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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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52
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Fanelli F, De Benedetti PG. Update 1 of: computational modeling approaches to structure-function analysis of G protein-coupled receptors. Chem Rev 2011; 111:PR438-535. [PMID: 22165845 DOI: 10.1021/cr100437t] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Francesca Fanelli
- Dulbecco Telethon Institute, University of Modena and Reggio Emilia, via Campi 183, 41125 Modena, Italy.
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53
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Hu J, Thor D, Zhou Y, Liu T, Wang Y, McMillin SM, Mistry R, Challiss RAJ, Costanzi S, Wess J. Structural aspects of M₃ muscarinic acetylcholine receptor dimer formation and activation. FASEB J 2011; 26:604-16. [PMID: 22031716 DOI: 10.1096/fj.11-191510] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
To explore the structural mechanisms underlying the assembly and activation of family A GPCR dimers, we used the rat M(3) muscarinic acetylcholine receptor (M3R) as a model system. Studies with Cys-substituted mutant M3Rs expressed in COS-7 cells led to the identification of several mutant M3Rs that exclusively existed as cross-linked dimers under oxidizing conditions. The cross-linked residues were located at the bottom of transmembrane domain 5 (TM5) and within the N-terminal portion of the third intracellular loop (i3 loop). Studies with urea-stripped membranes demonstrated that M3R disulfide cross-linking did not require the presence of heterotrimeric G proteins. Molecular modeling studies indicated that the cross-linking data were in excellent agreement with the existence of a low-energy M3R dimer characterized by a TM5-TM5 interface. [(35)S]GTPγS binding/Gα(q/11) immunoprecipitation assays revealed that an M3R dimer that was cross-linked within the N-terminal portion of the i3 loop (264C) was functionally severely impaired (∼50% reduction in receptor-G-protein coupling, as compared to control M3R). These data support the novel concept that agonist-induced activation of M3R dimers requires a conformational change of the N-terminal segment of the i3 loop. Given the high degree of structural homology among family A GPCRs, these findings should be of broad significance.
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Affiliation(s)
- Jianxin Hu
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD 20892-0810, USA
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54
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Feierler J, Wirth M, Welte B, Schüssler S, Jochum M, Faussner A. Helix 8 plays a crucial role in bradykinin B(2) receptor trafficking and signaling. J Biol Chem 2011; 286:43282-93. [PMID: 22016392 DOI: 10.1074/jbc.m111.256909] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Upon activation the human bradykinin B(2) receptor (B(2)R) acts as guanine nucleotide exchange factor for the G proteins G(q/11) and G(i). Thereafter, it gets phosphorylated by G protein-coupled receptor kinases (GRKs) and recruits β-arrestins, which block further G protein activation and promote B(2)R internalization via clathrin-coated pits. As for most G protein-coupled receptors of family A, an intracellular helix 8 after transmembrane domain 7 is also predicted for the B(2)R. We show here that disruption of helix 8 in the B(2)R by either C-terminal truncation or just by mutation of a central amino acid (Lys-315) to a helix-breaking proline resulted in strong reduction of surface expression. Interestingly, this malfunction could be overcome by the addition of the membrane-permeable B(2)R antagonist JSM10292, suggesting that helix 8 has a general role for conformational stabilization that can be accounted for by an appropriate antagonist. Intriguingly, an intact helix 8, but not the C terminus with its phosphorylation sites, was indispensable for receptor sequestration and for interaction of the B(2)R with GRK2/3 and β-arrestin2 as shown by co-immunoprecipitation. Recruitment of β-arrestin1, however, required the presence of the C terminus. Taken together, our results demonstrate that helix 8 of the B(2)R plays a crucial role not only in efficient trafficking to the plasma membrane or the activation of G proteins but also for the interaction of the B(2)R with GRK2/3 and β-arrestins. Additional data obtained with chimera of B(2)R with other G protein-coupled receptors of family A suggest that helix 8 might have similar functions in other GPCRs as well.
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Affiliation(s)
- Jens Feierler
- Abteilung für Klinische Chemie und Klinische Biochemie, Ludwig-Maximilians-Universität, Nussbaumstrasse 20, D-80336 München, Germany
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55
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Qin K, Dong C, Wu G, Lambert NA. Inactive-state preassembly of G(q)-coupled receptors and G(q) heterotrimers. Nat Chem Biol 2011; 7:740-7. [PMID: 21873996 PMCID: PMC3177959 DOI: 10.1038/nchembio.642] [Citation(s) in RCA: 115] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2011] [Accepted: 06/29/2011] [Indexed: 12/29/2022]
Abstract
G protein-coupled receptors (GPCRs) transmit signals by forming active-state complexes with heterotrimeric G proteins. It has been suggested that some GPCRs also assemble with G proteins before ligand-induced activation and that inactive-state preassembly facilitates rapid and specific G protein activation. However, no mechanism of preassembly has been described, and no functional consequences of preassembly have been demonstrated. Here we show that M(3) muscarinic acetylcholine receptors (M3R) form inactive-state complexes with G(q) heterotrimers in intact cells. The M3R C terminus is sufficient, and a six-amino-acid polybasic sequence distal to helix 8 ((565)KKKRRK(570)) is necessary for preassembly with G(q). Replacing this sequence with six alanine residues prevents preassembly, slows the rate of G(q) activation and decreases steady-state agonist sensitivity. That other G(q)-coupled receptors possess similar polybasic regions and also preassemble with G(q) suggests that these GPCRs may use a common preassembly mechanism to facilitate activation of G(q) heterotrimers.
