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Caniceiro AB, Bueschbell B, Barreto CA, Preto AJ, Moreira IS. MUG: A mutation overview of GPCR subfamily A17 receptors. Comput Struct Biotechnol J 2022; 21:586-600. [PMID: 36659920 PMCID: PMC9822836 DOI: 10.1016/j.csbj.2022.12.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Revised: 12/15/2022] [Accepted: 12/15/2022] [Indexed: 12/24/2022] Open
Abstract
G protein-coupled receptors (GPCRs) mediate several signaling pathways through a general mechanism that involves their activation, upholding a chain of events that lead to the release of molecules responsible for cytoplasmic action and further regulation. These physiological functions can be severely altered by mutations in GPCR genes. GPCRs subfamily A17 (dopamine, serotonin, adrenergic and trace amine receptors) are directly related with neurodegenerative diseases, and as such it is crucial to explore known mutations on these systems and their impact in structure and function. A comprehensive and detailed computational framework - MUG (Mutations Understanding GPCRs) - was constructed, illustrating key reported mutations and their effect on receptors of the subfamily A17 of GPCRs. We explored the type of mutations occurring overall and in the different families of subfamily A17, as well their localization within the receptor and potential effects on receptor functionality. The mutated residues were further analyzed considering their pathogenicity. The results reveal a high diversity of mutations in the GPCR subfamily A17 structures, drawing attention to the considerable number of mutations in conserved residues and domains. Mutated residues were typically hydrophobic residues enriched at the ligand binding pocket and known activating microdomains, which may lead to disruption of receptor function. MUG as an interactive web application is available for the management and visualization of this dataset. We expect that this interactive database helps the exploration of GPCR mutations, their influence, and their familywise and receptor-specific effects, constituting the first step in elucidating their structures and molecules at the atomic level.
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Affiliation(s)
- Ana B. Caniceiro
- CNC - Center for Neuroscience and Cell Biology, Center for Innovative Biomedicine and Biotechnology, University of Coimbra, Coimbra, Portugal
- PhD in Biosciences, Department of Life Sciences, University of Coimbra, Calçada Martim de Freitas, 3000-456 Coimbra, Portugal
| | - Beatriz Bueschbell
- CNC - Center for Neuroscience and Cell Biology, Center for Innovative Biomedicine and Biotechnology, University of Coimbra, Coimbra, Portugal
- PhD Programme in Experimental Biology and Biomedicine, Institute for Interdisciplinary Research (IIIUC), University of Coimbra, Casa Costa Alemão, 3030-789 Coimbra, Portugal
| | - Carlos A.V. Barreto
- CNC - Center for Neuroscience and Cell Biology, Center for Innovative Biomedicine and Biotechnology, University of Coimbra, Coimbra, Portugal
- PhD Programme in Experimental Biology and Biomedicine, Institute for Interdisciplinary Research (IIIUC), University of Coimbra, Casa Costa Alemão, 3030-789 Coimbra, Portugal
| | - António J. Preto
- CNC - Center for Neuroscience and Cell Biology, Center for Innovative Biomedicine and Biotechnology, University of Coimbra, Coimbra, Portugal
- PhD Programme in Experimental Biology and Biomedicine, Institute for Interdisciplinary Research (IIIUC), University of Coimbra, Casa Costa Alemão, 3030-789 Coimbra, Portugal
| | - Irina S. Moreira
- CNC - Center for Neuroscience and Cell Biology, Center for Innovative Biomedicine and Biotechnology, University of Coimbra, Coimbra, Portugal
- Department of Life Sciences, University of Coimbra, Calçada Martim de Freitas, 3000-456 Coimbra, Portugal
- Corresponding author at: Department of Life Sciences, University of Coimbra, Calçada Martim de Freitas, 3000-456 Coimbra, Portugal.
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Stäubert C, Wozniak M, Dupuis N, Laschet C, Pillaiyar T, Hanson J. Superconserved receptors expressed in the brain: Expression, function, motifs and evolution of an orphan receptor family. Pharmacol Ther 2022; 240:108217. [PMID: 35644261 DOI: 10.1016/j.pharmthera.2022.108217] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Revised: 05/20/2022] [Accepted: 05/23/2022] [Indexed: 12/14/2022]
Abstract
GPR27, GPR85 and GPR173 constitute a small family of G protein-coupled receptors (GPCR) that share the distinctive characteristics of being highly conserved throughout vertebrate evolution and predominantly expressed in the brain. Accordingly, they have been coined as "Superconserved Receptors Expressed in the Brain" (SREB), although their expression profile is more complex than what was originally thought. SREBs have no known validated endogenous ligands and are thus labeled as "orphan" receptors. The investigation of this particular category of uncharacterized receptors holds great promise both in terms of physiology and drug development. In the largest GPCR family, the Rhodopsin-like or Class A, around 100 receptors are considered orphans. Because GPCRs are the most successful source of drug targets, the discovery of a novel function or ligand most likely will lead to significant breakthroughs for the discovery of innovative therapies. The high level of conservation is one of the characteristic features of the SREBs. We propose herein a detailed analysis of the putative evolutionary origin of this family. We highlight the properties that distinguish SREBs from other rhodopsin-like GPCRs. We present the current evidence for these receptors downstream signaling pathways and functions. We discuss the pharmacological challenge for the identification of natural or synthetic ligands of orphan receptors like SREBs. The different SREB-related scientific questions are presented with a highlight on what should be addressed in the near future, including the confirmation of published evidence and their validation as drug targets. In particular, we discuss in which pathological conditions these receptors may be of great relevance to solve unmet medical needs.
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Affiliation(s)
- Claudia Stäubert
- Rudolf Schönheimer Institute of Biochemistry, Faculty of Medicine, Leipzig University, Leipzig, Germany.
| | - Monika Wozniak
- Laboratory of Molecular Pharmacology, GIGA-Molecular Biology of Diseases, University of Liège, Liège, Belgium
| | - Nadine Dupuis
- Laboratory of Molecular Pharmacology, GIGA-Molecular Biology of Diseases, University of Liège, Liège, Belgium
| | - Céline Laschet
- Laboratory of Molecular Pharmacology, GIGA-Molecular Biology of Diseases, University of Liège, Liège, Belgium
| | - Thanigaimalai Pillaiyar
- Institute of Pharmacy, Pharmaceutical/Medicinal Chemistry and Tuebingen Center for Academic Drug Discovery, Eberhard Karls University Tübingen, Tübingen, Germany
| | - Julien Hanson
- Laboratory of Molecular Pharmacology, GIGA-Molecular Biology of Diseases, University of Liège, Liège, Belgium; Laboratory of Medicinal Chemistry, Center for Interdisciplinary Research on Medicines, University of Liège, Liège, Belgium.
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3
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Tian X, Zhang J, Wang S, Gao H, Sun Y, Liu X, Fu W, Tan B, Su R. Tyrosine 7.43 is important for mu-opioid receptor downstream signaling pathways activated by fentanyl. Front Pharmacol 2022; 13:919325. [PMID: 36120357 PMCID: PMC9478952 DOI: 10.3389/fphar.2022.919325] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 08/01/2022] [Indexed: 11/13/2022] Open
Abstract
G protein–coupled receptors can signal through both G proteins and ß-arrestin2. For the µ-opioid receptor (MOR), early experimental evidence from a single study suggested that G protein signaling mediates analgesia and sedation, whereas ß-arrestin signaling mediates respiratory depression and constipation. Then, receptor mutations were used to clarify which residues interact with ligands to selectively regulate signals in a ligand-specific manner. However, there is no systematic study on how to determine these residues and clarify the molecular mechanism of their influence on signal pathways. We have therefore used molecular docking to predict the amino acid sites that affect the binding of ligands and MOR. Then, the corresponding sites were mutated to determine the effect of the structural determinant of MOR on Gi/o protein and ß-arrestin pathways. The pharmacological and animal behavioral experiments in combination with molecular dynamics simulations were used to elucidate the molecular mechanism of key residues governing the signaling. Without affecting ligand binding to MOR, MORY7.43A attenuated the activation of both Gi/o protein and ß-arrestin signaling pathways stimulated by fentanyl, whereas it did not change these two pathways stimulated by morphine. Likewise, the activation peak time of extracellular regulated protein kinases was significantly prolonged at MORY7.43A compared with that at MORwildtype stimulated by fentanyl, but there was no difference stimulated by morphine. In addition, MORY7.43A significantly enhanced analgesia by fentanyl but not by morphine in the mice behavioral experiment. Furthermore, the molecular dynamics simulations showed that H6 moves toward the cellular membrane. H6 of the fentanyl–Y7.43A system moved outward more than that in the morphine–Y7.43A system. Y7.43 mutation disrupted hydrophobic interactions between W6.48 and Y7.43 in the fentanyl–Y7.43A system but not in the morphine–Y7.43A system. Our results have disclosed novel mechanisms of Y7.43 mutation affecting MOR signaling pathways. Y7.43 mutation reduced the activation of the Gi/o protein pathway and blocked the ß-arrestin2 recruitment, increased the H6 outward movement of MOR, and disrupted hydrophobic interactions. This may be responsible for the enhanced fentanyl analgesia. These findings are conducive to designing new drugs from the perspective of ligand and receptor binding, and Y7.43 is also expected to be a key site to structure optimization of synthesized compounds.
