Identification and bioactivity assessment of a host-defence peptide, QUB-2654, from the skin secretion of the frog, Agalychnis callidryas

  • Ruiling Chen

Student thesis: Masters ThesisMaster of Philosophy


Amphibian skin secretions contain a wide array of antimicrobial peptides with biological activities, providing an effective first-line of defence against microbial invasion. This thesis aims to characterise an antimicrobial peptide from the skin secretion of the Central American red-eyed tree frog, Agalychnis callidryas and to study its biological properties. Firstly, the cDNA sequence encoding an antimicrobial peptide (QUB-2654) precursor, was identified from the frog skin secretions extracted mRNAs through rapid-amplification of cDNA ends (RACE) PCR, molecular cloning and Sanger sequencing strategies. Next, the peptide was synthesised using a solid-phase peptide synthesiser, purified by reversed-phase high-performance liquid chromatography and corroborated by MALDI-TOF mass spectrometry. The purified peptide was tested for its antimicrobial activity, anti-lung cancer cell activity and haemolytic effect, by a series of bioassays. This study showed that QUB-2654 had significant bacteriostatic and bactericidal activities against a Gram-positive bacterium, Staphylococcus aureus (ATCC-CRM 6538) (MIC=3.125 µM, MBC=6.25 µM) and a Gram-negative bacterium, Escherichia coli (ATCC-CRM 8739) (MIC/MBC=6.25 µM), but the MIC value against Candida albicans (ATCC-CRM 10231) was not detected even at the highest peptide concentration. In addition, QUB-2654 statistically demonstrated anti-proliferative and killing effects against NCI-H838 human lung cancer cells at and above a concentration of 10 µM. The peptide concentration required to achieve half-maximal inhibition (IC50) of the NCI-H838 cells was 11.32 µM. This peptide was not haemolytic (<5% haemolysis) at the MBC values for S.aureus and E.coli, and at the IC50 value for NCI-H838 cells. These results suggest that peptide QUB-2654 has the potential to be developed as an antibacterial and anticancer drug.

Thesis is embargoed until 31 December 2027.
Date of AwardDec 2022
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SupervisorLei Wang (Supervisor), Tianbao Chen (Supervisor) & Xiaoling Chen (Supervisor)


  • Antimicrobial peptides
  • Agalychnis callidryas
  • antibacterial
  • anti-lung cancer
  • haemolytic activity

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