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Affiliation(s)
- Kou Qin
- Department of Pharmacology and Toxicology, Georgia Health Sciences University, Augusta, Georgia, USA
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56
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McMillin SM, Heusel M, Liu T, Costanzi S, Wess J. Structural basis of M3 muscarinic receptor dimer/oligomer formation. J Biol Chem 2011; 286:28584-98. [PMID: 21685385 PMCID: PMC3151100 DOI: 10.1074/jbc.m111.259788] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2011] [Indexed: 01/03/2023] Open
Abstract
Class A G protein-coupled receptors (GPCRs) are known to form dimers and/or oligomeric arrays in vitro and in vivo. These complexes are thought to play important roles in modulating class A GPCR function. Many studies suggest that residues located on the "outer" (lipid-facing) surface of the transmembrane (TM) receptor core are critically involved in the formation of class A receptor dimers (oligomers). However, no clear consensus has emerged regarding the identity of the TM helices or TM subsegments involved in this process. To shed light on this issue, we have used the M(3) muscarinic acetylcholine receptor (M3R), a prototypic class A GPCR, as a model system. Using a comprehensive and unbiased approach, we subjected all outward-facing residues (70 amino acids total) of the TM helical bundle (TM1-7) of the M3R to systematic alanine substitution mutagenesis. We then characterized the resulting mutant receptors in radioligand binding and functional studies and determined their ability to form dimers (oligomers) in bioluminescence resonance energy transfer saturation assays. We found that M3R/M3R interactions are not dependent on the presence of one specific structural motif but involve the outer surfaces of multiple TM subsegments (TM1-5 and -7) located within the central and endofacial portions of the TM receptor core. Moreover, we demonstrated that the outward-facing surfaces of most TM helices play critical roles in proper receptor folding and/or function. Guided by the bioluminescence resonance energy transfer data, molecular modeling studies suggested the existence of multiple dimeric/oligomeric M3R arrangements, which may exist in a dynamic equilibrium. Given the high structural homology found among all class A GPCRs, our results should be of considerable general relevance.
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Affiliation(s)
| | | | - Tong Liu
- From the Laboratory of Bioorganic Chemistry and
| | - Stefano Costanzi
- Laboratory of Biological Modeling, NIDDK, National Institutes of Health, Bethesda, Maryland 20892
| | - Jürgen Wess
- From the Laboratory of Bioorganic Chemistry and
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57
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Site-specific in vitro and in vivo incorporation of molecular probes to study G-protein-coupled receptors. Curr Opin Chem Biol 2011; 15:392-8. [DOI: 10.1016/j.cbpa.2011.03.010] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2011] [Revised: 03/15/2011] [Accepted: 03/17/2011] [Indexed: 12/20/2022]
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58
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González-Maeso J. GPCR oligomers in pharmacology and signaling. Mol Brain 2011; 4:20. [PMID: 21619615 PMCID: PMC3128055 DOI: 10.1186/1756-6606-4-20] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2011] [Accepted: 05/27/2011] [Indexed: 12/15/2022] Open
Abstract
G protein-coupled receptors (GPCRs) represent one of the largest families of cell surface receptors, and are the target of more than half of the current therapeutic drugs on the market. When activated by an agonist, the GPCR undergoes conformational changes that facilitate its interaction with heterotrimeric G proteins, which then relay signals to downstream intracellular effectors. Although GPCRs were thought to function as monomers, many studies support the hypothesis that G protein coupling involves the formation of GPCR homo- and/or hetero-complexes. These complex systems have been suggested to exhibit specific signaling cascades, pharmacological, internalization, and recycling properties. In this review, we summarize recent advances in our understanding of the structure, function and dynamics of GPCR complexes, as well as the findings obtained in animal models.
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Affiliation(s)
- Javier González-Maeso
- Departments of Psychiatry and Neurology, Friedman Brain Institute, Mount Sinai School of Medicine, New York, NY, USA.