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Affiliation(s)
- Xiangyun Tian
- State Key Laboratory of Toxicology and Medical Countermeasures, Beijing Key Laboratory of Neuropsychopharmacology, Beijing Institute of Pharmacology and Toxicology, Beijing, China
| | - Junjie Zhang
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, Shanghai, China
| | - Shaowen Wang
- State Key Laboratory of Toxicology and Medical Countermeasures, Beijing Key Laboratory of Neuropsychopharmacology, Beijing Institute of Pharmacology and Toxicology, Beijing, China
- Nanjing University of Chinese Medicine, Nanjing, China
| | - Huan Gao
- State Key Laboratory of Toxicology and Medical Countermeasures, Beijing Key Laboratory of Neuropsychopharmacology, Beijing Institute of Pharmacology and Toxicology, Beijing, China
- School of Pharmacy, Yantai University, Yantai, China
| | - Yi Sun
- State Key Laboratory of Toxicology and Medical Countermeasures, Beijing Key Laboratory of Neuropsychopharmacology, Beijing Institute of Pharmacology and Toxicology, Beijing, China
| | - Xiaoqian Liu
- State Key Laboratory of Toxicology and Medical Countermeasures, Beijing Key Laboratory of Neuropsychopharmacology, Beijing Institute of Pharmacology and Toxicology, Beijing, China
| | - Wei Fu
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, Shanghai, China
| | - Bo Tan
- State Key Laboratory of Toxicology and Medical Countermeasures, Beijing Key Laboratory of Neuropsychopharmacology, Beijing Institute of Pharmacology and Toxicology, Beijing, China
- *Correspondence: Bo Tan, , ; Ruibin Su, ,
| | - Ruibin Su
- State Key Laboratory of Toxicology and Medical Countermeasures, Beijing Key Laboratory of Neuropsychopharmacology, Beijing Institute of Pharmacology and Toxicology, Beijing, China
- *Correspondence: Bo Tan, , ; Ruibin Su, ,
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Geng S, Xu T, Sun Y. Genome-wide identification and analysis of chemokine receptor superfamily in miiuy croaker, Miichthys miiuy. FISH & SHELLFISH IMMUNOLOGY 2021; 118:343-353. [PMID: 34555531 DOI: 10.1016/j.fsi.2021.09.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2021] [Revised: 09/16/2021] [Accepted: 09/16/2021] [Indexed: 06/13/2023]
Abstract
The chemokine receptor (ChemR) superfamily, which is divided into 4 subfamilies (CXCR, CCR, XCR, and CX3CR), is the main receptors of chemokines in innate immune responses. In the current study, we have identified 27 ChemRs in miiuy croaker: 13 CCR genes, 11 CXCR genes, and 3 XCR genes. Multiple characteristics of these genes, including phylogeny, gene structures, conserved motifs, chromosome locations, evolutionary mechanism, and expression levels upon the bacterial challenge were analyzed. Gene structure and location analysis showed that all ChemR genes contain fewer introns (≤4) and they are unevenly distributed on the 12 chromosomes. And the XCR subfamily of miiuy croaker don't have the DRY motif of ChemR. Phylogenetic and synteny analysis showed that these genes experienced tandem and segmental duplication event in several species, and tandem duplication might be the main expansion way in miiuy croaker. The major ChemRs of each orthologous group in vertebrates were selected for molecular evolution analysis, the results of which indicated that compared with vertebrates, ChemRs of teleost fishes may have a relatively high evolutionary dynamic. In addition, a total of 21 positively selected codons were detected in vertebrate ChemRs under Model 8. RNA-Seq analysis and qRT-PCR verification demonstrated that CXCR3.2, CXCR5, and XCR1 genes were up-regulated significantly upon the Vibrio harveyi infection. These results provide valuable information for investigating the evolutionary relationships of chemokine receptor superfamily in miiuy croaker and laid the basis for further functional analysis.
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Affiliation(s)
- Shang Geng
- Laboratory of Fish Molecular Immunology, College of Fisheries and Life Science, Shanghai Ocean University, Shanghai, China
| | - Tianjun Xu
- Laboratory of Fish Molecular Immunology, College of Fisheries and Life Science, Shanghai Ocean University, Shanghai, China; Laboratory of Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China; National Pathogen Collection Center for Aquatic Animals, Shanghai Ocean University, China
| | - Yuena Sun
- Laboratory of Fish Molecular Immunology, College of Fisheries and Life Science, Shanghai Ocean University, Shanghai, China; Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources (Shanghai Ocean University), Ministry of Education, China.
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5
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Wang T, Yang Z, Zhou N, Sun L, Lv Z, Wu C. Identification and functional characterisation of 5-HT4 receptor in sea cucumber Apostichopus japonicus (Selenka). Sci Rep 2017; 7:40247. [PMID: 28059140 PMCID: PMC5216381 DOI: 10.1038/srep40247] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Accepted: 12/05/2016] [Indexed: 02/07/2023] Open
Abstract
Serotonin (5-HT) is an important neurotransmitter and neuromodulator that controls a variety of sensory and motor functions through 5-HT receptors (5-HTRs). The 5-HT4R subfamily is linked to Gs proteins, which activate adenylyl cyclases (ACs), and is involved in many responses in peripheral organs. In this study, the 5-HT4R from Apostichopus japonicus (Aj5-HT4R) was identified and characterised. The cloned full-length Aj5-HT4R cDNA is 1,544 bp long and contains an open reading frame 1,011 bp in length encoding 336 amino acid proteins. Bioinformatics analysis of the Aj5-HT4R protein indicated this receptor was a member of class A G protein coupled receptor (GPCR) family. Further experiments using Aj5-HT4R-transfected HEK293 cells demonstrated that treatment with 5-HT triggered a significant increase in intracellular cAMP level in a dose-dependent manner and induced a rapid internalisation of Aj5-HT4R fused with enhanced green fluorescent protein (Aj5-HT4R-EGFP) from the cell surface into the cytoplasm. In addition, the transcriptional profiles of Aj5-HT4R in aestivating A. japonicas and phosphofructokinase (AjPFK) in 5-HT administrated A. japonicus have been analysed by real-time PCR assays. Results have led to a basic understanding of Aj5-HT4R in A. japonicus, and provide a foundation for further exploration of the cell signaling and regulatory functions of this receptor.
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Affiliation(s)
- Tianming Wang
- National Engineering Research Center of Marine Facilities Aquaculture, Marine Science College, Zhejiang Ocean University, Zhoushan, Zhejiang 316022, People's Republic of China
| | - Zhen Yang
- National Engineering Research Center of Marine Facilities Aquaculture, Marine Science College, Zhejiang Ocean University, Zhoushan, Zhejiang 316022, People's Republic of China
| | - Naiming Zhou
- Institute of Biochemistry, College of LifeSciences, Zijingang Campus, Zhejiang University, Hangzhou, Zhejiang 310058, People's Republic of China
| | - Lina Sun
- Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, Shandong 266071, People's Republic of China
| | - Zhenming Lv
- National Engineering Research Center of Marine Facilities Aquaculture, Marine Science College, Zhejiang Ocean University, Zhoushan, Zhejiang 316022, People's Republic of China
| | - Changwen Wu
- National Engineering Research Center of Marine Facilities Aquaculture, Marine Science College, Zhejiang Ocean University, Zhoushan, Zhejiang 316022, People's Republic of China
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6
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Yaddaden L, Véronneau S, Thompson MD, Rola-Pleszczynski M, Stankova J. Cellular signalling of cysteinyl leukotriene type 1 receptor variants CysLT₁-G300S and CysLT₁-I206S. Prostaglandins Leukot Essent Fatty Acids 2016; 105:1-8. [PMID: 26869085 DOI: 10.1016/j.plefa.2015.12.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/14/2015] [Revised: 11/05/2015] [Accepted: 12/12/2015] [Indexed: 11/19/2022]
Abstract
Cysteinyl-leukotrienes are pro-inflammatory lipid mediators, involved in allergic asthma, that bind the G-protein-coupled receptors CysLT1, CysLT2 and GPR99. A polymorphism in one of these receptors, CysLT1-G300S was strongly associated with atopy, whereas the CysLT1-I206S polymorphism was not. In the present work, our aim was to characterize these two variants by studying their cellular signalling. Cell surface expression of mutant receptors in transfected HEK-293 cells was comparable to that of the wild-type receptor. Compared to CysLT1-WT, production of inositol phosphates as well as IL-8 and IL-13 promoter transactivation in response to either LTD4 or LTC4 was significantly increased in CysLT1-G300S-transfected cells. Moreover, LTD4-induced phosphorylation of the signalling effector Erk, but not p38, p65 or c-Jun was higher in CysLT1-G300S-transfected cells. On the other hand, the variant CysLT1-I206S did not show a significant difference in its signal transduction compared to the wild-type receptor. Taken together, our results indicate that the variant CysLT1-G300S can induce a greater signal than the CysLT1-WT receptor, a feature that may be relevant to its association with atopy.
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Affiliation(s)
- Louiza Yaddaden
- Immunology Division, Department of Pediatrics, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Quebec, Canada J1H 5N4
| | - Steeve Véronneau
- Immunology Division, Department of Pediatrics, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Quebec, Canada J1H 5N4
| | - Miles D Thompson
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada
| | - Marek Rola-Pleszczynski
- Immunology Division, Department of Pediatrics, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Quebec, Canada J1H 5N4
| | - Jana Stankova
- Immunology Division, Department of Pediatrics, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Quebec, Canada J1H 5N4.
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7
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Guo S, Zhang J, Zhang S, Li J. A Single Amino Acid Mutation (R104P) in the E/DRY Motif of GPR40 Impairs Receptor Function. PLoS One 2015; 10:e0141303. [PMID: 26505901 PMCID: PMC4624708 DOI: 10.1371/journal.pone.0141303] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Accepted: 10/06/2015] [Indexed: 11/18/2022] Open
Abstract
Type 2 Diabetes Mellitus with insulin resistance, pancreatic β cell dysfunction, and hepatic glucose overproduction is increasing in epidemic proportions worldwide. G protein-coupled receptor 40 (GPR40), a clinically proven anti-diabetic drug target, is mainly expressed in pancreatic β cells and insulin-secreting cell lines. Long chain fatty acids (LCFA) increase intracellular calcium concentration and amplify glucose-stimulated insulin secretion by activating GPR40. Here we report that the arginine 104 (R104) is critical for the normal function of GPR40. Mutation of R104 to Proline (R104P) results in complete loss of the receptor function. Linoleic acid, ligand of GPR40, could not elicit calcium increase and ERK phosphorylation in cells expressing this mutant receptor. Further study indicated the R104P mutation reduces cell surface localization of GPR40 without affecting the expression of the protein. The small portion of GPR40 R104P mutant that is still located on the membrane has no physiological function, and does not internalize in response to linoleic acid stimulation. These data demonstrate that R104 in GPR40 is critically involved in the normal receptor functions. Interestingly, R104P is a registered single-nucleotide polymorphism of GPR40. The relationship of this GPR40 variant and type 2 diabetes warrants further investigation.
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Affiliation(s)
- Shimeng Guo
- School of life sciences, Shanghai University, Shanghai, China
- Chinese Academy of Sciences Key Laboratory of Receptor Research, National Center for Drug Screening, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Jiandong Zhang
- College of Pharmacy, Nanchang University, Nanchang, China
- Chinese Academy of Sciences Key Laboratory of Receptor Research, National Center for Drug Screening, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
| | - Shuyong Zhang
- Chinese Academy of Sciences Key Laboratory of Receptor Research, National Center for Drug Screening, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
- * E-mail: (SZ); (JL)
| | - Jing Li
- Chinese Academy of Sciences Key Laboratory of Receptor Research, National Center for Drug Screening, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China
- * E-mail: (SZ); (JL)
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8
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Singh SP, Foley JF, Zhang HH, Hurt DE, Richards JL, Smith CS, Liao F, Farber JM. Selectivity in the Use of Gi/o Proteins Is Determined by the DRF Motif in CXCR6 and Is Cell-Type Specific. Mol Pharmacol 2015; 88:894-910. [PMID: 26316539 DOI: 10.1124/mol.115.099960] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2015] [Accepted: 08/21/2015] [Indexed: 01/02/2023] Open
Abstract
CXCR6, the receptor for CXCL16, is expressed on multiple cell types and can be a coreceptor for human immunodeficiency virus 1. Except for CXCR6, all human chemokine receptors contain the D(3.49)R(3.50)Y(3.51) sequence, and all but two contain A(3.53) at the cytoplasmic terminus of the third transmembrane helix (H3C), a region within class A G protein-coupled receptors that contacts G proteins. In CXCR6, H3C contains D(3.49)R(3.50)F(3.51)I(3.52)V(3.53) at positions 126-130. We investigated the importance and interdependence of the canonical D126 and the noncanonical F128 and V130 in CXCR6 by mutating D126 to Y, F128 to Y, and V130 to A singly and in combination. For comparison, we mutated the analogous positions D142, Y144, and A146 to Y, F, and V, respectively, in CCR6, a related receptor containing the canonical sequences. Mutants were analyzed in both human embryonic kidney 293T and Jurkat E6-1 cells. Our data show that for CXCR6 and/or CCR6, mutations in H3C can affect both receptor signaling and chemokine binding; noncanonical H3C sequences are functionally linked, with dual changes mitigating the effects of single mutations; mutations in H3C that compromise receptor activity show selective defects in the use of individual Gi/o proteins; and the effects of mutations in H3C on receptor function and selectivity in Gi/o protein use can be cell-type specific. Our findings indicate that the ability of CXCR6 to make promiscuous use of the available Gi/o proteins is exquisitely dependent on sequences within the H3C and suggest that the native sequence allows for preservation of this function across different cellular environments.
