title: Mechanism of the receptor-catalyzed activation of heterotrimeric G proteins.
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.
authors.affiliation: Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6600, USA.
authors.forename: William M
authors.initials: WM
authors.lastname: Oldham
authors.forename: Ned
authors.initials: N
authors.lastname: Van Eps
authors.forename: Anita M
authors.initials: AM
authors.lastname: Preininger
authors.forename: Wayne L
authors.initials: WL
authors.lastname: Hubbell
authors.forename: Heidi E
authors.initials: HE
authors.lastname: Hamm
mesh_terms: D000818:Animals; D002384:Catalysis; D002417:Cattle; D004578:Electron Spin Resonance Spectroscopy; D006153:Guanosine Diphosphate / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D050505:Mutant Proteins / Q000378:metabolism; D017433:Protein Structure, Secondary; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D013113:Spin Labels
chemical_list: D050505:Mutant Proteins; D043562:Receptors, G-Protein-Coupled; D013113:Spin Labels; D006153:Guanosine Diphosphate; D020962:Heterotrimeric GTP-Binding Proteins