title: Consequences of weak interaction of rho GDI with the GTP-bound forms of rho p21 and rac p21.
abstract: rho GDI is an inhibitory GDP/GTP exchange protein for the rho family. Recently, rho GDI has been reported to interact with the GTP-bound form of G25K and rac1 p21 and to inhibit their basal and GTPase-activating protein (GAP)-stimulated GTPase activity. Here, we examined whether rho GDI interacts with the GTP-bound form of rho p21 and rac p21 and inhibits their basal and rho GAP-stimulated GTPase activity, rho GDI interacted with both the GDP- and GTP-bound forms of rhoA p21 and rac1 p21 as estimated by measuring its ability to form a complex with both forms and to inhibit the membrane-binding activity of both forms. The efficiency of rho GDI for interaction with the GTP-bound form was, however, about 10% that for interaction with the GDP-bound form. Moreover, rho GDI inhibited both the basal and rho GAP-stimulated GTPase activity of rhoA p21 and rac1 p21 in a dose-dependent manner. The doses of rho GDI necessary for this action were, however, about 10-fold higher than those necessary for the action to inhibit their GDP/GTP exchange reaction. These results indicate that rho GDI interacts with the GTP-bound form of its substrate small G proteins, as well as with the GDP-bound form, but much less efficiently than with the GDP-bound form.
authors.affiliation: Department of Biochemistry, Kobe University School of Medicine, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Sasaki
authors.forename: M
authors.initials: M
authors.lastname: Kato
authors.forename: Y
authors.initials: Y
authors.lastname: Takai
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation; D004910:Erythrocyte Membrane / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020730:Guanine Nucleotide Dissociation Inhibitors; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism*; D009036:Moths; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D020744:rac GTP-Binding Proteins; D020741:rho GTP-Binding Proteins; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors
chemical_list: D020730:Guanine Nucleotide Dissociation Inhibitors; D011994:Recombinant Proteins; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; D006153:Guanosine Diphosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020744:rac GTP-Binding Proteins; D020741:rho GTP-Binding Proteins