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Affiliation(s)
- Satya P Singh
- Laboratory of Molecular Immunology (S.P.S., J.F.F., H.H.Z., J.L.R., C.S.S., F.L., J.M.F.) and Bioinformatics and Scientific IT Program, Office of Technology Information Systems, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland (D.E.H.); and Howard Hughes Medical Institute, National Institutes of Health Research Scholars Program, Bethesda, Maryland (C.S.S.)
| | - John F Foley
- Laboratory of Molecular Immunology (S.P.S., J.F.F., H.H.Z., J.L.R., C.S.S., F.L., J.M.F.) and Bioinformatics and Scientific IT Program, Office of Technology Information Systems, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland (D.E.H.); and Howard Hughes Medical Institute, National Institutes of Health Research Scholars Program, Bethesda, Maryland (C.S.S.)
| | - Hongwei H Zhang
- Laboratory of Molecular Immunology (S.P.S., J.F.F., H.H.Z., J.L.R., C.S.S., F.L., J.M.F.) and Bioinformatics and Scientific IT Program, Office of Technology Information Systems, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland (D.E.H.); and Howard Hughes Medical Institute, National Institutes of Health Research Scholars Program, Bethesda, Maryland (C.S.S.)
| | - Darrell E Hurt
- Laboratory of Molecular Immunology (S.P.S., J.F.F., H.H.Z., J.L.R., C.S.S., F.L., J.M.F.) and Bioinformatics and Scientific IT Program, Office of Technology Information Systems, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland (D.E.H.); and Howard Hughes Medical Institute, National Institutes of Health Research Scholars Program, Bethesda, Maryland (C.S.S.)
| | - Jennifer L Richards
- Laboratory of Molecular Immunology (S.P.S., J.F.F., H.H.Z., J.L.R., C.S.S., F.L., J.M.F.) and Bioinformatics and Scientific IT Program, Office of Technology Information Systems, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland (D.E.H.); and Howard Hughes Medical Institute, National Institutes of Health Research Scholars Program, Bethesda, Maryland (C.S.S.)
| | - Craig S Smith
- Laboratory of Molecular Immunology (S.P.S., J.F.F., H.H.Z., J.L.R., C.S.S., F.L., J.M.F.) and Bioinformatics and Scientific IT Program, Office of Technology Information Systems, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland (D.E.H.); and Howard Hughes Medical Institute, National Institutes of Health Research Scholars Program, Bethesda, Maryland (C.S.S.)
| | - Fang Liao
- Laboratory of Molecular Immunology (S.P.S., J.F.F., H.H.Z., J.L.R., C.S.S., F.L., J.M.F.) and Bioinformatics and Scientific IT Program, Office of Technology Information Systems, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland (D.E.H.); and Howard Hughes Medical Institute, National Institutes of Health Research Scholars Program, Bethesda, Maryland (C.S.S.)
| | - Joshua M Farber
- Laboratory of Molecular Immunology (S.P.S., J.F.F., H.H.Z., J.L.R., C.S.S., F.L., J.M.F.) and Bioinformatics and Scientific IT Program, Office of Technology Information Systems, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland (D.E.H.); and Howard Hughes Medical Institute, National Institutes of Health Research Scholars Program, Bethesda, Maryland (C.S.S.)
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9
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Characterization of G protein coupling mediated by the conserved D134(3.49) of DRY motif, M241(6.34), and F251(6.44) residues on human CXCR1. FEBS Open Bio 2015; 5:182-90. [PMID: 25834784 PMCID: PMC4372616 DOI: 10.1016/j.fob.2015.03.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Revised: 02/27/2015] [Accepted: 03/03/2015] [Indexed: 01/01/2023] Open
Abstract
Mutations in the DRY motif of CXCR1 abolish ligand binding and receptor activation. Point mutations between TM6 and i3 loop result in constitutive activity of CXCR1. Constitutive activity of mutant CXCR1 occurs via Gα15 signaling activation. The highly conserved DRY motifs have distinct roles in CXCR1 and CXCR2.
CXCR1, a receptor for interleukin-8 (IL-8), plays an important role in defending against pathogen invasion during neutrophil-mediated innate immune response. Human CXCR1 is a G protein-coupled receptor (GPCR) with its characteristic seven transmembrane domains (TMs). Functional and structural analyses of several GPCRs have revealed that conserved residues on TM3 (including the highly conserved Asp-Arg-Tyr (DRY) motif) and TM6 near intracellular loops contain domains critical for G protein coupling as well as GPCR activation. The objective of this study was to elucidate the role of critical amino acid residues on TM3 near intracellular loop 2 (i2) and TM6 near intracellular loop 3 (i3), including S1323.47 (Baldwin location), D1343.49, M2416.34, and F2516.44, in G protein coupling and CXCR1 activation. The results demonstrate that mutations of D1343.49 at DRY motif of CXCR1 (D134N and D134V) completely abolished the ligand binding and functional response of the receptor. Additionally, point mutations at positions 241 and 251 between TM6 and i3 loop generated mutant receptors with modest constitutive activity via Gα15 signaling activation. Our results show that D1343.49 on the highly conserved DRY motif has a distinct role for CXCR1 compared to its homologues (CXCR2 and KSHV-GPCR) in G protein coupling and receptor activation. In addition, M2416.34 and F2516.44 along with our previously identified V2476.40 on TM6 are spatially located in a “hot spot” likely essential for CXCR1 activation. Identification of these amino acid residues may be useful for elucidating mechanism of CXCR1 activation and designing specific antagonists for the treatment of CXCR1-mediated diseases.
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Key Words
- CXCR1
- CXCR1, CXC receptor 1
- Chemokine receptor
- Constitutive activity
- DRY motif, Asp-Arg-Tyr motif
- G protein coupled receptor
- GPCR, G protein-coupled receptor
- Gα15
- Gαi
- IL-8, interleukin 8
- IP, inositol phosphate
- Kd, affinity constants
- PLC, phospholipase C
- PTX, pertussis toxin
- TMs, transmembrane domain
- WT, wild type
- i2, intracellular loop 2
- i3, intracellular loop 3
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Kim B, Song HS, Jin HJ, Park EJ, Lee SH, Lee BY, Park TH, Hong S. Highly selective and sensitive detection of neurotransmitters using receptor-modified single-walled carbon nanotube sensors. NANOTECHNOLOGY 2013; 24:285501. [PMID: 23792421 DOI: 10.1088/0957-4484/24/28/285501] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We present receptor-modified carbon nanotube sensors for the highly selective and sensitive detection of acetylcholine (ACh), one kind of neurotransmitter. Here, we successfully expressed the M1 muscarinic acetylcholine receptor (M1 mAChR), a family of G protein-coupled receptors (GPCRs), in E. coli and coated single-walled carbon nanotube (swCNT)-field effect transistors (FETs) with lipid membrane including the receptor, enabling highly selective and sensitive ACh detection. Using this sensor, we could detect ACh at 100 pM concentration. Moreover, we showed that this sensor could selectively detect ACh among other neurotransmitters. This is the first demonstration of the real-time detection of ACh using specific binding between ACh and M1 mAChR, and it may lead to breakthroughs for various applications such as disease diagnosis and drug screening.
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Affiliation(s)
- Byeongju Kim
- Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea
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11
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Hulme EC. GPCR activation: a mutagenic spotlight on crystal structures. Trends Pharmacol Sci 2012; 34:67-84. [PMID: 23245528 DOI: 10.1016/j.tips.2012.11.002] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2012] [Revised: 10/26/2012] [Accepted: 11/07/2012] [Indexed: 11/28/2022]
Abstract
The crystal structures of antagonist and agonist complexes of isolated β(2) and β(1) adrenoceptors have recently been supplemented by antagonist structures of M(2) and M(3) muscarinic acetylcholine receptors. Importantly, a structure of an agonist-ligated β(2) adrenoceptor complexed with its cognate G protein has provided the first view of a ternary complex representing the transition state in agonist-mediated G protein activation. This review interprets these G-protein-coupled receptor (GPCR) structures through the focus provided by extensive mutagenesis studies on muscarinic receptors, revealing an activation mechanism that is both modular and dynamic. Specific motifs, based around highly conserved residues, functionalise the seven-transmembrane architecture of these receptors. While exploiting conserved motifs, the ligand binding and signal transduction pathways work around and through water-containing cavities, an emerging feature of GPCR structures. These cavities may have undergone evolutionary selection to adapt GPCRs to particular signalling niches, and may provide targeting opportunities to enhance drug selectivity.
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Affiliation(s)
- Edward C Hulme
- Division of Physical Biochemistry, MRC National Institute for Medical Research, Mill Hill, London, UK.
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12
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Abstract
There has been great interest in the structure-function relationships of the muscarinic acetylcholine receptors (mAChRs) because these prototypical Family A/class 1 G protein-coupled receptors (GPCRs) are attractive therapeutic targets for both peripheral and central nervous system disorders. A multitude of drugs that act at the mAChRs have been identified over the years, but many of these show minimal selectivity for any one of the five mAChR subtypes over the others, which has hampered their development into therapeutics due to adverse side effects. The lack of drug specificity is primarily due to high sequence similarity in this family of receptor, especially in the orthosteric binding pocket. Thus, there remains an ongoing need for a molecular understanding of how mAChRs bind their ligands, and how selectivity in binding and activation can be achieved. Unfortunately, there remains a paucity of solved high-resolution structures of GPCRs, including the mAChRs, and thus most of our knowledge of structure-function mechanisms related to this receptor family to date has been obtained indirectly through approaches such as mutagenesis. Nonetheless, such studies have revealed a wealth of information that has led to novel insights and may be used to guide future rational drug design campaigns.
