All <span style="font-variant: small-caps">d</span>-Lysine Analogues of the Antimicrobial Peptide HPA3NT3-A2 Increased Serum Stability and without Drug Resistance

• Main Authors: Jong-Kook Lee, Yoonkyung Park
• Format: Article
• Language: English
• Published: MDPI AG 2020-08-01
• Series: International Journal of Molecular Sciences
• Subjects: drug-resistant bacteria; sheep RBCs; <span style="font-variant: small-caps">d</span>-enantiomer; antimicrobial peptide; physiological condition
• Online Access: https://www.mdpi.com/1422-0067/21/16/5632
• ISSN: 1661-6596; 1422-0067

Novel antibiotic drugs are urgently needed because of the increase in drug-resistant bacteria. The use of antimicrobial peptides has been suggested to replace antibiotics as they have strong antimicrobial activity and can be extracted from living organisms such as insects, marine organisms, and mammals. HPA3NT3-A2 ([Ala^1,8] HPA3NT3) is an antimicrobial peptide that is an analogue of the HP (2–20) peptide derived from <i>Helicobacter pylori</i> ribosomal protein L1. Although this peptide was shown to have strong antimicrobial activity against drug-resistant bacteria, it also showed lower toxicity against sheep red blood cells (RBCs) and HaCaT cells compared to HPA3NT3. The <span style="font-variant: small-caps;">l</span>-Lys residues of HPA3NT3-A2 was substituted with <span style="font-variant: small-caps;">d</span>-Lys residues (HPA3NT3-A2D; [<span style="font-variant: small-caps;">d</span>-Lys^{2,5,6,9,10,15}] HPA3NT3-A2) to prevent the cleavage of peptide bonds by proteolytic enzymes under physiological conditions. This peptide showed an increased half-life and maintained its antimicrobial activity in the serum against <i>Escherichia coli</i> (<i>E. coli</i>) and <i>Staphylococcus aureus</i> (<i>S. aureus</i>) (pathogen). Furthermore, the antimicrobial activity of HPA3NT3-A2D was not significantly affected in the presence of mono- or divalent ions (Na⁺, Mg²⁺, Ca²⁺). Finally, <span style="font-variant: small-caps;">l</span>- or <span style="font-variant: small-caps;">d</span>-HPA3NT3-A2 peptides exhibited the strongest antimicrobial activity against antibiotic-resistant bacteria and failed to induce resistance in <i>Staphylococcus aureus</i> after 12 passages.