Investigation of the Mechanisms of Antimicrobial Peptides Interacting with Membranes by Fluorescence Correlation Spectroscopy

The interaction of four antimicrobial peptides, including magainin 2, melittin, polymyxin B and an artificial peptide V4, with phospholipid membranes was investigated by fluorescence correlation spectroscopy (FCS) and confocal imaging. Fluorophore entrapping and labeled vesicles were used to quantitatively determine the extent of antimicrobial peptides interacting with membrane mimics and unravel their different mechanisms of action. It is shown that at high peptide/lipid ratio, magainin 2 and melittin form pores to induce comparable level of membrane permeation while polymyxin B and V4 disrupt the membrane. Considering its low solubility, V4 is much more active than others. Due to the hydrophobic interactions, melittin, polymyxin B and V4 all promote aggregation when they perform their function. These experiments demonstrate the feasibility of mechanistic studies by an FCS based approach.