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Hulme EC, Lu ZL, Bee MS. Scanning Mutagenesis Studies of the M 1 Muscarinic Acetylcholine Receptor. ACTA ACUST UNITED AC 2011. [DOI: 10.3109/10606820308261] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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14
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Daiyasu H, Hirokawa T, Kamiya N, Toh H. Computational analysis of ligand recognition mechanisms by prostaglandin E2 (subtype 2) and D2 receptors. Theor Chem Acc 2011. [DOI: 10.1007/s00214-011-1034-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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15
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Forfar R, Lu ZL. Role of the transmembrane domain 4/extracellular loop 2 junction of the human gonadotropin-releasing hormone receptor in ligand binding and receptor conformational selection. J Biol Chem 2011; 286:34617-26. [PMID: 21832286 DOI: 10.1074/jbc.m111.240341] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Recent crystal structures of G protein-coupled receptors (GPCRs) show the remarkable structural diversity of extracellular loop 2 (ECL2), implying its potential role in ligand binding and ligand-induced receptor conformational selectivity. Here we have applied molecular modeling and mutagenesis studies to the TM4/ECL2 junction (residues Pro(174(4.59))-Met(180(4.66))) of the human gonadotropin-releasing hormone (GnRH) receptor, which uniquely has one functional type of receptor but two endogenous ligands in humans. We suggest that the above residues assume an α-helical extension of TM4 in which the side chains of Gln(174(4.60)) and Phe(178(4.64)) face toward the central ligand binding pocket to make H-bond and aromatic contacts with pGlu(1) and Trp(3) of both GnRH I and GnRH II, respectively. The interaction between the side chains of Phe(178(4.64)) of the receptor and Trp(3) of the GnRHs was supported by reciprocal mutations of the interacting residues. Interestingly, alanine mutations of Leu(175(4.61)), Ile(177(4.63)), and Met(180(4.66)) decreased mutant receptor affinity for GnRH I but, in contrast, increased affinity for GnRH II. This suggests that these residues make intramolecular or intermolecular contacts with residues of transmembrane (TM) domain 3, TM5, or the phospholipid bilayer, which couple the ligand structure to specific receptor conformational switches. The marked decrease in signaling efficacy of I177A and F178A also indicates that IIe(177(4.63)) and Phe(178(4.64)) are important in stabilizing receptor-active conformations. These findings suggest that the TM4/ECL2 junction is crucial for peptide ligand binding and, consequently, for ligand-induced receptor conformational selection.
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Affiliation(s)
- Rachel Forfar
- MRC Technology, Mill Hill, London NW7 1AD, United Kingdom
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Leach K, Davey AE, Felder CC, Sexton PM, Christopoulos A. The Role of Transmembrane Domain 3 in the Actions of Orthosteric, Allosteric, and Atypical Agonists of the M4Muscarinic Acetylcholine Receptor. Mol Pharmacol 2011; 79:855-65. [DOI: 10.1124/mol.111.070938] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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17
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Aizaki Y, Maruyama K, Nakano-Tetsuka M, Saito Y. Distinct roles of the DRY motif in rat melanin-concentrating hormone receptor 1 in signaling control. Peptides 2009; 30:974-81. [PMID: 19428776 DOI: 10.1016/j.peptides.2009.01.017] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/28/2008] [Revised: 01/17/2009] [Accepted: 01/21/2009] [Indexed: 10/21/2022]
Abstract
Rhodopsin family (class A) G protein-coupled receptors possess common key residues or motifs that appear to be important for receptor function. To clarify the roles of the highly conserved amino acid triplet Asp(3.49)-Arg(3.50)-Tyr(3.51) (DRY motif), we examined how single-substitution mutations of the amino acids in the motif influenced specific features of rat melanin-concentrating hormone receptor 1 (MCH1R) activity. Substitution of either Asp140(3.49) or Tyr142(3.51) to Ala resulted in nonfunctional receptors, despite the retention of apparent potencies for agonist binding. These loss-of-function phenotypes may be caused by the lack of stimulation for GDP-GTP exchange observed in GTPgammaS-binding assays. On the other hand, substitution of Arg141(3.50) to Ala caused a 4-fold reduction in the agonist binding affinity and, concomitantly, a rightward shift of the dose-dependency curve for calcium mobilization and inhibition of cyclic AMP production. Although many experimental studies have suggested that the DRY motif is involved in maintaining the receptor in its ground state, none of the DRY motif substitutions to Ala in MCH1R led to constitutive activation, in terms of the basal signaling level for ERK1/2 activation or GTPgammaS binding. These data suggest that the major contribution of the DRY motif in MCH1R is to govern receptor conformation and G protein coupling/recognition.
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Affiliation(s)
- Yoshimi Aizaki
- Department of Pharmacology, Saitama Medical School of Medicine, Iruma-gun, Saitama, Japan
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18
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Coetsee M, Millar RP, Flanagan CA, Lu ZL. Identification of Tyr(290(6.58)) of the human gonadotropin-releasing hormone (GnRH) receptor as a contact residue for both GnRH I and GnRH II: importance for high-affinity binding and receptor activation. Biochemistry 2008; 47:10305-13. [PMID: 18771291 DOI: 10.1021/bi800911z] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Molecular modeling showed interactions of Tyr (290(6.58)) in transmembrane domain 6 of the GnRH receptor with Tyr (5) of GnRH I, and His (5) of GnRH II. The wild-type receptor exhibited high affinity for [Phe (5)]GnRH I and [Tyr (5)]GnRH II, but 127- and 177-fold decreased affinity for [Ala (5)]GnRH I and [Ala (5)]GnRH II, indicating that the aromatic ring in position 5 is crucial for receptor binding. The receptor mutation Y290F decreased affinity for GnRH I, [Phe (5)]GnRH I, GnRH II and [Tyr (5)]GnRH II, while Y290A and Y290L caused larger decreases, suggesting that both the para-OH and aromatic ring of Tyr (290(6.58)) are important for binding of ligands with aromatic residues in position 5. Mutating Tyr (290(6.58)) to Gln increased affinity for Tyr (5)-containing GnRH analogues 3-12-fold compared with the Y290A and Y290L mutants, suggesting a hydrogen-bond between Gln of the Y290Q mutant and Tyr (5) of GnRH analogues. All mutations had small effects on affinity of GnRH analogues that lack an aromatic residue in position 5. These results support direct interactions of the Tyr (290(6.58)) side chain with Tyr (5) of GnRH I and His (5) of GnRH II. Tyr (290(6.58)) mutations, except for Y290F, caused larger decreases in GnRH potency than affinity, indicating that an aromatic ring is important for the agonist-induced receptor conformational switch.
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Affiliation(s)
- Marla Coetsee
- MRC Human Reproductive Sciences Unit, Centre for Reproductive Biology, The Queen's Medical Research Institute, 47 Little France Crescent, Edinburgh EH16 4TJ, Scotland, United Kingdom
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20
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Zakutskiĭ AN, Chalisova NI, Subbotina TF. [Functional arginine-containing amino acid sequences in peptides and proteins]. RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY 2008; 34:149-59. [PMID: 18522270 DOI: 10.1134/s1068162008020015] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
L-arginine is a source of nitrogen oxide and plays a great role in a number of other biochemical processes. Functions and prospects for practical application of five groups of arginine-containing amino acid sequences and synthetic polyarginine sequences are considered. The physiological characteristics of well-known arginine-containing peptides, such as RGD peptides, kyotorphin, and tuftsin, are described in detail. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2008, vol. 34, no. 2; see also http://www.maik.ru
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21
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Kim JH, Cho EY, Min C, Park JH, Kim KM. Characterization of functional roles of DRY motif in the 2nd intracellular loop of dopamine D2 and D3 receptors. Arch Pharm Res 2008; 31:474-81. [PMID: 18449505 DOI: 10.1007/s12272-001-1181-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2007] [Indexed: 10/22/2022]
Abstract
Dopamine D(2)R and D(3)R (D(2)R, D(3)R) show very high sequence homology and employ virtually identical signaling pathways even though D(2)R is 2 approximately 5 times more active. Among the structural motifs identified, a triplet sequence, Asp-Arg-Tyr (DRY motif), plays critical roles in the determination of receptor conformations for signaling and intracellular trafficking of G protein-coupled receptors by forming intramolecular interactions. Thus, it is possible that different signaling efficiencies of D(2)R and D(3)R might be caused by the receptor activation levels stabilized by their own DRY motifs. In this study, the Arg and Asp residues of D(2)R and D(3)R were mutated, and resulting changes in their signaling and intracellular trafficking properties were comparatively studied. Mutation of the Arg residues of D(2)R and D(3)R abolished their signaling but differently affected their intracellular localizations. The wildtype and R132H-D(2)R were expressed mainly on the plasma membrane. On the other hand, compared with the wildtype D(3)R, a substantial amount of R128H-D(3)R was localized intracellularly. The expression of receptor proteins on the plasma membrane and their signaling efficiencies were more drastically affected by the mutation of the Asp residue of D(3)R than D(2)R. Therefore, it was concluded that the different levels of conformational strain exerted by the DRY motif might partly determine the quantitative differences in the signaling efficiencies between D(2)R and D(3)R.
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Affiliation(s)
- Ju-Heon Kim
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee, Knoxville, TN 37996, USA
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22
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Case R, Sharp E, Benned-Jensen T, Rosenkilde MM, Davis-Poynter N, Farrell HE. Functional analysis of the murine cytomegalovirus chemokine receptor homologue M33: ablation of constitutive signaling is associated with an attenuated phenotype in vivo. J Virol 2008; 82:1884-98. [PMID: 18057236 PMCID: PMC2258698 DOI: 10.1128/jvi.02550-06] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2006] [Accepted: 11/20/2007] [Indexed: 01/28/2023] Open
Abstract
The murine cytomegalovirus (MCMV) M33 gene is conserved among all betaherpesviruses and encodes a homologue of seven-transmembrane receptors (7TMR) with the capacity for constitutive signaling. Previous studies have demonstrated that M33 is important for MCMV dissemination to or replication within the salivary glands. In this study, we probed N- and C-terminal regions of M33 as well as known 7TMR signature motifs in transmembrane (TM) II and TM III to determine the impact on cell surface expression, constitutive signaling, and in vivo phenotype. The region between amino acids R(340) and A(353) of the C terminus was found to be important for CREB- and NFAT-mediated signaling, although not essential for phosphatidylinositol turnover. Tagging or truncation of the N terminus of M33 resulted in loss of cell surface expression. Within TM II, an F79D mutation abolished constitutive signaling, demonstrating a role, as in other cellular and viral 7TMR, of TM II in receptor activation. In TM III, the arginine (but not the asparagine) residue of the NRY motif (the counterpart of the common DRY motif in cellular 7TMR) was found to be essential for constitutive signaling. Selected mutations incorporated into recombinant MCMV showed that disruption of constitutive signaling for a viral 7TMR homologue resulted in a reduced capacity to disseminate to or replicate in the salivary glands. In addition, HCMV UL33 was found to partially compensate for the lack of M33 in vivo, suggesting conserved biological roles of the UL33 gene family.
