1
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Pilon A, Goven D, Raymond V. Pharmacological and molecular characterization of the A-type muscarinic acetylcholine receptor from Anopheles gambiae. INSECT MOLECULAR BIOLOGY 2022; 31:497-507. [PMID: 35357052 DOI: 10.1111/imb.12775] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 02/03/2022] [Accepted: 03/24/2022] [Indexed: 06/14/2023]
Abstract
Muscarinic acetylcholine receptors (mAChRs) which are G protein-coupled receptors play key roles in insect physiology. Whereas vertebrate mAChRs are important targets for pharmaceutical drugs, insect mAChRs are under-exploited by the agro-chemical industry. Moreover, insect mAChRs have been less well studied than their vertebrate counterparts. Their critical functions mean that a better knowledge of the insect mAChRs is crucial for the effort to develop a new molecular-level strategy for insect pest management. Almost all insects possess three mAChRs named A, B and C which differ according to their coupling effector systems and their pharmacological profile. The aim of this study was to characterize the A-type mAChR (mAChR-A) from Anopheles gambiae which is the major vector of malaria in order to develop new strategies in pest management. In this paper, we reported that mAChR-A is more expressed in adult mosquitoes than in larvae. Furthermore, using calcium imaging recordings, we found that the An. gambiae mAChR-A expressed in Sf9 cells is activated by specific muscarinic agonists acetylcholine, muscarine and oxotremorine M and blocked by several mAChR antagonists. Moreover, using inhibitors of phosphoinositide pathway such as Gαq/11 protein blocker, we have shown that an increased intracellular calcium concentration elicited by the acetylcholine application was mediated by PLC/IP3R pathway. As a rise in intracellular calcium concentration could lead to an increase in the insecticide target sensitivity, these results suggest that An. gambiae mAChR-A should not be only considered as a potential target for new molecules but also as a key element to optimize the efficacy of insecticide in vector control.
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Affiliation(s)
- Alexandre Pilon
- Univ Angers, INRAE, SiFCIR Laboratory, SFR QUASAV, F-49000 Angers, France
| | - Delphine Goven
- Univ Angers, INRAE, SiFCIR Laboratory, SFR QUASAV, F-49000 Angers, France
| | - Valerie Raymond
- Univ Angers, INRAE, SiFCIR Laboratory, SFR QUASAV, F-49000 Angers, France
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2
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Punn A, Chen J, Delidaki M, Tang J, Liapakis G, Lehnert H, Levine MA, Grammatopoulos DK. Mapping structural determinants within third intracellular loop that direct signaling specificity of type 1 corticotropin-releasing hormone receptor. J Biol Chem 2012; 287:8974-85. [PMID: 22247544 PMCID: PMC3308756 DOI: 10.1074/jbc.m111.272161] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The type 1 corticotropin-releasing hormone receptor (CRH-R1) influences biological responses important for adaptation to stressful stimuli, through activation of multiple downstream effectors. The structural motifs within CRH-R1 that mediate G protein activation and signaling selectivity are unknown. The aim of this study was to gain insights about important structural determinants within the third intracellular loop (IC3) of the human CRH-R1α important for cAMP and ERK1/2 pathways activation and selectivity. We investigated the role of the juxtamembrane regions of IC3 by mutating amino acid cassettes or specific residues to alanine. Although simultaneous tandem alanine mutations of both juxtamembrane regions Arg292-Met295 and Lys311-Lys314 reduced ligand binding and impaired signaling, all other mutant receptors retained high affinity binding, indistinguishable from wild-type receptor. Agonist-activated receptors with tandem mutations at the proximal or distal terminal segments enhanced activation of adenylyl cyclase by 50–75% and diminished activation of inositol trisphosphate and ERK1/2 by 60–80%. Single Ala mutations identified Arg292, Lys297, Arg310, Lys311, and Lys314 as important residues for the enhanced activation of adenylyl cyclase, partly due to reduced inhibition of adenylyl cyclase activity by pertussis toxin-sensitive G proteins. In contrast, mutation of Arg299 reduced receptor signaling activity and cAMP response. Basic as well as aliphatic amino acids within both juxtamembrane regions were identified as important for ERK1/2 phosphorylation through activation of pertussis toxin-sensitive G proteins as well as Gq proteins. These data uncovered unexpected roles for key amino acids within the highly conserved hydrophobic N- and C-terminal microdomains of IC3 in the coordination of CRH-R1 signaling activity.
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Affiliation(s)
- Anu Punn
- Department of Endocrinology and Metabolism, Clinical Sciences Research Institute, Warwick Medical School, University of Warwick, Coventry, United Kingdom
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3
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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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4
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Brubaker PL, Drucker DJ. Structure-Function of the Glucagon Receptor Family of G Protein-Coupled Receptors: The Glucagon, GIP, GLP-1, and GLP-2 Receptors. ACTA ACUST UNITED AC 2011. [DOI: 10.3109/10606820213687] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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5
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Kendall RT, Senogles SE. Isoform-specific uncoupling of the D2 dopamine receptors subtypes. Neuropharmacology 2010; 60:336-42. [PMID: 20888845 DOI: 10.1016/j.neuropharm.2010.09.018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2010] [Revised: 08/09/2010] [Accepted: 09/16/2010] [Indexed: 10/19/2022]
Abstract
Dopaminergic transmission is fundamental to many neural pathways of clinical interest. We have analyzed the alternatively-spliced isoforms of the D(2) dopamine receptor, D(2) long (D(2l)) and D(2) short (D(2s)), which differ only by a 29-amino acid insertion in the third cytoplasmic loop. Well-known determinants for GPCR signal transduction--the third intracellular loop regions--were co-expressed with the wild-type receptors to test for their ability to antagonize parent receptor function. We found that the D(2l)-mediated inhibition of forskolin-stimulated adenylyl cyclase was blocked by the co-expression of the third cytoplasmic loop of D(2l). However, expression of the third cytoplasmic loop of D(2s) did not inhibit D(2l)-mediated signal transduction. Conversely, expression of the D(2s) third cytoplasmic loop antagonized the D(2s) receptor's function and the D(2l) third cytoplasmic loop did not. In contrast, expression of the alternatively-spliced insert region had no effect when co-expressed with either wild-type receptor isoform. These results suggest that the third cytoplasmic loops of each receptor adopt unique conformations and that the primary sequence of the insert region is not the basis for differences in signaling between D(2s) and D(2l). These findings further support previous studies suggesting that the D2 receptor isoforms use distinct signal transduction mechanisms.
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Affiliation(s)
- Ryan T Kendall
- Department of Molecular Sciences, College of Medicine, University of Tennessee Health Science Center, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA
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6
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Chee MJS, Mörl K, Lindner D, Merten N, Zamponi GW, Light PE, Beck-Sickinger AG, Colmers WF. The third intracellular loop stabilizes the inactive state of the neuropeptide Y1 receptor. J Biol Chem 2008; 283:33337-46. [PMID: 18812316 PMCID: PMC2662261 DOI: 10.1074/jbc.m804671200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2008] [Revised: 09/15/2008] [Indexed: 11/06/2022] Open
Abstract
Constitutively active G-protein-coupled receptors (GPCRs) can signal even in the absence of ligand binding. Most Class I GPCRs are stabilized in the resting conformation by intramolecular interactions involving transmembrane domain (TM) 3 and TM6, particularly at loci 6.30 and 6.34 of TM6. Signaling by Gi/Go-coupled receptors such as the Neuropeptide Y1 receptor decreases already low basal metabolite levels. Thus, we examined constitutive activity using a biochemical assay mediated by a Gi/Gq chimeric protein and a more direct electrophysiological assay. Wild-type (WT-Y1) receptors express no measurable, agonist-independent activation, while mu-opioid receptors (MOR) and P2Y12 purinoceptors showed clear evidence of constitutive activation, especially in the electrophysiological assay. Neither point mutations at TM6 (T6.30A or N6.34A) nor substitution of the entire TM3 and TM6 regions from the MOR into the Y1 receptor increased basal WT-Y1 activation. By contrast, chimeric substitution of the third intracellular loop (ICL3) generated a constitutively active, Y1-ICL3-MOR chimera. Furthermore, the loss of stabilizing interactions from the native ICL3 enhanced the role of surrounding residues to permit basal receptor activation; because constitutive activity of the Y1-ICL3-MOR chimera was further increased by point mutation at locus 6.34, which did not alter WT-Y1 receptor activity. Our results indicate that the ICL3 stabilizes the Y1 receptor in the inactive state and confers structural properties critical for regulating Y receptor activation and signal transduction. These studies reveal the active participation of the ICL3 in the stabilization and activation of Class I GPCRs.
