Anti-microbial action of melanocortin peptides and identification of a novel X-Pro-D/L-Val sequence in Gram-positive and Gram-negative bacteria.

The melanocortin peptides alpha-MSH, Lys-Pro-Val and Lys-Pro-D-Val are known to be potent anti-inflammatory agents; however their role as antibacterial peptides is less clear. The aim of this study was to determine whether these peptides displayed antibacterial properties, and specifically whether the Lys-Pro-D-Val tripeptide was more potent than Lys-Pro-Val, consistent with their anti-inflammatory actions. alpha-MSH, Ac-Lys-Pro-D-Val-NH2 and Ac-Lys-Pro-Val-NH2 were found to be antibacterial against both Gram-positive and Gram-negative bacteria (Staphylococcus aureus and Escherichia coli) over a broad range of concentrations compared to a control peptide, Ac-Ala-Ala-Ala-NH2. However, the relative potency of alpha-MSH, Ac-Lys-Pro-D-Val-NH2, Ac-Lys-Pro-Val-NH2 did not differ. Furthermore, it was found that the cationic charge on the lysine residue was not required for activity as a variant peptide Ac-Ala-Pro-D-Val-NH2 was also antibacterial. We therefore describe a novel X-Pro-D/L-Val peptide sequence with similarity to the short melanocortin peptides, which possess antibacterial activity. The combined anti-inflammatory and antibacterial action of such peptides may also have potential value therapeutically.