Effects of single amino acid substitutions on peptide interaction with lipid membranes and bacteria–variants of GKE21, an internal sequence from human LL-37

Effects of helix destabilization on lipid membrane interaction, liposome rupture, and bacterial killing was investigated for variants of the antimicrobial peptide GKE21 (GKEFKRIVQRIKDFLRNLVPR), an internal sequence of human cathelicidin LL-37, by ellipsometry, circular dichroism, fluorescence spectroscopy, and bacterial radial diffusion assay. GKE21 displayed moderate helix induction in buffer, which increased on interaction with phospholipid membranes. Substituting either of the two valines (V) in GKE21 with either proline (P) or d-valine (dV) resulted in helix destabilization, while peptide isoelectric point, net charge at pH 7.4, and mean hydrophobicity remained unchanged. The decreased tendency for helix formation in GKE21 (V → P, V → dV) resulted in a lower induced (helix-related) amphiphilicity, and correlated to a lower peptide adsorption at supported phospholipid membranes, as well as to decreased peptide-induced liposome leakage, particularly at high electrolyte concentration where conformation-invariant electrostatic interactions are screened. In addition, bacterial killing was reduced for the substituted peptides, indicating that even minor changes in induced peptide amphiphilicity may be of relevance for the bactericidal properties of this type of antimicrobial peptides.