DEER/PELDOR Study of the Effect of Extremely Low Concentrations of the Antimicrobial Peptide Chalciporin A on the Membrane Lipid Organization

Antimicrobial peptides (AMPs) are promising therapeutic agents against drug-resistant bacteria. Many AMPs can directly interact with bacterial membranes, disturbing their integrity and/or functionality. Chalciporin A is a naturally occurring 14-mer AMP, belonging to the class of peptaibiotic. Spin-label electron paramagnetic resonance in its pulsed versions is a suitable tool to study intermolecular interactions in biological media. Here, we applied double electron–electron resonance (DEER, also known as PELDOR) and electron spin echo envelope modulation, to study model membranes of palmitoyl-oleoyl-glycero-phosphocholine in the presence of chalciporin A. The spin-labeled molecules were either chalciporin A or doxyl-spin-labeled stearic acids (DSAs). We observed that chalciporin A influences DSA clustering, disturbing the formation of the alternative sub-clusters in two opposing leaflets that was recently found in peptide-free membranes (Smorygina et al. in Langmuir 37:13909–13916, 2021). The intriguing point of this influence is that it takes place for peptide concentrations as small as 0.01 mol% (1/10,000 peptide-to-lipid ratio). The possible reasons for this membrane perturbation at extremely low concentrations are discussed.