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MESH Headings
- Animals
- COS Cells
- Chlorocebus aethiops
- GTP-Binding Protein alpha Subunits, Gi-Go/genetics
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- GTP-Binding Protein alpha Subunits, Gq-G11/genetics
- GTP-Binding Protein alpha Subunits, Gq-G11/metabolism
- Humans
- Point Mutation
- Protein Structure, Secondary/physiology
- Protein Structure, Tertiary/physiology
- Receptors, Neuropeptide Y/genetics
- Receptors, Neuropeptide Y/metabolism
- Receptors, Opioid, mu/genetics
- Receptors, Opioid, mu/metabolism
- Receptors, Purinergic P2/genetics
- Receptors, Purinergic P2/metabolism
- Receptors, Purinergic P2Y12
- Recombinant Fusion Proteins/genetics
- Recombinant Fusion Proteins/metabolism
- Signal Transduction/physiology
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Affiliation(s)
- Melissa J S Chee
- Department of Pharmacology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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7
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Bakker RA, Jongejan A, Sansuk K, Hacksell U, Timmerman H, Brann MR, Weiner DM, Pardo L, Leurs R. Constitutively active mutants of the histamine H1 receptor suggest a conserved hydrophobic asparagine-cage that constrains the activation of class A G protein-coupled receptors. Mol Pharmacol 2007; 73:94-103. [PMID: 17959710 DOI: 10.1124/mol.107.038547] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The aim of this study was to create and characterize constitutively active mutant (CAM) histamine H(1) receptors (H(1)R) using random mutagenesis methods to further investigate the activation process of the rhodopsin-like family of G protein-coupled receptors (GPCRs). This approach identified position 6.40 in TM 6 as a "hot spot" because mutation of Ile6.40(420) either to Glu, Gly, Ala, Arg, Lys, or Ser resulted in highly active CAM H(1)Rs, for which almost no histamine-induced receptor activation response could be detected. The highly conserved hydrophobic amino acid at position 6.40 defines, in a computational model of the H(1)R, the asparagine cage motif that restrains the side chain of Asn7.49 of the NPxxY motif toward transmembrane domain (TM 6) in the inactive state of the receptor. Mutation of the asparagine cage into Ala or Gly, removing the interfering bulky constraints, increases the constitutive activity of the receptor. The fact that the Ile6.40(420)Arg/Lys/Glu mutant receptors are highly active CAM H(1)Rs leads us to suggest that a positively charged residue, presumably the highly conserved Arg3.50 from the DRY motif, interacts in a direct or an indirect (through other side chains or/and internal water molecules) manner with the acidic Asp2.50..Asn7.49 pair for receptor activation.
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Affiliation(s)
- Remko A Bakker
- Leiden/Amsterdam Center for Drug Research, Department of Medicinal Chemistry, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
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8
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Conner AC, Simms J, Conner MT, Wootten DL, Wheatley M, Poyner DR. Diverse functional motifs within the three intracellular loops of the CGRP1 receptor. Biochemistry 2006; 45:12976-85. [PMID: 17059214 DOI: 10.1021/bi0615801] [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: 11/29/2022]
Abstract
The CGRP(1) receptor exists as a heterodimeric complex between a single-pass transmembrane accessory protein (RAMP1) and a family B G-protein-coupled receptor (GPCR) called the calcitonin receptor-like receptor (CLR). This study investigated the structural motifs found in the intracellular loops (ICLs) of this receptor. Molecular modeling was used to predict active and inactive conformations of each ICL. Conserved residues were altered to alanine by site-directed mutagenesis. cAMP accumulation, cell-surface expression, agonist affinity, and CGRP-stimulated receptor internalization were characterized. Within ICL1, L147 and particularly R151 were important for coupling to G(s). R151 may interact directly with the G-protein, accessing it following conformational changes involving ICL2 and ICL3. At the proximal end of ICL3, I290 and L294, probably lying on the same face of an alpha helix, formed a G-protein coupling motif. The largest effects on coupling were observed with I290A; additionally, it reduced CGRP affinity and impaired internalization. I290 may interact with TM6 to stabilize the conformation of ICL3, but it could also interact directly with Gs. R314, at the distal end of ICL3, impaired G-protein coupling and to a lesser extent reduced CGRP affinity; it may stabilize the TM6-ICL3 junction by interacting with the polar headgroups of membrane phospholipids. Y215 and L214 in ICL2 are required for cell-surface expression; they form a microdomain with H216 which has the same function. This study reveals similarities between the activation of CLR and other GPCRs in the role of TM6 and ICL3 but shows that other conserved motifs differ in their function.
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Affiliation(s)
- Alex C Conner
- School of Life and Health Sciences, Aston University, Birmingham B4 7ET, UK
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9
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Matsumoto ML, Narzinski K, Kiser PD, Nikiforovich GV, Baranski TJ. A comprehensive structure-function map of the intracellular surface of the human C5a receptor. I. Identification of critical residues. J Biol Chem 2006; 282:3105-21. [PMID: 17135254 DOI: 10.1074/jbc.m607679200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
G protein-coupled receptors are one of the largest protein families in nature; however, the mechanisms by which they activate G proteins are still poorly understood. To identify residues on the intracellular face of the human C5a receptor that are involved in G protein activation, we performed a genetic analysis of each of the three intracellular loops and the carboxyl-terminal tail of the receptor. Amino acid substitutions were randomly incorporated into each loop, and functional receptors were identified in yeast. The third intracellular loop contains the largest number of preserved residues (positions resistant to amino acid substitutions), followed by the second loop, the first loop, and lastly the carboxyl terminus. Surprisingly, complete removal of the carboxyl-terminal tail did not impair C5a receptor signaling. When mapped onto a three-dimensional structural model of the inactive state of the C5a receptor, the preserved residues reside on one half of the intracellular surface of the receptor, creating a potential activation face. Together these data provide one of the most comprehensive functional maps of the intracellular surface of any G protein-coupled receptor to date.
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Affiliation(s)
- Marissa L Matsumoto
- Department of Medicine and Molecular Biology, Washington School of Medicine, Missouri 63110, USA
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10
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Braden MR, Parrish JC, Naylor JC, Nichols DE. Molecular interaction of serotonin 5-HT2A receptor residues Phe339(6.51) and Phe340(6.52) with superpotent N-benzyl phenethylamine agonists. Mol Pharmacol 2006; 70:1956-64. [PMID: 17000863 DOI: 10.1124/mol.106.028720] [Citation(s) in RCA: 180] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Experiments were conducted to examine the molecular basis for the high affinity and potency of a new class of 5-HT(2A) receptor agonists, N-benzyl phenethylamines. Competition binding assays at several serotonin receptors confirmed that an N-arylmethyl substitution was necessary for affinity increases up to 300-fold over simple N-alkyl homologs, as well as enhanced selectivity for 5-HT(2A) versus 5-HT(2C) and 5-HT(1A) receptors. PI hydrolysis functional assays confirmed that these N-benzyl phenethylamines are potent and highly efficacious agonists at the rat 5-HT(2A) receptor. Virtual docking of these compounds into a human 5-HT(2A) receptor homology model indicated that the N-benzyl moiety might be interacting with Phe339((6.51)), whereas the phenethylamine portion was likely to be interacting with Phe340((6.52)). Experiments in h5-HT(2A) receptors with Phe339((6.51))L and Phe340((6.52))L mutations seem to support this hypothesis. Dramatic detrimental effects on affinity, potency, and intrinsic activity were observed with the Phe339((6.51))L mutation for all N-benzyl analogs, whereas most N-unsubstituted phenethylamines and traditional agonists were only weakly affected, if at all. Consistent with other published studies, the Phe340((6.52))L mutation detrimentally affected affinity, potency, and intrinsic activity of nearly all compounds tested, although a strong change in intrinsic activity was not seen with most N-aryl analogs. These data further validate the topology of our h5-HT(2A) receptor homology model. It is noteworthy that this study is the first to identify a hitherto unrecognized role for residue 6.51 in agonist activation of a serotonin G protein-coupled receptor (GPCR), whereas most previous reports have suggested a varied and sometimes contradictory role in homologous GPCRs.
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Affiliation(s)
- Michael R Braden
- Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmaceutical Sciences, 575 Stadium Mall Drive, Purdue University, West Lafayette, IN 47907-2091, USA
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11
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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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12
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Kushwaha N, Harwood SC, Wilson AM, Berger M, Tecott LH, Roth BL, Albert PR. Molecular determinants in the second intracellular loop of the 5-hydroxytryptamine-1A receptor for G-protein coupling. Mol Pharmacol 2006; 69:1518-26. [PMID: 16410407 DOI: 10.1124/mol.105.019844] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study provides the first comprehensive evidence that the second intracellular loop C-terminal domain (Ci2) is critical for receptor-G protein coupling to multiple responses. Although Ci2 is weakly conserved, its role in 5-hydroxytryptamine-1A (5-HT1A) receptor function was suggested by the selective loss of Gbetagamma-mediated signaling in the T149A-5-HT1A receptor mutant. More than 60 point mutant 5-HT1A receptors in the alpha-helical Ci2 sequence (143DYVNKRTPRR152) were generated. Most mutants retained agonist binding and were tested for Gbetagamma signaling to adenylyl cyclase II or phospholipase C and Galphai coupling to detect constitutive and agonist-induced Gi/Go coupling. Remarkably, most point mutations markedly attenuated 5-HT1A signaling, indicating that the entire Ci2 domain is critical for receptor G-protein coupling. Six signaling phenotypes were observed: wild-type-like, Galphai-coupled/weak Gbetagamma-coupled, Gbetagamma-uncoupled, Gbetagamma-selective coupled, uncoupled, and inverse coupling. Our data elucidate specific roles of Ci2 residues consistent with predictions based on rhodopsin crystal structure. The absolute coupling requirement for lysine, arginine, and proline residues is consistent with a predicted amphipathic alpha-helical Ci2 domain that is kinked at Pro150. Polar residues (Thr149, Asn146) located in the externally oriented positively charged face were required for Gbetagamma but not Galphai coupling, suggesting a direct interface with Gbetagamma subunits. The hydrophobic face includes the critical Tyr144 that directs the specificity of coupling to both Gbetagamma and Galphai pathways. The key coupling residues Tyr144/Lys147 (Ci2) are predicted to orient internally, forming hydrogen and ionic bonds with Asp133/Arg134 (Ni2 DRY motif) and Glu340 (Ci3) to stabilize the Gprotein coupling domain. Thus, the 5-HT1A receptor Ci2 domain determines Gbetagamma specificity and stabilizes Galphai-mediated signaling.
