Palmitoylation of a G protein α(i) subunit requires membrane localization not myristoylation

Palmitoylation is a dynamic, post-translational modification of the amino terminus of heterotrimeric G protein α subunits. Since myristoylation, βγ interactions, and membrane attachment also involve the amino terminus of the G protein α(i1) subunit, we studied the relationships between palmitoylation and these events. Using COS cell transfection, the turnover of palmitate was slower on α(i1) subunits co-expressed with β and γ subunits than on the α(i1) subunit expressed alone. Mutation of cysteine 3 of α(i1) prevented [³H]palmitate but not [³H]myristate incorporation and decreased the membrane localization of this protein. This nonpalmitoylated mutant could form a heterotrimer with co-expressed βγ subunits which restored its membrane localization. A nonmyristoylated α(i1) mutant (glycine 2 to alanine) could incorporate [³H]palmitate when co-expressed with βγ subunits and localized to the membrane. The [³H]palmitate turnover of this nonmyristoylated mutant was more rapid than seen with the wild-type α(i1) subunit. While myristoylation is not required for palmitoylation, both myristoylation and βγ association can slow the turnover of palmitate on α(i1). These results suggest that palmitoylation maintains the membrane attachment of the free α subunit and changes in βγ association could modulate palmitoylation during signaling.