Allosteric coupling from G protein to the agonist-binding pocket in GPCRs.

TitleAllosteric coupling from G protein to the agonist-binding pocket in GPCRs.
Publication TypeJournal Article
Year of Publication2016
AuthorsDevree, B. T., J. P. Mahoney, G. A. Vélez-Ruiz, S. G. F. Rasmussen, A. J. Kuszak, E. Edwald, J-J. Fung, A. Manglik, M. Masureel, Y. Du, R. A. Matt, E. Pardon, J. Steyaert, B. K. Kobilka, and R. K. Sunahara
Date Published2016 Jul 07
KeywordsAdrenergic beta-2 Receptor Agonists, Adrenergic beta-2 Receptor Antagonists, Allosteric Regulation, Allosteric Site, GTP-Binding Protein alpha Subunits, Gs, Guanine, Humans, Kinetics, Ligands, Models, Molecular, Protein Binding, Protein Conformation, Receptors, Adrenergic, beta-2, Single-Chain Antibodies

G-protein-coupled receptors (GPCRs) remain the primary conduit by which cells detect environmental stimuli and communicate with each other. Upon activation by extracellular agonists, these seven-transmembrane-domain-containing receptors interact with heterotrimeric G proteins to regulate downstream second messenger and/or protein kinase cascades. Crystallographic evidence from a prototypic GPCR, the β2-adrenergic receptor (β2AR), in complex with its cognate G protein, Gs, has provided a model for how agonist binding promotes conformational changes that propagate through the GPCR and into the nucleotide-binding pocket of the G protein α-subunit to catalyse GDP release, the key step required for GTP binding and activation of G proteins. The structure also offers hints about how G-protein binding may, in turn, allosterically influence ligand binding. Here we provide functional evidence that G-protein coupling to the β2AR stabilizes a ‘closed’ receptor conformation characterized by restricted access to and egress from the hormone-binding site. Surprisingly, the effects of G protein on the hormone-binding site can be observed in the absence of a bound agonist, where G-protein coupling driven by basal receptor activity impedes the association of agonists, partial agonists, antagonists and inverse agonists. The ability of bound ligands to dissociate from the receptor is also hindered, providing a structural explanation for the G-protein-mediated enhancement of agonist affinity, which has been observed for many GPCR–G-protein pairs. Our data also indicate that, in contrast to agonist binding alone, coupling of a G protein in the absence of an agonist stabilizes large structural changes in a GPCR. The effects of nucleotide-free G protein on ligand-binding kinetics are shared by other members of the superfamily of GPCRs, suggesting that a common mechanism may underlie G-protein-mediated enhancement of agonist affinity.

Alternate JournalNature
PubMed ID27362234
Grant ListP60DK-20572 / DK / NIDDK NIH HHS / United States
R01-GM068603 / GM / NIGMS NIH HHS / United States
R01-GM083118 / GM / NIGMS NIH HHS / United States
R01-NS28471 / NS / NINDS NIH HHS / United States
T32GM007315 / GM / NIGMS NIH HHS / United States
T32GM007767 / GM / NIGMS NIH HHS / United States
T32GM008270 / GM / NIGMS NIH HHS / United States
U19-GM106990 / GM / NIGMS NIH HHS / United States
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