WLBU2 is an engineered cationic amphiphilic peptide that targets Gram-positive and Gram-negative bacteria, and envelopes endotoxin while avoiding other cell types. The exact mechanism of how WLBU2 targets, binds, and disrupts bacterial cell membranes is still not completely known. Thus, the overall goal of this investigation is to determine the structural basis for recognition and specific interactions between the engineered antimicrobial peptide WLBU2 and cell membranes. Currently, it is believed that WLBU2 binds parallel to the surface of the cell membrane in an α-helical confirmation, and at a critical interfacial concentration, WLBU2 starts to disrupt the lipids that make up the cell. In this investigation – we tested this proposed mechanism by using a set of surface and interface specific spectroscopy tools to probe the biophysical interactions between the peptide and both zwitterionic and negatively charged model cell membranes.
This surface analysis approach demonstrates that binding between WLBU2 and cell membranes is induced by electrostatic interactions between charged amino acids within the peptide and charged lipids. Our experiments also suggest that for zwitterionic membranes WLBU2 binds to the surface in a β-sheet conformation, while for negatively charged membranes folds in an α-helical conformation at the interface. The observed difference in folding demonstrates WLBU2 selectivity toward negatively charged membranes (i.e. bacteria) and inactivity toward zwitterionic membranes (i.e. mammalian cells and other cell types).