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Affiliation(s)
- Neena Kushwaha
- Ottawa Health Research Institute (Neuroscience), and Department of Cellular and Molecular Medicine, University of Ottawa, 451 Smyth Road, Ottawa, Ontario, Canada, K1H 8M5
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13
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Parrish JC, Braden MR, Gundy E, Nichols DE. Differential phospholipase C activation by phenylalkylamine serotonin 5-HT 2A receptor agonists. J Neurochem 2005; 95:1575-84. [PMID: 16277614 DOI: 10.1111/j.1471-4159.2005.03477.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Experiments compared a series of phenethylamine hallucinogens with their phenylisopropylamine analogues for binding affinity and ability to stimulate serotonin 5-HT 2A receptor-mediated hydrolysis of phosphatidyl inositol in cells expressing cloned rat and human 5-HT 2A receptors. The (+/-)phenylisopropylamine analogues had significantly higher intrinsic activities for 5-HT 2A receptor-mediated hydrolysis of phosphatidyl inositol compared to their phenethylamine analogues. With respect to the effects of the stereochemistry of the phenylisopropylamines, those with the (R) absolute configuration at the alpha carbon had higher intrinsic activities for hydrolysis of phosphatidyl inositol in a cell line expressing the human 5-HT 2A receptor compared to those with the (S) absolute configuration. In virtual docking studies comparing the (R)- and (S)-phenylisopropylamines with their phenethylamine analogues, there were distinct differences in the orientations of key ligand binding domain residues that have been identified as important by previous mutagenesis studies. In conclusion, our data support the hypothesis that phenylisopropylamines have higher hallucinogenic potency than their phenethylamine analogues primarily because they have higher intrinsic activities at 5-HT 2A receptors. Although virtual ligand binding led to significant perturbations of certain key residues, our results emphasize the conclusion reached by others that overall three-dimensional structural microdomains within the receptor must be considered.
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Affiliation(s)
- Jason C Parrish
- Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy and Pharmaceutical Sciences, Purdue University, West Lafayette, Indiana 47907-2091, USA
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14
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Phatarpekar PV, Durdan SF, Copeland CM, Crittenden EL, Neece JD, García DM. Molecular and pharmacological characterization of muscarinic receptors in retinal pigment epithelium: role in light-adaptive pigment movements. J Neurochem 2005; 95:1504-20. [PMID: 16269010 DOI: 10.1111/j.1471-4159.2005.03512.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Muscarinic receptors are the predominant cholinergic receptors in the central and peripheral nervous systems. Recently, activation of muscarinic receptors was found to elicit pigment granule dispersion in retinal pigment epithelium isolated from bluegill fish. Pigment granule movement in retinal pigment epithelium is a light-adaptive mechanism in fish. In the present study, we used pharmacological and molecular approaches to identify the muscarinic receptor subtype and the intracellular signaling pathway involved in the pigment granule dispersion in retinal pigment epithelium. Of the muscarinic receptor subtype-specific antagonists used, only antagonists specific for M1 and M3 muscarinic receptors were found to block carbamyl choline (carbachol)-induced pigment granule dispersion. A phospholipase C inhibitor also blocked carbachol-induced pigment granule dispersion, and a similar result was obtained when retinal pigment epithelium was incubated with an inositol trisphosphate receptor inhibitor. We isolated M2 and M5 receptor genes from bluegill and studied their expression. Only M5 was found to be expressed in retinal pigment epithelium. Taken together, pharmacological and molecular evidence suggest that activation of an odd subtype of muscarinic receptor, possibly M5, on fish retinal pigment epithelium induces pigment granule dispersion.
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MESH Headings
- Acetylcholine/pharmacology
- Adaptation, Ocular
- Alkaloids
- Animals
- Behavior, Animal
- Carbachol/pharmacology
- Cholinergic Agonists/pharmacology
- Cholinesterase Inhibitors/pharmacology
- Cloning, Molecular/methods
- Colforsin/pharmacology
- Dose-Response Relationship, Drug
- Drug Interactions
- Enzyme Inhibitors/pharmacology
- Perciformes
- Phylogeny
- Pigment Epithelium of Eye/drug effects
- Pigment Epithelium of Eye/metabolism
- Pigment Epithelium of Eye/radiation effects
- Pigments, Biological/physiology
- RNA, Messenger/biosynthesis
- Receptors, Muscarinic/classification
- Receptors, Muscarinic/genetics
- Receptors, Muscarinic/metabolism
- Reverse Transcriptase Polymerase Chain Reaction/methods
- Sequence Analysis, DNA/methods
- Sequence Analysis, Protein/methods
- Sesquiterpenes/pharmacology
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Affiliation(s)
- Prasad V Phatarpekar
- Department of Biology, Texas State University-San Marcos, San Marcos, Texas 78666, USA
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15
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Hui H, Zhao X, Perfetti R. Structure and function studies of glucagon-like peptide-1 (GLP-1): the designing of a novel pharmacological agent for the treatment of diabetes. Diabetes Metab Res Rev 2005; 21:313-31. [PMID: 15852457 DOI: 10.1002/dmrr.553] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Glucagon-like peptide-1 (GLP-1) is a proglucagon-derived peptide secreted from gut endocrine cells in response to nutrient ingestion. The multifaceted actions of GLP-1 include the following: (1) the stimulation of insulin secretion and of its gene expression, (2) the inhibition of glucagon secretion, (3) the inhibition of food intake, (4) the proliferation and differentiation of beta cells, and (5) the protection of beta-cells from apoptosis. The therapeutic utility of the native GLP-1 molecule is limited by its rapid enzymatic degradation by a serine protease termed dipeptidyl peptidase-IV (DPP-IV). The present article reviews the research studies aimed at elucidating the biosynthesis, metabolism, and molecular characteristics of GLP-1 since it is from these studies that the development of a GLP-1-like pharmacological agent may be derived.
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Affiliation(s)
- Hongxiang Hui
- Division of Endocrinology and Metabolism, Cedars-Sinai Medical Center, Los Angeles, California 90048, USA
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16
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Huang W, Osman R, Gershengorn MC. Agonist-induced conformational changes in thyrotropin-releasing hormone receptor type I: disulfide cross-linking and molecular modeling approaches. Biochemistry 2005; 44:2419-31. [PMID: 15709754 DOI: 10.1021/bi048808+] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The conformational changes at the cytoplasmic ends of transmembrane helices 5 and 6 (TMH5 and TMH6) of thyrotropin-releasing hormone (TRH) receptor type I (TRH-R1) during activation were analyzed by cysteine-scanning mutagenesis followed by disulfide cross-linking and molecular modeling. Sixteen double cysteine mutants were constructed by substitution of one residue at the cytoplasmic end of TMH5 and the other at that of TMH6. The cross-linking experiments indicate that four mutants, Q263C/G212C, Q263C/Y211C, T265C/G212C, and T265C/Y211C, exhibited disulfide bond formation that was sensitive to TRH occupancy. We refined our previous TRH-R1 models by embedding them into a hydrated explicit lipid bilayer. Molecular dynamics simulations of the models, as well as in silico double cysteine models, generated trajectories that were in agreement with experimental results. Our findings suggest that TRH binding induces a separation of the cytoplasmic ends of TMH5 and TMH6 and a rotation of TMH6. These changes likely increase the surface accessible area at the juxtamembrane region of intracellular loop 3 that could promote interactions between G proteins and key residues within the receptor.
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Affiliation(s)
- Wei Huang
- Clinical Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, 50 South Drive, Building 50/4134, Bethesda, Maryland 20892-1818, USA
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17
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Langer I, Robberecht P. Mutations in the carboxy-terminus of the third intracellular loop of the human recombinant VPAC1 receptor impair VIP-stimulated [Ca2+]i increase but not adenylate cyclase stimulation. Cell Signal 2005; 17:17-24. [PMID: 15451021 DOI: 10.1016/j.cellsig.2004.05.009] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2004] [Revised: 05/11/2004] [Accepted: 05/17/2004] [Indexed: 11/23/2022]
Abstract
The vasoactive intestinal polypeptide (VIP) VPAC1 receptor is preferentially coupled to Galphas protein that stimulates adenylate cyclase activity and also to Galphaq and Galphai proteins that stimulate the inositol phosphate/calcium pathway. Previous studies indicated the importance of the third intracellular loop of the receptor for G protein coupling. By site-directed mutation of the human recombinant receptor expressed in Chinese hamster ovary cells, we identified two domains in this loop that contain clusters of basic residues conserved in most of the G-protein-coupled seven transmembrane domains receptors. We found that mutations in the proximal domain (K322) reduced the capability of VIP to increase adenylate cyclase activity without any change in the calcium response, whereas mutations in the distal part of the loop (R338, L339, R341) markedly reduced the calcium increase and Galphai coupling but only weakly the adenylate cyclase activity. Thus, the interaction of different G proteins with the VPAC1 receptor involves different receptor sub-domains.
