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.