Inhibition of NADPH oxidase activation by synthetic peptides mapping within the carboxyl-terminal domain of small GTP-binding proteins: Lack of amino acid sequence specificity and importance of polybasic motif

The small GTP-binding protein (G protein) Rac1 is an obligatory participant in the assembly of the superoxide (O₂^̇-)-generating NADPH oxidase complex of macrophages. We investigated the effect of synthetic peptides, mapping within the near carboxyl-terminal domains of Rac1 and of related G proteins, on the activity of NADPH oxidase in a cell-free system consisting of solubilized guinea pig macrophage membrane, a cytosolic fraction enriched in p47^phox and p67^phox (or total cytosol), highly purified Rac1-GDP dissociation inhibitor for Rho (Rho GDI) complex, and the activating amphiphile, lithium dodecyl sulfate. Peptides Rac1-(178-188) and Rac1-(178-191), but not Rac2-(178-188), inhibited NADPH oxidase activity in a Rac1-dependent system when added prior to or simultaneously with the initiation of activation. However, undecapeptides corresponding to the near carboxyl-terminal domains of RhoA and RhoC and, most notably, a peptide containing the same amino acids as Rac1-(178-188), but in reversed orientation, were also inhibitory. Surprisingly, O₂^̇- production in a Rac2-dependent cell-free system was inhibited by Rac1-(178-188) but not by Rac2-(178-188). Finally, basic polyamino acids containing lysine, histidine, or arginine, also inhibited NADPH oxidase activation. We conclude that inhibition of NADPH oxidase activation by synthetic peptides mapping within the carboxyl-terminal domain of certain small G proteins is not amino acid sequencespecific but related to the presence of a polybasic motif. It has been proposed that such a motif serves as a plasma membrane targeting signal for a number of small G proteins (Hancock, J.F., Paterson, H., and Marshall, C.J. (1990) Cell 63, 133-139).