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Affiliation(s)
- Ingrid Langer
- Department of Biological Chemistry and Nutrition, Faculty of Medicine, Université Libre de Bruxelles, Campus Erasme, Bât G/E, 808 route de Lennik CP611, B-1070 Brussels, Belgium.
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18
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Kristiansen K. Molecular mechanisms of ligand binding, signaling, and regulation within the superfamily of G-protein-coupled receptors: molecular modeling and mutagenesis approaches to receptor structure and function. Pharmacol Ther 2004; 103:21-80. [PMID: 15251227 DOI: 10.1016/j.pharmthera.2004.05.002] [Citation(s) in RCA: 394] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The superfamily of G-protein-coupled receptors (GPCRs) could be subclassified into 7 families (A, B, large N-terminal family B-7 transmembrane helix, C, Frizzled/Smoothened, taste 2, and vomeronasal 1 receptors) among mammalian species. Cloning and functional studies of GPCRs have revealed that the superfamily of GPCRs comprises receptors for chemically diverse native ligands including (1) endogenous compounds like amines, peptides, and Wnt proteins (i.e., secreted proteins activating Frizzled receptors); (2) endogenous cell surface adhesion molecules; and (3) photons and exogenous compounds like odorants. The combined use of site-directed mutagenesis and molecular modeling approaches have provided detailed insight into molecular mechanisms of ligand binding, receptor folding, receptor activation, G-protein coupling, and regulation of GPCRs. The vast majority of family A, B, C, vomeronasal 1, and taste 2 receptors are able to transduce signals into cells through G-protein coupling. However, G-protein-independent signaling mechanisms have also been reported for many GPCRs. Specific interaction motifs in the intracellular parts of these receptors allow them to interact with scaffold proteins. Protein engineering techniques have provided information on molecular mechanisms of GPCR-accessory protein, GPCR-GPCR, and GPCR-scaffold protein interactions. Site-directed mutagenesis and molecular dynamics simulations have revealed that the inactive state conformations are stabilized by specific interhelical and intrahelical salt bridge interactions and hydrophobic-type interactions. Constitutively activating mutations or agonist binding disrupts such constraining interactions leading to receptor conformations that associates with and activate G-proteins.
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Affiliation(s)
- Kurt Kristiansen
- Department of Pharmacology, Institute of Medical Biology, University of Tromsø, N-9037 Tromsø, Norway.
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19
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Weiner DM, Goodman MW, Colpitts TM, Feddock MA, Duggento KL, Nash NR, Levey AI, Brann MR. Functional Screening of Drug Target Genes. ACTA ACUST UNITED AC 2004; 4:119-28. [PMID: 15059034 DOI: 10.2165/00129785-200404020-00006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
BACKGROUND AND OBJECTIVES A number of recent studies surveying single nucleotide polymorphisms within the exonic regions of human genes have revealed a significant number of such variants, including many non-synonymous variants. This highlights the need to directly identify, within individual clinically well-defined patients, those variants that alter protein function as well as structure. We report on the development of a novel phenotypic screening process that combines high-throughput molecular cloning techniques with functional expression utilizing the cell-based assay R-SAT. METHODS We applied the phenotypic screening process to an analysis of the m1 muscarinic acetylcholine receptor (CHRM1) gene in a cohort of 74 individuals, including 48 diagnosed with neurodegenerative disease, primarily Alzheimer disease, who have been stratified according to their clinical response to the acetylcholinesterase inhibitor donepezil. Phenotypic screening of the CHRM1 gene involved PCR-based amplification from genomic DNA and heterologous expression in mammalian cells. RESULTS Phenotypic screening yielded functional responses to the agonist carbachol displaying a mean potency (-pEC(50)+/- standard deviation) of 5.8 +/- 0.2, which did not differ from that observed with expression of the wild-type receptor gene (6.0 +/- 0.3). No altered levels of constitutive receptor activity were observed. Dideoxy sequencing did not reveal any non-synonymous variants in the coding exon of this gene within this clinical cohort, while detecting three synonymous variants. CONCLUSION The results confirm that the m1 receptor gene (CHRM1) is not highly polymorphic in the human population, suggesting that genetic variation within the coding exon of this gene is not a contributing factor to the clinical variability observed during treatment of dementia with cholinergic enhancement therapies.
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Affiliation(s)
- David M Weiner
- ACADIA Pharmaceuticals, Inc., San Diego, California 92121, USA.
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20
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Gray JA, Compton-Toth BA, Roth BL. Identification of two serine residues essential for agonist-induced 5-HT2A receptor desensitization. Biochemistry 2003; 42:10853-62. [PMID: 12962510 DOI: 10.1021/bi035061z] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
5-HT(2A) serotonin receptors represent the principal molecular targets for LSD-like hallucinogens and atypical antipsychotic drugs. It has been proposed that a dysregulation of 5-HT(2A) receptor-mediated signaling may contribute to the pathogenesis of schizophrenia and related diseases. A major mechanism for the attenuation of GPCR signaling following agonist activation typically involves the phosphorylation of serine and/or threonine residues by various kinases. Ser/Thr phosphorylation leads to the binding of accessory proteins and the uncoupling of the G proteins, thereby preventing further signaling. The molecular mechanisms by which 5-HT(2A) receptors are desensitized are unknown, and to date, no residues essential for agonist-mediated desensitization have been identified. Thus, we mutated, individually or in groups, all of the 37 serines and threonines in the cytoplasmic domains of the 5-HT(2A) receptor and assessed the effects of these mutations on agonist-mediated desensitization. We discovered that mutation of two residues, S421 in the C-terminal tail and S188 in the second intracellular loop, to alanine resulted in a significant block of agonist-induced desensitization. Intriguingly, a single-nucleotide polymorphism, of unreported frequency, at the S421 locus has been reported (S421F); the S421F mutation, like the S421A mutation, significantly attenuated agonist-mediated desensitization. Taken together, these findings indicate that the process of agonist-mediated desensitization of 5-HT(2A) receptors requires the presence of two nonconserved serine residues located in distinct intracellular loops.
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Affiliation(s)
- John A Gray
- Department of Biochemistry, Case Western Reserve University School of Medicine, 10900 Euclid Avenue, Cleveland, Ohio 44106, USA
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21
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Cheng KW, Leung PCK. The expression, regulation and signal transduction pathways of the mammalian gonadotropin-releasing hormone receptor. Can J Physiol Pharmacol 2000. [DOI: 10.1139/y00-096] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Normal mammalian sexual maturation and reproductive functions require the integration and precise coordination of hormones at the hypothalamic, pituitary, and gonadal levels. Hypothalamic gonadotropin-releasing hormone (GnRH) is a key regulator in this system; after binding to its receptor (GnRHR), it stimulates de novo synthesis and release of gonadotropins in anterior pituitary gonadotropes. Since the isolation of the GnRHR cDNA, the expression of GnRHR mRNA has been detected not only in the pituitary, but also in extrapituitary tissues, including the ovary and placenta. It has been shown that change in GnRHR mRNA is one of the mechanisms for regulating the expression of the GnRHR. To help understand the molecular mechanism(s) involved in transcriptional regulation of the GnRHR gene, the 5' flanking region of the GnRHR gene has recently been isolated. Initial characterization studies have identified several DNA regions in the GnRHR 5' flanking region which are responsible for both basal expression and GnRH-mediated homologous regulation of this gene in pituitary cells. The mammalian GnRHR lacks a C-terminus and possesses a relatively short third intracellular loop; both features are important in desensitization of many others G-protein coupled receptors (GPCRs), Homologous desensitization of GnRHR has been shown to be regulated by various serine-threonine protein kinases including protein kinase A (PKA) and protein kinase C (PKC), as well as by G-protein coupled receptor kinases (GRKs). Furthermore, GnRHR was demonstrated to couple with multiple G proteins (Gq/11, Gs, and Gi), and to activate cascades that involved the PKC, PKA, and mitogen-activator protein kinases. These results suggest the diversity of GnRHR-G protein coupling and signal transduction systems. The identification of second form of GnRH (GnRH-II) in mammals adds to the complexity of the GnRH-GnRHR system. This review summaries our recent progress in understanding the regulation of GnRHR gene expression and the GnRHR signal transduction pathways.Key words: gonadotropin-releasing hormone receptor, transcriptional regulation, desensitization, signal transduction.
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22
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Abstract
Upon the binding of their ligands, G protein-coupled receptors couple to the heterotrimeric G proteins to transduce a signal. One receptor family may couple to a single G protein subtype and another family to several ones. Is there a signal in the receptor sequence that can give an indication of the G protein subtype selectivity? We used a sequence analysis method on biogenic amine and adenosine receptors and concluded that a weak signal can be detected in receptor families where specialization for coupling to a given G protein occurred during a recent divergent evolutionary process. Proteins 2000;41:448-459.
