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Title: The discovery and functional assessment of novel peptides from the skin secretions of frogs
Author: Li, Miaoran
ISNI:       0000 0004 8504 1767
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2019
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Three dermaseptins, named QUB2605, QUB2651 and QUB2687, were isolated from from skin secretions of Phyllomedusa tarsius, Phyllomedusa palliata and Agalychnis callidryas, respectively. The complementary DNAs (cDNAs) encoding biosynthetic precursors of the three peptides were cloned through 3’RACE PCR. Briefly, degenerate primers were designed based on the 5’-untranslated regions of other dermaseptin cDNAs. Bioinformatic tools were used to reveal the open-reading frames and putative signal peptides, acidic spacer peptides and mature peptides, were thus identified. The structures of the mature peptides were confirmed by MS/MS fragmentation sequencing and analysed by the BLAST programme available online through the (NCBI) portal. Once the primary structures were confirmed, solid-phase peptide synthesis was performed, and the synthesized peptides were identified and purified by MALDI-TOF and RP-HPLC. Then, after chemical synthesis of the peptides, various functional bioassays were used to evaluate their antimicrobial, haemolytic and anticancer activities. In addition, a cationicity-enhanced analogue was designed according to the primary structure of QUB2605. Both QUB2605 and its analogue displayed obvious effects against the microorganisms and the human cancer cells through cell membrane disruption and they exhibited weak haemolytic activity towards horse erythrocytes at their effective concentrations. The modified analogue significantly increased the antimicrobial and anticancer potency of QUB2605. Compared with the human cancer cells, both peptides showed less cytotoxicity on human normal cells. QUB2651, with potent antimicrobial activity, exhibited antiproliferative activity against the human cancer cell U251MG and disrupted the cancer cell membrane at high concentrations. However, it Displayed moderate anticancer effect on the cancer cell at the low concentration without cell membrane damage. The further investigation revealed that the peptide induced apoptosis at 10-6 via activation of caspase-3 release. QUB2687 was found to have little ability to inhibit the tested microorganisms. However, it showed antiproliferative effects on a wide variety of human cancer cells and inhibited the cancer cells in a dose-dependent manner. The combination of aspirin or metformin with 10 μM QUB2687, produced an additive effect. The biological activities of the peptides in this project provide the new insight for natural drug discovery and these peptides have the potential as promising candidates for the development of new antimicrobial and anticancer agents.
Supervisor: Chen, Tianbao ; Zhou, Mei ; Wang, Lei Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available