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Batebi H, Pérez-Hernández G, Rahman SN, Lan B, Kamprad A, Shi M, Speck D, Tiemann JKS, Guixà-González R, Reinhardt F, Stadler PF, Papasergi-Scott MM, Skiniotis G, Scheerer P, Kobilka BK, Mathiesen JM, Liu X, Hildebrand PW. Mechanistic insights into G-protein coupling with an agonist-bound G-protein-coupled receptor. Nat Struct Mol Biol 2024:10.1038/s41594-024-01334-2. [PMID: 38867113 DOI: 10.1038/s41594-024-01334-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2024] [Accepted: 05/14/2024] [Indexed: 06/14/2024]
Abstract
G-protein-coupled receptors (GPCRs) activate heterotrimeric G proteins by promoting guanine nucleotide exchange. Here, we investigate the coupling of G proteins with GPCRs and describe the events that ultimately lead to the ejection of GDP from its binding pocket in the Gα subunit, the rate-limiting step during G-protein activation. Using molecular dynamics simulations, we investigate the temporal progression of structural rearrangements of GDP-bound Gs protein (Gs·GDP; hereafter GsGDP) upon coupling to the β2-adrenergic receptor (β2AR) in atomic detail. The binding of GsGDP to the β2AR is followed by long-range allosteric effects that significantly reduce the energy needed for GDP release: the opening of α1-αF helices, the displacement of the αG helix and the opening of the α-helical domain. Signal propagation to the Gs occurs through an extended receptor interface, including a lysine-rich motif at the intracellular end of a kinked transmembrane helix 6, which was confirmed by site-directed mutagenesis and functional assays. From this β2AR-GsGDP intermediate, Gs undergoes an in-plane rotation along the receptor axis to approach the β2AR-Gsempty state. The simulations shed light on how the structural elements at the receptor-G-protein interface may interact to transmit the signal over 30 Å to the nucleotide-binding site. Our analysis extends the current limited view of nucleotide-free snapshots to include additional states and structural features responsible for signaling and G-protein coupling specificity.
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Affiliation(s)
- Hossein Batebi
- Universität Leipzig, Medizinische Fakultät, Institut für Medizinische Physik und Biophysik, Leipzig, Germany
- Freie Universität Berlin, Fachbereich Physik, Berlin, Germany
| | - Guillermo Pérez-Hernández
- Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Medical Physics and Biophysics, Berlin, Germany
| | - Sabrina N Rahman
- University of Copenhagen, Department of Drug Design and Pharmacology, Copenhagen, Denmark
| | - Baoliang Lan
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, Beijing Frontier Research Center for Biological Structure, School of Pharmaceutical Sciences, Tsinghua University, Beijing, China
| | - Antje Kamprad
- Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Medical Physics and Biophysics, Group Structural Biology of Cellular Signaling, Berlin, Germany
| | - Mingyu Shi
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, Beijing Frontier Research Center for Biological Structure, School of Pharmaceutical Sciences, Tsinghua University, Beijing, China
| | - David Speck
- Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Medical Physics and Biophysics, Group Structural Biology of Cellular Signaling, Berlin, Germany
| | - Johanna K S Tiemann
- Universität Leipzig, Medizinische Fakultät, Institut für Medizinische Physik und Biophysik, Leipzig, Germany
- Novozymes A/S, Lyngby, Denmark
| | - Ramon Guixà-González
- Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Medical Physics and Biophysics, Berlin, Germany
- Department of Biological Chemistry, Institute for Advanced Chemistry of Catalonia (IQAC-CSIC), Barcelona, Spain
| | - Franziska Reinhardt
- Universität Leipzig, Department of Computer Science, Bioinformatics, Leipzig, Germany
| | - Peter F Stadler
- Universität Leipzig, Department of Computer Science, Bioinformatics, Leipzig, Germany
| | - Makaía M Papasergi-Scott
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA
| | - Georgios Skiniotis
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA
- Department of Structural Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Patrick Scheerer
- Charité-Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Medical Physics and Biophysics, Group Structural Biology of Cellular Signaling, Berlin, Germany
| | - Brian K Kobilka
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA, USA
| | - Jesper M Mathiesen
- University of Copenhagen, Department of Drug Design and Pharmacology, Copenhagen, Denmark
| | - Xiangyu Liu
- State Key Laboratory of Membrane Biology, Tsinghua-Peking Center for Life Sciences, Beijing Frontier Research Center for Biological Structure, School of Pharmaceutical Sciences, Tsinghua University, Beijing, China
| | - Peter W Hildebrand
- Universität Leipzig, Medizinische Fakultät, Institut für Medizinische Physik und Biophysik, Leipzig, Germany.
- Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Institute of Medical Physics and Biophysics, Berlin, Germany.
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2
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Jiang H, Galtes D, Wang J, Rockman HA. G protein-coupled receptor signaling: transducers and effectors. Am J Physiol Cell Physiol 2022; 323:C731-C748. [PMID: 35816644 PMCID: PMC9448338 DOI: 10.1152/ajpcell.00210.2022] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2022] [Revised: 06/27/2022] [Accepted: 07/10/2022] [Indexed: 01/14/2023]
Abstract
G protein-coupled receptors (GPCRs) are of considerable interest due to their importance in a wide range of physiological functions and in a large number of Food and Drug Administration (FDA)-approved drugs as therapeutic entities. With continued study of their function and mechanism of action, there is a greater understanding of how effector molecules interact with a receptor to initiate downstream effector signaling. This review aims to explore the signaling pathways, dynamic structures, and physiological relevance in the cardiovascular system of the three most important GPCR signaling effectors: heterotrimeric G proteins, GPCR kinases (GRKs), and β-arrestins. We will first summarize their prominent roles in GPCR pharmacology before transitioning into less well-explored areas. As new technologies are developed and applied to studying GPCR structure and their downstream effectors, there is increasing appreciation for the elegance of the regulatory mechanisms that mediate intracellular signaling and function.
