Effects Of Secondary Structure On The Antimicrobial Activity And Specificity Of Antimicrobial Peptides

A15-mer cationic α-helical antimicrobial peptide HPRP-A1was used as thetemplate to study the effects of peptide secondary structure on the antimicrobialactivity and specificity. Without changing the original amino acid composition HPRP-A1, we designed three α-helical peptides with either higher or lower helicalpropensity compared with the original peptide, a β-sheet peptide and a random coiledpeptide. Three truncated peptides were also designed. The secondary structures ofpeptides were determined by circular dichroism spectra both in aqueous solution andin hydrophobic environment. The biological activities of peptides were detectedagainst three Gram-negative bacterial strains, three Gram-positive bacterial strainsand human red blood cells. The three helical peptides exhibited comparableantibacterial activities, but their hemolytic potency (cytotoxicity) varied from extremehemolysis to no hemolysis, which was positively correlated with their helicalpropensity. The β-sheet peptide partially lost both of the biological activities. Moreinterestingly, the coiled peptide with no hemolytic activity showed somewhatantibacterial specificity to Gram-positive bacteria because of the considerable loss ofthe antibacterial activity against Gram-negative bacteria. Truncated peptides showedinevitable weaker antimicrobial activity compared to the parent peptide. Furtherinvestigation demonstrated that the antibacterial activity of peptides to Gram-negativebacteria was in accordance with their outer-membrane permeabilizing ability.Tryptophan fluorescence experiment revealed that the binding preference of all ofpeptides to the lipid vesicles for mimicking the cytoplasm of prokaryocyte oreukaryocyte was associated with their biological activity. Our results show thatpeptide secondary structure is strongly correlated with hemolytic activity but lesscorrelated with antimicrobial activity, which providing the insights of mechanism of action of antimicrobial peptide. In this case study, peptide with proper helical contentsmight represent a promising pattern for designing peptide antibiotics.