S-PRENYLATED CYSTEINE ANALOGS INHIBIT RECEPTOR-MEDIATED G-PROTEIN ACTIVATION IN NATIVE HUMAN GRANULOCYTE AND RECONSTITUTED BOVINE RETINAL ROD OUTER SEGMENT MEMBRANES

We have previously shown that the S-prenylated cysteine analogue N-acetyl-S-trans,trans-farnesyl-L-cysteine (L-AFC) inhibits basal and formyl peptide receptor-stimulated binding of guanosine 5'-O-(3-thiotriphosphate) (GTP[SI) to and hydrolysis of GTP by membranes of HL-60 granulocytes and have presented evidence suggesting that this inhibition was not caused by reduced protein carboxyl methylation [Scheer, A., and Gierschik, P. (1993) FEBS Lett. 319, 110-114]. We now report a detailed analysis of the structural properties of S-prenylated cysteine analogues required for this inhibition and demonstrate that S-prenylcysteines also suppress basal and receptor-stimulated GTP[S] binding to human peripheral neutrophil and HL-60 granulocyte membranes when stimulated by formyl peptide and complement C5a, respectively. S-Prenylcysteines did not affect pertussis toxin-mediated [P-32]ADP-ribosylation of G(i) proteins. The inhibitory effect of L-AFC was reversible and was not mimicked by farnesylic acid. L-AFC also interfered with GTP[S] binding to retinal transducin when stimulated by Light-activated rhodopsin in a reconstituted system. This inhibitory effect was fully reversed upon increasing the concentration of either the G protein beta gamma dimer or the activated receptor. On the basis of these results, we suggest that S-prenylated cysteine analogues like L-AFC inhibit receptor-mediated G protein activation by specifically and reversibly interfering with the interaction of activated receptors with G proteins, most likely with their beta gamma dimers, rather than by inhibiting alpha .beta gamma heterotrimer formation.