Directed alteration of a novel bovine β-defensin to improve antimicrobial efficacy against methicillin-resistant Staphylococcus aureus (MRSA)

β-Defensin antimicrobial peptides are critical components of the innate immune response in many species and may be useful against pathogens that have acquired resistance to standard antibiotic therapies. We analysed a panel of recently discovered bovine β-defensins in order to identify sites that may have particular functional importance against antibiotic-resistant bacteria. Modifications were introduced to increase charge at positively selected (PS) sites, to make charge-neutral changes at PS sites, to increase hydrophobicity and to confer a hydrophilic C-terminal. Whilst all four peptide modifications increased antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) compared with the native form of bovine β-defensin 123 (P = 0.02), conferring the hydrophilic tail caused the most significant increase, with a 50% lethal dose (LD50) of 3.91 μg/mL. The peptide with increased charge at PS sites showed the most significant increase in antimicrobial activity against a non-resistant strain of S. aureus (P = 0.02). Therefore, informed modifications of the amino acid sequence can significantly affect the specificity and antimicrobial activity of a peptide.