Lipid modifications of G proteins: α Subunits are palmitoylated

A small number of membrane-associated proteins are reversibly and covalently modified with palmitic acid. Palmitoylation of G-protein α and β subunits was assessed by metabolic labeling of subunits expressed in simian COS cells or insect Sf9 cells. The fatty acid was incorporated into all of the α subunits examined (α(s), α(o), α(i1), α(i2), α(i3), α(z), and α(q)), including those that are also myristoylated (α(o), α(i), and α(z)). Palmitate was released by treatment with base, suggesting attachment to the protein through a thioester or ester bond. Limited tryptic digestion of activated α(o) and α(s) resulted in release of the amino-terminal portions of the proteins and radioactive palmitate. These data are consistent with palmitoylation of the proteins near their amino termini, most likely on Cys-3. Reversible acylation of G-protein α subunits may provide an additional mechanism for regulation of signal transduction.