ACYL-COA-BINDING PROTEINS INHIBIT THE NONENZYMIC S-ACYLATION CYSTEINYL-CONTAINING PEPTIDE SEQUENCES BY LONG-CHAIN ACYL-COAS

Acyl-CoA binding proteins (ACBPs) from rat and bovine liver were found to inhibit the nonenzymic S-acylation of two representative types of peptides by long-chain acyl-CoAs. As demonstrated previously [Quesnel, S. & Silvius, J. R. (1994) Biochemistry 33 13340-13348; Bharadwaj, M. , & Bizzozero, O. A. (1995) J. Neurochem. 65, 1805-1815], peptides wit h the sequences myristoyl-GCG, myristoyl-GCV, and IRYCWLRR-NH2, all re presenting physiological S-acylation sites in mammalian proteins, beco me S-acylated at appreciable rates in the presence of long-chain acyl- CoAs and large unilamellar lipid vesicles. Addition of ACBP at physiol ogical molar ratios with respect to long-chain acyl-CoAs strongly inhi bits the spontaneous S-acylation reaction, in a manner that can be qua ntitatively described by assuming that the ACBP sequesters the acyl-Co A with nanomolar affinity in a complex unable to serve as an S-acyl do nor. From these results, we calculate that at physiological (intracell ular) concentrations of ACBP, long-chain acyl-CoAs, and membrane lipid s the expected half-times for spontaneous S-acylation of such protein sequences by long-chain acyl-CoAs will lie in the range of several ten s of hours. The nonenzymic reaction of protein cysteine residues with long-chain acyl-CoAs is thus unlikely to contribute significantly to t he physiological modification of signaling and other proteins that sho w relatively rapid rates of S-acylation in mammalian cells. However, i t cannot be excluded that a nonenzymic reaction with long-chain acyl-C oAs could contribute to the physiological S-acylation of certain membr ane proteins if the latter exhibit very slow kinetics of S-acylation i n vivo.