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Affiliation(s)
- Haoran Jiang
- Department of Medicine, Duke University Medical Center, Durham, North Carolina
| | - Daniella Galtes
- Department of Medicine, Duke University Medical Center, Durham, North Carolina
| | - Jialu Wang
- Department of Medicine, Duke University Medical Center, Durham, North Carolina
| | - Howard A Rockman
- Department of Medicine, Duke University Medical Center, Durham, North Carolina
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina
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3
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Kim HR, Xu J, Maeda S, Duc NM, Ahn D, Du Y, Chung KY. Structural mechanism underlying primary and secondary coupling between GPCRs and the Gi/o family. Nat Commun 2020; 11:3160. [PMID: 32572026 PMCID: PMC7308389 DOI: 10.1038/s41467-020-16975-2] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Accepted: 06/04/2020] [Indexed: 02/06/2023] Open
Abstract
Heterotrimeric G proteins are categorized into four main families based on their function and sequence, Gs, Gi/o, Gq/11, and G12/13. One receptor can couple to more than one G protein subtype, and the coupling efficiency varies depending on the GPCR-G protein pair. However, the precise mechanism underlying different coupling efficiencies is unknown. Here, we study the structural mechanism underlying primary and secondary Gi/o coupling, using the muscarinic acetylcholine receptor type 2 (M2R) as the primary Gi/o-coupling receptor and the β2-adrenergic receptor (β2AR, which primarily couples to Gs) as the secondary Gi/o-coupling receptor. Hydrogen/deuterium exchange mass spectrometry and mutagenesis studies reveal that the engagement of the distal C-terminus of Gαi/o with the receptor differentiates primary and secondary Gi/o couplings. This study suggests that the conserved hydrophobic residue within the intracellular loop 2 of the receptor (residue 34.51) is not critical for primary Gi/o-coupling; however, it might be important for secondary Gi/o-coupling. G protein-coupled receptors (GPCRs) can couple to more than one G protein subtype, and the coupling efficiency varies depending on the GPCR-G protein pair. Here authors use hydrogen/deuterium exchange mass spectrometry and mutagenesis to study the structural mechanism underlying primary and secondary Gi/o coupling.
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Affiliation(s)
- Hee Ryung Kim
- School of Pharmacy, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon, 16419, Republic of Korea
| | - Jun Xu
- Beijing Advanced Innovation Center for Structural Biology, School of Medicine, Tsinghua University, Beijing, 100084, China
| | - Shoji Maeda
- Department of Molecular and Cellular Physiology, School of Medicine, Stanford University, 279 Campus Drive, Stanford, CA, 94305, USA
| | - Nguyen Minh Duc
- School of Pharmacy, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon, 16419, Republic of Korea.,Division of Precision Medicine, Research Institute, National Cancer Center, 323 Ilsan-ro, Ilsandong-gu, Goyang, 10408, Republic of Korea
| | - Donghoon Ahn
- School of Pharmacy, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon, 16419, Republic of Korea
| | - Yang Du
- School of Life and Health Sciences, Kobilka Institute of Innovative Drug Discovery, Chinese University of Hong Kong, 2001 Longxiang Ave, Shenzhen, Guangdong, 518172, China.
| | - Ka Young Chung
- School of Pharmacy, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon, 16419, Republic of Korea.
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4
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Milano SK, Wang C, Erickson JW, Cerione RA, Ramachandran S. Gain-of-function screen of α-transducin identifies an essential phenylalanine residue necessary for full effector activation. J Biol Chem 2018; 293:17941-17952. [PMID: 30266806 DOI: 10.1074/jbc.ra118.003746] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Revised: 09/21/2018] [Indexed: 11/06/2022] Open
Abstract
Two regions on the α subunits of heterotrimeric GTP-binding proteins (G-proteins), the Switch II/α2 helix (which changes conformation upon GDP-GTP exchange) and the α3 helix, have been shown to contain the binding sites for their effector proteins. However, how the binding of Gα subunits to their effector proteins is translated into the stimulation of effector activity is still poorly understood. Here, we took advantage of a reconstituted rhodopsin-coupled phototransduction system to address this question and identified a distinct surface and an essential residue on the α subunit of the G-protein transducin (αT) that is necessary to fully activate its effector enzyme, the cGMP phosphodiesterase (PDE). We started with a chimeric G-protein α subunit (αT*) comprising residues mainly from αT and a short stretch of residues from the Gi1 α subunit (αi1), which only weakly stimulates PDE activity. We then reinstated the αT residues by systematically replacing the corresponding αi1 residues within αT* with the aim of fully restoring PDE stimulatory activity. These experiments revealed that the αG/α4 loop and a phenylalanine residue at position 283 are essential for conferring the αT* subunit with full PDE stimulatory capability. We further demonstrated that this same region and amino acid within the α subunit of the Gs protein (αs) are necessary for full adenylyl cyclase activation. These findings highlight the importance of the αG/α4 loop and of an essential phenylalanine residue within this region on Gα subunits αT and αs as being pivotal for their selective and optimal stimulation of effector activity.
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Affiliation(s)
- Shawn K Milano
- From the Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301
| | - Chenyue Wang
- From the Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301
| | - Jon W Erickson
- From the Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301
| | - Richard A Cerione
- From the Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301; Department of Molecular Medicine, Cornell University, Ithaca, New York 14853-6401.
| | - Sekar Ramachandran
- From the Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853-1301
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5
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Ballister ER, Rodgers J, Martial F, Lucas RJ. A live cell assay of GPCR coupling allows identification of optogenetic tools for controlling Go and Gi signaling. BMC Biol 2018; 16:10. [PMID: 29338718 PMCID: PMC5771134 DOI: 10.1186/s12915-017-0475-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Accepted: 12/18/2017] [Indexed: 11/10/2022] Open
Abstract
Background Animal opsins are light-sensitive G-protein-coupled receptors (GPCRs) that enable optogenetic control over the major heterotrimeric G-protein signaling pathways in animal cells. As such, opsins have potential applications in both biomedical research and therapy. Selecting the opsin with the best balance of activity and selectivity for a given application requires knowing their ability to couple to a full range of relevant Gα subunits. We present the GsX assay, a set of tools based on chimeric Gs subunits that transduce coupling of opsins to diverse G proteins into increases in cAMP levels, measured with a real-time reporter in living cells. We use this assay to compare coupling to Gi/o/t across a panel of natural and chimeric opsins selected for potential application in gene therapy for retinal degeneration. Results Of the opsins tested, wild-type human rod opsin had the highest activity for chimeric Gs proxies for Gi and Gt (Gsi and Gst) and was matched in Go proxy (Gso) activity only by a human rod opsin/scallop opsin chimera. Rod opsin drove roughly equivalent responses via Gsi, Gso, and Gst, while cone opsins showed much lower activities with Gso than Gsi or Gst, and a human rod opsin/amphioxus opsin chimera demonstrated higher activity with Gso than with Gsi or Gst. We failed to detect activity for opsin chimeras bearing three intracellular fragments of mGluR6, and observed unexpectedly complex response profiles for scallop and amphioxus opsins thought to be specialized for Go. Conclusions These results identify rod opsin as the most potent non-selective Gi/o/t-coupled opsin, long-wave sensitive cone opsin as the best for selectively activating Gi/t over Go, and a rod opsin/amphioxus opsin chimera as the best choice for selectively activating Go over Gi/t. Electronic supplementary material The online version of this article (doi:10.1186/s12915-017-0475-2) contains supplementary material, which is available to authorized users.
