title: Structure of Gialpha1.GppNHp, autoinhibition in a galpha protein-substrate complex.
abstract: The structure of the G protein Gialpha1 complexed with the nonhydrolyzable GTP analog guanosine-5'-(betagamma-imino)triphosphate (GppNHp) has been determined at a resolution of 1.5 A. In the active site of Gialpha1. GppNHp, a water molecule is hydrogen bonded to the side chain of Glu43 and to an oxygen atom of the gamma-phosphate group. The side chain of the essential catalytic residue Gln204 assumes a conformation which is distinctly different from that observed in complexes with either guanosine 5'-O-3-thiotriphosphate or the transition state analog GDP.AlF4-. Hydrogen bonding and steric interactions position Gln204 such that it interacts with a presumptive nucleophilic water molecule, but cannot interact with the pentacoordinate transition state. Gln204 must be released from this auto-inhibited state to participate in catalysis. RGS proteins may accelerate the rate of GTP hydrolysis by G protein alpha subunits, in part, by inserting an amino acid side chain into the site occupied by Gln204, thereby destabilizing the auto-inhibited state of Galpha.
authors.affiliation: Department of Biochemistry, The University of Texas Southwestern Medical Center, Dallas, Texas 75235-9050, USA.
authors.forename: D E
authors.initials: DE
authors.lastname: Coleman
authors.forename: S R
authors.initials: SR
authors.lastname: Sprang
mesh_terms: D000818:Animals; D020134:Catalytic Domain; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D020558:GTP Phosphohydrolases / Q000737:chemistry*; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics; D005973:Glutamine / Q000737:chemistry; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000737:chemistry; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives*; D006165:Guanylyl Imidodiphosphate / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry
chemical_list: D011994:Recombinant Proteins; D005973:Glutamine; D006165:Guanylyl Imidodiphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins