability of the different PTHS-associated TCF4 mutants to transactivate these promoters when coexpressed with different bHLH transcription factors. These data demonstrate that PTHS-associated missense mutations can have multiple effects on the function of the protein, and suggest that TCF4 may modulate the expression of NRXN1 and CNTNAP2 thereby defining a regulatory network in PTHS.
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Affiliation(s)
- Marc Forrest
- Institute of Psychological Medicine and Clinical Neurosciences, MRC Centre for Neuropsychiatric Genetics and Genomics, School of Medicine, Cardiff University, Cardiff, UK
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24
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Geng Y, Xiong D, Mosyak L, Malito DL, Kniazeff J, Chen Y, Burmakina S, Quick M, Bush M, Javitch JA, Pin JP, Fan QR. Structure and functional interaction of the extracellular domain of human GABA(B) receptor GBR2. Nat Neurosci 2012; 15:970-8. [PMID: 22660477 PMCID: PMC3374333 DOI: 10.1038/nn.3133] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Accepted: 05/10/2012] [Indexed: 11/08/2022]
Abstract
Inhibitory neurotransmission is mediated primarily by GABA. The metabotropic GABA(B) receptor is a G protein-coupled receptor central to mammalian brain function. Malfunction of GABA(B) receptor has been implicated in several neurological disorders. GABA(B) receptor functions as a heterodimeric assembly of GBR1 and GBR2 subunits, where GBR1 is responsible for ligand-binding and GBR2 is responsible for G protein coupling. Here we demonstrate that the GBR2 ectodomain directly interacts with the GBR1 ectodomain to increase agonist affinity by selectively stabilizing the agonist-bound conformation of GBR1. We present the crystal structure of the GBR2 ectodomain, which reveals a polar heterodimeric interface. We also identify specific heterodimer contacts from both subunits, and GBR1 residues involved in ligand recognition. Lastly, our structural and functional data indicate that the GBR2 ectodomain adopts a constitutively open conformation, suggesting a structural asymmetry in the active state of GABA(B) receptor that is unique to the GABAergic system.
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Affiliation(s)
- Yong Geng
- Department of Pharmacology, Columbia University, New York, New York, USA
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25
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Benke D, Zemoura K, Maier PJ. Modulation of cell surface GABA(B) receptors by desensitization, trafficking and regulated degradation. World J Biol Chem 2012; 3:61-72. [PMID: 22558486 PMCID: PMC3342575 DOI: 10.4331/wjbc.v3.i4.61] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/27/2011] [Revised: 12/08/2011] [Accepted: 12/15/2011] [Indexed: 02/05/2023] Open
Abstract
Inhibitory neurotransmission ensures normal brain function by counteracting and integrating excitatory activity. γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the mammalian central nervous system, and mediates its effects via two classes of receptors: the GABA(A) and GABA(B) receptors. GABA(A) receptors are heteropentameric GABA-gated chloride channels and responsible for fast inhibitory neurotransmission. GABA(B) receptors are heterodimeric G protein coupled receptors (GPCR) that mediate slow and prolonged inhibitory transmission. The extent of inhibitory neurotransmission is determined by a variety of factors, such as the degree of transmitter release and changes in receptor activity by posttranslational modifications (e.g., phosphorylation), as well as by the number of receptors present in the plasma membrane available for signal transduction. The level of GABA(B) receptors at the cell surface critically depends on the residence time at the cell surface and finally the rates of endocytosis and degradation. In this review we focus primarily on recent advances in the understanding of trafficking mechanisms that determine the expression level of GABA(B) receptors in the plasma membrane, and thereby signaling strength.
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Affiliation(s)
- Dietmar Benke
- Dietmar Benke, Khaled Zemoura, Patrick J Maier, Institute of Pharmacology and Toxicology, University of Zürich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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26
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Abstract
The G-protein-coupled receptors (GPCRs) are one of the largest super families of cell-surface receptors and play crucial roles in virtually every organ system. One particular family of GPCRs, the class C GPCRs, is distinguished by a characteristically large extracellular domain and constitutive dimerization. The structure and activation mechanism of this family result in potentially unique ligand recognition sites, thereby offering a variety of possibilities by which receptor activity might be modulated using novel compounds. In the present article, we aim to provide an overview of the exact sites and structural features involved in ligand recognition of the class C GPCRs. Furthermore, we demonstrate the precise steps that occur during the receptor activation process, which underlie the possibilities by which receptor function may be altered by different approaches. Finally, we use four typical family members to illustrate orthosteric and allosteric sites with representative ligands and their corresponding therapeutic potential.
