Comparative study of antibacterial activity and stability of D-enantiomeric and L-enantiomeric bovine NK-lysin peptide NK2A

Authors: Dassanayake, Rohana; Porter, Tracy; SAMORODNITSKY, DANIEL - US Department Of Agriculture (USDA); Falkenberg, Shollie; Nicholson, Eric; Tatum, Fred; Briggs, Robert; Palmer, Mitchell; Casas, Eduardo

Submitted to: Biochemical and Biophysical Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2022
Publication Date: 1/29/2022
Citation: Dassanayake, R.P., Porter, T.J., Samorodnitsky, D., Falkenberg, S.M., Nicholson, E.M., Tatum, F.M., Briggs, R.E., Palmer, M.V., Casas, E. 2022. Comparative study of antibacterial activity and stability of D-enantiomeric and L-enantiomeric bovine NK-lysin peptide NK2A. Biochemical and Biophysical Research Communications. 595:76-81. https://doi.org/10.1016/j.bbrc.2022.01.071.
DOI: https://doi.org/10.1016/j.bbrc.2022.01.071

Interpretive Summary: The increasing prevalence of antibiotic resistance among pathogenic microbes highlights the urgent need for the identification and development of reagents for an alternative to antibiotics. Antimicrobial peptides (AMPs) are highly effective against microbial pathogens causing diseases in humans and animals. However, AMPs are sensitive to proteases and renal clearance. Therefore, we have developed a protease-resistant small peptide (cattle NK-lysin, D-NK2A) and tested for trypsin and serum stability, toxicity, in vitro and in vivo antibacterial activities against Histophilus somni, one of the bacterial pathogens causing respiratory diseases in cattle. This Small peptide was able to kill H. somni very efficiently, showed minimal toxicity, and resistant to trypsin. Further studies are needed to assess whether small peptide tested in this study can be used for prophylaxis or treat cattle against bacteria causing respiratory diseases.

Technical Abstract: Antimicrobial peptides (AMPs), including bovine NK-lysins, are sensitive to proteolytic degradation; however, D-enantiomers of AMPs are expected to provide improved proteolytic protection. The present study aimed to comparatively investigate the in vitro antibacterial activity, trypsin and serum stability, toxicity, and in vivo antibacterial activity of L-enantiomeric bovine NK2A (L-NK2A) and its D-enantiomeric NK2A (D-NK2A). Circular dichroism spectroscopy of D-NK2A and L-NK2A in anionic liposomes showed a-helical structures and the a-helical conformation of D-NK2A was a mirror image of L-NK2A. Both D-NK2A and L-NK2A displayed minimal in vitro and in vivo toxicities in cattle red blood cells and mice. RP-HPLC analyses revealed that D-NK2A, but not L-NK2A, was resistant to trypsin digestion. D-NK2A and L-NK2A showed similar in vitro bacterial killing activities against Histophilus somni. Slightly reduced antibacterial activity was observed when D-NK2A and L-NK2A were pre-incubated with serum. Confocal and transmission electron microscopic findings confirmed that both peptides induced disruption of bacterial inner- and outer-membranes. Slightly improved survivals for D-NK2A compared to L-NK2A in a murine model of acute H. somni septicemia. We conclude that antibacterial activity and mode of action of NK2A are not chiral specific. With further optimization, D-NK2A may be a potential candidate AMP to combat bacterial infections.