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Affiliation(s)
- Ruth Case
- Clinical Medical Virology Centre, University of Queensland, Sir Albert Sakzewski Virus Research Centre, Royal Children's Hospital, Herston 4029, Queensland, Australia
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Tokunaga H, Matsuura B, Dong M, Miller LJ, Ueda T, Furukawa S, Hiasa Y, Onji M. Mutational analysis of predicted intracellular loop domains of human motilin receptor. Am J Physiol Gastrointest Liver Physiol 2008; 294:G460-6. [PMID: 18032475 DOI: 10.1152/ajpgi.00244.2007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Motilin is an important endogenous regulator of gastrointestinal motor function, mediated by the class I G protein-coupled motilin receptor. Motilin and erythromycin, two chemically distinct full agonists of the motilin receptor, are known to bind to distinct regions of this receptor, based on previous systematic mutagenesis of extracellular regions that dissociated the effects on these two agents. In the present work, we examined the predicted intracellular loop regions of this receptor for effects on motilin- and erythromycin-stimulated activity. We prepared motilin receptor constructs that included sequential deletions throughout the predicted first, second, and third intracellular loops, as well as replacing the residues in key regions with alanine, phenylalanine, or histidine. Each construct was transiently expressed in COS cells and characterized for motilin- and erythromycin-stimulated intracellular calcium responses and for motilin binding. Deletions of receptor residues 63-66, 135-137, and 296-301 each resulted in substantial loss of intracellular calcium responses to stimulation by both motilin and erythromycin. Constructs with mutations of residues Tyr66, Arg136, and Val299 were responsible for the negative impact on biological activity stimulated by both agonists. These data suggest that action by different chemical classes of agonists that are known to interact with distinct regions of the motilin receptor likely yield a common activation state of the cytosolic face of this receptor that is responsible for interaction with its G protein. The identification of functionally important residues in the predicted cytosolic face provides strong candidates for playing roles in receptor-G protein interaction.
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Affiliation(s)
- Hitoo Tokunaga
- Department of Gastroenterology and Metabology, Ehime University Graduate School of Medicine, Shitsukawa 454, Tohon, Ehime 791-0295, Japan
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Stewart AJ, Sellar R, Wilson DJ, Millar RP, Lu ZL. Identification of a Novel Ligand Binding Residue Arg38(1.35)in the Human Gonadotropin-Releasing Hormone Receptor. Mol Pharmacol 2007; 73:75-81. [DOI: 10.1124/mol.107.040816] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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25
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Goodwin JA, Hulme EC, Langmead CJ, Tehan BG. Roof and floor of the muscarinic binding pocket: variations in the binding modes of orthosteric ligands. Mol Pharmacol 2007; 72:1484-96. [PMID: 17848601 DOI: 10.1124/mol.107.038265] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Alanine substitution mutagenesis has been used to investigate residues that make up the roof and floor of the muscarinic binding pocket and regulate ligand access. We mutated the amino acids in the second extracellular loop of the M1 muscarinic acetylcholine receptor that are homologous to the cis-retinal contact residues in rhodopsin, the disulfide-bonded Cys178 and Cys98 that anchor the loop to transmembrane helix 3, the adjoining acidic residue Asp99, and the conserved aromatic residues Phe197 and Trp378 in the transmembrane domain. The effects on ligand binding, kinetics, and receptor function suggest that the second extracellular loop does not provide primary contacts for orthosteric ligands, including acetylcholine, but that it does contribute to microdomains that are important for the conformational changes that accompany receptor activation. Kinetic studies suggest that the disulfide bond between Cys98 and Cys178 may contribute to structures that regulate the access of positively charged ligands such as N-methyl scopolamine to the binding pocket. Asp99 may act as a gatekeeper residue to this channel. In contrast, the bulkier lipophilic ligand 3-quinuclidinyl benzilate may require breathing motions of the receptor to access the binding site. Trp378 is a key residue for receptor activation as well as binding, whereas Phe197 represents the floor of the N-methyl scopolamine binding pocket but does not interact with acetylcholine or 3-quinuclidinyl benzilate. Differences between the binding modes of N-methyl scopolamine, 3-quinuclidinyl benzilate, and acetylcholine have been modeled. Although the head groups of these ligands occupy overlapping volumes within the binding site, their side chains may follow significantly different directions.
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Affiliation(s)
- J Alex Goodwin
- Division of Physical Biochemistry, MRC National Institute for Medical Research, Mill Hill, London NW7 1AA
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26
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Bee MS, Hulme EC. Functional analysis of transmembrane domain 2 of the M1 muscarinic acetylcholine receptor. J Biol Chem 2007; 282:32471-9. [PMID: 17823120 DOI: 10.1074/jbc.m703909200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ala substitution scanning mutagenesis has been used to probe the functional role of amino acids in transmembrane (TM) domain 2 of the M1 muscarinic acetylcholine receptor, and of the highly conserved Asn43 in TM1. The mutation of Asn43, Asn61, and Leu64 caused an enhanced ACh affinity phenotype. Interpreted using a rhodopsin-based homology model, these results suggest the presence of a network of specific contacts between this group of residues and Pro415 and Tyr418 in the highly conserved NPXXY motif in TM7 that exhibit a similar mutagenic phenotype. These contacts may be rearranged or broken when ACh binds. D71A, like N414A, was devoid of signaling activity. We suggest that formation of a direct hydrogen bond between the highly conserved side chains of Asp71 and Asn414 may be a critical feature stabilizing the activated state of the M1 receptor. Mutation of Leu67, Ala70, and Ile74 also reduced the signaling efficacy of the ACh-receptor complex. The side chains of these residues are modeled as an extended surface that may help to orient and insulate the proposed hydrogen bond between Asp71 and Asn414. Mutation of Leu72, Gly75, and Met79 in the outer half of TM2 primarily reduced the expression of functional receptor binding sites. These residues may mediate contacts with TM1 and TM7 that are preserved throughout the receptor activation cycle. Thermal inactivation measurements confirmed that a reduction in structural stability followed the mutation of Met79 as well as Asp71.
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Affiliation(s)
- Mark S Bee
- Division of Physical Biochemistry, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom
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27
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Cotecchia S. Constitutive activity and inverse agonism at the α1adrenoceptors. Biochem Pharmacol 2007; 73:1076-83. [PMID: 17125741 DOI: 10.1016/j.bcp.2006.10.024] [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: 08/29/2006] [Revised: 10/20/2006] [Accepted: 10/24/2006] [Indexed: 10/23/2022]
Abstract
Mutations of G protein-coupled receptors (GPCR) can increase their constitutive (agonist-independent) activity. Some of these mutations have been artificially introduced by site-directed mutagenesis, others occur spontaneously in human diseases. The alpha(1B)adrenoceptor was the first GPCR in which point mutations were shown to trigger receptor activation. This article briefly summarizes some of the findings reported in the last several years on constitutive activity of the alpha(1)adrenoceptor subtypes, the location where mutations have been found in the receptors, the spontaneous activity of native receptors in recombinant as well as physiological systems. In addition, it will highlight how the analysis of the pharmacological and molecular properties of the constitutively active adrenoceptor mutants provided an important contribution to our understanding of the molecular mechanisms underlying the mechanism of receptor activation and inverse agonism.
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Affiliation(s)
- Susanna Cotecchia
- Department of Pharmacology and Toxicology, University of Lausanne, Rue du Bugnon 27, 1005 Lausanne, Switzerland.
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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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29
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Rovati GE, Capra V, Neubig RR. The highly conserved DRY motif of class A G protein-coupled receptors: beyond the ground state. Mol Pharmacol 2006; 71:959-64. [PMID: 17192495 DOI: 10.1124/mol.106.029470] [Citation(s) in RCA: 278] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Despite extensive study of heptahelical G protein-coupled receptors (GPCRs), the precise mechanism of G protein activation is unknown. The role of one highly conserved stretch of residues, the amino acids glutamic acid/aspartic acid-arginine-tyrosine (i.e., the E/DRY motif), has received considerable attention with respect to regulating GPCR conformational states. In the consensus view, glutamic acid/aspartic acid maintains the receptor in its ground state, because mutations frequently induce constitutive activity (CA). This hypothesis has been confirmed by the rhodopsin ground-state crystal structure and by computational modeling approaches. However, some class A GPCRs are resistant to CA, suggesting alternative roles for the glutamic acid/aspartic acid residue and the E/DRY motif. Here, we propose two different subgroups of receptors within class A GPCRs that make different use of the E/DRY motif, independent of the G protein type (G(s), G(i), or G(q)) to which the receptor couples. In phenotype 1 receptors, nonconservative mutations of the glutamic acid/aspartic acid-arginine residues, besides inducing CA, increase affinity for agonist binding, retain G protein coupling, and retain an agonist-induced response. In contrast, in second phenotype receptors, the E/DRY motif is more directly involved in governing receptor conformation and G protein coupling/recognition. Hence, mutations of the glutamic acid/aspartic acid residues do not induce CA. Conversely, nonconservative mutations of the arginine of the E/DRY motif always impair agonist-induced receptor responses and, generally, reduce agonist binding affinity. Thus, it is essential to look beyond the rhodopsin ground-state model of conformational activation to clarify the role of this highly conserved triplet in GPCR activation and function.
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Affiliation(s)
- G Enrico Rovati
- Laboratory of Molecular Pharmacology, Department of Pharmacological Sciences, University of Milan, Via Balzaretti 9, 20133 Milan, Italy.
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30
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Peng JYC, Vaidehi N, Hall SE, Goddard WA. The predicted 3D structures of the human M1 muscarinic acetylcholine receptor with agonist or antagonist bound. ChemMedChem 2006; 1:878-90. [PMID: 16902941 DOI: 10.1002/cmdc.200600047] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The muscarinic acetylcholine G-protein-coupled receptors are implicated in diseases ranging from cognitive dysfunctions to smooth-muscle disorders. To provide a structural basis for drug design, we used the MembStruk computational method to predict the 3D structure of the human M1 muscarinic receptor. We validated this structure by using the HierDock method to predict the binding sites for three agonists and four antagonists. The intermolecular ligand-receptor contacts at the predicted binding sites agree well with deductions from available mutagenesis experiments, and the calculated relative binding energies correlate with measured binding affinities. The predicted binding site of all four antagonists is located between transmembrane (TM) helices 3, 4, 5, 6, and 7, whereas the three agonists prefer a site involving residues from TM3, TM6, and TM7. We find that Trp 157(4) contributes directly to antagonist binding, whereas Pro 159(4) provides an indirect conformational switch to position Trp 157(4) in the binding site (the number in parentheses indicates the TM helix). This explains the large decrease in ligand binding affinity and signaling efficacy by mutations of Trp 157(4) and Pro 159(4) not previously explained by homology models. We also found that Asp 105(3) and aromatic residues Tyr 381(6), Tyr 404(7), and Tyr 408(7) are critical for binding the quaternary ammonium head group of the ligand through cation-pi interactions. For ligands with a charged tertiary amine head group, we suggest that proton transfer from the ligand to Asp 105(3) occurs upon binding. Furthermore, we found that an extensive aromatic network involving Tyr 106(3), Trp 157(4), Phe 197(5), Trp 378(6), and Tyr 381(6) is important in stabilizing antagonist binding. For antagonists with two terminal phenyl rings, this aromatic network extends to Trp 164(4), Tyr 179(extracellular loop 2), and Phe 390(6) located at the extracellular end of the TMs. We find that Asn 382(6) forms hydrogen bonds with selected antagonists. Tyr381(6) and Ser 109(3) form hydrogen bonds with the ester moiety of acetylcholine, which binds in the gauche conformation.