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27
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Smith NJ, Milligan G. Allostery at G protein-coupled receptor homo- and heteromers: uncharted pharmacological landscapes. Pharmacol Rev 2011; 62:701-25. [PMID: 21079041 DOI: 10.1124/pr.110.002667] [Citation(s) in RCA: 211] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
For many years seven transmembrane domain G protein-coupled receptors (GPCRs) were thought to exist and function exclusively as monomeric units. However, evidence both from native cells and heterologous expression systems has demonstrated that GPCRs can both traffic and signal within higher-order complexes. As for other protein-protein interactions, conformational changes in one polypeptide, including those resulting from binding of pharmacological ligands, have the capacity to alter the conformation and therefore the response of the interacting protein(s), a process known as allosterism. For GPCRs, allosterism across homo- or heteromers, whether dimers or higher-order oligomers, represents an additional topographical landscape that must now be considered pharmacologically. Such effects may offer the opportunity for novel therapeutic approaches. Allosterism at GPCR heteromers is particularly exciting in that it offers additional scope to provide receptor subtype selectivity and tissue specificity as well as fine-tuning of receptor signal strength. Herein, we introduce the concept of allosterism at both GPCR homomers and heteromers and discuss the various questions that must be addressed before significant advances can be made in drug discovery at these GPCR complexes.
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Affiliation(s)
- Nicola J Smith
- Molecular Pharmacology Laboratory,University Avenue, University of Glasgow, Glasgow, Scotland
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28
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Monnier C, Tu H, Bourrier E, Vol C, Lamarque L, Trinquet E, Pin JP, Rondard P. Trans-activation between 7TM domains: implication in heterodimeric GABAB receptor activation. EMBO J 2010; 30:32-42. [PMID: 21063387 DOI: 10.1038/emboj.2010.270] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2010] [Accepted: 10/06/2010] [Indexed: 02/06/2023] Open
Abstract
Seven-transmembrane domain (7TM) receptors have important functions in cell-cell communication and can assemble into dimers or oligomers. Such complexes may allow specific functional cross-talk through trans-activation of interacting 7TMs, but this hypothesis requires further validation. Herein, we used the GABAB receptor, which is composed of two distinct subunits, GABAB1, which binds the agonist, and GABAB2, which activates G proteins, as a model system. By using a novel orthogonal-labelling approach compatible with time-resolved FRET and based on ACP- and SNAP-tag technologies to verify the heterodimerization of wild-type and mutated GABAB subunits, we demonstrate the existence of a direct allosteric coupling between the 7TMs of GABAB heterodimers. Indeed, a GABAB receptor, in which the GABAB2 extracellular domain was deleted, was still capable of activating G proteins. Furthermore, synthetic ligands for the GABAB2 7TM could increase agonist affinity at the GABAB1 subunit in this mutated receptor. In addition to bringing new information on GABAB receptor activation, these data clearly demonstrate the existence of direct trans-activation between the 7TM of two interacting proteins.
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Affiliation(s)
- Carine Monnier
- CNRS, UMR 5203, Institut de Génomique Fonctionnelle, Département de Pharmacologie Moléculaire, Montpellier, France
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29
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Rondard P, Goudet C, Kniazeff J, Pin JP, Prézeau L. The complexity of their activation mechanism opens new possibilities for the modulation of mGlu and GABAB class C G protein-coupled receptors. Neuropharmacology 2010; 60:82-92. [PMID: 20713070 DOI: 10.1016/j.neuropharm.2010.08.009] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2010] [Revised: 07/30/2010] [Accepted: 08/06/2010] [Indexed: 12/24/2022]
Abstract
In the human genome, 22 genes are coding for the class C G protein-coupled receptors that are receptors for the two main neurotransmitters glutamate and γ-aminobutyric acid, for Ca(2+) and for sweet and amino acid taste compounds. In addition to the GPCR heptahelical transmembrane domain responsible for G-protein activation, class C receptors possess a large extracellular domain that is responsible for ligand recognition. Recent studies had revealed that class C receptors are homo- or heterodimers with unique mechanism of activation. In the present review, we present an up-to-date view of the structures and activation mechanism of these receptors in particular the metabotropic glutamate and GABA(B) receptors. We show how the complexity of functioning of these transmembrane proteins can be used for the development of therapeutics to modulate their activity. We emphasize on the new approaches and drugs that could potentially become important in the future pharmacology of these receptors.
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30
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Matsushita S, Nakata H, Kubo Y, Tateyama M. Ligand-induced rearrangements of the GABA(B) receptor revealed by fluorescence resonance energy transfer. J Biol Chem 2010; 285:10291-9. [PMID: 20129919 DOI: 10.1074/jbc.m109.077990] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The gamma-aminobutyric acid type B receptor (GABA(B)R), one of the family C G-protein-coupled receptor members, exists as a heterodimer comprised of subunits GB1 and GB2. To clarify the ligand-induced activation mechanism of the GABA(B)R, each subunit was fused with either Cerulean or enhanced yellow fluorescent protein at its intracellular loop, and fluorescence resonance energy transfer (FRET) changes upon agonist application were monitored. As a result, FRET decreases were observed between GB1a loop 2 and GB2 loop 2 and between GB1a loop 2 and GB2 loop 1, suggesting the dissociation of intracellular domains during the receptor activation. Both intersubunit FRET pairs were expected to faithfully capture the activation of the original receptor as their pharmacological properties were highly similar to that of the wild-type receptor. However, the intrasubunit data suggest that the receptor activation does not involve major structural changes within the transmembrane domain of each subunit. By combining the results obtained from two different levels, it was concluded that the GABA(B)R activation by agonist is associated with an asymmetrical intersubunit rearrangement of GB1a and GB2 on the membrane. This type of activation mode, an intersubunit rearrangement without apparent intrahelical structural changes, appears commonly shared by the GABA(B)R and the metabotropic glutamate receptor 1alpha, another family C G-protein-coupled receptor previously studied by our group. Nevertheless, the directions of intracellular domain movements and its asymmetry observed here highlight the qualitative difference between the two receptors.
