A novel bioactive peptide from the defensive skin secretion of the wild green mountain frog, Odorrana livida
In the view of the global antimicrobial resistance problem due to the over reliance on traditional antibiotics in medical treatment, conventional agriculture and intensive breeding industries, antimicrobial peptides (AMPs) are now regarded as promising antibiotic substitutes due to their novel structures, multi-target mechanisms, low propensity for resistance development and broad activity spectra against bacteria, fungi, viruses and even cancers. In this study, a novel cDNA encoding an AMP precursor was isolated and identified from the skin secretion of the wild green mountain frog, Odorrana livida, by molecular cloning. The deduced mature peptide was named QUB-2052 due to its molecular mass and consists of 18 amino acid residues, AVPLIYNRPGIYAPKRPK-NH2. This peptide was identified as a member of the odorranain peptide family with potential host defensive function. Subsequently, QUB-2052 was synthesised by SPPS and subjected to several bioactivity assays. QUB-2052 displayed moderate antimicrobial activity against three model microorganisms, namely Staphylococcus aureus (a Gram-positive bacterium), Escherichia coli (a Gram-negative bacterium) and Candida albicans (a fungi), with MIC values of 512, 512 and 128 μM, respectively. Meanwhile, a significantly low cytotoxicity on horse erythrocytes was observed for QUB-2052 with a haemolysis of below 10% at concentrations up to 512 μM. It was also surprising that as a member of AMP peptide family, QUB-2052 acted as a bradykinin (BK) antagonist to inhibit the BK-induced relaxation of rat tail artery. However, no obvious anticancer cell properties or trypsin inhibition propensity were observed for this novel AMP.
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