Inducing toxicity by introducing a leucine zipper like motif in frog antimicrobial peptide, magainin 2

Abstract

Cytotoxicity, a major obstacle in therapeutic application of antimicrobial peptides, is controlled by leucine zipper like sequences in melittin and other naturally-occurring antimicrobial peptides. Magainin 2 shows significantly lower cytotoxicity than many naturally-occurring antimicrobial peptides and lacks this structural element. To investigate the consequences of introducing a leucine zipper sequence in magainin 2, a novel analogue (Mag-mut) was designed by rearranging only the positions of its hydrophobic amino acids to include this structural element. Both magainin 2 and Mag-mut showed appreciable similarities in their secondary structures in presence of negatively charged lipid vesicles, in localizing and permeabilizing the selected bacteria and exhibiting bactericidal activities. However, Mag-mut bound and localized strongly onto the tested mammalian cells and exhibited significantly higher cytotoxicity than magainin 2. Only Mag-mut but not magainin 2 permeabilized human red blood cells and zwitterionic lipid vesicles. In contrast to magainin 2, Mag-mut self-assembled in aqueous environment and bound cooperatively onto zwitterionic lipid vesicles. The peptides formed pores of different sizes onto a selected mammalian cell. The results indicated an important role of leucine zipper sequence in cytotoxicity of magainin 2-analogue and demonstrated that its introduction into a non-toxic peptide without altering the amino acid composition can render cytotoxicity.