Acylation stabilizes a protease-resistant conformation of protoporphyrinogen oxidase, the molecular target of diphenyl ether-type herbicides

Protein acylation is an important way in which a number of proteins with a variety of functions are modified. The physiological role of the acylation of cellular proteins is still poorly understood. Covalent binding of fatty acids to nonintegral membrane proteins is thought to produce transient or p ermanent enhancement of the association of the polypeptide chains with biol ogical membranes. In this paper, we investigate the functional role for the palmitoylation of an atypical membrane-bound protein, yeast protoporphyrin ogen oxidase, which is the molecular target of diphenyl ether-type herbicid es. Palmitoylation stabilizes an active heat- and protease-resistant confor mation of the protein. Palmitoylation of protoporphyrinogen oxidase has bee n demonstrated to occur in vivo both in yeast cells and in a heterologous b acterial expression system, where it may be inhibited by cerulenin leading to the accumulation of degradation products of the protein. The thiol ester linking palmitoleic acid to the polypeptide chain was shown to be sensitiv e to hydrolysis by hydroxylamine and also by the widely used serine-proteas e inhibitor phenylmethylsulfonyl fluoride.