Effects of the hinge region of cecropin A(1–8)–magainin 2(1–12), a synthetic antimicrobial peptide, on liposomes, bacterial and tumor cells

Abstract

A 20-residue hybrid peptide (CA(1–8)–MA(1–12): KWKLFKKIGIGKFLHSAKKF–NH 2) incorporating 1–8 residues of cecropin A (CA) and 1–12 residues of magainin 2 (MA) has potent antibiotic activity without hemolytic activity. In order to investigate the effects of the flexible hinge sequence, Gly–Ile–Gly of CA(1–8)–MA(1–12) (CA–MA) on antibiotic activity, CA–MA and its three analogues, CA–MA1, CA–MA2 and CA–MA3 were synthesized. The Gly–Ile–Gly sequence of CA–MA was deleted in CA–MA1 and replaced with Pro and Gly–Pro–Gly in CA–MA2 and CA–MA3, respectively. CA–MA1 and CA–MA3 caused a significant decrease in the bactericidal rate against Escherichia coli and Bacillus subtilis and the tumoricidal activity against four different tumor cells, and the PC/PS (4:1, w/w) vesicle-aggregating and disrupting activities. However, CA–MA2 showed a similar bactericidal rate and antitumor, vesicle-aggregating and disrupting activities, as compared with CA–MA. These results suggested that the flexibility or β-turn induced by Gly–Ile–Gly or Pro in the central part of CA–MA may be important in the electrostatic interaction of the cationic short α-helical region in the N-terminus with the cell membrane surface and the hydrophobic interaction of amphipathic α-helical region in the C-terminus with the hydrophobic acyl chains in the cell membrane. CA–MA3 exhibited lower activity in antibacterial, antitumor, and vesicle-aggregating and disrupting activities than CA–MA and CA–MA2. This result suggested that the excessive β-turn structure by Gly–Pro–Gly in CA–MA3 seems to interrupt the ion channel/pore formation on the lipid bilayer. It was concluded that the appropriate flexibility or β-turn structure provided by the central hinge is responsible for the effective antibiotic activity of the antimicrobial peptides with the helix–hinge–helix structure.