Insertion of an Anionic Analogue of the Antimicrobial Peptide PGLa in Lipid Architectures Including S-Layer Supported Lipid Bilayers

The membrane – peptide insertion behavior of an artificial antimicrobial peptide analogue in liposomes, planar free-standing bilayer and planar lipid membranes supported by a crystalline bacterial surface layer, termed S-layer, was investigated. The template for this peptide was peptidyl-glycine-leucine-carboxyamide (PGLa) where all lysine residues were replaced by glutamic acid resulting in a negatively charged analogue termed PGLa(-). Zeta potential measurements and calcein release experiments on liposomes revealed that the insertion of PGLa(-) can be compared to that of native antimicrobial peptides. Patch clamp recordings on free-standing lipid membranes provided evidence of pore formation at a lipid to peptide ratio (L/P) of 1600 with a single pore conductance of 25 pS. However, also a lower conductance at a high L/P (3200) was observed which might be explained by membrane disordering effects caused by PGLa(-) interaction. In line with other studies on the action of membrane active peptides, the rupture of the lipid membrane was strongly influenced by the peptide concentration. S-layer supported lipid membranes were utilized to perform combined surface-sensitive (quartz crystal microbalance with dissipation measurements) and electrical (impedance spectroscopy) measurements. These data evidenced not only the attachment and/or insertion of PGLa(-) in the supported lipid membrane but also indicated toroidal pore formation in a concentration dependent fashion. Hence, S-layer supported lipid membranes constitute a promising platform for studying the interaction and insertion of antimicrobial peptides.