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

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.