Rational design and bioactive evaluation of an antimicrobial peptide, Palustrin-2ISb, from the skin secretion of the frog, Odorrana ishikawae

Abstract

Antimicrobial peptides (AMPs), vital components of innate immune systems in many organisms against invasion by pathogenic microorganisms, could be considered as promising antimicrobial agents. Palustrin-2 peptides were found to exhibit broad-spectrum antimicrobial activity against Gram-positive and Gram-negative bacteria and have low haemolytic activity. Therefore, GL-29, a truncated form of palustrine-2ISb, was used as a template in this study and in an attempt to investigate its structure-activity relationships and try to find a peptide with higher antimicrobial potency and good selectivity through modification.

In the third chapter, GL-29 as well as the truncated analogue GL-22, were studied to identify the function of the "Rana box", which was confirmed to have no impact on antimicrobial activity, but the deletion of this motif notably decreased the haemolytic activity and antiproliferative activity both against human cancer cells and normal cells. In chapter 4, five short truncates of GL-22, including the N-terminal short analogue GL-9 and C-terminal short derivatives LF-10, FV-9, VN-8, FV-8 were designed and they all exhibited nearly no antimicrobial activities. In the fifth chapter, the structure-activity relationships were studied by designing eight short analogues of GL-9, named from GL-9-a to GL-9-h with different characteristics. And the result showed that for the short N-terminal derivatives, higher hydrophobicity was crucial for the antimicrobial activity and the position of the hydrophobic residue is of great importance, however, the improvement of charge was useless for these short compounds. In the sixth Chapter, 9 analogues of GL-9-h were synthesized and the results exhibited that the enhancement of Trp could further increase the antimicrobial activities but led to serious haemolysis further increase the antimicrobial potency and the introduction of the motif "RRR" at the C-terminal end could further enhance the antimicrobial activity against Gram-negative bacteria and biofilm, accompanying with an attenuation of haemolysis and cytotoxicity against HaCAT.

Overall, the structure-activity study illustrated that the deletion of "Rana box" in the Palustrine peptide GL-29 could decrease the haemolysis and maintain the antimicrobial activities at the same time, and the study of structure-activity relationship elucidated that hydrophobicity was the most important characteristic for short peptide to maintain the antimicrobial potency and the introduction of the motif “RRR" with Trp together could expand the antimicrobial potency against Gram-negative bacteria of short analogues.

Thesis embargoed until 31 July 2027.

Date of Award	Jul 2022
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Mei Zhou (Supervisor), Lei Wang (Supervisor) & Xinping Xi (Supervisor)