Fluorescence correlation spectroscopy studies of antimicrobial peptide binding to phospholipid vesicles.

Abstract

Antimicrobial peptides (AMPs) perform an essential part of the innate immune defence of all organisms and are potential candidates for last-resort antibiotics. Aurein 1.2 is a natural AMP from the skin secretions of the Australian bell frog. The molecular details underpinning the mechanism of action, specificity and selectivity of this AMP are mostly unknown. We used fluorescence correlation spectroscopy (FCS) to assess the binding and membrane modulating properties of fluorescently labeled Aurein 1.2 and its specific mutants with lipid vesicles of different physicochemical characteristics. Our results indicate that aurein 1.2 binds non-specifically to all kinds of membranes; however, the presence of specific lipid species can prevent membrane disruption. We note the general absence of “carpet-like” disruption patterns; instead, a strong membrane modulating activity was observed. We confirmed that the FCS technique produces accurate binding measurements for nanomolar peptide concentrations, which is almost impossible with other techniques for studying the interaction of AMPs with lipid membranes. We suggest that our results could guide the design of membrane-active AMPs.