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Affiliation(s)
- Shinichi Matsushita
- Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, Okazaki, Aichi 444-8585, Japan
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31
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Heterodimerization of the GABAB receptor-implications for GPCR signaling and drug discovery. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2010; 58:63-91. [PMID: 20655478 DOI: 10.1016/s1054-3589(10)58003-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The identification of the molecular nature of the GABA(B) receptor and the demonstration of its heterodimeric structure has led to extensive studies investigating the mechanism of activation and signaling. Phylogenetic studies suggest that the formation of the heterodimer is a relatively recent event arising in conjunction with the evolution of the central nervous system. Heterodimerization has now been demonstrated for many other G-protein-coupled receptors (GPCRs) and plays a role in signaling and trafficking. This presents both challenges and opportunities for GPCR drug discovery. In the case of the GABA(B) receptor the best hope for the development of new drugs directed at this receptor is from allosteric modulators. This chapter summarizes our current understanding of the molecular function of the GABA(B) receptor and recent developments in the identification of allosteric modulators. The broader implication of heterodimerization on GPCR function and drug discovery is also discussed.
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32
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Terpager M, Scholl DJ, Kubale V, Martini L, Elling CE, Schwartz TW. Construction of covalently coupled, concatameric dimers of 7TM receptors. J Recept Signal Transduct Res 2009; 29:235-45. [PMID: 19747085 DOI: 10.1080/10799890903154217] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
7TM receptors are easily fused to proteins such as G proteins and arrestin but because of the fact that their terminals are found on each side of the membrane they cannot be joined directly in covalent dimers. Here, we use an artificial connector comprising a transmembrane helix composed of Leu-Ala repeats flanked by flexible spacers and positively charged residues to ensure correct inside-out orientation plus an extracellular HA-tag to construct covalently coupled dimers of 7TM receptors. Such 15 TM concatameric homo- and heterodimers of the beta(2)-adrenergic and the NK(1) receptors, which normally do not dimerize with each other, were expressed surprisingly well at the cell surface, where they bound ligands and activated signal transduction in a manner rather similar to the corresponding wild-type receptors. The concatameric heterodimers internalized upon stimulation with agonists for either of the protomers, which was not observed upon simple coexpression of the two receptors. It is concluded that covalently joined 7TM receptor dimers with surprisingly normal receptor properties can be constructed with use of an artificial transmembrane connector, which perhaps can be used to fuse other membrane proteins.
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Affiliation(s)
- Marie Terpager
- Laboratory for Molecular Pharmacology, Department of Neuroscience and Pharmacology, The Panum Institute, University of Copenhagen, DK-2200 Copenhagen, Denmark
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Monnier C, Dodé C, Fabre L, Teixeira L, Labesse G, Pin JP, Hardelin JP, Rondard P. PROKR2 missense mutations associated with Kallmann syndrome impair receptor signalling activity. Hum Mol Genet 2009; 18:75-81. [PMID: 18826963 PMCID: PMC3298864 DOI: 10.1093/hmg/ddn318] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Kallmann syndrome (KS) combines hypogonadism due to gonadotropin-releasing hormone deficiency, and anosmia or hyposmia, related to defective olfactory bulb morphogenesis. In a large series of KS patients, ten different missense mutations (p.R85C, p.R85H, p.R164Q, p.L173R, p.W178S, p.Q210R, p.R268C, p.P290S, p.M323I, p.V331M) have been identified in the gene encoding the G protein-coupled receptor prokineticin receptor-2 (PROKR2), most often in the heterozygous state. Many of these mutations were, however, also found in clinically unaffected individuals, thus raising the question of their actual implication in the KS phenotype. We reproduced each of the ten mutations in a recombinant murine Prokr2, and tested their effects on the signalling activity in transfected HEK-293 cells, by measuring intracellular calcium release upon ligand-activation of the receptor. We found that all mutated receptors except one (M323I) had decreased signalling activities. These could be explained by different defective mechanisms. Three mutations (L173R, W178S, P290S) impaired cell surface-targeting of the receptor. One mutation (Q210R) abolished ligand-binding. Finally, five mutations (R85C, R85H, R164Q, R268C, V331M) presumably impaired G protein-coupling of the receptor. In addition, when wild-type and mutant receptors were coexpressed in HEK-293 cells, none of the mutant receptors that were retained within the cells did affect cell surface-targeting of the wild-type receptor, and none of the mutant receptors properly addressed at the plasma membrane did affect wild-type receptor signalling activity. This argues against a dominant negative effect of the mutations in vivo.
