Regulation of binding of rhoB p20 to membranes by its specific regulatory protein, GDP dissociation inhibitor.

We have previously purified from bovine brain cytosol a novel regulatory protein for the GTP-binding proteins of the rho gene family. This regulatory protein, designated as rho GDP dissociation inhibitor (GDI), makes a complex stoichiometrically with the GDP-bound form of the rho gene products and thereby regulates the GDP/GTP exchange reaction by inhibiting the dissociation of GDP from and the subsequent binding of GTP to them. We show here that rho GDI also regulates the binding of rhoB p20, a member of the rho gene products, to various membranes including rat brain synaptic plasma membranes and human erythrocyte ghosts. Both the GDP- and GTP-bound forms of rhoB p20 bound to the membranes. This binding was not inhibited by prior treatment of the membranes with boiling or tryptic digestion, suggesting that a protein molecule of the membranes is not essential for the binding of rhoB p20 to the membranes. rho GDI inhibited the binding of the GDP-bound form of rhoB p20, but not that of the GTP-bound form, to the membranes. Moreover, rho GDI induced the dissociation of the GDP-bound form, but not that of the GTP-bound form, of rhoB p20 exogenously bound to the membranes from them. These results suggest that the rho gene products bind to the membranes, presumably in a reversible manner and that this binding is regulated by their specific GDI.