Mechanism of Action of the Antimicrobial Peptide Caerin1.1

© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Caerin1.1 is a 25-residue antimicrobial peptide secreted by the tree frog Litoria splendida. It is classified as an α-helical cationic membrane disrupting peptide, with a good activity against Gram positive bacteria. Given its length, it is believed that caerin1.1 acts via transmembrane pore formation. However, the exact mechanism of its action is unknown. Here the interactions of caerin1.1 with biomimetic membranes were studied to establish the molecular mechanism of action. The activity of the peptide against different model membranes was determined by dye leakage experiments. Caerin1.1 showed weak activity against neat dimyristoyl phosphatidylcholine (DMPC) membrane and minimal activity against negatively charged or cholesterol containing membrane mixtures. Circular dichroism spectroscopy revealed that the peptide exhibited only 8-16% helicity even in the DMPC membrane, yet quartz crystal microbalance fingerprinting suggested that the peptide was able to penetrate the membrane in each case. The results suggest that caerin1.1 is a membrane penetrating peptide but not a membrane disruptor, only causing incidental dye leakage while diffusing across the membrane. Consistently the main mode of action of caerin1.1 is likely exerted through an intracellular target.