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Affiliation(s)
- Joyce Yao-chun Peng
- Materials and Process Simulation Center, 74-139, California Institute of Technology, Pasadena, 91125, USA
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31
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Ye K, Lameijer EWM, Beukers MW, Ijzerman AP. A two-entropies analysis to identify functional positions in the transmembrane region of class A G protein-coupled receptors. Proteins 2006; 63:1018-30. [PMID: 16532452 DOI: 10.1002/prot.20899] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Residues in the transmembrane region of G protein-coupled receptors (GPCRs) are important for ligand binding and activation, but the function of individual positions is poorly understood. Using a sequence alignment of class A GPCRs (grouped in subfamilies), we propose a so-called "two-entropies analysis" to determine the potential role of individual positions in the transmembrane region of class A GPCRs. In our approach, such positions appear scattered, while largely clustered according to their biological function. Our method appears superior when compared to other bioinformatics approaches, such as the evolutionary trace method, entropy-variability plot, and correlated mutation analysis, both qualitatively and quantitatively.
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Affiliation(s)
- Kai Ye
- Division of Medicinal Chemistry, Leiden/Amsterdam Center for Drug Research, Leiden University, Leiden, The Netherlands
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32
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Spalding TA, Burstein ES. Constitutive activity of muscarinic acetylcholine receptors. J Recept Signal Transduct Res 2006; 26:61-85. [PMID: 16595339 DOI: 10.1080/10799890600567349] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
We review the literature describing constitutive activity of the five muscarinic acetylcholine receptors in native and recombinant systems and discuss the effect of constitutive activity on muscarinic pharmacology in the context of modern models of receptor activation. We include a summary of mutations found to cause constitutive activity and discuss the implications of these data for the structure, function, and activation mechanism of muscarinic receptors. Finally, we discuss the possible physiological significance of constitutive activity of muscarinic receptors, incorporating information provided by targeted deletion of each of the muscarinic subtypes.
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Affiliation(s)
- Tracy A Spalding
- Genomics Institute of the Novartis Research Foundation, San Diego, California 92121, USA.
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33
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Espinoza-Fonseca LM, Trujillo-Ferrara JG. Identification of multiple allosteric sites on the M1muscarinic acetylcholine receptor. FEBS Lett 2005; 579:6726-32. [PMID: 16310776 DOI: 10.1016/j.febslet.2005.10.069] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2005] [Revised: 10/11/2005] [Accepted: 10/27/2005] [Indexed: 10/25/2022]
Abstract
Staurosporine and four staurosporine derivatives were docked on the rhodopsin-based homology model of the M1 muscarinic acetylcholine receptor in order to localize the possible allosteric sites of this receptor. It was found that there were three major allosteric sites, two of which are located at the extracellular face of the receptor, and one in the intracellular domain of the receptor. In the present study, the localization of these binding sites is described for the first time. The present study confirms the existence of multiple allosteric sites on the M1 muscarinic receptor, and lays the ground for further experimental and computational analysis to better understand how muscarinic receptors are modulated via their allosteric sites. These findings will also help to design and develop novel drugs acting as allosteric modulators of the M1 receptor, which can be used in the treatment of the Alzheimer's disease.
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Affiliation(s)
- L Michel Espinoza-Fonseca
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA.
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34
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Conner AC, Simms J, Howitt SG, Wheatley M, Poyner DR. The second intracellular loop of the calcitonin gene-related peptide receptor provides molecular determinants for signal transduction and cell surface expression. J Biol Chem 2005; 281:1644-51. [PMID: 16293613 DOI: 10.1074/jbc.m510064200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The calcitonin gene-related peptide (CGRP) receptor is a heterodimer of a family B G-protein-coupled receptor, calcitonin receptor-like receptor (CLR), and the accessory protein receptor activity modifying protein 1. It couples to G(s), but it is not known which intracellular loops mediate this. We have identified the boundaries of this loop based on the relative position and length of the juxtamembrane transmembrane regions 3 and 4. The loop has been analyzed by systematic mutagenesis of all residues to alanine, measuring cAMP accumulation, CGRP affinity, and receptor expression. Unlike rhodopsin, ICL2 of the CGRP receptor plays a part in the conformational switch after agonist interaction. His-216 and Lys-227 were essential for a functional CGRP-induced cAMP response. The effect of (H216A)CLR is due to a disruption to the cell surface transport or surface stability of the mutant receptor. In contrast, (K227A)CLR had wild-type expression and agonist affinity, suggesting a direct disruption to the downstream signal transduction mechanism of the CGRP receptor. Modeling suggests that the loop undergoes a significant shift in position during receptor activation, exposing a potential G-protein binding pocket. Lys-227 changes position to point into the pocket, potentially allowing it to interact with bound G-proteins. His-216 occupies a position similar to that of Tyr-136 in bovine rhodopsin, part of the DRY motif of the latter receptor. This is the first comprehensive analysis of an entire intracellular loop within the calcitonin family of G-protein-coupled receptor. These data help to define the structural and functional characteristics of the CGRP-receptor and of family B G-protein-coupled receptors in general.
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Affiliation(s)
- Alex C Conner
- School of Life and Health Sciences, Aston University, Birmingham B4 7ET, United Kingdom
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35
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Hawtin SR. Charged residues of the conserved DRY triplet of the vasopressin V1a receptor provide molecular determinants for cell surface delivery and internalization. Mol Pharmacol 2005; 68:1172-82. [PMID: 16049168 DOI: 10.1124/mol.105.013359] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The highly conserved "Asp-Arg-Tyr" triplet in the distal region of the third transmembrane region of most G-protein-coupled receptors is implicated in their activation process and mediation of G-protein signaling. The aim of this study was to determine whether specific features at this locus are important for the vasopressin V(1a) receptor (V(1a)R) by performing site-directed mutagenesis. In transfected HEK 293T cells, mutation of Asp (D148A) resulted in a misfolded receptor that was nonfunctional, localized intracellularly, and not constitutively active. Nonconservative (D148R) substitution was not expressed, whereas asparagine (D148N) partially restored cell surface expression, although no specific ligand-binding or inositol phosphate signaling was detected. In contrast, conservative (D148E) substitution was expressed moderately higher, bound ligands, and signaled similarly to a hemagglutinin epitope-tagged wild-type receptor. However, D148E showed a greater tendency to be internalized once it was delivered to the membrane. Individual replacements of the conserved arginine and tyrosine (R149A, Y150A) led to decreased signal transduction without affecting surface expression, agonist affinity, or internalization or increasing basal signaling activity. Incorporation of aspartate (R149D) or reversal of charges (D148R/R149D) were nonfunctional, localized intracellularly, and indicated the absence of an ionic interaction between Asp-148 and Arg-149. It is noteworthy that an important role of arginine was identified for regulating agonist-mediated internalization when a histidine (R149H) was present. This mutant was expressed on the cell surface but was rapidly internalized after agonist treatment. This study highlights the importance of specific charged residues within this motif that provide important determinants for cell surface delivery, internalization and for normal V(1a)R function.
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Affiliation(s)
- Stuart R Hawtin
- Institute of Cell Signaling, University of Nottingham, Queen's Medical Centre, Nottingham NG7 2UH, UK.
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36
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Lu ZL, Gallagher R, Sellar R, Coetsee M, Millar RP. Mutations remote from the human gonadotropin-releasing hormone (GnRH) receptor-binding sites specifically increase binding affinity for GnRH II but not GnRH I: evidence for ligand-selective, receptor-active conformations. J Biol Chem 2005; 280:29796-803. [PMID: 15967801 DOI: 10.1074/jbc.m413520200] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The human gonadotropin-releasing hormone (GnRH) receptor is evolutionarily configured for high affinity binding of GnRH I ([Tyr(5),Leu(7),Arg(8)]GnRH) but at lower affinity for GnRH II ([His(5),Trp(7),Tyr(8)]GnRH). GnRH I is more potent in the activation of the G(q/11) protein in the gonadotrope; however, GnRH II is more potent in the stimulation of apoptosis and antiproliferative effects through activating G(i) protein-mediated signaling, implying that GnRH I and II selectively stabilize different receptor-active conformations that preferentially couple to different signaling pathways. Receptor activation involves ligand induction or conformational selection, but the molecular basis of the communication between ligand-binding sites and receptor allosteric sites remains unclear. We have sought conformational coupling between receptor-ligand intermolecular interactions and intramolecular interaction networks in the human GnRH receptor by mutating remote residues that induce differential ligand binding affinity shifts for GnRH I and II. We have demonstrated that certain Ala mutations in the intracellular segments of transmembrane domains 3 (Met(132)), 5 (Met(227)), 6 (Phe(272) and Phe(276)), and 7 (Ile(322) and Tyr(323)) of the human GnRH receptor allosterically increased ligand binding affinity for GnRH II but had little effect on GnRH I binding affinity. We examined the role of the three amino acids that differ in these two ligands, and we found that Tyr(8) in GnRH II plays a dominant role for the increased affinity of the receptor mutants for GnRH II. We propose that creation of a high affinity binding site for GnRH II accompanies receptor conformational changes, i.e."induced fit" or "conformational selection," mainly determined by the intermolecular interactions between Tyr(8) and the receptor contact residues, which can be facilitated by disruption of particular sets of receptor-stabilizing intramolecular interactions. The findings suggest that GnRH I and II binding may selectively stabilize different receptor-active conformations and therefore different ligand-induced selective signaling described previously for these ligands.
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Affiliation(s)
- Zhi-Liang Lu
- Medical Research Council Human Reproductive Sciences Unit, Centre for Reproductive Biology, Edinburgh, Scotland, UK.
