Characterization of Indolicidin-Membrane Interactions By Simultaneous Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy-Atomic Force Microscopy

Abstract

A detailed understanding of how antimicrobial peptides interact with bacterial membranes is a key step towards the effective design of novel antibiotics to treat infection. These interactions may include membrane-induced conformational changes to the peptide, membrane disordering, as well as peptide aggregation. To understand the effect of both membrane composition and peptide sequence on these phenomena, we applied simultaneous attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR)-atomic force (AFM) microscopy to directly visualize and characterize the interactions of the model antimicrobial peptide, indolicidin, with a series of supported planar lipid bilayers. This approach allows us to directly interrogate how peptide association, aggregation, and insertion alter the structure of the bilayer. It also allows us to directly assess changes to the secondary structure of the peptide as a consequence of both specific peptide-membrane interactions as well as peptide-peptide interactions. Simultaneously acquired AFM images provide direct confirmation of the effect of the peptide on membrane integrity, evidence of domain targeting, as well as the kinetics and structure of putative peptide aggregates. This coupled approach provides a unique opportunity to directly link spectroscopic details associated with peptide-membrane interactions with structural insights obtained on nanometer length scales.