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  • Title: Mechanism of GTP hydrolysis by G-protein alpha subunits.
    Author: Kleuss C, Raw AS, Lee E, Sprang SR, Gilman AG.
    Journal: Proc Natl Acad Sci U S A; 1994 Oct 11; 91(21):9828-31. PubMed ID: 7937899.
    Abstract:
    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 p21ras cause tumors in man. A conserved glutamic residue in the alpha 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 Gi alpha 1 refute this hypothesis. Based on the structure of the complex of Gi alpha 1 with GDP, Mg2+, and AlF-4, which appears to resemble the transition state for GTP hydrolysis, we believe that Gln-204 of Gi alpha 1, rather than Glu-207, supports catalysis of GTP hydrolysis by stabilization of the transition state.
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