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6
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Rose AS, Zachariae U, Grubmüller H, Hofmann KP, Scheerer P, Hildebrand PW. Role of Structural Dynamics at the Receptor G Protein Interface for Signal Transduction. PLoS One 2015; 10:e0143399. [PMID: 26606751 PMCID: PMC4659624 DOI: 10.1371/journal.pone.0143399] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Accepted: 11/04/2015] [Indexed: 11/19/2022] Open
Abstract
GPCRs catalyze GDP/GTP exchange in the α-subunit of heterotrimeric G proteins (Gαßγ) through displacement of the Gα C-terminal α5 helix, which directly connects the interface of the active receptor (R*) to the nucleotide binding pocket of G. Hydrogen-deuterium exchange mass spectrometry and kinetic analysis of R* catalysed G protein activation have suggested that displacement of α5 starts from an intermediate GDP bound complex (R*•GGDP). To elucidate the structural basis of receptor-catalysed displacement of α5, we modelled the structure of R*•GGDP. A flexible docking protocol yielded an intermediate R*•GGDP complex, with a similar overall arrangement as in the X-ray structure of the nucleotide free complex (R*•Gempty), however with the α5 C-terminus (GαCT) forming different polar contacts with R*. Starting molecular dynamics simulations of GαCT bound to R* in the intermediate position, we observe a screw-like motion, which restores the specific interactions of α5 with R* in R*•Gempty. The observed rotation of α5 by 60° is in line with experimental data. Reformation of hydrogen bonds, water expulsion and formation of hydrophobic interactions are driving forces of the α5 displacement. We conclude that the identified interactions between R* and G protein define a structural framework in which the α5 displacement promotes direct transmission of the signal from R* to the GDP binding pocket.
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Affiliation(s)
- Alexander S. Rose
- Institute of Medical Physics and Biophysics (CC2), Universitätsmedizin Berlin, Charitéplatz 1, 10098, Berlin, Germany
- Team ProteiInformatics, Universitätsmedizin Berlin, Charitéplatz 1, 10098, Berlin, Germany
| | - Ulrich Zachariae
- Dep. of Theoretical and Computational Biophysics, Max-Planck-Institute for Biophysical Chemistry, 37077, Göttingen, Germany
- Computational Biology, School of Life Sciences, and Physics, School of Science and Engineering, University of Dundee, Dow Street, Dundee, DD1 5EH, United Kingdom
| | - Helmut Grubmüller
- Dep. of Theoretical and Computational Biophysics, Max-Planck-Institute for Biophysical Chemistry, 37077, Göttingen, Germany
| | - Klaus Peter Hofmann
- Institute of Medical Physics and Biophysics (CC2), Universitätsmedizin Berlin, Charitéplatz 1, 10098, Berlin, Germany
- Centre of Biophysics and Bioinformatics, Humboldt-Universität zu Berlin, Invalidenstrasse 42, 10115, Berlin, Germany
| | - Patrick Scheerer
- Institute of Medical Physics and Biophysics (CC2), Universitätsmedizin Berlin, Charitéplatz 1, 10098, Berlin, Germany
- Team Protein X-ray Crystallography and Signal Transduction, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10098, Berlin, Germany
| | - Peter W. Hildebrand
- Institute of Medical Physics and Biophysics (CC2), Universitätsmedizin Berlin, Charitéplatz 1, 10098, Berlin, Germany
- Team ProteiInformatics, Universitätsmedizin Berlin, Charitéplatz 1, 10098, Berlin, Germany
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7
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Duc NM, Kim HR, Chung KY. Structural mechanism of G protein activation by G protein-coupled receptor. Eur J Pharmacol 2015; 763:214-22. [PMID: 25981300 DOI: 10.1016/j.ejphar.2015.05.016] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2015] [Revised: 03/03/2015] [Accepted: 05/11/2015] [Indexed: 12/17/2022]
Abstract
G protein-coupled receptors (GPCRs) are a family of membrane receptors that regulate physiology and pathology of various organs. Consequently, about 40% of drugs in the market targets GPCRs. Heterotrimeric G proteins are composed of α, β, and γ subunits, and act as the key downstream signaling molecules of GPCRs. The structural mechanism of G protein activation by GPCRs has been of a great interest, and a number of biochemical and biophysical studies have been performed since the late 80's. These studies investigated the interface between GPCR and G proteins and the structural mechanism of GPCR-induced G protein activation. Recently, arrestins are also reported to be important molecular switches in GPCR-mediated signal transduction, and the physiological output of arrestin-mediated signal transduction is different from that of G protein-mediated signal transduction. Understanding the structural mechanism of the activation of G proteins and arrestins would provide fundamental information for the downstream signaling-selective GPCR-targeting drug development. This review will discuss the structural mechanism of GPCR-induced G protein activation by comparing previous biochemical and biophysical studies.
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Affiliation(s)
- Nguyen Minh Duc
- School of Pharmacy, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon 440-746, Republic of Korea
| | - Hee Ryung Kim
- School of Pharmacy, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon 440-746, Republic of Korea
| | - Ka Young Chung
- School of Pharmacy, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon 440-746, Republic of Korea.
