Effects of Hydrophobic Peptoid Substitutions on the Bacterial Cell Selectivity and Antimicrobial Activity of Piscidin 1

Piscidin 1 (Pis-1) from hybrid striped bass possesses antibacterial activities with high cytotoxicity. Previously, we reported that Pis-1[NkG], where Gly(8) was substituted with positively charged Lys peptoid in Pis-1, shows high antibacterial activity with more potent bacterial cell selectivity than parent Pis-1 and Pis-1[PG] with Pro substitution at Gly(8). Here, we investigated the effects of hydrophobic peptoid substitutions on antimicrobial activity and cytotoxicity of Pis-1. We designed Pis-1[NaG] and Pis-1[NlG] peptides, where Gly(8) was replaced with alanine or leucine peptoids. Although hydrophobicity was increased in Pis-1[NaG] and Pis-1[NlG] compared with that in Pis-1[NkG], Pis-1, and Pis-1[PG], these peptides retained high antibacterial activity and showed no hemolytic activity when used at 100 M. All peptoid-substituted peptides penetrated well the bacterial membrane and localized inside of the cytoplasm, while Pis-1 and Pis-1[PG] depolarized membrane severely. The flexible hinge structure formed by peptoid residues compared with the rigid bent structure formed by proline may explain their differential mechanisms of action. Most hydrophobic peptide, Pis-1[NlG], showed the most efficient inhibition of LPS (lipopolysaccharide)-induced nitric oxide production, indicating that it can be a potent antimicrobial peptide with anti-inflammatory activities. Peptoid substitution may facilitate the development of potent peptide drugs with bacterial cell selectivity.