PSEUDO-ENZYMATIC S-ACYLATION OF A MYRISTOYLATED YES PROTEIN-TYROSINE KINASE PEPTIDE IN-VITRO MAY REFLECT NONENZYMATIC S-ACYLATION IN-VIVO

Covalent attachment of a variety of lipid groups to proteins is now re cognized as a major group of post-translational modifications. S-acyla tion of proteins at cysteine residues is the only modification conside red dynamic and thus has the potential for regulating protein function and/or localization. The activities that catalyse reversible S-acylat ion have not been well characterized and it is not clear whether both the acylation and the deacylation steps are regulated, since in princi ple it would be sufficient to control only one of them. Both apparentl y enzymatic and non-enzymatic S-acylation of proteins have previously been reported. Here we show that a synthetic myristoylated c-Yes prote in tyrosine kinase undecapeptide undergoes spontaneous S-acylation in vitro when using a long chain acyl-CoA as acyl donor in the absence of any protein. The S-acylation was dependent on myristoylation of the s ubstrate, the length of the incubation period, temperature and substra te concentration. When COS cell fractions were added to the S-acylatio n reaction no additional peptide:S-acyltransferase activity was detect ed. These results are consistent with the possibility that membrane-as sociated proteins may undergo S-acylation in vivo by nonenzymatic tran sfer of acyl groups from acyl-CoA. In this case, the S-acylation-deacy lation process could be controlled by a regulated depalmitoylation mec hanism.