Acetylation

Biologically active peptides and polypeptides are generated after proteolytic cleavage and other posttranslational modifications of precursor proteins. One of the most widely studied precursors is the prohormone precursor proopiomelanocortin (POMC), which gives rise to a number of peptide products with a range of biological activities. Interestingly, two of its posttranslational products (a-MSH and ?-endorphin) belong to a very rare group of secreted, biologically active peptides that are acetylated. Acetylation of a-MSH enhances activity through increased biological stability, whereas acetylation abolishes activity of ?-endorphin. These two peptides seem to have opposing roles in the regulation of energy balance, such that a-MSH inhibits feeding and ?-endorphin stimulates feeding. Similarly, a- MSH stimulates reproduction, whereas ?-endorphin is inhibitory. Thus, acetylation allows coordinate function of POMC-derived peptides, enhancing a-MSH function and reducing ?-endorphin activity. The regulation of the relevant acetyl transferase enzyme(s), which remains to be identified, may provide a crucial regulatory point for the opposing physiological actions of these two peptides.