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37
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Rosenkilde MM, Kledal TN, Schwartz TW. High Constitutive Activity of a Virus-Encoded Seven Transmembrane Receptor in the Absence of the Conserved DRY Motif (Asp-Arg-Tyr) in Transmembrane Helix 3. Mol Pharmacol 2005; 68:11-9. [PMID: 15788740 DOI: 10.1124/mol.105.011239] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The highly conserved Arg in the so-called DRY motif (Asp-Arg-Tyr) at the intracellular end of transmembrane helix 3 is in general considered as an essential residue for G protein coupling in rhodopsin-like seven transmembrane (7TM) receptors. In the open reading frame 74 (ORF74) receptor encoded by equine herpesvirus 2 (EHV2), the DRY motif is substituted with a DTW motif. Nevertheless, this receptor signaled with high constitutive activity through Gi as determined by a receptor-mediated inhibition of forskolin-induced cAMP-production and by an induction of the serum response element-driven transcriptional activity through a pertussis toxin-sensitive manner. Gs and Gq were not activated constitutively as determined by the lack of inositol phosphate turnover and activities of the three transcription factors: cAMP response element-binding protein (CREB), nuclear factor-kappaB, and nuclear factor of activated T cells. Coexpression of the ORF74-EHV2 receptor with the promiscuous G protein Gqi4myr supported the constitutive Gi activation as determined by inositol phosphate turnover and CREB activation. The constitutive activity was inhibited by nonpeptide inverse agonists with micromolar potencies, and the chemokine CXCL6 acted as a high-affinity agonist. It is noteworthy that reconstitution of the DRY motif resulted in a 4- to 5-fold decrease of the constitutive activity. Both the wild type and the receptor with the reconstituted DRY motif were expressed at the cell surface as indicated by immunohistochemistry and enzyme-linked immunosorbent assay analysis. It is concluded that the Arg of the DRY motif in transmembrane helix 3 is not essential for G protein coupling based on the constitutive as well as the ligand-mediated activity observed for ORF74-EHV2.
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Affiliation(s)
- Mette M Rosenkilde
- Laboratory for Molecular Pharmacology, Department of Pharmacology, The Panum Institute 18.6, Blegdamsvej 3, 2200 Copenhagen N, Denmark.
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38
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Abstract
A model for the human delta opioid receptor has been generated via sequence alignment, structure building using the crystal structure of bovine rhodopsin as a template, and refinement by molecular dynamics simulation. The model building suggested that, in addition to the previously postulated interaction between D128 and Y308, an internal salt bridge also exists between residues D128 and R192, both of which are conserved in all the opioid receptors. The model and salt bridge were then shown to be stable during a 20-nsec simulation in a lipid bilayer. It is therefore proposed that both of these interactions play a role in stabilizing the inactive state of the receptor. The model is also used in an effort to rationalize many of the mutational studies performed on delta opioid receptors, and to suggest a plausible explanation for the differences between known delta opioid agonists and antagonists.
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Affiliation(s)
- Mahalaxmi Aburi
- Department of Biochemistry, Kansas State University, Manhattan, Kansas 66506-3701, USA
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39
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Capra V, Veltri A, Foglia C, Crimaldi L, Habib A, Parenti M, Rovati GE. Mutational analysis of the highly conserved ERY motif of the thromboxane A2 receptor: alternative role in G protein-coupled receptor signaling. Mol Pharmacol 2004; 66:880-9. [PMID: 15229298 DOI: 10.1124/mol.104.001487] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The presence of highly conserved amino acid stretches in G protein-coupled receptors (GPCRs) usually predicts an important role in receptor function. Considerable attention has therefore been focused on the involvement of the highly conserved Glu/Asp-Arg-Tyr (E/DRY) motif at the cytoplasmic end of transmembrane domain 3 in the regulation of GPCR conformational states and/or the mediation of G protein activation. In the present study, we investigated the role of Glu129 and Arg130 in the ERY of thromboxane A2 receptor alpha (TPalpha) in transfected human embryonic kidney 293 cells. We show that no conservative or nonconservative substitutions of Glu129 and Arg130 generated a constitutively active TPalpha mutant, but a nonconservative mutation of Arg130 (R130V) yielded a mutant receptor with significantly impaired 9,11-dideoxy-9alpha,11alpha-methanoepoxy-prosta-5Z,13E-dien-1-oic acid (U46619)-induced accumulation of inositol phosphates (IPs). This loss-of-function phenotype seems to be caused by the uncoupling of the TPalpha receptor from Gq, as demonstrated by the loss of high-affinity agonist binding, and not by receptor internalization, as shown by localization studies with the R130V-green fluorescent protein fusion protein. It is interesting to note that U46619-induced activation of the nonconservative E129V mutant stimulated the production of IPs with a approximately 10-fold lower EC50 and a approximately 2-fold higher Emax than in the wild-type receptor. Collectively, these data demonstrate that, unlike other GPCRs, mutations of Glu129 do not induce constitutive activity, whereas Arg130 is involved in G protein coupling or recognition, and they suggest the existence within class A GPCRs of at least two different subclasses that make different uses of the highly conserved E/DRY motif.
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Affiliation(s)
- Valérie Capra
- Laboratory of Molecular Pharmacology, Department of Pharmacological Sciences, University of Milan, Via Balzaretti 9, 20133, Italy.
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40
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Gáborik Z, Jagadeesh G, Zhang M, Spät A, Catt KJ, Hunyady L. The role of a conserved region of the second intracellular loop in AT1 angiotensin receptor activation and signaling. Endocrinology 2003; 144:2220-8. [PMID: 12746278 DOI: 10.1210/en.2002-0135] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The pleiotropic actions of angiotensin II are mediated by the primarily G(q) protein-coupled type 1 angiotensin (AT(1)) receptor. In this study a mutational analysis of the function of the conserved DRYXXV/IXXPL domain in the second intracellular loop of the rat AT(1A) receptor was performed in COS7 cells. Alanine substitution studies showed that single replacement of the highly conserved Asp(125) and Arg(126), but not Tyr(127), moderately impaired angiotensin II-induced inositol phosphate signaling. However, concomitant substitution of both Asp(125) and Arg(126) caused marked reduction of both inositol phosphate signaling and receptor internalization. Alanine scanning of the adjacent residues showed that substitution of Ile(130), His(132), and Pro(133) reduced agonist-induced inositol phosphate signal generation, whereas mutations of Met(134) also impaired receptor internalization. Expression of the D125A mutant AT(1A) receptor in COS7 cells endowed the receptor with moderate constitutive activity, as indicated by its enhanced basal Elk1 promoter activity and inositol phosphate response to partial agonists. Angiotensin II-induced stimulation of the Elk1 promoter showed parallel impairment with inositol phosphate signal generation in receptors containing mutations in this region of the AT(1A) receptor. These data confirm that Ca(2+) signal generation is required for the nuclear effects of angiotensin II-induced ERK activation. They are also consistent with the role of the conserved DRY sequence of the AT(1A) receptor in receptor activation, and of Asp(125) in constraining the receptor in its inactive conformation. Furthermore, in the cytoplasmic helical extension of the third helix, an apolar surface that includes Ile(130) and Met(134) appears to have a direct role in G protein coupling.
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Affiliation(s)
- Zsuzsanna Gáborik
- Department of Physiology, Semmelweis University, Faculty of Medicine, H-1088 Budapest, Hungary
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41
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Feng W, Song ZH. Effects of D3.49A, R3.50A, and A6.34E mutations on ligand binding and activation of the cannabinoid-2 (CB2) receptor. Biochem Pharmacol 2003; 65:1077-85. [PMID: 12663043 DOI: 10.1016/s0006-2952(03)00005-4] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
In several G protein-coupled receptors (GPCRs), the Asp-Arg-Tyr (DRY) motif at the bottom of third transmembrane domain and the amino acid at position 6.34 in the sixth transmembrane domain have been shown to play important roles in signal transduction. In this study, we propose that in the cannabinoid-2 (CB2) receptor, R3.50 in the DRY motif may be crucial for interacting with G proteins, and D3.49 and A6.34 may be important for constraining the receptor in an inactive conformation. To test our hypothesis, R3.50A, D3.49A, and A6.34E mutations of the human CB2 receptor were made by site-directed mutagenesis. These mutant receptors were stably transfected into human embryonic 293 cells, and their ligand binding and signal transduction properties were analyzed. Similar to other GPCRs, R3.50 of the CB2 receptor is crucial for signal transduction. Unlike other GPCRs, D3.49 and A6.34 of the CB2 receptor do not seem to be important for keeping the receptor in an inactive state. Furthermore, D3.49A and A6.34E mutations abolished ligand binding, and all three mutations abolished constitutive activity of the wild-type CB2 receptor.
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Affiliation(s)
- Wenke Feng
- Department of Pharmacology and Toxicology, University of Louisville School of Medicine, Louisville, KY 40292, USA
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42
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Parnot C, Miserey-Lenkei S, Bardin S, Corvol P, Clauser E. Lessons from constitutively active mutants of G protein-coupled receptors. Trends Endocrinol Metab 2002; 13:336-43. [PMID: 12217490 DOI: 10.1016/s1043-2760(02)00628-8] [Citation(s) in RCA: 160] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
In the past decade, the concept of constitutive activity has profoundly modified our understanding of G protein-coupled-receptors (GPCRs). Here, we review the contribution of constitutively active mutants (CAMs) to our understanding of three aspects of GPCR physiopathology: (1) GPCR activation is a complex mechanism involving both the release of inactive state conformational constraints, mimicked by most CAMs, and the creation of new interactions that stabilize the active state and are mimicked by a restricted set of CAMs; (2) GPCR phosphorylation, internalization and desensitization processes are activated by receptor conformations, which partly overlap those activating G protein; (3) natural CAMs, mostly affecting GPCRs of the endocrine system, are found in several hereditary and acquired diseases, including cancers. One major remaining question is how CAMs recapitulate the different structural modifications of the agonist-induced active conformation(s) of the wild-type receptor. This characterization is a prerequisite for further use of CAMs as ligand-free models of active GPCRs in structural, cellular and physiological studies.
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Affiliation(s)
- Charles Parnot
- INSERM U567, CNRS UMR8104, Institut Cochin, Faculté de Médecine Cochin, 24 rue du Fg St Jacques, F-75014 Paris, France
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43
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Chung DA, Wade SM, Fowler CB, Woods DD, Abada PB, Mosberg HI, Neubig RR. Mutagenesis and peptide analysis of the DRY motif in the alpha2A adrenergic receptor: evidence for alternate mechanisms in G protein-coupled receptors. Biochem Biophys Res Commun 2002; 293:1233-41. [PMID: 12054508 DOI: 10.1016/s0006-291x(02)00357-1] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
In G protein-coupled receptors (GPCRs), a conserved aspartic acid in the DRY motif at the cytoplasmic end of helix 3 regulates the transition to the active state, while the adjacent arginine is crucial for G protein activation. To examine the functions of these two residues, we made D130I and R131Q mutations in the alpha2A adrenergic receptor (AR). We demonstrate that, unlike other GPCRs, the alpha2A AR is not constitutively activated by the D130I mutation, although the mutation increases agonist affinity. While the R131Q mutation severely disrupts function, it decreases rather than increasing agonist affinity as seen in other GPCRs. We then investigated the molecular effects of the same mutations in a peptide model and showed that Arg131 is not required for peptide-mediated G protein activation. These results indicate that the alpha2A AR does not follow the conventional GPCR mechanistic paradigm with respect to the function of the DRY motif.
