Abstract:
The emergence and spread of antibiotic resistant pathogens is one of the major health concerns of the 21st century, giving rise to an urgent need to develop new antibiotics with different mode of action. Peptides derived from non canonical amino acids such as β- and α -amino acids have attracted greater interest due to their proteolytic resistance and predictable folding properties. These fascinating features encouraged us to explore the anti-microbial properties of hybrid peptides composed of α- and γ -amino acids. In this regard, we have designed two types of hybrid peptides, short lipopeptides and amphiphilic hybrid helices and investigated their antimicrobial properties. The short lipopeptides are composed of 1:1 α-, and γ -amino acids with varied length of lipid tail and the helical peptides are composed of repeating units of ααγ tripeptide segment. These peptides were tested against various Gram positive, Gram negative bacteria as well as Fungi. In the first series, the designed lipopeptides displayed broad spectrum antimicrobial activity. The FITC uptake assay, β-galactosidase assay and AFM analysis reveal that peptides adopted different modes of action through membrane perturbation. In contrast to the lipopeptides composed of alpha and E-vinylogous γ-amino acids, the second series of lipopeptides composed of 1:1 α- and saturated γ-amino acids showed better antimicrobial properties with less haemolytic activity. In the third series, the amphiphilic helical peptides were designed based on the single crystal conformation of α, α, γ-hybrid peptide 10/12-helices to mimic the structural and functional properties of natural helical antibiotic magainin and LL37. As predicted, the 2D NMR (TOCSY and NOESY) experiments reveal that the α, α, γ -hybrid peptides adopted 10/12-helical conformations of in SDS. Similar to the lipopeptides, these α, α, γ -helical peptides displayed potent broad spectrum antimicrobial activity across the panel of Gram positive, Gram negative bacteria including MRSA. The mode of action suggests that they not only inhibit the bacterial growth through membrane depolarisation but also showed their ability to bind DNA. These results suggest the dual mode of action of hybrid helical peptides. Overall, this study underlines the potential of α, γ-hybrid peptides in the development of next generation antimicrobial therapeutics.
