Characterisation, bioactivity evaluation and rational design of bioactive peptides from Hylarana latouchii skin secretion

Abstract

There are numerous resources in Nature that can be utilised, and frogs' intricate living circumstances enables them to serve a purpose by secreting substances on their skin that shield them from the outside environment. Some of the complex problems of today may have been aided by their evolution. As many bacteria have evolved resistance to current antibiotics in use, antimicrobial peptides from frog skin secretions are among the most promising novel antimicrobial agents due to their wide-ranging antimicrobial activities and different mechanisms of action. This project aims to identify two novel antimicrobial peptides and to evaluate their biological activities and to find peptides with drug potential through modification. And their structure-activity relationships were studied. In Chapter 3, the full-length cDNA sequences of brevinin-1HL and palustrin-2LTb, two novel antimicrobial peptides, were cloned from skin secretion of Hylarana latouchii through “shotgun” cloning. In Chapter 4, brevinin-1HL identified in the skin secretion of Hylarana latouchii was evaluated for its biological activity. Five analogues were designed through D-type amino acid substitution and changing the amino acids in the hydrophobic face. It was found that the secondary structure, especially the helicity between these peptides, plays a significant role in their actions. And the designed analogue, brevinin-1HL-D-9L, was considered as a potential drug candidate with potent antibacterial activity with low haemolysis at its effective values. In Chapter 5, a novel peptide, palustrin-2LTb, identified in the skin secretion of Hylarana latouchii was shown to have good antibacterial activity against selected pathogens. To reduce the manufacturing cost and decrease toxicity, trypsin-cleavage mimicking modification strategy was ultilised to produce predicted fragments. Seven such truncated derivatives of palustrin-2LTb were synthesised and tested for their biological activities. Functional screening data indicated that truncated fragment 3 not only maintained and optimised antimicrobial efficacy of the parent peptide, but also showed great in vivo therapeutic potential in an MRSA-infected insect larvae model. Due to its strong antibacterial activity, minimal haemolytic activity, and ability to kill MRSA in an in vivo model, fragment 3 showed outstanding effects and had obvious potential to become a new antimicrobial agent.

Thesis is embargoed until 31 July 2028.

Date of Award	Jul 2023
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Lei Wang (Supervisor), Tianbao Chen (Supervisor) & Yangyang Jiang (Supervisor)