Addition of a small hydrophobic segment from the head region to an amphipathic leucine zipper like motif of E. coli toxin hemolysin E enhances the peptide-induced permeability of zwitterionic lipid vesicles

To find out the sequence requirement of the H-205 peptide, containing an amphipathic leucine zipper motif corresponding to the amino acid (a.a.) region 205–234 of hemolysin E (HlyE) to induce efficient permeation in zwitterionic lipid vesicles, the peptide was extended at the N-terminal after the addition of seven amino acids from the predicted transmembrane region in the head domain of the protein-toxin. The new peptide, H-198 (a.a. 198–234) and a scrambled mutant peptide of the same size were synthesized, fluorescently labeled and characterized functionally and structurally. The results showed that H-198 induced significantly higher permeation in the zwitterionic PC/Chol lipid vesicles than its shorter version, H-205. H-198 formed large aggregates in the PC/Chol vesicles unlike H-205 and also adopted more helical structure in the membrane mimetic environments compared to that of H-205. Fluorescence energy transfer experiments by flow cytometry indicated that only H-198 but not its mutant or H-205 oligomerized in the zwitterionic lipid vesicles, while in the negatively charged lipid vesicles both H-198 and H-205 formed oligomeric assembly. The results suggest a probable role of the hydrophobic residues of the head domain of HlyE in inducing permeability in the zwitterionic lipid vesicles by the peptide derived from the a.a. 198–234 of the toxin.