Investigating the Bactericidal Mechanism of Three Novel Histone-Derived Antimicrobial Peptides

Abstract

Many antimicrobial peptides elicit bacterial death via cell membrane lysis. However, buforin II (BF2), a 21-amino acid peptide derived from histone H2A, is unique due to its hypothesized ability to translocate across cell membranes and interact with bacterial nucleic acids to cause cell death. Since cell-entry peptides, such as BF2, often are effective at lower concentrations than peptides that target membranes, increasing their potential as therapeutics in vivo. To this end, we developed three novel histone-derived antimicrobial peptides based on fragments of histones H2A (Des1), H3 (Des2) and H4 (Des3). These histones were previously found to exhibit translocation behavior. The designed peptides' antimicrobial properties were verified using a radial diffusion assay. In this assay, BF2 exhibited the greatest antimicrobial activity, followed by Des1, Des3 and Des2, respectively. We also measured the absorbance of bacterial cells incubated with these peptides. Based on the similarity between the absorbance versus time trend for the designed peptides with other DNA-binding antimicrobial peptides, such as BF2 and indolicidin, molecular dynamics simulations were used to model the peptides' interactions with nucleic acids. MM-GBSA analyses of the simulations were used to calculate DNA binding energies of individual peptide residues. We used these analyses to create mutant versions of the designed peptides that were predicted to have altered DNA binding. Experimental measurements of the DNA binding and antimicrobial properties of these variants will help us determine whether nucleic acid interactions are important in the bactericidal mechanism of the designed peptides. Ongoing work on the designed peptides is aimed at investigating their translocation behavior in vitro with lipid vesicles and in vivo with bacterial cells using confocal microscopy and fluorescently tagged peptides.