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Affiliation(s)
- Carine Monnier
- CNRS UMR5203, Institut de Génomique Fonctionnelle, INSERM U661, Université Montpellier 1,2, Montpellier, France
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Aplin M, Bonde MM, Hansen JL. Molecular determinants of angiotensin II type 1 receptor functional selectivity. J Mol Cell Cardiol 2009; 46:15-24. [DOI: 10.1016/j.yjmcc.2008.09.123] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/22/2008] [Revised: 09/09/2008] [Accepted: 09/18/2008] [Indexed: 01/14/2023]
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Cui M, Chung F, Donahue CJ. Development of a robust GABABcalcium signaling cell line using β‐lactamase technology and sorting. Cytometry A 2008; 73:761-6. [DOI: 10.1002/cyto.a.20591] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Li X, Cao JH, Li Y, Rondard P, Zhang Y, Yi P, Liu JF, Nan FJ. Activity-Based Probe for Specific Photoaffinity Labeling γ-Aminobutyric Acid B (GABAB) Receptors on Living Cells: Design, Synthesis, and Biological Evaluation. J Med Chem 2008; 51:3057-60. [DOI: 10.1021/jm800140f] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Affiliation(s)
- Xin Li
- Key Laboratory of Molecular Biophysics of Ministry of Education, School of Life Science and Technology, Huazhong University of Science and Technology, 1037 Luo Yu Road, Wuhan, Hubei, China, National Center for Drug Screening, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, 189 Guo Shou Jing Road, Shanghai 201203, China, and Institute of Functional Genomics, CNRS UMR5203, INSERM U661, University of
| | - Jian-Hua Cao
- Key Laboratory of Molecular Biophysics of Ministry of Education, School of Life Science and Technology, Huazhong University of Science and Technology, 1037 Luo Yu Road, Wuhan, Hubei, China, National Center for Drug Screening, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, 189 Guo Shou Jing Road, Shanghai 201203, China, and Institute of Functional Genomics, CNRS UMR5203, INSERM U661, University of
| | - Ying Li
- Key Laboratory of Molecular Biophysics of Ministry of Education, School of Life Science and Technology, Huazhong University of Science and Technology, 1037 Luo Yu Road, Wuhan, Hubei, China, National Center for Drug Screening, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, 189 Guo Shou Jing Road, Shanghai 201203, China, and Institute of Functional Genomics, CNRS UMR5203, INSERM U661, University of
| | - Philippe Rondard
- Key Laboratory of Molecular Biophysics of Ministry of Education, School of Life Science and Technology, Huazhong University of Science and Technology, 1037 Luo Yu Road, Wuhan, Hubei, China, National Center for Drug Screening, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, 189 Guo Shou Jing Road, Shanghai 201203, China, and Institute of Functional Genomics, CNRS UMR5203, INSERM U661, University of
| | - Yang Zhang
- Key Laboratory of Molecular Biophysics of Ministry of Education, School of Life Science and Technology, Huazhong University of Science and Technology, 1037 Luo Yu Road, Wuhan, Hubei, China, National Center for Drug Screening, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, 189 Guo Shou Jing Road, Shanghai 201203, China, and Institute of Functional Genomics, CNRS UMR5203, INSERM U661, University of
| | - Ping Yi
- Key Laboratory of Molecular Biophysics of Ministry of Education, School of Life Science and Technology, Huazhong University of Science and Technology, 1037 Luo Yu Road, Wuhan, Hubei, China, National Center for Drug Screening, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, 189 Guo Shou Jing Road, Shanghai 201203, China, and Institute of Functional Genomics, CNRS UMR5203, INSERM U661, University of
| | - Jian-Feng Liu
- Key Laboratory of Molecular Biophysics of Ministry of Education, School of Life Science and Technology, Huazhong University of Science and Technology, 1037 Luo Yu Road, Wuhan, Hubei, China, National Center for Drug Screening, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, 189 Guo Shou Jing Road, Shanghai 201203, China, and Institute of Functional Genomics, CNRS UMR5203, INSERM U661, University of
| | - Fa-Jun Nan
- Key Laboratory of Molecular Biophysics of Ministry of Education, School of Life Science and Technology, Huazhong University of Science and Technology, 1037 Luo Yu Road, Wuhan, Hubei, China, National Center for Drug Screening, State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, 189 Guo Shou Jing Road, Shanghai 201203, China, and Institute of Functional Genomics, CNRS UMR5203, INSERM U661, University of
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Lagerström MC, Schiöth HB. Structural diversity of G protein-coupled receptors and significance for drug discovery. Nat Rev Drug Discov 2008; 7:339-57. [PMID: 18382464 DOI: 10.1038/nrd2518] [Citation(s) in RCA: 1057] [Impact Index Per Article: 66.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
G protein-coupled receptors (GPCRs) are the largest family of membrane-bound receptors and also the targets of many drugs. Understanding of the functional significance of the wide structural diversity of GPCRs has been aided considerably in recent years by the sequencing of the human genome and by structural studies, and has important implications for the future therapeutic potential of targeting this receptor family. This article aims to provide a comprehensive overview of the five main human GPCR families--Rhodopsin, Secretin, Adhesion, Glutamate and Frizzled/Taste2--with a focus on gene repertoire, general ligand preference, common and unique structural features, and the potential for future drug discovery.
