title: Conformational changes in the G protein Gs induced by the β2 adrenergic receptor.
abstract: G protein-coupled receptors represent the largest family of membrane receptors that instigate signalling through nucleotide exchange on heterotrimeric G proteins. Nucleotide exchange, or more precisely, GDP dissociation from the G protein α-subunit, is the key step towards G protein activation and initiation of downstream signalling cascades. Despite a wealth of biochemical and biophysical studies on inactive and active conformations of several heterotrimeric G proteins, the molecular underpinnings of G protein activation remain elusive. To characterize this mechanism, we applied peptide amide hydrogen-deuterium exchange mass spectrometry to probe changes in the structure of the heterotrimeric bovine G protein, Gs (the stimulatory G protein for adenylyl cyclase) on formation of a complex with agonist-bound human β(2) adrenergic receptor (β(2)AR). Here we report structural links between the receptor-binding surface and the nucleotide-binding pocket of Gs that undergo higher levels of hydrogen-deuterium exchange than would be predicted from the crystal structure of the β(2)AR-Gs complex. Together with X-ray crystallographic and electron microscopic data of the β(2)AR-Gs complex (from refs 2, 3), we provide a rationale for a mechanism of nucleotide exchange, whereby the receptor perturbs the structure of the amino-terminal region of the α-subunit of Gs and consequently alters the 'P-loop' that binds the β-phosphate in GDP. As with the Ras family of small-molecular-weight G proteins, P-loop stabilization and β-phosphate coordination are key determinants of GDP (and GTP) binding affinity.
authors.affiliation: Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305, USA.
authors.forename: Ka Young
authors.initials: KY
authors.lastname: Chung
authors.forename: Søren G F
authors.initials: SG
authors.lastname: Rasmussen
authors.forename: Tong
authors.initials: T
authors.lastname: Liu
authors.forename: Sheng
authors.initials: S
authors.lastname: Li
authors.forename: Brian T
authors.initials: BT
authors.lastname: DeVree
authors.forename: Pil Seok
authors.initials: PS
authors.lastname: Chae
authors.forename: Diane
authors.initials: D
authors.lastname: Calinski
authors.forename: Brian K
authors.initials: BK
authors.lastname: Kobilka
authors.forename: Virgil L
authors.initials: VL
authors.lastname: Woods
authors.forename: Roger K
authors.initials: RK
authors.lastname: Sunahara
mesh_terms: D058666:Adrenergic beta-2 Receptor Agonists / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D055162:Biocatalysis; D020134:Catalytic Domain; D002417:Cattle; D018360:Crystallography, X-Ray; D041961:Deuterium Exchange Measurement; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D018343:Receptors, Adrenergic, beta-2 / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D058666:Adrenergic beta-2 Receptor Agonists; D018343:Receptors, Adrenergic, beta-2; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D019205:GTP-Binding Protein alpha Subunits, Gs