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8
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Dynamics of bovine opsin bound to G-protein fragments. J Struct Biol 2014; 188:79-86. [DOI: 10.1016/j.jsb.2014.08.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Revised: 07/31/2014] [Accepted: 08/07/2014] [Indexed: 11/20/2022]
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9
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Rose AS, Elgeti M, Zachariae U, Grubmüller H, Hofmann KP, Scheerer P, Hildebrand PW. Position of Transmembrane Helix 6 Determines Receptor G Protein Coupling Specificity. J Am Chem Soc 2014; 136:11244-7. [DOI: 10.1021/ja5055109] [Citation(s) in RCA: 83] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
| | | | - Ulrich Zachariae
- Division
of Computational Biology, College of Life Sciences, and Division of
Physics, School of Engineering, Physics and Mathematics, University of Dundee, Dow Street, Dundee DD1
5EH, U.K
| | - Helmut Grubmüller
- Department
of Theoretical and Computational Biophysics, Max-Planck-Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
| | - Klaus Peter Hofmann
- Centre
of Biophysics and Bioinformatics, Humboldt-Universität zu Berlin, Invalidenstrasse
42, D-10115 Berlin, Germany
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10
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Chung KY. Structural Aspects of GPCR-G Protein Coupling. Toxicol Res 2014; 29:149-55. [PMID: 24386514 PMCID: PMC3877993 DOI: 10.5487/tr.2013.29.3.149] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2013] [Revised: 09/10/2013] [Accepted: 09/17/2013] [Indexed: 11/24/2022] Open
Abstract
G protein-coupled receptors (GPCRs) are membrane receptors; approximately 40% of drugs on the market target GPCRs. A precise understanding of the activation mechanism of GPCRs would facilitate the development of more effective and less toxic drugs. Heterotrimeric G proteins are important molecular switches in GPCR-mediated signal transduction. An agonist-activated receptor interacts with specific sites on G proteins and promotes the release of GDP from the Gα subunit. Because of the important biological role of the GPCR-G protein coupling, conformational changes in the G protein upon receptor coupling have been of great interest. One of the most important questions was the interface between the GPCR and G proteins and the structural mechanism of GPCR-induced G protein activation. A number of biochemical and biophysical studies have been performed since the late 80s to address these questions; there was a significant breakthrough in 2011 when the crystal structure of a GPCR-G protein complex was solved. This review discusses the structural aspects of GPCR-G protein coupling by comparing the results of previous biochemical and biophysical studies to the GPCR-G protein crystal structure.
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Affiliation(s)
- Ka Young Chung
- School of Pharmacy, Sungkyunkwan University, Suwon, Korea
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11
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Hamm HE, Kaya AI, Gilbert JA, Preininger AM. Linking receptor activation to changes in Sw I and II of Gα proteins. J Struct Biol 2013; 184:63-74. [PMID: 23466875 DOI: 10.1016/j.jsb.2013.02.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Revised: 12/28/2012] [Accepted: 02/22/2013] [Indexed: 10/27/2022]
Abstract
G-protein coupled receptors catalyze nucleotide exchange on G proteins, which results in subunit dissociation and effector activation. In the recent β2AR-Gs structure, portions of Switch I and II of Gα are not fully elucidated. We paired fluorescence studies of receptor-Gαi interactions with the β2AR-Gs and other Gi structures to investigate changes in Switch I and II during receptor activation and GTP binding. The β2/β3 loop containing Leu194 of Gαi is located between Switches I and II, in close proximity to IC2 of the receptor and the C-terminus of Gα, thus providing an allosteric connection between these Switches and receptor activation. We compared the environment of residues in myristoylated Gαi proteins in the heterotrimer to that upon receptor activation and subsequent GTP binding. Upon receptor activation, residues in both Switch regions are less solvent-exposed, as compared to the heterotrimer. Upon GTPγS binding, the environment of several residues in Switch I resemble the receptor-bound state, while Switch II residues display effects on their environment which are consistent with their role in GTP binding and Gβγ dissociation. The ability to merge available crystal structures with solution studies is a powerful tool to gain insight into conformational changes associated with receptor-mediated Gi protein activation.
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Affiliation(s)
- Heidi E Hamm
- Vanderbilt University Medical Center, Department of Pharmacology, Nashville, TN 37232-6600, United States
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12
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Caltabiano G, Gonzalez A, Cordomí A, Campillo M, Pardo L. The Role of Hydrophobic Amino Acids in the Structure and Function of the Rhodopsin Family of G Protein-Coupled Receptors. Methods Enzymol 2013; 520:99-115. [DOI: 10.1016/b978-0-12-391861-1.00005-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/19/2023]
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13
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Kimata N, Yamashita T, Matsuyama T, Imamoto Y, Shichida Y. The C-terminus of the G protein α subunit controls the affinity of nucleotides. Biochemistry 2012; 51:2768-74. [PMID: 22404167 DOI: 10.1021/bi201702d] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The C-terminus of the G protein α subunit has a well-known role in determining the selective coupling with the cognate G protein-coupled receptor (GPCR). In fact, rhodopsin, a prototypical GPCR, exhibits active state [metarhodopsin II (MII)] stabilization by interacting with G protein [extra formation of MII (eMII)], and the extent of stabilization is affected by the C-terminal sequence of Gα. Here we examine the relationship between the amount of eMII and the activation efficiency of Gi mutants whose Giα forms have different lengths of the C-terminal sequence of Goα. The results show that both the activation efficiencies of Gi and the amounts of eMII were affected by mutations; however, there was no correlation between them. This finding suggested that the C-terminal region of Gα not only stabilizes MII (active state) but also affects the nucleotide-binding site of Gα. Therefore, we measured the activation efficiency of these mutants by MII at several concentrations of GDP and GTP and calculated the rate constants of GDP release, GDP uptake, and GTP uptake. These rate constants of the Gi mutants were substantially different from those of the wild type, indicating that the replacement of the amino acid residues in the C-terminus alters the affinity of nucleotides. The rate constants of GDP uptake and GTP uptake showed a strong correlation, suggesting that the C-terminus of Giα controls the accessibility of the nucleotide-binding site. Therefore, our results strongly suggest that there is a long-range interlink between the C-terminus of Giα and its nucleotide-binding site.
