Role of positively charged residues on the polar and non-polar faces of amphipathic α-helical antimicrobial peptides (AMPs) on specificity and selectivity for Gram-negative pathogens

Abstract

We have designed de novo and synthesized eight 26-residue all D-conformation amphipathic α-helical cationic antimicrobial peptides (AMPs), four with "specificity determinants" which provide specificity for prokaryotic cells over eukaryotic cells and four AMPs without specificity determinants. The eight AMPs contain six positively charged Lys residues on the polar face in four different arrangements to understand the role of these residues have on antimicrobial activity against 14 Acinetobacter baumannii strains, 7 of which were resistant to polymyxin B and colistin; 6 diverse Pseudomonas aeruginosa strains and 17 Staphylococcus aureus strains, 9 of which were Methicillin-sensitive (MSSA) and 8 of which were Methicillin-resistant (MRSA). The four AMPs without specificity determinants are extremely hemolytic. In contrast, the four AMPs with specificity determinants had dramatic improvements in therapeutic indices showing the importance of specificity determinants in removing eukaryotic cell toxicity. The specificity determinants combined with the location of positively charged residues on the polar face provide Gram-negative pathogen selectivity between A. baumannii and S. aureus. Specificity determinants maintain excellent antimicrobial activity in the presence of human sera whereas the AMPs without specificity determinants were inactive. This study clearly shows the potential of amphipathic α-helical AMPs with specificity determinants as therapeutics to replace existing antibiotics.

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Specificity determinants (K13, K16, pink) in the center of the non-polar face combined with the arrangement of the positively charged lysine residues on the polar face(blue) enhance antimicrobial activity, reduce eukaryotic cell toxicity, dramatically improve the therapeutic index, prevent high affinity binding to serum proteins and provide selectivity for Gram-negative pathogens.

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