Mechanism of the receptor-catalyzed activation of heterotrimeric G proteins.
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.
Oldham
William M
WM
Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6600, USA.
Van Eps
Ned
N
Preininger
Anita M
AM
Hubbell
Wayne L
WL
Hamm
Heidi E
HE
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
D050505:Mutant Proteins; D043562:Receptors, G-Protein-Coupled; D013113:Spin Labels; D006153:Guanosine Diphosphate; D020962:Heterotrimeric GTP-Binding Proteins