Background: Antimicrobial Peptides (AMPs) are an attractive alternative to traditional
small molecule antibiotics as AMPs typically target the bacterial cell membrane. A Trp-rich peptide
sequence derived from water buffalo (Bubalus bubalis), BuCATHL4B was previously identified
as a broad-spectrum antimicrobial peptide.
Objective: In this work, native Trp residues were replaced with other naturally occurring aromatic
amino acids to begin to elucidate the importance of these residues on peptide activity.
Methods: Minimal Inhibitory Concentration (MIC) results demonstrated activity against seven
strains of bacteria. Membrane and bilayer permeabilization assays were performed to address the
role of bilayer disruption in the activity of the peptides. Lipid vesicle binding and quenching experiments
were also performed to gain an understanding of how the peptides interacted with lipid bilayers.
Results: MIC results indicate the original, tryptophan-rich sequence, and the phenylalanine substituted
sequences exhibit strong inhibition of bacterial growth. In permeabilization assays, peptides
with phenylalanine substitutions have higher levels of membrane permeabilization than those substituted
with tyrosine. In addition, one of the two-tyrosine substituted sequence, YWY, behaves
most differently in the lowest antimicrobial activity, showing no permeabilization of bacterial membranes.
Notably the antimicrobial activity is inherently species dependent, with varying levels of activity
against different bacteria.
Conclusion: There appears to be little correlation between membrane permeabilization and activity,
indicating these peptides may have additional mechanisms of action beyond membrane disruption.
The results also identify two sequences, denoted FFF and YYW, which retain antibacterial activity
but have markedly reduced hemolytic activity.