A CYTOPLASMIC ACYL-PROTEIN THIOESTERASE THAT REMOVES PALMITATE FROM G-PROTEIN ALPHA-SUBUNITS AND P21(RAS)

Thioacylation is one of a handful of reversible covalent protein modif ications, but the enzymes responsible for addition and removal of long chain fatty acids from protein cysteine residues in vivo have not yet been identified. The alpha subunits of some heterotrimeric G proteins cycle between thioacylated and deacylated states in a receptor-regula ted fashion. We have identified, purified, and characterized an enzyme acyl-protein thioesterase that deacylates G alpha proteins and at lea st some other thioacyl protein substrates, including Ha-RAS. The actio n of this enzyme oil thioacylated heterotrimeric G(s) is regulated by activation of the G protein. Although native and recombinant acyl-prot ein thioesterases act as both acyl-protein thioesterases and lysophosp holipases in vitro, we demonstrate by transfection that the enzyme can accelerate the turnover of thioacyl groups on G(s)alpha in vivo.