Synthesis and solid state F-NMR studies on fluorine-labeled antimicrobial peptide RK-21

Antimicrobial peptides act against bacteria by binding non-specifically and disrupting their outer membrane. LL-37 is the only member of the cathelicidin group of antimicrobial peptides present in humans and shows a broad range of antimicrobial activity. RK-21 is a fragment of human antimicrobial peptide LL-37, which is α-helical, cationic and amphipathic in nature. RK-21 displays similar antimicrobial activity to LL- 37. In order to understand the mechanism of lipid bilayer disruption, fluorine-labeled antimicrobial peptide RK-21 was chemically synthesized and 19F-NMR studies were done. NMR studies were done at various peptide concentrations, on different lipid bilayer compositions and temperatures. 31P-NMR studies did not show any micellar fragments, eliminating the detergent-like mechanism for activity. 19F-NMR studies indicated that labeled RK-21 is oriented on glass stack lipid samples. The peptide maintained this orientation at different lipid compositions, different peptide concentrations and different temperatures. Preliminary results support a mechanism of toroidal pore formation. i