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59
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Dai W, You Z, Zhou H, Zhang J, Hu Y. Structure–function relationships of the human bitter taste receptor hTAS2R1: insights from molecular modeling studies. J Recept Signal Transduct Res 2011; 31:229-40. [DOI: 10.3109/10799893.2011.578141] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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60
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DeMars G, Fanelli F, Puett D. The extreme C-terminal region of Gαs differentially couples to the luteinizing hormone and beta2-adrenergic receptors. Mol Endocrinol 2011; 25:1416-30. [PMID: 21622536 DOI: 10.1210/me.2011-0009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The mechanisms of G protein coupling to G protein-coupled receptors (GPCR) share general characteristics but may exhibit specific interactions unique for each GPCR/G protein partnership. The extreme C terminus (CT) of G protein α-subunits has been shown to be important for association with GPCR. Hypothesizing that the extreme CT of Gα(s) is an essential component of the molecular landscape of the GPCR, human LH receptor (LHR), and β(2)-adrenergic receptor (β(2)-AR), a model cell system was created for the expression and manipulation of Gα(s) subunits in LHR(+) s49 ck cells that lack endogenous Gα(s). On the basis of studies involving truncations, mutations, and chain extensions of Gα(s), the CT was found to be necessary for LHR and β(2)-AR signaling. Some general similarities were found for the responses of the two receptors, but significant differences were also noted. Computational modeling was performed with a combination of comparative modeling, molecular dynamics simulations, and rigid body docking. The resulting models, focused on the Gα(s) CT, are supported by the experimental observations and are characterized by the interaction of the four extreme CT amino acid residues of Gα(s) with residues in LHR and β(2)-AR helix 3, (including R of the DRY motif), helix 6, and intracellular loop 2. This portion of Gα(s) recognizes the same regions of the two GPCR, although with differences in the details of selected interactions. The predicted longer cytosolic extensions of helices 5 and 6 of β(2)-AR are expected to contribute significantly to differences in Gα(s) recognition by the two receptors.
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Affiliation(s)
- Geneva DeMars
- Department of Biochemistry and Molecular Biology, University of Georgia, Athens, Georgia 30602-7229, USA
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61
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Rodríguez D, Piñeiro Á, Gutiérrez-de-Terán H. Molecular Dynamics Simulations Reveal Insights into Key Structural Elements of Adenosine Receptors. Biochemistry 2011; 50:4194-208. [DOI: 10.1021/bi200100t] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Affiliation(s)
- David Rodríguez
- Fundación Pública Galega de Medicina Xenómica, Hospital Clínico Universitario de Santiago (CHUS), planta-2, A Choupana, s/n E-15706 Santiago de Compostela, Spain
| | - Ángel Piñeiro
- Soft Matter and Molecular Biophysics Group, Department of Applied Physics, University of Santiago de Compostela, Campus Vida s/n, E-15782 Santiago de Compostela, Spain
| | - Hugo Gutiérrez-de-Terán
- Fundación Pública Galega de Medicina Xenómica, Hospital Clínico Universitario de Santiago (CHUS), planta-2, A Choupana, s/n E-15706 Santiago de Compostela, Spain
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62
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Peng Z, Tang Y, Luo H, Jiang F, Yang J, Sun L, Li JD. Disease-causing mutation in PKR2 receptor reveals a critical role of positive charges in the second intracellular loop for G-protein coupling and receptor trafficking. J Biol Chem 2011; 286:16615-22. [PMID: 21454486 DOI: 10.1074/jbc.m111.223784] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Prokineticins are a pair of signal factors involved in many physiological processes by binding to two closely related G-protein-coupled receptors, PKR1 and PKR2. Recently, mutations in prokineticin 2 (PK2) and PKR2 are found to be associated with Kallmann syndrome and/or idiopathic hypogonadotropic hypogonadism, disorders characterized by delayed puberty and infertility. However, little is known how PKRs interact and activate G-proteins to elicit signal transduction. In the present study, we took advantage of one disease-associated mutation (R164Q) located in the second intracellular (IL2) loop of PKR2, to investigate the role of IL2 loop in the cell signaling, G-protein binding and receptor trafficking. R164Q mutant PKR2 showed normal cell surface expression and ligand binding capacity. However, the PKR2 signaling was abolished by R164Q mutation. We demonstrated that R164Q mutation disrupted the interaction of IL2 loop to the Gα(q), Gα(i), and Gα(16)-proteins. A positive-charged amino acid at this position is required for proper function, and the signaling efficacy and potency depend on the net amount of positive charges. We also demonstrated that the interactive partner of Arg-164 may localize in the C-terminal five residues of Gα(q)-protein. A series of mutation analysis indicated that the basic amino acids at the C terminus of IL2 loop may function cooperatively in GPCRs. Furthermore, R164Q mutation also results in minimal ligand-induced endocytosis of PKR2. As many GPCRs share structural homology in the C terminus of IL2 loop, our findings may have general application in understanding structure and function of GPCRs.
