Lipid-dependent pore formation by antimicrobial peptides arenicin-2 and melittin demonstrated by their proton transfer activity.

This work presents a comparative study of proton transfer activity (PTA) of two cationic (+6) antimicrobial peptides, β-structural arenicin-2 and α-helical melittin. A new approach was proposed for the detection of passive proton transfer by using proteoliposomes containing bacteriorhodopsin, which creates a small light-induced electrochemical proton gradient ∆ΔpH. Addition of several nanomoles of the peptides lowers ∆ΔpH that is proximately indicative of the pore formation. The quantitative analysis of sigmoidal dependences of ∆pH on the peptides concentration was carried out using liposomes prepared from PC, PC/PE, PC/PE/PI and PC/PG. Substitution of PC-containing liposomes with PE-containing ones, having negative spontaneous curvature, reduced the PTA of α-helical melittin and increased that of β-structural arenicin-2. This result indicates an essential difference in the pore formation by these peptides. Further increase of PTA in response to arenicin-2 (in contrast to melittin) was observed in the liposomes prepared from PC/PE/PI. The data analysis leads to the conclusion that PTA is influenced by (i) efficiency of the pore assemblage, which depends on the structure of pore-forming peptides, and the spontaneous curvature of lipids and (ii) the presence of mobile protons in the polar head groups of phospholipids.