Characterisation, bioactivity assessment and rational design of naturally- occurring peptides from frog skin secretion

Abstract

The brevinin-1 peptides, a well-characterised antimicrobial peptide (AMP) family, were previously demonstrated to have good antimicrobial activity and a high haemolytic capacity. In chapter three, a naturally - occurring peptide, brevinin-1pl, was isolated from the Northern leopard frog, Rana pipiens through the “shotgun” cloning technique. Chemically synthesised Brevinin-1pl and its four analogues were studied using a series of bioactivity assessment assays. Brevinin-1pl exhibited a broad spectrum of antimicrobial activity, especially against Gram-positive bacteria, S. aureus, and MRSA with the MIC of only 2 µM. It also shown a significant antibiofilm inhibitory activity against these two strains, with MBIC of 2 µM. Besides, it also showed good anti-proliferative activity against two types of cancer cell lines, H838 and MCF-7. Among the analogues, Brevinin-1pl-6K was found to have a better antimicrobial activity against Gram-negative bacteria, E. coli comparing with the parent peptide.In chapter four, five modified peptides were synthesised via rational design. Among these analogues, brevinin-1pl-del16 displayed an increased bactericidal activity against E. coli , also with a relatively mild haemolysis than the natural peptide. However, its antimicrobial activity was noticed to decreased with the presence of the metal ions. Meanwhile, mechanistic experiments showed that brevinin-1pl and brevinin-1pl-del16, can neutralise LPS and affect the inner and outer membrane permeability of E. coli strains.In chapter five, the peptide ranatensin-R was screened for its antimicrobial and anticancer activities and subjected to haemolytic and cytotoxicity assays. Meanwhile, 10 analogues were designed based on the parent peptide to increase its antimicrobial potential. After modification, the analogue ranatensin-2277 achieved a MIC of 4 μM for S. aureus, MRSA , and E. coli, whilst the parent peptide shown a much lower bacterial killing ability.

Thesis embargoed until 31 July 2029.

Date of Award	Jul 2024
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Lei Wang (Supervisor) & Tianbao Chen (Supervisor)