Palmitoylation of the murine leukemia virus envelope glycoprotein transmembrane subunits

Abstract

The envelope protein of Friend murine leukemia virus is modified by fatty acylation of the transmembrane (TM) protein subunit. The labeling by [3H]palmitic acid was found to be sensitive to treatment with the reducing reagents 2-mercaptoethanol and hydroxylamine, indicating the presence of a thioester linkage. Pulse-chase experiments showed that the precursor protein can be labeled by [3H]palmitic acid prior to its cleavage into the surface and TM subunits. By using site-directed mutagenesis, we determined that palmitoylation occurs on a cysteine residue, Cys 606, located in the transmembrane domain. A thin-layer chromatography assay after acid hydrolysis showed that incorporated label comigrated with palmitic acid. When another cysteine residue was introduced into the cytoplasmic tail 22 amino acids from the transmembrane domain, no palmitoylation was observed to occur on this cysteine residue, demonstrating the importance of the position of the cysteine residue for palmitoylation. Sequence comparison revealed that most retrovirus envelope proteins have one or two conserved cysteine residues in their transmembrane domain. Mutations that change the palmitoylation state of the murine leukemia virus envelope protein did not affect its transport, processing, surface expression, or cell fusion activity. The palmitate deficient viral envelope proteins were incorporated into virus particles, and replication of the virus in vitro was not affected significantly by the mutation of the palmitoylation site.