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Affiliation(s)
- Naoki Kimata
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
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14
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Gopalakrishna KN, Boyd KK, Artemyev NO. Comparative analysis of cone and rod transducins using chimeric Gα subunits. Biochemistry 2012; 51:1617-24. [PMID: 22324825 DOI: 10.1021/bi3000935] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The molecular nature of transducin-α subunits (Gα(t)) may contribute to the distinct physiology of cone and rod photoreceptors. Biochemical properties of mammalian cone Gα(t2) subunits and their differences with rod Gα(t1) are largely unknown. Here, we examined properties of chimeric Gα(t2) in comparison with its rod counterpart. The key biochemical difference between the rod- and cone-like Gα(t) was ~10-fold higher intrinsic nucleotide exchange on the chimeric Gα(t2). Presented mutational analysis suggests that weaker interdomain interactions between the GTPase (Ras-like) domain and the helical domain in Gα(t2) are in part responsible for its increased spontaneous nucleotide exchange. However, the rates of R*-dependent nucleotide exchange of chimeric Gα(t2) and Gα(t1) were equivalent. Furthermore, chimeric Gα(t2) and Gα(t1) exhibited similar rates of intrinsic GTPase activity as well as similar acceleration of GTP hydrolysis by the RGS domain of RGS9. Our results suggest that the activation and inactivation properties of cone and rod Gα(t) subunits in an in vitro reconstituted system are comparable.
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Affiliation(s)
- Kota N Gopalakrishna
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, United States
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15
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Huang CC, Tesmer JJG. Recognition in the face of diversity: interactions of heterotrimeric G proteins and G protein-coupled receptor (GPCR) kinases with activated GPCRs. J Biol Chem 2011; 286:7715-7721. [PMID: 21199869 DOI: 10.1074/jbc.r109.051847] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
G protein-coupled receptors (GPCRs) represent the largest class of integral membrane protein receptors in the human genome. Despite the great diversity of ligands that activate these GPCRs, they interact with a relatively small number of intracellular proteins to induce profound physiological change. Both heterotrimeric G proteins and GPCR kinases are well known for their ability to specifically recognize GPCRs in their active state. Recent structural studies now suggest that heterotrimeric G proteins and GPCR kinases identify activated receptors via a common molecular mechanism despite having completely different folds.
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Affiliation(s)
| | - John J G Tesmer
- From the Life Sciences Institute and; Department of Pharmacology, University of Michigan, Ann Arbor, Michigan 48109-2216.
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16
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Preininger AM, Funk MA, Oldham WM, Meier SM, Johnston CA, Adhikary S, Kimple AJ, Siderovski DP, Hamm HE, Iverson TM. Helix dipole movement and conformational variability contribute to allosteric GDP release in Galphai subunits. Biochemistry 2009; 48:2630-42. [PMID: 19222191 DOI: 10.1021/bi801853a] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Heterotrimeric G proteins (Galphabetagamma) transmit signals from activated G protein-coupled receptors (GPCRs) to downstream effectors through a guanine nucleotide signaling cycle. Numerous studies indicate that the carboxy-terminal alpha5 helix of Galpha subunits participates in Galpha-receptor binding, and previous EPR studies suggest this receptor-mediated interaction induces a rotation and translation of the alpha5 helix of the Galpha subunit [Oldham, W. M., et al. (2006) Nat. Struct. Mol. Biol. 13, 772-777]. On the basis of this result, an engineered disulfide bond was designed to constrain the alpha5 helix of Galpha(i1) into its EPR-measured receptor-associated conformation through the introduction of cysteines at position 56 in the alpha1 helix and position 333 in the alpha5 helix (I56C/Q333C Galpha(i1)). A functional mimetic of the EPR-measured alpha5 helix dipole movement upon receptor association was additionally created by introduction of a positive charge at the amino terminus of this helix, D328R Galpha(i1). Both proteins exhibit a dramatically elevated level of basal nucleotide exchange. The 2.9 A resolution crystal structure of I56C/Q333C Galpha(i1) in complex with GDP-AlF(4)(-) reveals the shift of the alpha5 helix toward the guanine nucleotide binding site that is anticipated by EPR measurements. The structure of the I56C/Q333C Galpha(i1) subunit further revealed altered positions for the switch regions and throughout the Galpha(i1) subunit, accompanied by significantly elevated crystallographic temperature factors. Combined with previous evidence in the literature, the structural analysis supports the critical role of electrostatics of the alpha5 helix dipole and overall conformational variability during nucleotide release.
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Affiliation(s)
- Anita M Preininger
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-6600, USA
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17
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Morizumi T, Kimata N, Terakita A, Imamoto Y, Yamashita T, Shichida Y. G Protein Subtype Specificity of Rhodopsin Intermediates Metarhodopsin Ib and Metarhodopsin II. Photochem Photobiol 2009; 85:57-62. [DOI: 10.1111/j.1751-1097.2008.00396.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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18
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Natochin M, Moussaif M, Artemyev NO. Probing the mechanism of rhodopsin-catalyzed transducin activation. J Neurochem 2008. [DOI: 10.1046/j.1471-4159.2001.00221.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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19
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Abstract
Heterotrimeric G proteins couple the activation of heptahelical receptors at the cell surface to the intracellular signaling cascades that mediate the physiological responses to extracellular stimuli. G proteins are molecular switches that are activated by receptor-catalyzed GTP for GDP exchange on the G protein alpha subunit, which is the rate-limiting step in the activation of all downstream signaling. Despite the important biological role of the receptor-G protein interaction, relatively little is known about the structure of the complex and how it leads to nucleotide exchange. This chapter will describe what is known about receptor and G protein structure and outline a strategy for assembling the current data into improved models for the receptor-G protein complex that will hopefully answer the question as to how receptors flip the G protein switch.
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Affiliation(s)
- William M Oldham
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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20
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Heterotrimeric G protein activation by G-protein-coupled receptors. Nat Rev Mol Cell Biol 2008; 9:60-71. [PMID: 18043707 DOI: 10.1038/nrm2299] [Citation(s) in RCA: 802] [Impact Index Per Article: 50.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Heterotrimeric G proteins have a crucial role as molecular switches in signal transduction pathways mediated by G-protein-coupled receptors. Extracellular stimuli activate these receptors, which then catalyse GTP-GDP exchange on the G protein alpha-subunit. The complex series of interactions and conformational changes that connect agonist binding to G protein activation raise various interesting questions about the structure, biomechanics, kinetics and specificity of signal transduction across the plasma membrane.