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Affiliation(s)
- Malin C Lagerström
- Department of Neuroscience, Functional Pharmacology, Uppsala University, BMC, BOX 593, 751 24, Uppsala, Sweden
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Functioning of the dimeric GABA(B) receptor extracellular domain revealed by glycan wedge scanning. EMBO J 2008; 27:1321-32. [PMID: 18388862 DOI: 10.1038/emboj.2008.64] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2007] [Accepted: 03/05/2008] [Indexed: 12/22/2022] Open
Abstract
The G-protein-coupled receptor (GPCR) activated by the neurotransmitter GABA is made up of two subunits, GABA(B1) and GABA(B2). GABA(B1) binds agonists, whereas GABA(B2) is required for trafficking GABA(B1) to the cell surface, increasing agonist affinity to GABA(B1), and activating associated G proteins. These subunits each comprise two domains, a Venus flytrap domain (VFT) and a heptahelical transmembrane domain (7TM). How agonist binding to the GABA(B1) VFT leads to GABA(B2) 7TM activation remains unknown. Here, we used a glycan wedge scanning approach to investigate how the GABA(B) VFT dimer controls receptor activity. We first identified the dimerization interface using a bioinformatics approach and then showed that introducing an N-glycan at this interface prevents the association of the two subunits and abolishes all activities of GABA(B2), including agonist activation of the G protein. We also identified a second region in the VFT where insertion of an N-glycan does not prevent dimerization, but blocks agonist activation of the receptor. These data provide new insight into the function of this prototypical GPCR and demonstrate that a change in the dimerization interface is required for receptor activation.
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Remelli R, Robbins MJ, McIlhinney RAJ. The C-terminus of the metabotropic glutamate receptor 1b regulates dimerization of the receptor. J Neurochem 2008; 104:1020-31. [DOI: 10.1111/j.1471-4159.2007.05034.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Nomura R, Suzuki Y, Kakizuka A, Jingami H. Direct detection of the interaction between recombinant soluble extracellular regions in the heterodimeric metabotropic gamma-aminobutyric acid receptor. J Biol Chem 2007; 283:4665-73. [PMID: 18165688 DOI: 10.1074/jbc.m705202200] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The gamma-aminobutyric acid, type B (GABAB) receptor is a heterodimeric receptor consisting of two complementary subunits, GABAB1 receptor (GBR1) and GABAB2 receptor (GBR2). GBR1 is responsible for GABA binding, whereas GBR2 is considered to perform a critical role in signal transduction toward downstream targets. Therefore, precise communication between GBR1 and GBR2 is thought to be essential for the proper signal transduction process. However, biochemical data describing the interaction of the two subunits, especially for the extracellular regions, are not sufficient. Thus we began by developing a protein expression system of the soluble extracellular regions. One of the soluble recombinant GBR1 proteins exhibited a ligand binding ability, which is similar to that of the full-length GBR1, and thus the ligand-binding domain was determined. Direct interaction between GBR1 and GBR2 extracellular soluble fragments was confirmed by co-expression followed by affinity column chromatography and a sucrose density gradient sedimentation. In addition, we also found homo-oligomeric states of these soluble extracellular regions. The interaction between the two soluble extracellular regions caused the enhancement of the agonist affinity for GBR1 as previously reported in a cell-based assay. These results not only open the way to future structural studies but also highlight the role of the interaction between the extracellular regions, which controls agonist affinity to the heterodimeric receptor.
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Affiliation(s)
- Rei Nomura
- Department of Molecular Biology, Biomolecular Engineering Research Institute, 6-2-3 Furuedai, Suita, Osaka 565-0874, Japan
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Brock C, Oueslati N, Soler S, Boudier L, Rondard P, Pin JP. Activation of a dimeric metabotropic glutamate receptor by intersubunit rearrangement. J Biol Chem 2007; 282:33000-8. [PMID: 17855348 DOI: 10.1074/jbc.m702542200] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Although many G protein-coupled receptors (GPCRs) can form dimers, a possible role of this phenomenon in their activation remains elusive. A recent and exciting proposal is that a dynamic intersubunit interplay may contribute to GPCR activation. Here, we examined this possibility using dimeric metabotropic glutamate receptors (mGluRs). We first developed a system to perfectly control their subunit composition and show that mGluR dimers do not form larger oligomers. We then examined an mGluR dimer containing one subunit in which the extracellular agonist-binding domain was uncoupled from the G protein-activating transmembrane domain. Despite this uncoupling in one protomer, agonist stimulation resulted in symmetric activation of either transmembrane domain in the dimer with the same efficiency. This, plus other data, can only be explained by an intersubunit rearrangement as the activation mechanism. Although well established for other types of receptors such as tyrosine kinase and guanylate cyclase receptors, this is the first clear demonstration that such a mechanism may also apply to GPCRs.
