Palmitoylation of the rat mu opioid receptor

We examined whether the mu opioid receptor was palmitoylated and attempted to determine sites of palmitoylation, Following metabolic labeling with [H- 3]palmitic acid and immunoaffinity purification of the mu opioid receptor, SDS-PAGE and fluorography revealed a broad labeled band with M-r of similar to 80 kDa in CHO cells stably expressing the rat mu receptor, but not in C HO cells transfected with the vector alone, indicating that the mu receptor is palmitoylated. Activation of the receptor with morphine did not affect the extent of palmitoylation, Hydroxylamine or dithiothreitol treatment rem oved most of the radioactivity, demonstrating that [H-3]palmitic acid is in corporated into Cys residue(s) via thioester bond(s), Surprisingly, mutatio ns of the only two Cys residues in the C-terminal domain did not reduce [H- 3]palmitic acid incorporation significantly. Thus, unlike many G-protein co upled receptors, the palmitoylation site(s) of the rat mu opioid receptor d o(es) not reside in the C-terminal domain, (C) 1998 Federation of European Biochemical Societies.