Mechanism of GTP Hydrolysis by G-Protein α Subunits

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 91; no. 21; pp. 9828 - 9831
• Main Authors: Kleuss, Christiane, Raw, André S., Lee, Ethan, Sprang, Stephen R., Gilman, Alfred G.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 11.10.1994; National Acad Sciences
• Subjects: Aluminum Compounds - metabolism; Amino Acid Sequence; Base Sequence; Biochemical mechanisms; Biochemistry; Carboxylates; Catalysis; Conserved Sequence; Crystal structure; DNA - chemistry; Equilibrium flow; Escherichia coli; Fluorides - metabolism; Gross domestic product; GTP Phosphohydrolases - metabolism; GTP-Binding Proteins - isolation & purification; GTP-Binding Proteins - metabolism; Guanosine 5'-O-(3-Thiotriphosphate) - metabolism; Guanosine Triphosphate - metabolism; Humans; Hydrolysis; Kinetics; Macromolecular Substances; Magnesium - metabolism; Molecular Sequence Data; Molecules; Mutagenesis, Site-Directed; Oligodeoxyribonucleotides; Phosphorus Radioisotopes; Plasmids; Proto-Oncogene Proteins p21(ras) - metabolism; Recombinant Proteins - isolation & purification; Recombinant Proteins - metabolism; Signal Transduction; Time Factors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.91.21.9828

Hydrolysis of GTP by a variety of guanine nucleotide-binding proteins is a crucial step for regulation of these biological switches. Mutations that impair the GTPase activity of certain heterotrimeric signal-transducing G proteins or of p21rascause tumors in man. A conserved glutamic residue in the α subunit of G proteins has been hypothesized to serve as a general base, thereby activating a water molecule for nucleophilic attack on GTP. The results of mutagenesis of this residue (Glu-207) in G$_{i\alpha1}$refute this hypothesis. Based on the structure of the complex of Giα 1with GDP, Mg2+, and AlF- 4, which appears to resemble the transition state for GTP hydrolysis, we believe that Gln-204 of G$_{i\alpha1}$, rather than Glu-207, supports catalysis of GTP hydrolysis by stabilization of the transition state.