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21
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Shpakov AO, Gur'yanov IA, Kuznetsova LA, Plesneva SA, Shpakova EA, Vlasov GP, Pertseva MN. Studies of the molecular mechanisms of action of relaxin on the adenylyl cyclase signaling system using synthetic peptides derived from the LGR7 relaxin receptor. ACTA ACUST UNITED AC 2007; 37:705-14. [PMID: 17763990 DOI: 10.1007/s11055-007-0071-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2005] [Revised: 01/10/2006] [Indexed: 10/22/2022]
Abstract
The peptide hormone relaxin produces dose-dependent stimulation of adenylyl cyclase activity in rat tissues (striatum, cardiac and skeletal muscle) and the muscle tissues of invertebrates, i.e., the bivalve mollusk Anodonta cygnea and the earthworm Lumbricus terrestris, adenylyl cyclase stimulation being more marked in the rat striatum and cardiac muscle. Our studies of the type of relaxin receptor involved in mediating these actions of relaxin involved the first synthesis of peptides 619-629, 619-629-Lys(Palm), and 615-629, which are derivatives of the primary structure of the C-terminal part of the third cytoplasmic loop of the type 1 relaxin receptor (LGR7). Peptides 619-629-Lys(Palm) and 615-629 showed competitive inhibition of adenylyl cyclase stimulation by relaxin in rat striatum and cardiac muscle but had no effect on the action of relaxin in rat skeletal muscle or invertebrate muscle, which is evidence for the tissue and species specificity of their actions. On the one hand, this indicates involvement of the LGR7 receptor in mediating the adenylyl cyclase-stimulating action of relaxin in rat striatum and cardiac muscle and, on the other, demonstrates the existence of other adenylyl cyclase signal mechanisms for the actions of relaxin in rat skeletal muscle and invertebrate muscle, not involving LGR7 receptors. The adenylyl cyclase-stimulating effect of relaxin in the striatum and cardiac muscles was found to be decreased in the presence of C-terminal peptide 385-394 of the alpha(s) subunit of the mammalian G protein and to be blocked by treatment of membranes with cholera toxin. These data provide evidence that in the striatum and cardiac muscle, relaxin stimulates adenylyl cyclase via the LGR7 receptor, this being functionally linked with G(s) protein. It is also demonstrated that linkage of relaxin-activated LGR7 receptor with the G(s) protein is mediated by interaction of the C-terminal half of the third cytoplasmic loop of the receptor with the C-terminal segment of the alpha(s) subunit of the G protein.
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Affiliation(s)
- A O Shpakov
- I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, 44 Torez Prospekt, 194223, St. Petersburg, Russia
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22
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Abstract
Rhodopsin is a member of the family of G-protein-coupled receptors (GPCRs), and is an excellent molecular switch for converting light signals into electrical response of the rod photoreceptor cells. Light initiates cis-trans isomerization of the retinal chromophore of rhodopsin and leads to the formation of several thermolabile intermediates during the bleaching process. Recent investigations have identified spectrally distinguishable two intermediate states that can interact with the retinal G-protein, transducin, and have elucidated the functional sharing of these intermediates. The initial contact with GDP-bound G-protein occurs in the meta-Ib intermediate state, which has a protonated Schiff base as its chromophore. The meta-Ib intermediate in the complex with the G-protein converts to the meta-II intermediate with releasing GDP from the alpha-subunit of the G protein. Meta-II has a de-protonated Schiff base chromophore and induces binding of GTP to the alpha-subunit of the G-protein. Thus, the GDP-GTP exchange reaction, namely G-protein activation, by rhodopsin proceeds through at least two steps, with conformational changes in both rhodopsin and the G-protein.
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Affiliation(s)
- Yoshinori Shichida
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, CREST, Japan Science and Technology Agency, Japan.
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23
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Herrmann R, Heck M, Henklein P, Kleuss C, Wray V, Hofmann KP, Ernst OP. Rhodopsin-transducin coupling: role of the Galpha C-terminus in nucleotide exchange catalysis. Vision Res 2006; 46:4582-93. [PMID: 17011013 DOI: 10.1016/j.visres.2006.07.027] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2006] [Revised: 07/26/2006] [Accepted: 07/26/2006] [Indexed: 11/21/2022]
Abstract
In the early steps of visual signal transduction, light-activated rhodopsin (R*) catalyzes GDP/GTP exchange in the heterotrimeric G protein (Galphabetagamma) transducin. We recently reported that the catalytic interaction involves two sequential steps. An initial docking between R* and Gbetagamma leads to conformational changes which make the C-terminus of Galpha (CTalpha) available for binding to R*. Binding of CTalpha by R* then triggers GDP/GTP exchange in the Galpha subunit. To further study this two-step mechanism, we investigated different single amino acid substitutions within CTalpha and discuss the effects of high affinity mutations on nucleotide exchange catalysis.
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Affiliation(s)
- Rolf Herrmann
- Institut für medizinische Physik und Biophysik (CCM), Charité-Universitätsmedizin Berlin, Schumannstr. 20/21, 10098 Berlin, Germany.
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24
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Oldham WM, Van Eps N, Preininger AM, Hubbell WL, Hamm HE. Mechanism of the receptor-catalyzed activation of heterotrimeric G proteins. Nat Struct Mol Biol 2006; 13:772-7. [PMID: 16892066 DOI: 10.1038/nsmb1129] [Citation(s) in RCA: 145] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2006] [Accepted: 07/06/2006] [Indexed: 12/31/2022]
Abstract
Heptahelical receptors activate intracellular signaling pathways by catalyzing GTP for GDP exchange on the heterotrimeric G protein alpha subunit (G alpha). Despite the crucial role of this process in cell signaling, little is known about the mechanism of G protein activation. Here we explore the structural basis for receptor-mediated GDP release using electron paramagnetic resonance spectroscopy. Binding to the activated receptor (R*) causes an apparent rigid-body movement of the alpha5 helix of G alpha that would perturb GDP binding at the beta6-alpha5 loop. This movement was not observed when a flexible loop was inserted between the alpha5 helix and the R*-binding C terminus, which uncouples R* binding from nucleotide exchange, suggesting that this movement is necessary for GDP release. These data provide the first direct observation of R*-mediated conformational changes in G proteins and define the structural basis for GDP release from G alpha.
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Affiliation(s)
- William M Oldham
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6600, USA
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25
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Chen CK. The vertebrate phototransduction cascade: amplification and termination mechanisms. Rev Physiol Biochem Pharmacol 2006; 154:101-21. [PMID: 16634148 DOI: 10.1007/s10254-005-0004-0] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Abstract
The biochemical cascade which transduces light into a neuronal signal in retinal photoreceptors is a heterotrimeric GTP-binding protein (G protein) signaling pathway called phototransduction. Works from psychophysicists, electrophysiologists, biochemists, and geneticists over several decades have come together to shape our understanding of how photon absorption leads to photoreceptor membrane hyperpolarization. The insights of phototransduction provide the foundation for a mechanistic account of signaling from many other G protein-coupled receptors (GPCR) found throughout nature. The application of reverse genetic techniques has strengthened many historic findings and helped to describe this pathway at greater molecular details. However, many important questions remain to be answered.
