Probing interaction of antimicrobial peptide duramycin with lipid monolayers

Antimicrobial peptides are group of peptides which disrupt the microbial cell membrane through hydrophobic insertion into the outer lipid layer. Duramycin is a small tetracyclic peptide antibiotic, which has recently been shown to bind specifically to phosphatidylethanolamine (PE) lipids. We report the interaction of duramycin with phospholipid monolayers at air-water interface, studied using vibrational sum-frequency generation spectroscopy (VSFG) and fluorescence microscopy (FM). For monolayers containing PE lipids, VSFG reveals binding of duramycin to the monolayer through the appearance of a vibrational peak at 3045 cm$^{-1}$, corresponding to the C-H stretching vibration of phenylalanine amino acid. In addition, the amide I vibrational region shows that peptide has a $\beta $-sheet conformation. Similar experiments performed on phosphatidylcholine (PC) monolayers show the interaction is specific with PE.