Bending Elasticity of Phospholipid Bilayers Containing an Amphipathic Peptide with Low Mammalian Cytotoxicity

Peptide mimetics imitate natural peptides’ structure but they could be specifically designed to be more selective concerning their toxicity to mammalian cells. In most cases this specificity is due to their ability to form α-helix in amphipathic environment. In addition, the specific activity depends on the ability of final structure to penetrate cell membrane. Being responsible for the cell integrity and compartmentalization, biomembranes also play a major role in cellular processes, in which the membrane deformations are important. In the present study we probe peptide-membrane interactions for a shortened amino acid sequence KLAKLAK-NH2 of an antimicrobial peptide with apoptotic effect. The bending rigidity of model lipid bilayers is measured by flicker spectroscopy of quasispherical unilamellar vesicles monitored and analyzed in phase contrast light microscopy. At high peptide concentrations ∼ 30 μmol/L and peptide-to-lipid total molar ratios ∼ 0.90 bilayer stacking formation is observed. A reduction of the bending constant is reported at peptide-to-lipid total molar ratio ∼ 0.80. The membrane softening indicates peripheral peptide orientation at the lipid bilayer, which is considered a prerequisite for channel formation. Based on KLAKLAK-NH2 effect on the membrane bending elasticity we provide an evaluation of the peptide partition coefficient characterizing its affinity to POPC bilayers. The acquired results might be helpful in efforts to further tailor the pharmacokinetic properties of antimicrobial peptides in combination with strengthened stability towards enzymatic degradation.