title: Ligand-specific regulation of the extracellular surface of a G-protein-coupled receptor.
abstract: G-protein-coupled receptors (GPCRs) are seven-transmembrane proteins that mediate most cellular responses to hormones and neurotransmitters. They are the largest group of therapeutic targets for a broad spectrum of diseases. Recent crystal structures of GPCRs have revealed structural conservation extending from the orthosteric ligand-binding site in the transmembrane core to the cytoplasmic G-protein-coupling domains. In contrast, the extracellular surface (ECS) of GPCRs is remarkably diverse and is therefore an ideal target for the discovery of subtype-selective drugs. However, little is known about the functional role of the ECS in receptor activation, or about conformational coupling of this surface to the native ligand-binding pocket. Here we use NMR spectroscopy to investigate ligand-specific conformational changes around a central structural feature in the ECS of the beta(2) adrenergic receptor: a salt bridge linking extracellular loops 2 and 3. Small-molecule drugs that bind within the transmembrane core and exhibit different efficacies towards G-protein activation (agonist, neutral antagonist and inverse agonist) also stabilize distinct conformations of the ECS. We thereby demonstrate conformational coupling between the ECS and the orthosteric binding site, showing that drugs targeting this diverse surface could function as allosteric modulators with high subtype selectivity. Moreover, these studies provide a new insight into the dynamic behaviour of GPCRs not addressable by static, inactive-state crystal structures.
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Bokoch
authors.forename: Yaozhong
authors.initials: Y
authors.lastname: Zou
authors.forename: Søren G F
authors.initials: SG
authors.lastname: Rasmussen
authors.forename: Corey W
authors.initials: CW
authors.lastname: Liu
authors.forename: Rie
authors.initials: R
authors.lastname: Nygaard
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Rosenbaum
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Fung
authors.forename: Hee-Jung
authors.initials: HJ
authors.lastname: Choi
authors.forename: Foon Sun
authors.initials: FS
authors.lastname: Thian
authors.forename: Tong Sun
authors.initials: TS
authors.lastname: Kobilka
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Puglisi
authors.forename: William I
authors.initials: WI
authors.lastname: Weis
authors.forename: Leonardo
authors.initials: L
authors.lastname: Pardo
authors.forename: R Scott
authors.initials: RS
authors.lastname: Prosser
authors.forename: Luciano
authors.initials: L
authors.lastname: Mueller
authors.forename: Brian K
authors.initials: BK
authors.lastname: Kobilka
mesh_terms: D058666:Adrenergic beta-2 Receptor Agonists; D058672:Adrenergic beta-2 Receptor Antagonists; D000494:Allosteric Regulation / Q000187:drug effects; D001665:Binding Sites; D018360:Crystallography, X-Ray; D054314:Drug Inverse Agonism; D004983:Ethanolamines / Q000494:pharmacology; D000068759:Formoterol Fumarate; D006801:Humans; D008024:Ligands; D008239:Lysine / Q000031:analogs & derivatives / Q000378:metabolism; D008745:Methylation; D008958:Models, Molecular; D050505:Mutant Proteins; D019906:Nuclear Magnetic Resonance, Biomolecular; D011412:Propanolamines / Q000378:metabolism / Q000494:pharmacology; D017434:Protein Structure, Tertiary / Q000187:drug effects; D018343:Receptors, Adrenergic, beta-2 / Q000737:chemistry* / Q000378:metabolism*; D055672:Static Electricity; D013379:Substrate Specificity
chemical_list: D058666:Adrenergic beta-2 Receptor Agonists; D058672:Adrenergic beta-2 Receptor Antagonists; D004983:Ethanolamines; D008024:Ligands; D050505:Mutant Proteins; D011412:Propanolamines; D018343:Receptors, Adrenergic, beta-2; C018926:epsilon N-dimethyllysine; C014382:carazolol; D008239:Lysine; D000068759:Formoterol Fumarate