First Example of Kinetic Modelling of Multi-state Membrane Binding, Exapnsion and Disruption for an Antimicrobial Peptide

Abstract

Antimicrobial peptide disruption of the membrane bilayer involves a series of defined states during binding and insertion, and are all associated with significant changes in the bilayer structure. We recently identified a complex series of bilayer state changes for the binding of an analogue of magainin 2, (Ala-8,13,18)-Magainin 2-amide (MagA), to lipid bilayers. However, the presence of multiple structural states of the membrane prevented the determination of kinetic constants using currently available kinetic models, but this information is necessary to allow the full definition of the mechanism of action. In this study the binding and dissociation of MagA to lipid bilayers with different charge and fluidity properties was studied with dual polarization interferometry, an optical technique capable of measuring real-time simultaneous changes in mass and birefringence (an optical parameter representing bilayer order). The dependence of birefringence vs. mass were categorised into several discrete mechanistic profiles and new multiple-state kinetic models were developed and fitted to the experimental data, with a three-state model with lateral bilayer expansion providing distinctly superior fits to simpler model types. Overall this is the first study to quantitatively analyse complex peptide-membrane binding data in terms of specific states of membrane disruption by an antimicrobial peptide.