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Affiliation(s)
- F Horn
- BIOcomputing, European Molecular Biology Laboratory, Heidelberg, Germany
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23
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Schmidt PS, Duvernell DD, Eanes WF. Adaptive evolution of a candidate gene for aging in Drosophila. Proc Natl Acad Sci U S A 2000; 97:10861-5. [PMID: 10995474 PMCID: PMC27114 DOI: 10.1073/pnas.190338897] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Examination of the phenotypic effects of specific mutations has been extensively used to identify candidate genes affecting traits of interest. However, such analyses do not reveal anything about the evolutionary forces acting at these loci, or whether standing allelic variation contributes to phenotypic variance in natural populations. The Drosophila gene methuselah (mth) has been proposed as having major effects on organismal stress response and longevity phenotype. Here, we examine patterns of polymorphism and divergence at mth in population level samples of Drosophila melanogaster, D. simulans, and D. yakuba. Mth has experienced an unusually high level of adaptive amino acid divergence concentrated in the intra- and extracellular loop domains of the receptor protein, suggesting the historical action of positive selection on those regions of the molecule that modulate signal transduction. Further analysis of single nucleotide polymorphisms (SNPs) in D. melanogaster provided evidence for contemporary and spatially variable selection at the mth locus. In ten surveyed populations, the most common mth haplotype exhibited a 40% cline in frequency that coincided with population level differences in multiple life-history traits including lifespan. This clinal pattern was not associated with any particular SNP in the coding region, indicating that selection is operating at a closely linked site that may be involved in gene expression. Together, these consistently nonneutral patterns of inter- and intraspecific variation suggest adaptive evolution of a signal transduction pathway that may modulate lifespan in nature.
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Affiliation(s)
- P S Schmidt
- Department of Ecology and Evolution, State University of New York at Stony Brook, Stony Brook, NY 11794-5245, USA
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24
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Jensen AA, Spalding TA, Burstein ES, Sheppard PO, O'Hara PJ, Brann MR, Krogsgaard-Larsen P, Bräuner-Osborne H. Functional importance of the Ala(116)-Pro(136) region in the calcium-sensing receptor. Constitutive activity and inverse agonism in a family C G-protein-coupled receptor. J Biol Chem 2000; 275:29547-55. [PMID: 10835431 DOI: 10.1074/jbc.m910023199] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The calcium-sensing receptor (CaR) belongs to family C of the G-protein-coupled receptor superfamily. To date 14 activating mutations in CaR showing increased sensitivity to Ca(2+) have been identified in humans with autosomal dominant hypocalcemia. Four of these activating mutations are found in the Ala(116)-Pro(136) region of CaR, indicating that this part of the receptor is particularly sensitive to mutation-induced activation. This region was subjected to random saturation mutagenesis, and 219 mutant receptor clones were isolated and screened pharmacologically in a high throughput screening assay. Selected mutants were characterized further in an inositol phosphate assay. The vast majority of the mutants tested displayed an increased affinity for Ca(2+). Furthermore, 21 of the mutants showed increased basal activity in the absence of agonist. This constitutive activity was not diminished when the mutations were transferred to a chimeric receptor Ca/1a consisting of the amino-terminal domain of the CaR and the 7 transmembrane and intracellular domains of the metabotropic glutamate receptor mGluR1a. CPCCOEt, a noncompetitive antagonist acting at the 7 transmembrane domain of mGluR1a, suppressed the elevated basal response of the constitutively activated Ca/1a mutants demonstrating inverse agonist activity of CPCCOEt. Taken together, our results demonstrate that the Ala(116)-Pro(136) region is of key importance for the maintenance of the inactive conformation of CaR.
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Affiliation(s)
- A A Jensen
- NeuroScience PharmaBiotec Research Centre, Department of Medicinal Chemistry, The Royal Danish School of Pharmacy, 2 Universitetsparken, DK-2100 Copenhagen, Denmark
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25
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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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26
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Moreau JL, Huber G. Central adenosine A(2A) receptors: an overview. BRAIN RESEARCH. BRAIN RESEARCH REVIEWS 1999; 31:65-82. [PMID: 10611496 DOI: 10.1016/s0165-0173(99)00059-4] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recent advances in molecular biology, biochemistry, cell biology and behavioral pharmacology together with the development of more selective ligands to the various adenosine receptors have increased our understanding of the functioning of central adenosine A(2A) receptors. The A(2A) receptor is one of four adenosine receptors found in the brain. Its expression is highest in striatum, nucleus accumbens and olfactory tubercles, although it also occurs in neurons and microglia in most other brain regions. The receptor has seven transmembrane domains and couples via Gs to adenyl cyclase stimulation. Antagonistic interactions between A(2A) receptors and dopamine D(2) receptors have been described, as stimulation of the A(2A) receptor leads to a reduction in the affinity of D(2) receptors for D(2) receptor agonists. The A(2A) receptor is thought to play a role in a number of physiological responses and pathological conditions. Indeed, A(2A) receptor antagonists may be useful for the treatment of acute and chronic neurodegenerative disorders such as cerebral ischemia or Parkinson's disease. A(2A) receptor agonists may treat certain types of seizures or sleep disorders. This review discusses the characteristics, distribution, pharmacochemical properties and regulation of central A(2A) receptors, as well as A(2A) receptor-mediated behavioural responses and their potential role in various neuropsychiatric disorders.
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Affiliation(s)
- J L Moreau
- Pharma Division, Preclinical CNS Research, F. Hoffmann-La Roche, PRPN, 72/141, CH-4070, Basel, Switzerland.
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27
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Cypess AM, Unson CG, Wu CR, Sakmar TP. Two cytoplasmic loops of the glucagon receptor are required to elevate cAMP or intracellular calcium. J Biol Chem 1999; 274:19455-64. [PMID: 10383462 DOI: 10.1074/jbc.274.27.19455] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The glucagon receptor is a member of a distinct class of G protein-coupled receptors (GPCRs) sharing little amino acid sequence homology with the larger rhodopsin-like GPCR family. To identify the components of the glucagon receptor necessary for G-protein coupling, we replaced sequentially all or part of each intracellular loop (i1, i2, and i3) and the C-terminal tail of the glucagon receptor with the 11 amino acids comprising the first intracellular loop of the D4 dopamine receptor. When expressed in transiently transfected COS-1 cells, the mutant receptors fell into two different groups with respect to hormone-mediated signaling. The first group included the loop i1 mutants, which bound glucagon and signaled normally. The second group comprised the loop i2 and i3 chimeras, which caused no detectable adenylyl cyclase activation in COS-1 cells. However, when expressed in HEK 293T cells, the loop i2 or i3 chimeras caused very small glucagon-mediated increases in cAMP levels and intracellular calcium concentrations, with EC50 values nearly 100-fold higher than those measured for wild-type receptor. Replacement of both loops i2 and i3 simultaneously was required to completely abolish G protein signaling as measured by both cAMP accumulation and calcium flux assays. These results show that the i2 and i3 loops play a role in glucagon receptor signaling, consistent with recent models for the mechanism of activation of G proteins by rhodopsin-like GPCRs.
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Affiliation(s)
- A M Cypess
- The Rockefeller University, New York, New York 10021, USA
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28
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Hulme EC, Lu ZL, Ward SD, Allman K, Curtis CA. The conformational switch in 7-transmembrane receptors: the muscarinic receptor paradigm. Eur J Pharmacol 1999; 375:247-60. [PMID: 10443581 DOI: 10.1016/s0014-2999(99)00297-6] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The rhodopsin-like superfamily of 7-transmembrane receptors is the largest class of signalling molecules in the mammalian genome. Recently, a combination of mutagenesis, biophysical and modelling studies have suggested a credible model for the alpha-carbon backbone in the transmembrane region of the 7-transmembrane receptors, and have started to reveal the structural basis of the conformational switch from the inactive to the active state. A key feature may be the replacement of a network of radial constraints, centred on transmembrane helix three, which stabilise the inactive ground state of the receptor by a new set of axial interactions which help to stabilise the activated state. Transmembrane helix three may act as a rotary switch in the activation mechanism.
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Affiliation(s)
- E C Hulme
- Division of Physical Biochemistry, National Institute for Medical Research, The Ridgeway, Mill Hill, London, UK.
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29
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Baranski TJ, Herzmark P, Lichtarge O, Gerber BO, Trueheart J, Meng EC, Iiri T, Sheikh SP, Bourne HR. C5a receptor activation. Genetic identification of critical residues in four transmembrane helices. J Biol Chem 1999; 274:15757-65. [PMID: 10336477 DOI: 10.1074/jbc.274.22.15757] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Hormones and sensory stimuli activate serpentine receptors, transmembrane switches that relay signals to heterotrimeric guanine nucleotide-binding proteins (G proteins). To understand the switch mechanism, we subjected 93 amino acids in transmembrane helices III, V, VI, and VII of the human chemoattractant C5a receptor to random saturation mutagenesis. A yeast selection identified 121 functioning mutant receptors, containing a total of 523 amino acid substitutions. Conserved hydrophobic residues are located on helix surfaces that face other helices in a modeled seven-helix bundle (Baldwin, J. M., Schertler, G. F., and Unger, V. M. (1997) J. Mol. Biol. 272, 144-164), whereas surfaces predicted to contact the surrounding lipid tolerate many substitutions. Our analysis identified 25 amino acid positions resistant to nonconservative substitutions. These appear to comprise two distinct components of the receptor switch, a surface at or near the extracellular membrane interface and a core cluster in the cytoplasmic half of the bundle. Twenty-one of the 121 mutant receptors exhibit constitutive activity. Amino acids substitutions in these activated receptors predominate in helices III and VI; other activating mutations truncate the receptor near the extracellular end of helix VI. These results identify key elements of a general mechanism for the serpentine receptor switch.