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Affiliation(s)
- C K Chen
- Virginia Commonwealth University, Department of Biochemistry, 1101 E. Marshall Street, Rm 2-032, Richmond, 23298-0614 VA, USA.
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26
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Shpakov AO, Pertseva MN. Use of Peptide Strategy for Study of Molecular Mechanisms of Hormonal Signal Transduction into Cell. J EVOL BIOCHEM PHYS+ 2005. [DOI: 10.1007/s10893-005-0088-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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27
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Shpakov AO, Korol'kov VI, Plesneva SA, Kuznetsova LA, Pertseva MN. Effects of the C-terminal peptide of the alphaS subunit of the G protein on the regulation of adenylyl cyclase and protein kinase A activities by biogenic amines and glucagon in mollusk and rat muscles. ACTA ACUST UNITED AC 2005; 35:177-86. [PMID: 15779331 DOI: 10.1007/s11055-005-0066-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The C-terminal parts of the a subunits of heteromeric G proteins play an important role in the functional linkage of G proteins with receptors of the serpentine type. The present report describes studies of the effects of the C-terminal octapeptide 387-394 of the alphaS subunit of the mammalian G protein on the transmission of the hormonal signal via the hormone-sensitive adenylyl cyclase signal system, whose major components are receptors of the serpentine type, G proteins, and the enzymes adenylyl cyclase and protein kinase A. The peptide synthesized here, 387-394 amide (10(-7) - 10(-4) M), dose-dependently decreased adenylyl cyclase and protein kinase A activities stimulated by serotonin and glucagon in smooth muscle from the freshwater bivalve mollusk Anodonta cygnea and by the beta agonist isoproterenol in rat skeletal muscle. At a concentration as low as 10(-7) M, the peptide released potentiation of the stimulatory effects of hormones on adenylyl cyclase activity due to the non-hydrolyzable guanine nucleotide analog Gpp[NH]p. At the same time, it had almost no effect on the stimulation of adenylyl cyclase activity by non-hormonal agents (NaF, Gpp[NH]p, and forskolin). The inhibitory effects of hormones on adenylyl cyclase and protein kinase A activities persisted in the presence of the peptide. Our data demonstrate the importance of the C-terminal part of the alphaS subunit of the stimulatory G protein for its functional linkage with receptors of the serpentine type and throw light on the molecular mechanisms of the interactions between G proteins and receptors.
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Affiliation(s)
- A O Shpakov
- I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, 44 M. Torez Prospekt, 194223 St. Petersburg, Russia
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28
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Abstract
A large body of experimental evidence exists that links heterotrimeric guanosine triphosphate-binding protein (G protein) structure to function. The determination of the crystal structures of G proteins in various activational states and, more recently, in complexes with effectors and other signaling partners highlights the varied mechanisms involved in G protein regulation. Signaling complexes, such as the recently solved complex of Gbetagamma and G protein receptor kinase 2 (GRK2), provide new insights into the mechanisms underlying the regulation of these highly conserved signaling molecules. In this Review, we discuss the latest findings and their implications for G protein-signaling paradigms.
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Affiliation(s)
- Anita M Preininger
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN 37232-6600, USA
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29
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Slessareva JE, Ma H, Depree KM, Flood LA, Bae H, Cabrera-Vera TM, Hamm HE, Graber SG. Closely related G-protein-coupled receptors use multiple and distinct domains on G-protein alpha-subunits for selective coupling. J Biol Chem 2003; 278:50530-6. [PMID: 14525988 DOI: 10.1074/jbc.m304417200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The molecular basis of selectivity in G-protein receptor coupling has been explored by comparing the abilities of G-protein heterotrimers containing chimeric Galpha subunits, comprised of various regions of Gi1alpha, Gtalpha, and Gqalpha, to stabilize the high affinity agonist binding state of serotonin, adenosine, and muscarinic receptors. The data indicate that multiple and distinct determinants of selectivity exist for individual receptors. While the A1 adenosine receptor does not distinguish between Gi1alpha and Gtalpha sequences, the 5-HT1A and 5-HT1B serotonin and M2 muscarinic receptors can couple with Gi1 but not Gt. It is possible to distinguish domains that eliminate coupling and are defined as "critical," from those that impair coupling and are defined as "important." Domains within the N terminus, alpha4-helix, and alpha4-helix-alpha4/beta6-loop of Gi1alpha are involved in 5-HT and M2 receptor interactions. Chimeric Gi1alpha/Gqalpha subunits verify the critical role of the Galpha C terminus in receptor coupling, however, the individual receptors differ in the C-terminal amino acids required for coupling. Furthermore, the EC50 for interactions with Gi1 differ among the individual receptors. These results suggest that coupling selectivity ultimately involves subtle and cooperative interactions among various domains on both the G-protein and the associated receptor as well as the G-protein concentration.
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Affiliation(s)
- Janna E Slessareva
- Department of Biochemistry and Molecular Pharmacology, West Virginia University School of Medicine, Morgantown, West Virginia 26506, USA
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30
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Terakita A, Yamashita T, Nimbari N, Kojima D, Shichida Y. Functional interaction between bovine rhodopsin and G protein transducin. J Biol Chem 2002; 277:40-6. [PMID: 11606568 DOI: 10.1074/jbc.m104960200] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To elucidate the mechanisms of specific coupling of bovine rhodopsin with the G protein transducin (G(t)), we have constructed the bovine rhodopsin mutants whose second or third cytoplasmic loop (loop 2 or 3) was replaced with the corresponding loop of the G(o)-coupled scallop rhodopsin and investigated the difference in the activation abilities for G(t), G(o), and G(i) among these mutants and wild type. We have also prepared the Galpha(i) mutants whose C-terminal 11 or 5 amino acids were replaced with those of Galpha(t), Galpha(o), and Galpha(q) to evaluate the role of the C-terminal tail of the alpha-subunit on the specific coupling of bovine rhodopsin with G(t). Replacement of loop 2 of bovine rhodopsin with that of the scallop rhodopsin caused about a 40% loss of G(t) and G(o) activation, whereas that of loop 3 enhanced the G(o) activation four times with a 60% decrease in the G(t) activation. These results indicated that loop 3 of bovine rhodopsin is one of the regions responsible for the specific coupling with G(t). Loop 3 of bovine rhodopsin discriminates the difference of the 6-amino acid sequence (region A) at a position adjacent to the C-terminal 5 amino acids of the G protein, resulting in the different activation efficiency between G(t) and G(o). In addition, the binding of region A to loop 3 of bovine rhodopsin is essential for activation of G(t) but not G(i), even though the sequence of the region A is almost identical between Galpha(t) and Galpha(i). These results suggest that the binding of loop 3 of bovine rhodopsin to region A in Galpha(t) is one of the mechanisms of specific G(t) activation by bovine rhodopsin.
