Structure and mode of action of the antimicrobial peptide arenicin.

The solution structure and the mode of action of arenicin isoform 1, an antimicrobial peptide with a unique 18-residue loop structure, from the lugworm Arenicola marina were elucidated here. Arenicin folds into a two-stranded antiparallel beta-sheet. It exhibits high antibacterial activity at 37 and 4 degrees C against Gram-negative bacteria, including polymyxin B-resistant Proteus mirabilis. Bacterial killing occurs within minutes and is accompanied by membrane permeabilization, membrane detachment and release of cytoplasm. Interaction of arenicin with reconstituted membranes that mimic the lipopolysaccharide-containing outer membrane or the phospholipid-containing plasma membrane of Gram-negative bacteria exhibited no pronounced lipid specificity. Arenicin-induced current fluctuations in planar lipid bilayers correspond to the formation of short-lived heterogeneously structured lesions. Our results strongly suggest that membrane interaction plays a pivotal role in the antibacterial activity of arenicin.