POSTTRANSLATIONAL MODIFICATIONS OF PROTEI NS BY LIPIDS

Covalent modifications of proteins by lipids were first associated wit h a passive role in membrane anchoring. Most recently, post-translatio nal modifications of proteins by covalent lipids have been identified and they seem to have more than just a structural function. These are two types of post-translational modifications by lipids: palmitoylatio n and isoprenylation. The first is reversible and the modified protein s are found at the cytoplasmic face of the plasma membrane or at the e ndoplasmic reticulum. The second is irreversible and the modified prot eins are found in almost all intracellular locations such as the cytop lasm, cell membrane and nucleus. Palmitoylation principally occurs on cysteines, but no consensus sequences have been identified, so far. Co nversely, isoprenylation is found only on proteins with particular C-t erminal sequences containing one or two cysteines. These two modificat ions were shown to be involved in the regulation of many proteins such as beta(2)-adrenergic receptor and Ras proteins. Post-translational m odifications of proteins by covalent lipids appear to play an importan t role in the regulation of cellular functions.