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Affiliation(s)
- Carsten Brock
- University of Montpellier 1 and 2, CNRS UMR 5203, Institute of Functional Genomics, 141 rue de la Cardonille, Montpellier, France
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Marshall FH. The role of GABA(B) receptors in the regulation of excitatory neurotransmission. Results Probl Cell Differ 2007; 44:87-98. [PMID: 17549439 DOI: 10.1007/400_2007_038] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
GABA(B) receptors are the metabotrophic receptors for GABA. They are members of the G-protein coupled superfamily of receptors but are highly unusual as they are made up of a dimer of 7-transmembrane spanning subunits. The receptors are widely distributed throughout the central nervous system where they act post-synaptically to cause a long-lasting hyperpolarisation through the activation of a potassium conductance. They are also present pre-synaptically where they act as auto and heteroreceptors to inhibit neurotransmitter release. GABA(B) receptors play a complex role in the regulation of excitatory transmission and their activation can have both inhibitory and dis-inhibitory effects. This has profound physiological and behavioural consequences including modification of LTP and memory, regulation of seizure activity and nociception.
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Affiliation(s)
- Fiona H Marshall
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, UK.
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Tu H, Rondard P, Xu C, Bertaso F, Cao F, Zhang X, Pin JP, Liu J. Dominant role of GABAB2 and Gbetagamma for GABAB receptor-mediated-ERK1/2/CREB pathway in cerebellar neurons. Cell Signal 2007; 19:1996-2002. [PMID: 17582742 DOI: 10.1016/j.cellsig.2007.05.004] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2007] [Accepted: 05/20/2007] [Indexed: 11/23/2022]
Abstract
gamma-aminobutyric acid type B (GABA(B)) receptor is an allosteric complex made of two subunits, GABA(B1) and GABA(B2). GABA(B2) plays a major role in the coupling to G protein whereas GABA(B1) binds GABA. It has been shown that GABA(B) receptor activates ERK(1/2) in neurons of the central nervous system, but the molecular mechanisms underlying this event are poorly characterized. Here, we demonstrate that activation of GABA(B) receptor by either GABA or the selective agonist baclofen induces ERK(1/2) phosphorylation in cultured cerebellar granule neurons. We also show that CGP7930, a positive allosteric regulator specific of GABA(B2), alone can induce the phosphorylation of ERK(1/2). PTX, a G(i/o) inhibitor, abolishes both baclofen and CGP7930-mediated-ERK(1/2) phosphorylation. Moreover, both baclofen and CGP7930 induce ERK-dependent CREB phosphorylation. Furthermore, by using LY294002, a PI-3 kinase inhibitor, and a C-term of GRK-2 that has been reported to sequester Gbetagamma subunits, we demonstrate the role of Gbetagamma in GABA(B) receptor-mediated-ERK(1/2) phosphorylation. In conclusion, the activation of GABA(B) receptor leads to ERK(1/2) phosphorylation via the coupling of GABA(B2) to G(i/o) and by releasing Gbetagamma subunits which in turn induce the activation of CREB. These findings suggest a role of GABA(B) receptor in long-term change in the central nervous system.
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Affiliation(s)
- Haijun Tu
- Sino-France Laboratory for Drug Screening, Key Laboratory of Molecular Biophysics, Ministry of Education, School of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei, China
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Pin JP, Neubig R, Bouvier M, Devi L, Filizola M, Javitch JA, Lohse MJ, Milligan G, Palczewski K, Parmentier M, Spedding M. International Union of Basic and Clinical Pharmacology. LXVII. Recommendations for the Recognition and Nomenclature of G Protein-Coupled Receptor Heteromultimers. Pharmacol Rev 2007; 59:5-13. [PMID: 17329545 DOI: 10.1124/pr.59.1.5] [Citation(s) in RCA: 204] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
G protein-coupled receptors (GPCRs) have long been considered to be monomeric membrane proteins. Although numerous recent studies have indicated that GPCRs can form multimeric complexes, the functional and pharmacological consequences of this phenomenon have remained elusive. With the discovery that the functional GABA(B) receptor is an obligate heterodimer and with the use of energy transfer technologies, it is now accepted that GPCRs can form heteromultimers. In some cases, specific properties of such heteromers not shared by their respective homomers have been reported. Although in most cases these properties have only been observed in heterologous expression systems, there are a few reports describing data consistent with such heteromultimeric GPCR complexes also existing in native tissues. The present article illustrates well-documented examples of such native multimeric complexes, lists a number of recommendations for recognition and acceptance of such multimeric receptors, and gives recommendations for their nomenclature.
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Affiliation(s)
- Jean-Philippe Pin
- Institut de Génomique Fonctionnelle, 141, rue de la Cardonille, 34094 Montpellier cedex 5, France.
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Binet V, Duthey B, Lecaillon J, Vol C, Quoyer J, Labesse G, Pin JP, Prézeau L. Common structural requirements for heptahelical domain function in class A and class C G protein-coupled receptors. J Biol Chem 2007; 282:12154-63. [PMID: 17310064 PMCID: PMC2565688 DOI: 10.1074/jbc.m611071200] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
G protein-coupled receptors (GPCRs) are key players in cell communication. Several classes of such receptors have been identified. Although all GPCRs possess a heptahelical domain directly activating G proteins, important structural and sequence differences within receptors from different classes suggested distinct activation mechanisms. Here we show that highly conserved charged residues likely involved in an interaction network between transmembrane domains (TM) 3 and 6 at the cytoplasmic side of class C GPCRs are critical for activation of the gamma-aminobutyric acid type B receptor. Indeed, the loss of function resulting from the mutation of the conserved lysine residue into aspartate or glutamate in the TM3 of gamma-aminobutyric acid type B(2) can be partly rescued by mutating the conserved acidic residue of TM6 into either lysine or arginine. In addition, mutation of the conserved lysine into an acidic residue leads to a nonfunctional receptor that displays a high agonist affinity. This is reminiscent of a similar ionic network that constitutes a lock stabilizing the inactive state of many class A rhodopsin-like GPCRs. These data reveal that despite their original structure, class C GPCRs share with class A receptors at least some common structural feature controlling G protein activation.
