A novel bioactive peptide QUB-2022 from the skin secretion of Phyllomedusa bicolor

Abstract

The antimicrobial peptide (AMP) is a type of small molecular peptides that are produced by the body against infection. They are commonly considered as a fundamental component of innate immunity and have been extensively discovered in the insects and other non-vertebrate organisms. Amphibian skin secretions are also known to be a rich source of AMPs. They possess broad-spectrum action on killing both Gram-positive and Gram-negative bacteria, especially including those strains which are resistant to conventional antibiotics. In this research, it is, therefore, mainly aimed at evaluating bioactive peptides from the skin secretion of Phyllomedusa bicolor. A complementary deoxyribonucleic acid (cDNA) encoding a phylloseptin-like peptide was initially obtained by molecular cloning and Sanger sequencing. Subsequently, the mature peptide sequence of QUB-2022 was predicted as: FLSLIPHIATGVASIAKHF-NH2. Then the peptide synthesiser was used to synthesize the peptide. The synthetic peptide was purified by reversed-phase high-performance liquid chromatography (RP-HPLC). To test the bioactivities of QUB-2022, a series assays, such as antimicrobial assay, anticancer assay and haemolysis assay were performed. The results showed that peptide QUB-2022 has a significant effect against Gram-positive bacteria but a little effect against Gram-negative bacteria. It exhibited lower potency against fungus. In addition, the peptide is cytotoxic to the red blood cells. Nevertheless, it has no anti-cancer effect on the tested tumour cells including human lung cancer cell line, prostate cancer cell line and glioblastoma cell line. In this study, since the secondary structure of QUB-2022 was only predicted by software, therefore, further research regarding its secondary structure needs to be confirmed by circular dichroism spectroscopy. Thesis embargoed until 31st October 2024