The discovery and functional study of a bioactive peptide, QUB-3000, from the defensive skin secretion of the northern leopard frog, Rana pipiens

  • Wei Xu

Student thesis: Masters ThesisMaster of Philosophy


To solve the drug-resistant microorganism problem, antimicrobial peptides (AMPs) have been studied as alternatives for traditional antibiotics. AMPs can inhibit and kill gram-negative bacteria, gram-positive bacteria, fungi and even cancer cells. Compared with traditional antibiotics, it is much more difficult for pathogens to develop drug-resistance towards AMPs, which is because of the distinct mechanisms of action of AMPs.
In this study, an AMP precursor encoded by a cDNA was isolated and identified from the lyophilised skin secretion of the northern leopard frog, Rana pipiens, by “shotgun” cloning. According to its molecular mass, the mature peptide was named QUB-3000. Then, QUB-3000 was synthesised by solid phase peptide synthesis (SPPS), purified by RP-HPLC. The purified synthetic QUB-3000 was then subjected to several functional experiments analysis.
QUB-3000 exhibited strong antimicrobial ability against the Gram-positive bacterium Staphylococcus aureus and the Gram-negative bacterium Escherichia coli. The minimum inhibitory concentration (MIC) values and minimum bactericidal concentration (MBC) values were 16 μM and 8 μM, respectively. While QUB-3000 possessed weak antimicrobial ability against the fungus Candida albicans with the MIC value at 256 μM and no MBC value. At the same time, QUB-3000 showed low haemolytic activity on horse blood cells. However, the 10-5 M QUB-3000 had very weak effects in inhibiting the growth of cancer cells (H-157, PC-3, U251MG), and it even could promote the growth of certain cancer cells (MCF-7). In the future, more functional investigations can be performed to develop QUB-3000 into a clinical drug. For example, circular dichroism (CD) can be used to confirm the secondary structure of QUB-3000. Furthermore, more drug-resistant bacteria can be used for assessing the antimicrobial activity of QUB-3000.
Date of AwardJul 2018
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SupervisorYuxin Wu (Supervisor), Tianbao Chen (Supervisor), Christopher Shaw (Supervisor), Lei Wang (Supervisor) & Mei Zhou (Supervisor)

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