PALMITOYLATION OF A G-PROTEIN ALPHA(I) SUBUNIT REQUIRES MEMBRANE LOCALIZATION NOT MYRISTOYLATION

Palmitoylation is a dynamic, post-translational modification of the am ino terminus of heterotrimeric G protein alpha subunits. Since myristo ylation, beta gamma interactions, and membrane attachment also involve the amino terminus of the G protein alpha(i1) subunit, we studied the relationships between palmitoylation and these events. Using COS cell transfection, the turnover of palmitate was slower on alpha(i1) subun its co-expressed with beta and gamma subunits than on the alpha(i1) su bunit expressed alone. Mutation of cysteine 3 of alpha(i1) prevented [ H-3]palmitate but not [H-3]myristate incorporation and decreased the m embrane localization of this protein. This nonpalmitoylated mutant cou ld form a heterotrimer with co-expressed beta gamma subunits which res tored its membrane localization. A nonmyristoylated alpha(i1) mutant ( glycine 2 to alanine) could incorporate [H-3]palmitate when co-express ed with beta gamma subunits and localized to the membrane. The [H-3]pa lmitate turnover of this nonmyristoylated mutant was more rapid than s een with the wild-type alpha(i1) subunit. While myristoylation is not required for palmitoylation, both myristoylation and beta gamma associ ation can slow the turnover of palmitate on alpha(i1). These results s uggest that palmitoylation maintains the membrane attachment of the fr ee alpha subunit and changes in beta gamma association could modulate palmitoylation during signaling.