Differentiating antimicrobial peptides interacting with lipid bilayer: Molecular signatures derived from Quartz Crystal Microbalance with Dissipation Monitoring

• Interactions between lipid bilayers and 4 structurally diverse AMPs were examined.
• Each peptide’s interaction mechanism produces a unique molecular QCM-D signature.
• QCM-D signatures give information about the dynamics of AMP-membrane interactions.
• Mechanistic variations were related to AMP structural properties (e.g. hydrophobicity).

Many antimicrobial peptides (AMPs) kill bacteria by disrupting the lipid bilayer structure of their inner membrane, with either stable pore formation or membrane lysis as the mode of membrane disruption. However, there is only limited quantitative information in the literature to differentiate between AMPs of differing molecular properties, in terms of how they interact with the membrane. In this study, we have used quartz crystal microbalance with dissipation monitoring (QCM-D) to probe the interactions between a supported bilayer membrane of egg phosphatidylcholine (egg PC) and four structurally different AMPs: alamethicin, chrysophsin-3, indolicidin, and sheep myeloid antimicrobial peptide (SMAP-29) and demonstrate that QCM-D provides molecular signatures clearly differentiating the mechanism of action of one peptide from another. Multiple signatures from the QCM-D measurements were extracted that provide information on peptide addition to and lipid removal from the membrane, the dynamics of peptide-membrane interactions and the rates at which the peptide actions are initiated. The QCM-D signatures were interpreted in terms of molecular processes including surface adsorption of peptide, pore formation with a water channel and the insertion of the peptide or peptide aggregate into the bilayer. We found that the membrane interactions of each peptide involved a different sequence of molecular processes. These mechanistic variations in peptide action were related to the fundamental structural properties of the peptides including the number of amino acids, net charge, hydrophobicity, hydrophobic moment, accessible surface area and the probability of α-helical secondary structures. The study demonstrates that QCM-D provides a rich collection of molecular signatures capable of differentiating the detailed mechanism of action of antimicrobial peptides.