Marine antimicrobial peptide arenicin adopts a monomeric twisted β-hairpin structure and forms low conductivity pores in zwitterionic lipid bilayers.

Arenicins are 21-residue β-hairpin antimicrobial peptides (AMPs) isolated from the marine lugworm Arenicola marina [Ovchinnikova et al., FEBS Lett. 2004;577:209-214]. The peptides have a high positive charge (+6) and display a broad spectrum of antimicrobial activities against bacteria and fungi. Arenicins adopt the monomeric highly twisted β-hairpin in water or planar β-structural dimers in anionic liposomes and detergent micelles. Until now, the interaction of cationic β-structural AMPs with zwitterionic phospholipid bilayers mimicking eukaryotic membranes is not well understood. To study the structural basis of arenicins activity against eukaryotic cells, we investigated arenicin-2 in the solvents of low polarity (ethanol, 4% dioxane) and in zwitterionic soybean PC and PC/PE liposomes by CD and FTIR spectroscopy. It was shown that arenicin-2 adopted the twisted β-hairpin structure in all the environments studied. Measurements of the Trp fluorescence and H→D exchange in soybean PC liposomes and boundary potential in the planar DPhPC bilayers confirmed the partitioning of the arenicin-2 monomers into interfacial region of the zwitterionic membranes. The low-conductivity (0.12 nS) arenicin-2 pores were detected in the DPhPC bilayers. The lifetime of the open state (up to 260 ms) was significantly longer than lifetime of low-conductivity (0.23 nS) pores previously described in partially anionic membranes (44 ms). The formation of narrow arenicin-2 pores without disruption of the membrane was discussed in the light of the disordered toroidal pore model previously proposed for β-structural AMPs [Jean - Francois et al. Biophys. J. 2008;95:5748 - 5756]. A novel non-lytic mechanism of the arenicin-2 action was proposed.