Characterisation and bioactivity evaluation of a frog-skin derived peptide, RT-5Cc, and its analogues, from the skin secretion of the American Bullfrog, Rana catesbeiana.

Abstract

Since the discovery and confirmation of the antimicrobial properties of AMPs, they have gained  significant attention amid the escalating threat of antibiotic resistance (AMR).  Traditional antibiotics face increasing challenges with AMR, making the exploration of new strategies, such as replacing antibiotics with AMPs or using them in combination, crucial. One of the primary  sources of AMPs is the skin secretions of frogs, with Ranaturin-5Cc (RT-5Cc) identified as a natural  active AMP found in Rana catesbeiana. In Chapter 3, the antimicrobial activity of RT-5Cc against  common Gram-negative and Gram-positive bacteria, its anticancer activity, and cytotoxicity were  explored.In Chapter 4, the modifications were made to RT-5Cc, maintaining the concept of extending the alpha-helix length. A sequence of 6 amino acids was added to the tail of RT-5Cc. The modified peptide, (5Cc-FL, 5Cc-FG, 5Cc-13, 5Cc-16, 5Cc-63), exhibited improved alpha-helix composition. The increased charge in the modified peptide's sequence from 1 to 4 positively also affected its effectiveness  against Gram-negative bacteria, especially Escherichia coli, without significant haemolysis. Moreover, results from the permeability and membrane potential suggested that the increased activity of 5Cc-modified peptides manifests in more pronounced disruption and damage to bacterial membranes. Optimizing AMP activity aims to apply it practically, especially in the context of the growing threat of AMR. Chapter 5 delved into the synergistic effects of the modified peptides from Chapter 4 and four  antibiotics. Results showed significant synergy, particularly between 5Cc-13/5Cc-63 and Rifampicin  against Rifampicin-resistant Escherichia coli, lowering the antibiotic concentration and at least  preventing the resistance growth. Subsequent experiments with the subsrate EtBr of influx and Efflux  corroborate that bacterial resistance to Rifampicin is initially accompanied by reduced exposure of  exogenous substances, which gradually decreases in efficiency as resistance develops. Moreover, when  administered in combination, AMPs and antibiotics elicit positive responses from increased drug  retention purpose.

  Thesis is 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)