title: Effect of Mg(2+) on the kinetics of guanine nucleotide binding and hydrolysis by Cdc42.
abstract: The biological activities of Rho family GTPases are controlled by their guanine nucleotide binding states in cell. Mg(2+) ions play key roles in guanine nucleotide binding and in preserving the structural integrity of GTPases. We describe here the kinetics of the interaction of GTP with the Rho family small GTPase Cdc42 in the absence and presence of Mg(2+). In contrast to the cases of Ras and Rab proteins, which require Mg(2+) for the nucleotide binding and intrinsic hydrolysis of GTP, our results show that in the absence of Mg(2+), the binding affinity of GTP to Cdc42 is in the submicromolar concentration, and the Mg(2+) cofactor has only a minor effect on the Cdc42-catalyzed intrinsic hydrolysis rate of GTP. These results suggest that the intrinsic GTPase reaction mechanism of Cdc42 may differ significantly from that of other subfamily members of the Ras superfamily.
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Academia Sinica, Beijing 100101, PR China.
authors.forename: Ju
authors.initials: J
authors.lastname: Zhao
authors.forename: Wei-Ning
authors.initials: WN
authors.lastname: Wang
authors.forename: Ying-Cai
authors.initials: YC
authors.lastname: Tan
authors.forename: Yi
authors.initials: Y
authors.lastname: Zheng
authors.forename: Zhi-Xin
authors.initials: ZX
authors.lastname: Wang
mesh_terms: D002413:Cations, Divalent / Q000494:pharmacology; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D013053:Spectrophotometry; D020764:cdc42 GTP-Binding Protein / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002413:Cations, Divalent; D011994:Recombinant Proteins; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases; D020764:cdc42 GTP-Binding Protein; D008274:Magnesium