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Affiliation(s)
- Virginie Binet
- IGF, Institut de génomique fonctionnelle
CNRS : UMR5203INSERM : U661Université Montpellier IUniversité Montpellier II - Sciences et Techniques du Languedoc141, Rue de la Cardonille
34094 MONTPELLIER CEDEX 5,FR
- Centre Hospitalo-Universitaire de Montpellier
CHUI MontpellierFR
| | - Béatrice Duthey
- IGF, Institut de génomique fonctionnelle
CNRS : UMR5203INSERM : U661Université Montpellier IUniversité Montpellier II - Sciences et Techniques du Languedoc141, Rue de la Cardonille
34094 MONTPELLIER CEDEX 5,FR
| | - Jennifer Lecaillon
- IGF, Institut de génomique fonctionnelle
CNRS : UMR5203INSERM : U661Université Montpellier IUniversité Montpellier II - Sciences et Techniques du Languedoc141, Rue de la Cardonille
34094 MONTPELLIER CEDEX 5,FR
| | - Claire Vol
- IGF, Institut de génomique fonctionnelle
CNRS : UMR5203INSERM : U661Université Montpellier IUniversité Montpellier II - Sciences et Techniques du Languedoc141, Rue de la Cardonille
34094 MONTPELLIER CEDEX 5,FR
| | - Julie Quoyer
- IGF, Institut de génomique fonctionnelle
CNRS : UMR5203INSERM : U661Université Montpellier IUniversité Montpellier II - Sciences et Techniques du Languedoc141, Rue de la Cardonille
34094 MONTPELLIER CEDEX 5,FR
| | - Gilles Labesse
- CBS, Centre de biochimie structurale
CNRS : UMR5048INSERM : U554IFR3Université Montpellier IUniversité Montpellier II - Sciences et Techniques du Languedoc29 rue de Navacelles
34090 MONTPELLIER,FR
| | - Jean-Philippe Pin
- IGF, Institut de génomique fonctionnelle
CNRS : UMR5203INSERM : U661Université Montpellier IUniversité Montpellier II - Sciences et Techniques du Languedoc141, Rue de la Cardonille
34094 MONTPELLIER CEDEX 5,FR
| | - Laurent Prézeau
- IGF, Institut de génomique fonctionnelle
CNRS : UMR5203INSERM : U661Université Montpellier IUniversité Montpellier II - Sciences et Techniques du Languedoc141, Rue de la Cardonille
34094 MONTPELLIER CEDEX 5,FR
- * Correspondence should be adressed to: Laurent Prézeau
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Prabhu Y, Eichinger L. The Dictyostelium repertoire of seven transmembrane domain receptors. Eur J Cell Biol 2006; 85:937-46. [PMID: 16735079 DOI: 10.1016/j.ejcb.2006.04.003] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The availability of fully sequenced genomes allows the in silico analysis of whole gene families in a given genome. A particularly large and interesting gene family is the G-protein-coupled receptor family. These receptors detect a variety of extracellular signals and transduce them, generally via heterotrimeric G-proteins, to effector proteins inside the cell and thus elicit a physiological response. G-protein-coupled receptors are found in all eukaryotes and constitute in vertebrates 3-5% of all genes. They are also very important drug targets and approximately 25 of the top 100 selling drugs are directed against these receptors. The Dictyostelium discoideum genome contains a surprisingly high number of 55 such receptors, approximately 0.5% of the encoded genes. Besides the four well-studied cAMP receptors the genome encodes eight additional cAMP receptor-like proteins and one of these is distinguished by a novel domain structure, one secretin-like receptor, 17 GABA(B)-like and 25 Frizzled-like receptors. The existence of the latter three types of receptors in D. discoideum was surprising because they had not been observed outside the animal kingdom before. Their presence suggests unprecedentedly complex and so far unknown signaling activities in this lower eukaryote.
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Affiliation(s)
- Yogikala Prabhu
- Centre for Biochemistry, Medical Faculty, University of Cologne, Joseph-Stelzmann-Str. 52, D-50931 Köln, Germany
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47
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Kornau HC. GABAB receptors and synaptic modulation. Cell Tissue Res 2006; 326:517-33. [PMID: 16932937 DOI: 10.1007/s00441-006-0264-7] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2006] [Accepted: 05/31/2006] [Indexed: 12/18/2022]
Abstract
GABA(B) receptors modulate transmitter release and postsynaptic membrane potential at various types of central synapses. They function as heterodimers of two related seven-transmembrane domain receptor subunits. Trafficking, activation and signalling of GABA(B) receptors are regulated both by allosteric interactions between the subunits and by the binding of additional proteins. Recent studies have shed light on the roles of GABA(B) receptors in plasticity processes at excitatory synapses. This review summarizes our knowledge of the localization, structure and function of GABA(B) receptors in the central nervous system and their use as drug targets for neurological and psychiatric disorders.
