Interaction of an artificial antimicrobial peptide with lipid membranes

Antimicrobial peptides constitute an important part of the innate immune defense and are promising new candidates for antibiotics. Naturally occurring antimicrobial peptides often possess hemolytic activity and are not suitable as drugs. Therefore, a range of new synthetic antimicrobial peptides have been developed in recent years with promising properties. But their mechanism of action is in most cases not fully understood. One of these peptides, called V4, is a cyclized 19 amino acid peptide whose amino acid sequence has been modeled upon the hydrophobic/cationic binding pattern found in Factor C of the horseshoe crab (Carcinoscorpius rotundicauda). In this work we used a combination of biophysical techniques to elucidate the mechanism of action of V4. Langmuir–Blodgett trough, atomic force microscopy, Fluorescence Correlation Spectroscopy, Dual Polarization Interference, and confocal microscopy experiments show how the hydrophobic and cationic properties of V4 lead to a) selective binding of the peptide to anionic lipids (POPG) versus zwitterionic lipids (POPC), b) aggregation of vesicles, and above a certain concentration threshold to c) integration of the peptide into the bilayer and finally d) to the disruption of the bilayer structure. The understanding of the mechanism of action of this peptide in relation to the properties of its constituent amino acids is a first step in designing better peptides in the future.