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Affiliation(s)
- Zhen Peng
- State Key Laboratory of Medical Genetics, Central South University, Changsha, Hunan 410078, China
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63
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Wichard JD, ter Laak A, Krause G, Heinrich N, Kühne R, Kleinau G. Chemogenomic analysis of G-protein coupled receptors and their ligands deciphers locks and keys governing diverse aspects of signalling. PLoS One 2011; 6:e16811. [PMID: 21326864 PMCID: PMC3033908 DOI: 10.1371/journal.pone.0016811] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2010] [Accepted: 01/12/2011] [Indexed: 11/28/2022] Open
Abstract
Understanding the molecular mechanism of signalling in the important super-family of G-protein-coupled receptors (GPCRs) is causally related to questions of how and where these receptors can be activated or inhibited. In this context, it is of great interest to unravel the common molecular features of GPCRs as well as those related to an active or inactive state or to subtype specific G-protein coupling. In our underlying chemogenomics study, we analyse for the first time the statistical link between the properties of G-protein-coupled receptors and GPCR ligands. The technique of mutual information (MI) is able to reveal statistical inter-dependence between variations in amino acid residues on the one hand and variations in ligand molecular descriptors on the other. Although this MI analysis uses novel information that differs from the results of known site-directed mutagenesis studies or published GPCR crystal structures, the method is capable of identifying the well-known common ligand binding region of GPCRs between the upper part of the seven transmembrane helices and the second extracellular loop. The analysis shows amino acid positions that are sensitive to either stimulating (agonistic) or inhibitory (antagonistic) ligand effects or both. It appears that amino acid positions for antagonistic and agonistic effects are both concentrated around the extracellular region, but selective agonistic effects are cumulated between transmembrane helices (TMHs) 2, 3, and ECL2, while selective residues for antagonistic effects are located at the top of helices 5 and 6. Above all, the MI analysis provides detailed indications about amino acids located in the transmembrane region of these receptors that determine G-protein signalling pathway preferences.
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Affiliation(s)
- Jörg D. Wichard
- Leibniz-Institut für Molekulare Pharmakologie, Berlin, Germany
- Bayer-Schering Pharma, Berlin, Germany
| | | | - Gerd Krause
- Leibniz-Institut für Molekulare Pharmakologie, Berlin, Germany
| | | | - Ronald Kühne
- Leibniz-Institut für Molekulare Pharmakologie, Berlin, Germany
- * E-mail:
| | - Gunnar Kleinau
- Leibniz-Institut für Molekulare Pharmakologie, Berlin, Germany
- Institute of Experimental Pediatric Endocrinology, Charité Universitätsmedizin Berlin, Berlin, Germany
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64
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Bosch-Presegué L, Iarriccio L, Aguilà M, Toledo D, Ramon E, Cordomí A, Garriga P. Hydrophobic amino acids at the cytoplasmic ends of helices 3 and 6 of rhodopsin conjointly modulate transducin activation. Arch Biochem Biophys 2011; 506:142-9. [DOI: 10.1016/j.abb.2010.11.019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2010] [Revised: 11/22/2010] [Accepted: 11/22/2010] [Indexed: 11/26/2022]
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65
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Kaye RG, Saldanha JW, Lu ZL, Hulme EC. Helix 8 of the M1 muscarinic acetylcholine receptor: scanning mutagenesis delineates a G protein recognition site. Mol Pharmacol 2011; 79:701-9. [PMID: 21247934 DOI: 10.1124/mol.110.070177] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
We have used alanine-scanning mutagenesis followed by functional expression and molecular modeling to analyze the roles of the 14 residues, Asn422 to Cys435, C-terminal to transmembrane (TM) helix 7 of the M(1) muscarinic acetylcholine receptor. The results suggest that they form an eighth (H8) helix, associated with the cytoplasmic surface of the cell membrane in the active state of the receptor. We suggest that the amide side chain of Asn422 may act as a cap to the C terminus of TM7, stabilizing its junction with H8, whereas the side chain of Phe429 may restrict the relative movements of H8 and the C terminus of TM7 in the inactive ground state of the receptor. We have identified four residues, Phe425, Arg426, Thr428, and Leu432, which are important for G protein binding and signaling. These may form a docking site for the C-terminal helix of the G protein α subunit, and collaborate with G protein recognition residues elsewhere in the cytoplasmic domain of the receptor to form a coherent surface for G protein binding in the activated state of the receptor.
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Affiliation(s)
- Robert G Kaye
- Division of Physical Biochemistry, MRC National Institute for Medical Research, London, United Kingdom
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