Neutron Reflectivity Studies of the Antimicrobial Peptide Maculatin 1.1 in Supported Lipid Bilayers

Abstract

Maculatin 1.1 is a member of a small group of α-helical antimicrobial peptides isolated from the skin secretions of Australian amphibians. Previous studies using solid-state NMR, surface plasmon resonance, quartz crystal microbalance, calorimetry and fluorescence measurements have revealed that this peptide acts via different mechanisms dependent on concentration and membrane charge, which lead to the disruption of bacterial membranes. Neutron reflection is a method that provides information about the distribution of materials on the axis perpendicular to a membrane surface (the z-axis). Neutron scattering can discriminate between hydrogen and its isotope deuterium, making neutron reflection a powerful tool for dissecting how lipid, protein and solvent relate to one another along the z-axis and provides a method in which certain components can be highlighted or made invisible by choosing the correct isotopic contrast. In this case deuterated lipid chains and a hydrogenated peptide were used. The interaction of maculatin 1.1 in solid-supported lipid bilayers that mimic the essential charge characteristics of eukaryotic (neutral) and prokaryotic (anionic) membranes were studied using neutron reflection. The peptide was found to bind to both bilayers but the action of the peptide was different between each bilayer. When maculatin 1.1 bound to neutral bilayers the bilayer structure was lost and lipid order diminished whereas when maculatin 1.1 bound to negatively charged bilayers lipid order increased and the bilayer structure was retained suggesting that maculatin 1.1 formed pores when bound to negatively charged bilayers.