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Affiliation(s)
- Akihisa Terakita
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
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31
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Thomas TO, Bae H, Medkova M, Hamm HE. An intramolecular contact in Galpha transducin that participates in maintaining its intrinsic GDP release rate. MOLECULAR CELL BIOLOGY RESEARCH COMMUNICATIONS : MCBRC 2001; 4:282-91. [PMID: 11529678 DOI: 10.1006/mcbr.2001.0293] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Receptor mediated stimulation of the G protein-alpha subunit leads to exchange of GDP for GTP, activating the protein. Spontaneous GDP release from Galpha can also lead to the active state, if GTP in solution binds the nucleotide binding pocket. The purpose of this study is to evaluate the molecular determinants for maintaining the spontaneous GDP release rates between two Galpha subunits. Galpha(t) has a low rate of nucleotide release, compared to Galpha(i1). Galpha(t/i1) chimeras were used to explore the molecular basis for this behavior. The C-terminal alpha4-helix, the N-terminal 56 residues and the Switch I/II regions of Galpha(t) were shown to affect the low spontaneous GDP release rate in Galpha(t). A specific molecular contact between Asp26 and Asn191 was found in Galpha(t) that is not present in Galpha(i1). In two chimeras disrupting this interaction produced an increased spontaneous GDP release; restoring the contact present in Galpha(t) into these chimeras decreased the GDP release rate by half as compared to the original chimeras. Similarly, introduction of this contact in wild-type Galpha(i1) decreased the GDP release rate of Galpha(i1) by half. Differences in GDP release rates may reflect physiological roles these proteins play in living systems.
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Affiliation(s)
- T O Thomas
- Institute for Neuroscience, Northwestern University, Chicago, Illinois, USA
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32
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Cai K, Itoh Y, Khorana HG. Mapping of contact sites in complex formation between transducin and light-activated rhodopsin by covalent crosslinking: use of a photoactivatable reagent. Proc Natl Acad Sci U S A 2001; 98:4877-82. [PMID: 11320237 PMCID: PMC33131 DOI: 10.1073/pnas.051632898] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Interaction of light-activated rhodopsin with transducin (T) is the first event in visual signal transduction. We use covalent crosslinking approaches to map the contact sites in interaction between the two proteins. Here we use a photoactivatable reagent, N-[(2-pyridyldithio)-ethyl], 4-azido salicylamide. The reagent is attached to the SH group of cytoplasmic monocysteine rhodopsin mutants by a disulfide-exchange reaction with the pyridylthio group, and the derivatized rhodopsin then is complexed with T by illumination at lambda >495 nm. Subsequent irradiation of the complex at lambda310 nm generates covalent crosslinks between the two proteins. Crosslinking was demonstrated between T and a number of single cysteine rhodopsin mutants. However, sites of crosslinks were investigated in detail only between T and the rhodopsin mutant S240C (cytoplasmic loop V-VI). Crosslinking occurred predominantly with T(alpha). For identification of the sites of crosslinks in T(alpha), the strategy used involved: (i) derivatization of all of the free cysteines in the crosslinked proteins with N-ethylmaleimide; (ii) reduction of the disulfide bond linking the two proteins and isolation of all of the T(alpha) species carrying the crosslinked moiety with a free SH group; (iii) adduct formation of the latter with the N-maleimide moiety of the reagent, maleimido-butyryl-biocytin, containing a biotinyl group; (iv) trypsin degradation of the resulting T(alpha) derivatives and isolation of T(alpha) peptides carrying maleimido-butyryl-biocytin by avidin-agarose chromatography; and (v) identification of the isolated peptides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. We found that crosslinking occurred mainly to two C-terminal peptides in T(alpha) containing the amino acid sequences 310-313 and 342-345.
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Affiliation(s)
- K Cai
- Departments of Biology and Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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33
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Aris L, Gilchrist A, Rens-Domiano S, Meyer C, Schatz PJ, Dratz EA, Hamm HE. Structural requirements for the stabilization of metarhodopsin II by the C terminus of the alpha subunit of transducin. J Biol Chem 2001; 276:2333-9. [PMID: 11018024 DOI: 10.1074/jbc.m002533200] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The retinal receptor rhodopsin undergoes a conformational change upon light excitation to form metarhodopsin II (Meta II), which allows interaction and activation of its cognate G protein, transducin (G(t)). A C-terminal 11-amino acid peptide from transducin, G(talpha)-(340-350), has been shown to both bind and stabilize the Meta II conformation, mimicking heterotrimeric G(t). Using a combinatorial library we identified analogs of G(talpha)-(340-350) that bound light-activated rhodopsin with high affinity (Martin, E. L., Rens-Domiano, S., Schatz, P. J., and Hamm, H. E. (1996) J. Biol. Chem. 271, 361-366). We have made peptides with key substitutions either on the background of the native G(talpha)-(340-350) sequence or on the high affinity sequences and used the stabilization of Meta II as a tool to determine which amino acids are critical in G protein-rhodopsin interaction. Removal of the positive charge at the N termini by acylation or delocalization of the charge by K to R substitution enhances the affinity of the G(talpha)-(340-350) peptides for Meta II, whereas a decrease was observed following C-terminal amidation. Cys-347, a residue conserved in pertussis toxin-sensitive G proteins, was shown to interact with a hydrophobic site in Meta II. These studies provide further insight into the mechanism of interaction between the G(talpha) C terminus and light-activated rhodopsin.
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Affiliation(s)
- L Aris
- Institute for Neuroscience, Northwestern University, Chicago, Illinois 60611, USA
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