Proline-15 creates an amphipathic wedge in maculatin 1.1 peptides that drives lipid membrane disruption

The membrane interaction of peptides derived from maculatin 1.1 and caerin 1.1, with the sequence motif of N and C termini of maculatin 1.1, were compared in order to understand the role of these common sequence motifs, which encompass critical proline residues, on peptide secondary structure and on membrane binding and disruption in zwitterionic and anionic membranes. The peptides incorporated a single substitution with lysine or deletion of the central region to mimic the length of the antimicrobial peptides, citropin 1.1 and aurein 1.2. The impact of these changes in the sequence, length and physicochemical properties, on lytic activity and structure was assessed by dye-release from lipid vesicles and the change in the bilayer order as a function of membrane-bound peptide mass. All peptides adopted similar degrees of helical structure in both membrane systems. In addition, all peptide analogues were less active than either maculatin 1.1 or caerin 1.1 in dye release assays. The membrane binding was analysed by dual polarisation interferometry and the results showed that membrane binding was significantly affected by changes in the hydrophobic environment of Pro-15. Moreover, changes in the relative distribution of charge and hydrophobicity flanking Pro-15 also caused significant changes to the membrane order. Overall, the proline residue plays an important role in inducing a peptide structure that enhances the activity of these antimicrobial peptides.