title: GDP dissociation inhibitor prevents intrinsic and GTPase activating protein-stimulated GTP hydrolysis by the Rac GTP-binding protein.
abstract: The majority of the GTP-binding proteins of the Ras superfamily hydrolyze GTP to GDP very slowly. A notable exception to this are the Rac proteins, which have intrinsic GTPase rates at least 50-fold those of Ras or Rho. A protein (or proteins) capable of inhibiting this GTPase activity exists in human neutrophil cytosol. Since Rac appears to exist normally in neutrophils as a cytosolic protein complexed to (Rho)GDI, we examined the ability of (Rho)GDI to inhibit GTP hydrolysis by Rac. (Rho)GDI produced a concentration-dependent inhibition of GTP hydrolysis by Rac1 that paralleled its ability to inhibit GDP dissociation from the Rac protein. Maximal inhibition occurred at or near equimolar concentrations of the GDI and the Rac substrate. The ability of two molecules exhibiting GTPase activating protein (GAP) activity toward Rac to stimulate GTP hydrolysis was also inhibited by the presence of (Rho)GDI. The inhibitory effect of the GDI could be overcome by increasing the GAP concentration to levels equal to that of the GDI. (Rho)GDI weakly, but consistently, inhibited GTP gamma S (guanosine 5'-3-O-(thio)triphosphate) dissociation from Rac1, confirming an interaction of (Rho)GDI with the GTP-bound form of the protein. These data describe an additional activity of (Rho)GDI and suggest a mechanism by which Rac might be maintained in an active form in vivo in the presence of regulatory GAPs.
authors.affiliation: Department of Immunology, Scripps Research Institute, La Jolla, California 92037.
authors.forename: T H
authors.initials: TH
authors.lastname: Chuang
authors.forename: X
authors.initials: X
authors.lastname: Xu
authors.forename: U G
authors.initials: UG
authors.lastname: Knaus
authors.forename: M J
authors.initials: MJ
authors.lastname: Hart
authors.forename: G M
authors.initials: GM
authors.lastname: Bokoch
mesh_terms: D000818:Animals; D002460:Cell Line; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D019204:GTP-Binding Proteins / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D020730:Guanine Nucleotide Dissociation Inhibitors; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism*; D007313:Insecta; D007700:Kinetics; D011485:Protein Binding; D011506:Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection; D020744:rac GTP-Binding Proteins; D020703:ras GTPase-Activating Proteins; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors
chemical_list: D020690:GTPase-Activating Proteins; D020730:Guanine Nucleotide Dissociation Inhibitors; D011506:Proteins; D011994:Recombinant Proteins; D020703:ras GTPase-Activating Proteins; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins; D020744:rac GTP-Binding Proteins