Cell selectivity and mechanism of action of short antimicrobial peptides designed from the cell-penetrating peptide Pep-1.

Pep-1-K (PK) is a good cell-selective antimicrobial peptide designed from cell-penetrating peptide Pep-1. To develop novel short antimicrobial peptides with higher cell selectivity and shorter length compared with PK, several PK analogs were designed by the deletion, addition and/or substitution of amino acids. Among these analogs, PK-12-KKP (KKPWWKPWWPKWKK) showing the sequence and structure homology with a Trp/Pro-rich natural antimicrobial peptide, indolicidin (IN), displayed a 20-fold higher cell selectivity as compared to IN. Circular dichroism analysis revealed that PK-12-KKP adopts a folded structure combined with some portions of unordered structure. PK-12-KKP selectively binds to negatively charged bacterial membrane-mimetic vesicles, and its high phospholipid selectivity corresponds well with its high cell selectivity. Moreover, it showed very weak potential in depolarization of the cytoplasmic membrane of Staphylococcus aureus at 8 microM (4x minimal inhibitory concentration) and dye leakage from negatively charged liposomes. These results suggest that the ultimate target of our designed PK-12-KKP maybe the intracellular components (e.g. protein, DNA or RNA) rather than the cytoplasmic membranes. Collectively, our designed short Trp/Pro-rich peptide, PK-12-KKP, appears to be an excellent candidate for future development as a novel antimicrobial agent.