Effect of Secondary Structure on Biological Activities of Antimicrobial Peptides

Abstract

A 15-mer cationic α-helical antibacterial peptide was used as the framework to study the effect of peptide secondary structure on antimicrobial activities. We designed an α-helical peptide with higher helical propensity compared with the original peptide, a β-sheet peptide and a random coiled peptide without changing the original amino acid composition of the peptide sequence. Three truncated peptides were also designed. The secondary structures of the peptides were determined by circular dichroism spectra both in aqueous solution and in hydrophobic environment. The biological activities of the peptides were detected against three Gram-negative bacterial strains, three Gram-positive bacterial strains and human red blood cells. The results showed that the two helical peptides exhibited comparable antibacterial activities but their hemolytic potency (cytotoxicity) varied from extreme hemolysis to no hemolysis, which was positively correlated with their helical propensity. The β-sheet peptide partially lost both of the biological activities. The random coiled peptide with the lowest improvement in hemolytic activity showed comparable antibacterial activity against Gram-positive bacteria but weaker antibacterial activity against Gram-negative bacteria. Truncated peptides showed inevitable weaker antimicrobial activity compared to the parent peptide. Our results show that peptide secondary structure is strongly correlated with hemolytic activity and relatively less correlated with antimicrobial activity, which provides an insight into the mechanism of action of the antimicrobial peptide.

Keywords: Antimicrobial peptide, secondary structure, specificity, mechanism of action.