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Affiliation(s)
- Hans-Christian Kornau
- Center for Molecular Neurobiology (ZMNH), University of Hamburg, Falkenried 94, 20251 Hamburg, Germany.
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48
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Albizu L, Balestre MN, Breton C, Pin JP, Manning M, Mouillac B, Barberis C, Durroux T. Probing the existence of G protein-coupled receptor dimers by positive and negative ligand-dependent cooperative binding. Mol Pharmacol 2006; 70:1783-91. [PMID: 16926282 DOI: 10.1124/mol.106.025684] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
An increasing amount of ligand binding data on G protein-coupled receptors (GPCRs) is not compatible with the prediction of the simple mass action law. This may be related to the propensity of most GPCRs, if not all, to oligomerize. Indeed, one of the consequences of receptor oligomerization could be a possible cross-talk between the protomers, which in turn could lead to negative or positive cooperative ligand binding. We prove here that this can be demonstrated experimentally. Saturation, dissociation, and competition binding experiments were performed on vasopressin and oxytocin receptors expressed in Chinese hamster ovary or COS-7 cells. Linear, concave, and convex Scatchard plots were then obtained, depending on the ligand used. Moreover, some competition curves exhibited an increase of the radiotracer binding for low concentrations of competitors, suggesting a cooperative binding process. These data demonstrate that various vasopressin analogs display either positive or negative cooperative binding. Because positive cooperative binding cannot be explained without considering receptor as multivalent, these binding data support the concept of GPCR dimerization process. The results, which are in good accordance with the predictions of previous mathematical models, suggest that binding experiments can be used to probe the existence of receptor dimers.
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Affiliation(s)
- Laura Albizu
- Institut de Génomique Fonctionnelle, Centre National de la Recherche Scientifique Unité Mixte Recherche 5203, 141 rue de la Cardonille, 34094 Montpellier CEDEX 5, France
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Rondard P, Liu J, Huang S, Malhaire F, Vol C, Pinault A, Labesse G, Pin JP. Coupling of agonist binding to effector domain activation in metabotropic glutamate-like receptors. J Biol Chem 2006; 281:24653-61. [PMID: 16787923 DOI: 10.1074/jbc.m602277200] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Many membrane receptors are made of a ligand binding domain and an effector domain mediating intracellular signaling. This is the case for the metabotropic glutamate-like G-protein-coupled receptors. How ligand binding leads to the active conformation of the effector domain in such receptors is largely unknown. Here, we used an evolutionary trace analysis and mutagenesis to identify critical residues involved in the allosteric coupling between the Venus flytrap ligand binding domain (VFT) and the heptahelical G-protein activating domain of the metabotropic glutamate-like receptors. We have shown that a conserved interdomain disulfide bridge is required for this allosteric interaction. Taking into account that these receptors are homodimers, this finding provides important new information explaining how the different conformations of the dimer of VFT lead to different signaling of such dimeric receptors.
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Affiliation(s)
- Philippe Rondard
- CNRS Unité Mixte de Recherche 5203, INSERM U661, Universités Montpellier 1 and 2, France
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Asay MJ, Boyd SK. Characterization of the binding of [3H]CGP54626 to GABAB receptors in the male bullfrog (Rana catesbeiana). Brain Res 2006; 1094:76-85. [PMID: 16725130 DOI: 10.1016/j.brainres.2006.03.008] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2005] [Revised: 03/06/2006] [Accepted: 03/07/2006] [Indexed: 10/24/2022]
Abstract
Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the vertebrate brain. GABA activates both ionotropic (GABA(A)) and metabotropic (GABA(B)) receptors in mammals. Whether non-mammalian vertebrates possess receptors with similar characteristics is not well understood. We used a mammalian GABA(B)-specific antagonist to determine the pharmacology of putative receptors in the brain of an anuran amphibian, the male bullfrog (Rana catesbeiana). Receptor binding assays with the antagonist [(3)H]CGP54626 revealed a single class of high affinity binding sites (with a K(D) of 2.97 nM and a B(max) of 2619 fmol/mg protein). Binding was time- and temperature-dependent, saturable and specific. Specific binding of [(3)H]CGP54626 was inhibited by several mammalian GABA(B) receptor agonists and antagonists. The rank order potency of agonists was: GABA = SKF97541 > (R)-Baclofen > 3-APPA. The rank order for antagonists was: CGP54626 = CGP55845 > CGP52432 > CGP35348. The GABA(A) receptor ligands muscimol and SR95531 had very low affinity for [(3)H]CGP54626 binding sites, while bicuculline compounds had no affinity. Binding of GABA was positively modulated by CGP7930. Taurine did not allosterically modulate GABA binding but did inhibit [(3)H]CGP54626 binding in a linear fashion. Bullfrog brain thus possesses binding sites with significant similarity to mammalian GABA(B) receptors. These receptors differ from mammalian receptors, however, in dissociation kinetics, ligand specificity and allosteric modulation.
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Affiliation(s)
- Matthew J Asay
- Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA.
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