Discovery, modifications and functional evaluations of peptides extracted from amphibians for combating drug-resistant microorganisms

Abstract

Antibiotic resistance is rising globally, with new resistance mechanisms continuously emerging and spreading rapidly. As the effectiveness of antibiotics declines, many common infections such as pneumonia, tuberculosis, sepsis, gonorrhoea and foodborne illnesses, are becoming increasingly difficult to treat, and in some cases, are untreatable. Antimicrobial peptides (AMPs) derived from amphibians present a vital important role in the research of potential alternatives to conventional antibiotics due to their broad-spectrum antimicrobial activity, rapid killing effects and low risk of drug resistance development. However, they still exhibit a variety of challenges including poor antimicrobial potency, salt tolerance, antimicrobial stability, and high toxicity. Therefore, a series of rational design systems based on AMPs are proposed in the following chapters. In Chapter 3, a novel antimicrobial peptide (AMP) named Rugosin-RD was discovered from Hylarana nigrovittata and the Lys substituted analogue, Rugosin-K12, shows the most potent antimicrobial activity against various microorganisms including vancomycin-resistant Enterococcus faecalis (VRE). In Chapter 4, a Temporin-RN2-based sequential Lys compensation strategy was established, and RN2-4K and RN2-5K are presented as potent broad-spectrum and salt-stable leads. In Chapter 5, a rationally designed analogue, RN2-4Dap-PEG214, is presented which incorporated helical structure optimisation using unnatural amino acids and balanced hydrophilic-hydrophobic property through use of polyethylene glycolylation (PEGylation) and structural PEGylation strategies. RN2-4Dap-PEG214 exhibited potent broad-spectrum antimicrobial activity, excellent membrane selectivity and stability. Mechanistic studies suggested membrane disruption and depolarisation. In Chapter 6, several novel Bowman Birk inhibitor (BBI) peptide-based rational designs were presented to treat Candida albicans (C. albicans) by enabling translocation, adjusting the steric hindrance at the P1 residue, enhancing substrate interactions through hydrogen-bond formation, employing a dual-targeting approach, and incorporating synergy-based strategies. Through antimicrobial screening against 3 strains of C. albicans, TAT-HECI-NAL and TAT-FF-HECI demonstrated enhanced antifungal activity against amphotericin B-resistant C. albicans NCYC 1467. Moreover, TAT-FF-HECI exhibited synergistic effects when used in combination with the mitochondria-targeting peptide, KChaA. Also both peptides displayed negligible cytotoxicity at their antifungal effective concentrations. Despite the need for further in vivo confirmation, this research offers an adaptable BBI peptide-based platform for tackling antifungal-resistant C. albicans NCYC 1467.

Thesis is embargoed until 31 July 2031.

Date of Award	Jul 2026
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Tianbao Chen (Supervisor), Mei Zhou (Supervisor) & Lei Wang (Supervisor)