Synthesis of an isotopically labelled analog of the antimicrobial peptide ll-37

LL-37 is a cationic cathelin-associated broad spectrum antibiotic peptide of human neutrophils. Its mechanism of action is by disruption of the bacterial cell membrane structure. LL-21 is a simplified form of the peptide that contains only the core portion of LL-37, which retains antimicrobial activity and is easier to synthesize. We synthesized an 15N –Val-labeled LL-21 peptide which allows us to perform antimicrobial assays to know the antimicrobial activity of the new peptide LL-21 on various gram positive and gram negative bacteria. We found that our new peptide LL-21 shows good minimum inhibitory concentrations on various gram positive and gram negative bacteria except in the case of Bacillus subtilis and when compared with the parent analog, the new peptide requires slightly higher concentrations to kill the bacteria. Solid state NMR studies on LL-21 help to measure helix tilt in the bacterial cell membranes. This will provide information on its precise mode of action, either detergentlike activity or pore formation. In the future, the replacement of some of the amino acids in LL-21 with 19F and deuterium labels in specified positions will give more information on the orientation, dynamics, and rotation of the peptide in bacterial cell bilayers