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Affiliation(s)
- Duane A Chung
- Biophysics Research Division, The University of Michigan, Ann Arbor, MI 48109, USA
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44
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Abstract
The X-ray structure of the photoreceptor rhodopsin has provided the first atomic-resolution structure of a seven-transmembrane (7-TM) G-protein-coupled receptor. This has provided an improved template for interpreting the huge body of structure--activity, mutagenesis and affinity labelling data available for related 7-TM receptors, such as muscarinic acetylcholine receptors. Ligand contacts, and the intramolecular interactions that stabilize the ground state structure, can be identified with some degree of confidence. We now have a firm basis for attempts to predict the structure of the receptor--G-protein complex, and understand the mechanism by which the agonist--receptor complex activates the G protein.
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Affiliation(s)
- Zhi-Liang Lu
- MRC Human Reproductive Sciences Unit, Centre for Reproductive Biology, Edinburgh, UK
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45
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Lu ZL, Saldanha JW, Hulme EC. Transmembrane domains 4 and 7 of the M(1) muscarinic acetylcholine receptor are critical for ligand binding and the receptor activation switch. J Biol Chem 2001; 276:34098-104. [PMID: 11441014 DOI: 10.1074/jbc.m104217200] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Activation of the muscarinic acetylcholine receptors requires agonist binding followed by a conformational change, but the ligand binding and conformation-switching residues have not been completely identified. Systematic alanine-scanning mutagenesis has been used to assess residues 142-164 in transmembrane helix 4 and 402-421 in transmembrane helix 7 of the M(1) muscarinic acetylcholine receptor. Several inward-facing amino acid side chains in the exofacial parts of transmembrane helices 4 and 7 contribute to acetylcholine binding. Alanine substitution of the aromatic residues in this group reduced signaling efficacy, suggesting that they may form part of a charge-stabilized aromatic cage, which triggers rotation and movement of the transmembrane helices. The mutation of adjacent residues modulated receptor activation, either reducing signaling or causing constitutive activation. In the buried endofacial section of transmembrane helix 7, alanine substitution mutants of the conserved NSXXNPXXY motif displayed strongly reduced signaling efficacy, despite having increased or unchanged acetylcholine affinity. These residues may have dual functions, forming intramolecular contacts that stabilize the receptor in the inactive ground state, but that are broken, allowing them to form new intramolecular bonds in the activated state. This conformational rearrangement is critical to produce a G protein binding site and may represent a key mechanism of receptor activation.
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Affiliation(s)
- Z L Lu
- Division of Physical Biochemistry, Medical Research Council National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom.
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46
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Erlenbach I, Kostenis E, Schmidt C, Hamdan FF, Pausch MH, Wess J. Functional expression of M(1), M(3) and M(5) muscarinic acetylcholine receptors in yeast. J Neurochem 2001; 77:1327-37. [PMID: 11389184 DOI: 10.1046/j.1471-4159.2001.00344.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The goal of this study was to functionally express the three G(q)-coupled muscarinic receptor subtypes, M(1), M(3) and M(5), in yeast (Saccharomyces cerevisiae). Transformation of yeast with expression constructs coding for the full-length receptors resulted in very low numbers of detectable muscarinic binding sites (B(max) < 5 fmol/mg). Strikingly, deletion of the central portion of the third intracellular loops of the M(1), M(3) and M(5) muscarinic receptors resulted in dramatic increases in B(max) values (53-214 fmol/mg). To monitor productive receptor/G-protein coupling, we used specifically engineered yeast strains that required agonist-stimulated receptor/G-protein coupling for cell growth. These studies showed that the shortened versions of the M(1), M(3) and M(5) receptors were unable to productively interact with the endogenous yeast G protein alpha-subunit, Gpa1p, or a Gpa1 mutant subunit that contained C-terminal mammalian Galpha(s) sequence. In contrast, all three receptors gained the ability to efficiently couple to a Gpa1/Galpha(q) hybrid subunit containing C-terminal mammalian Galpha(q) sequence, indicating that the M(1), M(3) and M(5) muscarinic receptors retained proper G-protein coupling selectivity in yeast. This is the first study to report the expression of muscarinic receptors in a coupling-competent form in yeast. The strategy described here, which involves structural modification of both receptors and co-expressed G proteins, should facilitate the functional expression of other classes of G protein-coupled receptors in yeast.
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Affiliation(s)
- I Erlenbach
- Laboratory of Bioorganic Chemistry, NIDDK, National Institutes of Health, Bethesda, MD 20892, USA
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47
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Milligan G, Kellett E, Dacquet C, Dubreuil V, Jacoby E, Millan MJ, Lavielle G, Spedding M. S 14506: novel receptor coupling at 5-HT(1A) receptors. Neuropharmacology 2001; 40:334-44. [PMID: 11166326 DOI: 10.1016/s0028-3908(00)00162-3] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
S 14506 is chemically related to the inverse agonist at 5-HT(1A) receptors, spiperone, but S 14506 behaves as one of the most potent agonists known at these receptors, both in vitro and in vivo. In hippocampal membranes, the specific binding of [(3)H]-S 14506 (K(d)=0.79+/-0.2 nM; B(max)=400+/-32 fmol/mg protein) to 5-HT(1A) receptors resembled that of an antagonist in that it was increased by GppNHp, whereas GppNHp reduced the binding of the classic agonist [(3)H]-8-OH-DPAT (K(d)=1.5+/-0.5 nM; B(max)=303+/-20 fmol/mg protein). Manganese, magnesium and calcium reduced the binding of [(3)H]-S 14506 to 5-HT(1A) receptors whereas the binding of [(3)H]-8-OH-DPAT was increased. Further, sodium markedly reduced the binding of [(3)H]-8-OH-DPAT, without affecting the binding of [(3)H]-S 14506. [(3)H]-S 14506 also bound with high affinity to h 5-HT(1A) receptors stably expressed in membranes of CHO cells (K(d)=0.13+/-0.05 nM; B(max)=2.99+/-0.60 pmol/mg protein): the B(max) was double that of [(3)H]-8-OH-DPAT. GppNHp strongly decreased [(3)H]-8-OH-DPAT binding but scarcely changed [(3)H]-S 14506 binding; calcium, magnesium and manganese had little effect on [(3)H]-S 14506 binding in CHO cells. Antagonists (WAY 100635, WAY 100135) and inverse agonists (spiperone and metitepine) displaced [(3)H]-S 14506 binding with high affinity and Hill slopes close to unity, whereas agonists (5-HT and 5-CT) displayed low affinity with low Hill slopes: partial agonists (buspirone, ipsapirone) showed intermediate properties. In fusion proteins of h 5-HT(1A) receptors with G(ialpha1) the compound potently increased high-affinity GTPase, with a steeper Hill slope than for 5-HT, which may indicate positive cooperativity. The maximum response for S 14506 in these assays was equivalent to 5-HT, indicating it to be a full agonist.In molecular modelling studies, using a three-site model of the 5-HT(1A) receptor, S 14506 spanned between the 5-HT recognition site and the "arginine switch" (DRY microdomain) postulated to activate the interaction of the receptor with the G protein. Thus it is possible to synthesise ligands at G-protein-coupled receptors which are highly potent agonists, but which are structurally related to inverse agonists and show some features of antagonist/inverse agonist binding.
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Affiliation(s)
- G Milligan
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, University of Glasgow, G12 8QQ, Glasgow, UK
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48
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Chen S, Lin F, Xu M, Hwa J, Graham RM. Dominant-negative activity of an alpha(1B)-adrenergic receptor signal-inactivating point mutation. EMBO J 2000; 19:4265-71. [PMID: 10944109 PMCID: PMC302026 DOI: 10.1093/emboj/19.16.4265] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
alpha(1)-adrenergic receptors (alpha(1)-ARs) are members of the G-protein-coupled receptor (GPCR) superfamily and activate inositol phosphate (IP) turnover. We show that glycine and asparagine mutations of Phe303 in transmembrane segment VI (TMVI) of the alpha(1B)-AR, a highly conserved residue in GPCRs, although increasing agonist affinity, abolish agonist-activated IP signalling. Co-expression of the Phe303 mutants also inhibited (-)epinephrine-stimulated IP signalling by wild-type alpha(1B)-AR and other G(q)-coupled receptors, as well as IP signalling mediated by AlF(4)(-) stimulation of both wild-type G(q alpha) and a constitutively active mutant. The inability of the Phe303 mutants to signal is due to induction of a receptor conformation that dissociates G-protein binding from activation. As a result, the Phe303 mutants sequester G(q alpha) and stoichiometrically inhibit Gq signalling in a dominant-negative manner. We further show that both the enhanced basal and agonist-stimulated IP-signalling activity of the constitutively active alpha(1B)-AR mutants, C128F and A293E, are inhibited in the double mutants, C128F/F303G and A293E/F303G. Phe303, therefore, appears to be critically involved in coupling TMVI alpha-helical movement, a key step in receptor activation, to activation of the cognate G-protein.
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Affiliation(s)
- S Chen
- Molecular Cardiology Unit, Victor Chang Cardiac Research Institute, St Vincent's Hospital, Sydney 2010, Australia
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49
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Lu ZL, Hulme EC. A network of conserved intramolecular contacts defines the off-state of the transmembrane switch mechanism in a seven-transmembrane receptor. J Biol Chem 2000; 275:5682-6. [PMID: 10681552 DOI: 10.1074/jbc.275.8.5682] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Activation of the rhodopsin-like 7-transmembrane (7-TM) receptors requires switching interhelical constraints that stabilize the inactive state to a new set of contacts in the activated state, which binds the cognate G-protein. The free energy to drive this is provided by agonist binding, which has higher affinity to the active than to the inactive conformation. We have sought specific interhelical constraint contacts, using the M(1) muscarinic acetylcholine receptor as a model. Histidine substitutions of particular groups of amino acids, in transmembrane domains 3, 6, and 7, created high-affinity Zn(2+) binding sites, demonstrating the close proximity of their side chains in the inactive state. Alanine point substitutions have shown the effect of weakening the individual intramolecular contacts. In each case, the acetylcholine affinity was increased, implying promotion of the activated state. These amino acids are highly conserved throughout the 7-TM receptor superfamily. We propose that they form an important part of a network of conserved interhelical contacts that defines the off-state of a general transmembrane switch mechanism.
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Affiliation(s)
- Z L Lu
- Division of Physical Biochemistry, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom.
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50
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Abstract
G protein-coupled, seven-transmembrane segment receptors (GPCRs or 7TM receptors), with more than 1000 different members, comprise the largest superfamily of proteins in the body. Since the cloning of the first receptors more than a decade ago, extensive experimental work has uncovered multiple aspects of their function and challenged many traditional paradigms. However, it is only recently that we are beginning to gain insight into some of the most fundamental questions in the molecular function of this class of receptors. How can, for example, so many chemically diverse hormones, neurotransmitters, and other signaling molecules activate receptors believed to share a similar overall tertiary structure? What is the nature of the physical changes linking agonist binding to receptor activation and subsequent transduction of the signal to the associated G protein on the cytoplasmic side of the membrane and to other putative signaling pathways? The goal of the present review is to specifically address these questions as well as to depict the current awareness about GPCR structure-function relationships in general.
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Affiliation(s)
- U Gether
- Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark.
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