Amphibian skin gradually formed a series of protective mechanisms in the long-term natural selection process in order to resist the effects of harmful environmental factors. The skin secretion contains a large number of active peptides, which can help the amphibian defence system to kill microorganisms and to deter predators.
In this study, an antimicrobial peptide (AMP) named QUB3203 was isolated from the skin secretion of the frog, Pelophylax kl. esculentus, found in Europe. The peptide precursor encoding cDNA was successfully cloned from a cDNA library made from the stimulated skin secretion. Once the full-length open reading frame was obtained, the predicted mature peptide was subjected to chemical synthesis to acquire a large quantity of peptide replicate. The synthetic peptide was then subjected to several functional assays including antimicrobial assays, anticancer assays and haemolytic assays.
In this research, QUB3203 shown significant effective antimicrobial bioactivity against the Gram-positive bacterium, S. aureus, the Gram-negative bacterium, E. coli and the yeast, C. albicans, at minimum inhibitory concentrations (MICs) of 128, 64 and 64 μM, respectively. The MBCs of QUB3203 against these three microorganisms were 256, 128 and 128 μM, respectively. Meanwhile, QUB3203 was able to inhibit the proliferation of the selected human cancer cell lines (MB435S, H157 and U251MG) at the concentration of 10 μM (65.40%, 31.91% and 82.55%) but insignificant effect against the PC-3 cells (117.03%). QUB3203 exhibited remarkable anticancer effects on the human lung cancer cell line, H157. However, QUB3203 also possessed moderate haemolytic activity with a HC50 of 101.2 μM.