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Affiliation(s)
- T J Baranski
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California 94143, USA
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30
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Gelber EI, Kroeze WK, Willins DL, Gray JA, Sinar CA, Hyde EG, Gurevich V, Benovic J, Roth BL. Structure and function of the third intracellular loop of the 5-hydroxytryptamine2A receptor: the third intracellular loop is alpha-helical and binds purified arrestins. J Neurochem 1999; 72:2206-14. [PMID: 10217304 DOI: 10.1046/j.1471-4159.1999.0722206.x] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Understanding the precise structure and function of the intracellular domains of G protein-coupled receptors is essential for understanding how receptors are regulated, and how they transduce their signals from the extracellular milieu to intracellular sites. To understand better the structure and function of the intracellular domain of the 5-hydroxytryptamine2A (5-HT2A) receptor, a model G(alpha)q-coupled receptor, we overexpressed and purified to homogeneity the entire third intracellular loop (i3) of the 5-HT2A receptor, a region previously implicated in G-protein coupling. Circular dichroism spectroscopy of the purified i3 protein was consistent with alpha-helical and beta-loop, -turn, and -sheet structure. Using random peptide phage libraries, we identified several arrestin-like sequences as i3-interacting peptides. We subsequently found that all three known arrestins (beta-arrestin, arrestin-3, and visual arrestin) bound specifically to fusion proteins encoding the i3 loop of the 5-HT(2A) receptor. Competition binding studies with synthetic and recombinant peptides showed that the middle portion of the i3 loop, and not the extreme N and C termini, was likely to be involved in i3-arrestin interactions. Dual-label immunofluorescence confocal microscopic studies of rat cortex indicated that many cortical pyramidal neurons coexpressed arrestins (beta-arrestin or arrestin-3) and 5-HT2A receptors, particularly in intracellular vesicles. Our results demonstrate (a) that the i3 loop of the 5-HT2A receptor represents a structurally ordered domain composed of alpha-helical and beta-loop, -turn, and -sheet regions, (b) that this loop interacts with arrestins in vitro, and is hence active, and (c) that arrestins are colocalized with 5-HT2A receptors in vivo.
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Affiliation(s)
- E I Gelber
- Department of Biochemistry, Case Western Reserve University Medical School, Cleveland, Ohio 44106-4935, USA
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31
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Abstract
The accumulation of hundreds of olfactory receptor (OR) sequences, along with the recent availability of detailed models of other G-protein-coupled receptors, allows us to analyze the OR amino acid variability patterns in a structural context. A Fourier analysis of 197 multiply aligned olfactory receptor sequences showed an alpha-helical periodicity in the variability profile. This was particularly pronounced in the more variable transmembranal segments 3, 4, and 5. Rhodopsin-based homology modeling demonstrated that the inferred variable helical faces largely point to the interior of the receptor barrel. We propose that a set of 17 hypervariable residues, which point to the barrel interior and are more extracellularly disposed, constitute the odorant complementarity determining regions. While 12 of these residues coincide with established ligand-binding contact positions in other G-protein-coupled receptors, the rest are suggested to form an olfactory-unique aspect of the binding pocket. Highly conserved olfactory receptor-specific sequence motifs, found in the second and third intracellular loops, may comprise the G-protein recognition epitope. The prediction of olfactory receptor functional sites provides concrete suggestions of site-directed mutagenesis experiments for altering ligand and G-protein specificity.
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Affiliation(s)
- Y Pilpel
- Department of Molecular Genetics and Crown Human Genome Center, The Weizmann Institute of Science, Rehovot, Israel
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32
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Abstract
Functional proteomic methods have been developed and applied to the investigation of signal transduction systems involving platelet-derived growth factor (PDGF), endothelin and bradykinin receptors. Mouse fibroblast cells have been stimulated with PDGF or endothelin. Phosphorylation/dephosphorylation of several hundred proteins has been followed as a function of time following stimulation using 2-D gel electrophoresis and anti-phosphotyrosine or anti-phosphoserine antibodies. Up to 100 of these proteins showed strong changes in phosphorylation with minutes of receptor stimulation. Identification of some of these proteins by mass fingerprinting using matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry and by partial peptide sequencing with ion trap electrospray mass spectrometry has identified proteins which were previously known to be associated with PDGF signaling, proteins which have been shown to be involved in other signaling pathways, but not PDGF and proteins not previously associated with signal transduction. Parallel to these studies, new methods for rapid, single-step isolation of peptide receptors using a peptide coupled to a (dA)30 oligonucleotide have been developed and applied to mass spectrometric studies of post-translational modifications of the endothelin B and bradykinin B2 receptors under in vivo conditions. Both receptors have been shown to undergo extensive phosphorylation as well as palmitoylation. The patterns of post-translational modifications are more complex than previously recognized and provide new indications of possible roles for these modifications in the regulation and response of these receptors.
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33
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LeVine H. Structural features of heterotrimeric G-protein-coupled receptors and their modulatory proteins. Mol Neurobiol 1999; 19:111-49. [PMID: 10371466 DOI: 10.1007/bf02743657] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Over the past 20 years, the general mechanism for signaling through 7-transmembrane helix receptors coupled to GTP hydrolysis has been worked out. Although similar in overall organization, subtype variability and subcellular localization of components have built in considerable signaling specificity. Atomic resolution structures for many of the components have delineated the domain organization of these complex proteins and have given physical form to the idea of subtype specificity. This review describes what is known about the physical structures of the 7-transmembrane helix receptors, the heterotrimeric GTP binding coupling proteins, the adenylate cyclase and phospholipase C effector proteins, and signaling modulatory proteins, such as arrestin, phosducin, recoverin-type myristoyl switch proteins, and the pleckstrin homology domain of G-protein receptor kinase-2. These images allow experimenters to contemplate the details of the supramolecular organization of the multiprotein complexes involved in the transmission of signals across the cellular lipid bilayer.
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Affiliation(s)
- H LeVine
- Parke-Davis Pharmaceutical Research Division of Warner-Lambert Company, Ann Arbor, MI 48105, USA
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34
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Soskic V, Nyakatura E, Roos M, Müller-Esterl W, Godovac-Zimmermann J. Correlations in palmitoylation and multiple phosphorylation of rat bradykinin B2 receptor in Chinese hamster ovary cells. J Biol Chem 1999; 274:8539-45. [PMID: 10085087 DOI: 10.1074/jbc.274.13.8539] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rat bradykinin B2 receptor from unstimulated Chinese hamster ovary cells transfected with the corresponding cDNA has been isolated, and subsequent mass spectrometric analysis of multiple phosphorylated species and of the palmitoylation attachment site is described. Bradykinin B2 receptor was isolated on oligo(dT)-cellulose using N-(epsilon-maleimidocaproyloxy)succinimide-Met-Lys-bradykinin coupled to a protected (dA)30-mer. This allowed a one-step isolation of the receptor on an oligo(dT)-cellulose column via variation solely of salt concentration. After enzymatic in-gel digestion, matrix-assisted laser desorption ionization and electrospray ion trap mass spectrometric analysis of the isolated rat bradykinin B2 receptor showed phosphorylation at Ser365, Ser371, Ser378, Ser380, and Thr374. Further phosphorylation at Tyr352 and Tyr161 was observed. Rat bradykinin receptor B2 receptor is also palmitoylated at Cys356. All of the phosphorylation sites except for Tyr161 cluster at the carboxyl-terminal domain of the receptor located on the cytoplasmic face of the cell membrane. Surprisingly, many of the post-translational modifications were shown by MSn mass spectroscopic analysis to be correlated pairwise, e.g. diphosphorylation at Ser365 and Ser371, at Ser378 and Ser380, and at Thr374 and Ser380 as well as mutually exclusive phosphorylation at Tyr352 and palmitoylation at Cys356. The last correlation may be involved in a receptor internalization motif. Pairwise correlations and mutual exclusion of phosphorylation and palmitoylation suggest critical roles of multiple post-translational modifications for the regulation of activity, coupling to intracelluar signaling pathways, and/or sequestration of the bradykinin receptor.
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Affiliation(s)
- V Soskic
- Institute of Molecular Biotechnology e.V., 07745 Jena, Germany
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35
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Albert PR, Morris SJ, Ghahremani MH, Storring JM, Lembo PM. A putative alpha-helical G beta gamma-coupling domain in the second intracellular loop of the 5-HT1A receptor. Ann N Y Acad Sci 1998; 861:146-61. [PMID: 9928252 DOI: 10.1111/j.1749-6632.1998.tb10186.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We have identified a conserved threonine residue in the second intracellular (i2) loop of the 5-HT1A receptor that when mutated to alanine prevents coupling to G beta gamma-mediated signaling, while preserving G alpha i-induced actions. In this review, we investigate the characteristics and potential role of the i2 domain in the coupling of the 5-HT1A receptor and other receptors to G proteins. The i2 domain, as well as portions of the i3 domain, is predicted to form an amphipathic alpha-helix with a positively charged face and a hydrophobic face. Mutagenesis experiments support a model in which the hydrophobic faces of these alpha-helical domains form an intracellular binding "pocket" for interaction with G proteins. Embedded in the hydrophobic face, Thr 149 is crucial for signaling through G beta gamma subunits, perhaps via interaction with its hydroxyl side-chain. Mutation of other residues of the i2 domain of Gi-coupled receptors is required to substantiate the importance of the alpha-helical i2 domain in receptor-G beta gamma signaling. If confirmed in other receptors, these results support a general model in which activated receptor and G beta gamma subunits remain associated to interact with effectors in a receptor-specific manner.
