G-protein α-subunit expression, myristoylation, and membrane association in COS cells

Myristoylation of seven different a subunits of guanine nucleotide-binding regulatory proteins (G proteins) was examined by expressing these proteins in monkey kidney COS cells. Metabolic labeling studies of cells transfected with cytomegalovirus-based expression vectors indicated that [³H]myristate was incorporated into α_i2, α_i2, α_i3, α₀, α_t, and α_z, but not α_s subunits. The role of myristoylation in the association of α subunits with membranes was analyzed by site-directed mutagenesis and by substitution of myristate with a less hydrophobic analog, 10-(propoxy)decanoate (11-oxamyristate). Myristoylation of α₀ was blocked when an alanine residue was substituted for its amino-terminal glycine, as was association of the protein with membranes. Substitution of the myristoyl group with 11-oxamyristate affected the cellular distribution of a subset of acylated a subunits. The results are consistent with a model wherein the hydrophobic interaction of myristate with the bilayer permits continued association of the protein with the plasma membrane when G-protein α subunits dissociate from βγ.