AbstractWith the abuse of traditional antibiotics, the problem of bacterial resistance is becoming more and more serious. The skin secretions of frogs contain many bioactive molecules, some of which are polypeptides with antibacterial activity. Antimicrobial peptides(AMPs) play a significant role in the innate immune system of frogs and work as the first defence line to fight pathogens. Frogs have been known as the primary source of amphibian-derived AMPs, and the data of discovered novel peptides continuously grow yearly. These AMPs showed a broad spectrum of bacteria-killing activity, and some exhibited further anti-cancer and antioxidant activities. But the low bio-stability and high cytotoxicity are still issues waiting for solve. This study focused on a novel naturally- occurring peptide, QUB-2618, isolated from the skin secretion of hybrid frog Pelophylax esculentus. QUB-2618 was identified following the construction and interrogation of a skin secretion-derived cDNA library through ‘shotgun’ cloning technology, and the amino acid sequence of the gene product was obtained. After the peptide was synthesised and purified, the bactericidal activity assay was used to characterize the novel peptide's bacterial inhibitory/killing activity. QUB-2618 was effective against Escherichia coli (Gram-negative bacterium) at only 32μM and Staphylococcus aureus (Gram-positive bacterium) at 128 μM. It showed no significant effect on Candida albicans (yeast). QUB-2618 had no inhibitory effect on the proliferation of human lung adenocarcinoma cells (NCI-H838) and had low haemolytic activity. Although the antibacterial and anticancer effects of QUB-2618 are not apparent, the relative outstanding gram-negative bacteria-killing activity and low blood cell toxicity make the peptide the potential antibiotic candidate. Besides, this peptide family also showed good antioxidant activity according to the recent research, so QUB-2618 still has much research value and modification potential.
Thesis is embargoed until 31 December 2027.
|Date of Award||Dec 2022|
|Supervisor||Mei Zhou (Supervisor), Tianbao Chen (Supervisor) & Yangyang Jiang (Supervisor)|
- Pelophylax esculentus
- Antimicrobial peptides
- shotgun’ cloning
- skin secretions
- bacteria-killing activity