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Affiliation(s)
- P R Albert
- Department of Medicine, University of Ottawa, Canada.
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36
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Abstract
Molecular cloning studies have shown that G-protein-coupled receptors form one of the largest protein families found in nature, and it is estimated that approximately 1000 different such receptors exist in mammals. Characteristically, when activated by the appropriate ligand, an individual receptor can recognize and activate only a limited set of the many structurally closely related heterotrimeric G-proteins expressed within a cell. To understand how this selectivity is achieved at a molecular level has become the focus of an ever increasing number of laboratories. This review provides an overview of recent structural, molecular genetic, biochemical, and biophysical studies that have led to novel insights into the molecular mechanisms governing receptor-mediated G-protein activation and receptor/G-protein coupling selectivity.
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Affiliation(s)
- J Wess
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
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37
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Abstract
The molecular mechanisms governing the coupling selectivity of G protein-coupled receptors activated by peptide ligands are not well understood. To shed light on this issue, we have used the Gq/11-linked V1a and the Gs-coupled V2 vasopressin peptide receptors as model systems. To explore the structural basis underlying the ability of the V2 receptor to selectively recognize Gs, we systematically substituted distinct V2 receptor segments (or single amino acids) into the V1a receptor and studied whether the resulting hybrid receptors gained the ability to mediate hormone-dependent cAMP production. This strategy appeared particularly attractive since hormone stimulation of the V1a receptor has virtually no effect on intracellular cAMP levels. Functional analysis of a large number of mutant receptors transiently expressed in COS-7 cells indicated that the presence of V2 receptor sequence at the N terminus of the third intracellular loop is critical for efficient activation of Gs. More detailed mutational analysis of this receptor region showed that two polar V2 receptor residues, Gln225 and Glu231, play key roles in Gs recognition. In addition, a short sequence at the N terminus of the cytoplasmic tail was found to make an important contribution to V2 receptor/Gs coupling selectivity. We also made the novel observation that the efficiency of V2 receptor/Gs coupling can be modulated by the length of the central portion of the third intracellular loop (rather than the specific amino acid sequence within this domain). These findings provide novel insights into the molecular mechanisms regulating peptide receptor/G protein coupling selectivity.
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Affiliation(s)
- I Erlenbach
- Laboratory of Bioorganic Chemistry, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA
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38
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Stepwise phosphorylation mechanisms and signal transmission within a ligand–receptor–Gαβγ-protein-complex. ACTA ACUST UNITED AC 1998. [DOI: 10.1016/s0166-1280(98)00073-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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39
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Burstein ES, Spalding TA, Brann MR. The second intracellular loop of the m5 muscarinic receptor is the switch which enables G-protein coupling. J Biol Chem 1998; 273:24322-7. [PMID: 9733718 DOI: 10.1074/jbc.273.38.24322] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have completed a systematic search of the intracellular loops of a muscarinic acetylcholine receptor for domains that govern G-protein coupling. A unique feature of the second intracellular (i2) loop was an ordered cluster of residues where diverse substitutions cause constitutive activation. A second group of residues in i2 was identified where mutations compromised receptor/G-protein coupling. The residues of each group alternate and are spaced three to four positions apart, suggesting an alpha-helical structure where these groups form opposing faces of the helix. We propose that the constitutively activating face normally constrains the receptor in the "off-state," while the other face couples G-proteins in the "on-state." Therefore, the i2 loop functions as the switch enabling G-protein activation.
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Affiliation(s)
- E S Burstein
- ACADIA Pharmaceuticals Inc., San Diego, California 92121, USA
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40
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Spalding TA, Burstein ES, Henderson SC, Ducote KR, Brann MR. Identification of a ligand-dependent switch within a muscarinic receptor. J Biol Chem 1998; 273:21563-8. [PMID: 9705286 DOI: 10.1074/jbc.273.34.21563] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
G-protein-coupled receptors spontaneously switch between active and inactive conformations. Agonists stabilize the active conformation, whereas antagonists stabilize the inactive conformation. In a systematic search for residues that participate in receptor function, several regions of the m5 muscarinic receptor were randomly mutated and tested for their functional properties. Mutations spanning one face of transmembrane 6 (TM6) were found to induce high levels of receptor activity in the absence of agonists (constitutive activity). The same face of TM6 contained several residues crucial for receptor activation by agonists and one residue identified as a contact site for both agonists and antagonists. In addition, one mutation induced agonist-like responses from the receptor when exposed to classical antagonists. These results suggest that TM6 is a switch that defines the activation state of the receptor, and that ligand interactions with TM6 stabilize the receptor in either an active or an inactive conformation.
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Affiliation(s)
- T A Spalding
- ACADIA Pharmaceuticals, Inc., San Diego, California 92121, USA.
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41
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Bikker JA, Trumpp-Kallmeyer S, Humblet C. G-Protein coupled receptors: models, mutagenesis, and drug design. J Med Chem 1998; 41:2911-27. [PMID: 9685229 DOI: 10.1021/jm970767a] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- J A Bikker
- Parke-Davis Neuroscience Research Centre, Forvie Site, Robinson Way, Cambridge, United Kingdom CB2 2QB, and Parke-Davis Pharmaceutical Research Division, Warner-Lambert Company, Ann Arbor, Michigan 48105, USA
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42
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Kostenis E, Zeng FY, Wess J. Structure-function analysis of muscarinic acetylcholine receptors. JOURNAL OF PHYSIOLOGY, PARIS 1998; 92:265-8. [PMID: 9789820 DOI: 10.1016/s0928-4257(98)80030-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The structural basis underlying the G protein coupling selectivity of different muscarinic receptor subtypes was analyzed by using a combined molecular genetic/biochemical approach. These studies led to the identification of key residues on the receptors as well as the associated G proteins that are critically involved in determining proper receptor/G protein recognition. Mutational analysis of the m3 muscarinic receptor showed that most native cysteine residues are not required for productive receptor/G protein coupling. The putative extracellular disulfide bond was found to be essential for efficient trafficking of the receptor protein to the cell surface but not for receptor-mediated G protein activation.
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Affiliation(s)
- E Kostenis
- Laboratory of Bioorganic Chemistry, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA
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43
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Burstein ES, Spalding TA, Brann MR. Structure/function relationships of a G-protein coupling pocket formed by the third intracellular loop of the m5 muscarinic receptor. Biochemistry 1998; 37:4052-8. [PMID: 9521726 DOI: 10.1021/bi972132j] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Using random saturation mutagenesis, we have previously identified the amino acids K439, A440, and A441 in the C-terminus of the third intracellular loop (Ci3) of the m5 muscarinic receptor as being critical for G-protein coupling [Burstein, E. S., Spalding, T. A., Hill-Eubanks, D., and Brann, M. R. (1995) J. Biol. Chem. 270, 3141-3146]. In the present study, we have constructed a series of point mutants at each of these residues and characterized their functional phenotypes in order to define the structure/function relationships of each of these residues for G-protein coupling. Although a wide variety of substitutions were tolerated at K439, most caused significant increases in the EC50 of carbachol and decreases in the maximum response (Rmax). Only other basic residues were well tolerated (<10-fold increase in EC50, >70% of wild type). Acidic substitutions had the largest effects, reducing Rmax to under 20% of wild type. At A440, only the conservative substitution threonine was well tolerated. Substitutions by hydrophobic, polar, and basic residues caused 10-80-fold increases in EC50 values and in many cases also significantly reduced Rmax (<70% of wild type). In contrast, at A441 mutations selectively affected EC50 but not Rmax values. Previously we identified I216, Y217, T220, and R223 as the residues in the N-terminus of the i3 loop of m5 (Ni3) that are critical for G-protein coupling [Burstein, E. S., Spalding, T. S., and Brann, M. R. (1996) J. Biol. Chem. 271, 2882-2885]. To investigate whether there were additive contributions of Ni3 and Ci3 to G-protein coupling, the functional responses of two double mutants, R223E/K439E and Y217S/A441T, were evaluated. Though these mutations were tolerated individually, both double mutant receptors produced almost indetectable responses. Little or no changes in expression levels or ligand binding properties were detected, suggesting the observed effects were caused primarily by changes receptor/G-protein coupling. We conclude that K439 participates in G-protein activation through an ionic mechanism, that A440 fulfills a structural role forming part of the G-protein coupling pocket, and that A441 contributes to receptor affinity for G-proteins. We propose that the third intracellular loop forms a G-protein coupling pocket comprised of a positively charged "lip" and a hydrophobic core.
