Ceratotoxin A (CtxA), a 36-residue alpha-helical cationic peptide isolated from the medfly Ceratitis capitata, exhibits strong antibacterial activity. To determine its mode of action against bacteria, we investigated the behavior of ceratotoxin A by incorporating it into planar lipid bilayers. Macroscopic and single channel conductance experiments showed that ceratotoxin A forms voltage-dependent ion channels in bilayers according to the barrel-stave model. The characteristics of the channel suggest that the C-terminal regions form bundles of five or six helices embedded in the membrane, such that the N-terminal moieties lie on the polar side of the lipid bilayer.
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