Isolation and characterization of a prenylcysteine lyase from bovine brain

Prenylated proteins contain one of two isoprenoid lipids, either the 15-carbon farnesyl or the 20-carbon geranylgeranyl, covalently attached to cysteine residues at or near their C terminus. The cellular abundance of prenylated proteins, which can comprise up to 2% of total cellular protein, raises the question of how cells dispose of prenylcysteines produced during the normal turnover of prenylated proteins. We have identified and characterized a novel enzyme, which we term prenylcysteine lyase, that is capable of cleaving the thioether bond of prenylcysteines. The enzyme was isolated from bovine brain membranes and exhibits an apparent molecular mass of 63 kDa. The enzyme did not require NADPH as cofactor for prenylcysteine degradation, thus distinguishing it from cytochrome P450- and flavin-containing monooxygenases that catalyze S-oxidation of thioethers. Purified prenylcysteine lyase shows similar kinetics in utilization of both farnesylcysteine and geranylgeranylcysteine as substrates, although Vmax is 2-fold higher with the former compound. Interaction of prenylcysteine substrates with the enzyme requires that they possess a free amino group; N-acetylated prenylcysteines and prenyl peptides are not substrates. These findings suggest that prenylcysteine lyase is a specific enzyme involved in prenylcysteine metabolism in mammalian cells, most likely comprising the final step in the degradation of prenylated proteins.