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Affiliation(s)
- E S Burstein
- Acadia Pharmaceuticals, Incorporated, San Diego, California 92121, USA
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44
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Roos M, Soskic V, Poznanovic S, Godovac-Zimmermann J. Post-translational modifications of endothelin receptor B from bovine lungs analyzed by mass spectrometry. J Biol Chem 1998; 273:924-31. [PMID: 9422751 DOI: 10.1074/jbc.273.2.924] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
A new mild experimental approach for isolation of peptide membrane receptors and subsequent analysis of post-translational modifications is described. Endothelin receptors A and B were isolated on oligo(dT)-cellulose using N-(epsilon-maleimidocaproyloxy)succinimide endothelin coupled to a protected (dA)-30-mer. This allowed a one-step isolation of the receptor from oligo(dT)-cellulose via variation solely of salt concentration. The identity of the receptor was confirmed by direct amino acid sequencing of electroblotted samples or by using antibodies against ETA and ETB receptors. The method used here is very fast, requires only very mild elution conditions and, for the first time, gave both ETA and ETB receptors concurrently in very good yield. Following enzymatic in-gel digestion, MALDI, and electrospray ion trap mass spectrometric analysis of the isolated endothelin B receptor showed phosphorylation at Ser-304, -418, -438, -439, -440, and -441. Further phosphorylation at either Ser-434 or -435 was observed. The endothelin B receptor is also palmitoylated at Cys residues 402 and 404. Phosphorylation of Ser304 may play a role in Hirschsprung's disease.
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Affiliation(s)
- M Roos
- Institute of Molecular Biotechnology e.V, Beutenbergstrasse 11, 07745 Jena, Germany
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45
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Valdenaire O, Vernier P. G protein coupled receptors as modules of interacting proteins: a family meeting. PROGRESS IN DRUG RESEARCH. FORTSCHRITTE DER ARZNEIMITTELFORSCHUNG. PROGRES DES RECHERCHES PHARMACEUTIQUES 1997; 49:173-218. [PMID: 9388388 DOI: 10.1007/978-3-0348-8863-9_6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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46
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Abell AN, Segaloff DL. Evidence for the direct involvement of transmembrane region 6 of the lutropin/choriogonadotropin receptor in activating Gs. J Biol Chem 1997; 272:14586-91. [PMID: 9169417 DOI: 10.1074/jbc.272.23.14586] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The luteinizing hormone/chorionic gonadotropin receptor (LHR) is a heptahelical receptor that interacts primarily with Gs. Previous studies by others have shown that some forms of familial male precocious puberty are associated with mutations of the human LHR in the sixth transmembrane region that result in constitutive activation of the receptor. This study demonstrates that a peptide corresponding to the lower portion of the sixth transmembrane region of the LHR can significantly activate adenylyl cyclase activity. Experiments with membranes derived from wild-type versus cyc- S49 cells demonstrate that the stimulation of cyclase by this peptide is due to an activation of Gs. As such, our data demonstrate a direct role for transmembrane region 6 of the rat LHR in activating Gs and therefore raise the possibility that mutations in transmembrane region 6 of the LHR may directly affect the coupling of the receptor to Gs. Significantly, these data are the first to demonstrate the ability of a transmembrane portion of a G protein-coupled receptor, in the absence of any contributions from an intracellular loop region, to activate a G protein.
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Affiliation(s)
- A N Abell
- Department of Physiology and Biophysics, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA
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47
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Wang HL. A site-directed mutagenesis study on the conserved alanine residue in the distal third intracellular loops of cholecystokininB and neurotensin receptors. Br J Pharmacol 1997; 121:310-6. [PMID: 9154342 PMCID: PMC1564675 DOI: 10.1038/sj.bjp.0701117] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
1. An alanine residue at the C-terminal tail of the third intracellular loop is highly conserved among various Gq protein-coupled receptors including rat cholecystokininB (CCKB) and neurotensin receptors. To investigate the functional significance of the conserved alanine in the activation of Gq proteins and phospholipase C (PLC) by CCKB and neurotensin receptors, the alanine residue was mutated in the present study. Subsequently, the ability of resulting mutant receptors to activate PLC was investigated by measuring the formation of inositol phosphates (IP) in COS-7 cells and recording Ca(2+)-activated chloride currents from Xenopus oocytes. 2. Site-directed mutagenesis was performed to mutate alanine at position 332 of rat CCKB receptor to glutamate. When the (A332E) mutant receptor was expressed in COS-7 cells and Xenopus oocytes, the efficacy and the potency of sulphated cholecystokinin octapeptide (CCK-8) to stimulate polyphosphoinositide hydrolysis in COS-7 cells and evoke calcium-dependent Cl- currents in oocytes were not significantly affected. 3. Alanine residue at position 302 of rat neurotensin receptor was also mutated to glutamate. When expressed in COS-7 cells and Xenopus oocytes, the resulting (A302E) mutant receptor was strongly defective in stimulating phosphatidylinositol turnover in COS-7 cells and evoking Ca(2+)-dependent chloride currents in oocytes. 4. In summary, the present study demonstrates that alanine residue at the C-terminus of third cytoplasmic domain is required for the full activation of Gq proteins and PLC by neurotensin receptors. However, in contrast to other Gq protein-coupled receptors, alanine at the distal third intracellular loop does not play a significant role in CCKB receptor activation of PLC.
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Affiliation(s)
- H L Wang
- Department of Physiology, Chang Gung College of Medicine and Technology, Tao-Yuan, Taiwan, R.O.C
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48
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Mathi SK, Chan Y, Li X, Wheeler MB. Scanning of the glucagon-like peptide-1 receptor localizes G protein-activating determinants primarily to the N terminus of the third intracellular loop. Mol Endocrinol 1997; 11:424-32. [PMID: 9092794 DOI: 10.1210/mend.11.4.9913] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
It is well known that glucagon-like peptide-1 (7-36 amide) (tGLP-1) is a potent insulinotropic hormone with powerful antidiabetogenic effects. In the present study we sought to determine the precise regions of the intracellular domains of the tGLP-1 receptor that are required for its efficient coupling to adenylyl cyclase because cAMP is the primary candidate second messenger coupling tGLP-1 to insulin secretion. Recently, we identified an amino acid within the third intracellular loop, K334, that was required for efficient coupling of tGLP-1 receptor to adenylyl cyclase. A similar mutagenesis-based strategy was employed here to examine the first and second intracellular loops and to further define sequences in the third loop required for the efficient coupling of the receptor to its second messengers. Receptor mutants were expressed in COS-7 cells and examined for tGLP-1 binding and cAMP stimulation. Three alanine substitution mutations, V327A, 1328A, and V331A, resulted in significantly lower tGLP-1-stimulated cAMP production without reductions in receptor expression. Analysis of the first and second intracellular loops revealed only one mutation contained within the first loop, R176A, where a significant reduction in cAMP activation was observed with normal receptor expression. These studies suggest that specific determinants of coupling for tGLP-1 receptor are primarily localized to the predicted junction of the fifth transmembrane helix and the third intracellular loop. We predict that V327, 1328, and V331 form part of a hydrophobic face that directly contacts the G protein.
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Affiliation(s)
- S K Mathi
- Department of Medicine, University of Toronto, Ontario, Canada
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49
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Abstract
Stimulated by hormones and sensory stimuli, serpentine receptors promote the release of GDP that is bound to the alpha subunit of trimeric G proteins and its replacement by GTP. Recent investigations have begun to define the sizes, shapes, and relative orientations of receptors and G proteins, the surfaces through which they interact with one another, and conformational changes in both sets of molecules that underlie receptor-catalyzed guanine-nucleotide exchange.
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Affiliation(s)
- H R Bourne
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA 94143, USA.
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50
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Shao W, Everitt L, Manchester M, Loeb DD, Hutchison CA, Swanstrom R. Sequence requirements of the HIV-1 protease flap region determined by saturation mutagenesis and kinetic analysis of flap mutants. Proc Natl Acad Sci U S A 1997; 94:2243-8. [PMID: 9122179 PMCID: PMC20072 DOI: 10.1073/pnas.94.6.2243] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/24/1996] [Indexed: 02/04/2023] Open
Abstract
The retroviral proteases (PRs) have a structural feature called the flap, which consists of a short anti-parallel beta-sheet with a turn. The flap extends over the substrate binding cleft and must be flexible to allow entry and exit of the polypeptide substrates and products. We analyzed the sequence requirements of the amino acids within the flap region (positions 46-56) of the HIV-1 PR. The phenotypes of 131 substitution mutants were determined using a bacterial expression system. Four of the mutant PRs with mutations in different regions of the flap were selected for kinetic analysis. Our phenotypic analysis, considered in the context of published structures of the HIV-1 PR with a bound substrate analogs, shows that: (i) Met-46 and Phe-53 participate in hydrophobic interactions on the solvent-exposed face of the flap; (ii) Ile-47, Ile-54, and Val-56 participate in hydrophobic interactions on the inner face of the flap; (iii) Ile-50 has hydrophobic interactions at the distance of both the delta and gamma carbons; (iv) the three glycine residues in the beta-turn of the flap are virtually intolerant of substitutions. Among these mutant PRs, we have identified changes in both kcat and Km. These results establish the nature of the side chain requirements at each position in the flap and document a role for the flap in both substrate binding and catalysis.
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Affiliation(s)
- W Shao
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, 27599, USA
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