Membrane Phase Characteristics Control NA-CATH Activity

The “catastrophic threat” of antibiotic resistance has prompted research into biological methods of combating bacterial infection. One such pervasive strategy employs cationic antimicrobial peptides, AMPs. These peptides use their structure to target and disrupt bacterial membranes. They specifically attach to PG (phosphatidylglycerol) and CL (cardiolipin) rich membranes, common anionic bacterial lipids of the outer leaflet. Most have shown broad spectrum activity, adequate potency, and minimal resistance. Considering these peptides have been active against pathogens for millions of years and have not developed any broad resistance, they are of particular interest to study. Our studies focus on the behavior of NA-CATH, an α-helical cathelicidin antimicrobial peptide, originally discovered in the Naja atra snake. Here we examine the kinetics, behaviors and potential mechanisms of the peptide in the presence of model membrane mimics, specifically that of E. Coli, whose membrane exhibits two lipid phases (liquid disordered and gel). To understand NA-CATH interactions, the role of lipid phases is critical. We test three different lipid compositions to detangle the effect of phase on NA-CATH's activity using a series of leakage experiments. From these studies, we observe that NA-CATH changes from membrane disruption to pore-based leakage, depending on phases and lipid composition. This behavior also plays a major role in its kinetics.