Exploration of the structure-function relationships of two novel peptides from amphibian skin secretion, through rational design and in vitro studies

Abstract

Antimicrobial peptides (AMPs) obtained from amphibian skin, have made significant strides toward becoming possible substitutes for traditional antibiotics. In this study, two new AMPs were initially identified from frog skin secretion. In order to assess their bioactivities, a number of bioassays were carried out, and the natural AMPs were utilized as models to investigate the structure-function correlations and enhance their bioactivities.

The first novel peptide, namely Kas-4, was identified in the skin secretion of the African running frog, Kassina senegalensis, and possessed both intense anti-bacterial and anti-cancer activities. In Chapter 3, several modifications such as net charge enhancement, hydrophobicity decrease and Proline removal, were employed to explore its optimised structure for bioactivities. Then, one antimicrobial-oriented peptide Des-Pro-Kas-4 and one anticancer peptide, W7W10-Kas-4, were designed. Based on Chapter 3, Chapter 4 induced a unique motif “FFY” to further increase the bioactivities of Kas-4. Here, F-Kas-4 was found to possess similar antimicrobial activities but better antibiofilm activity towards MRSA 12493. These discoveries provided both novel and useful new understanding of how natural medicines are discovered.

The second novel peptide, Kas-2, was identified from the skin secretion of the African hyperoliid frog, Kassina maculata. Studies showed that Kas-2 had potent bactericidal effects on Gram-positive bacteria and anti-proliferation activity on tested cancer cells. After the modifications were performed in Chapter 5 and Chapter 6, the results showed that charge enhancement was effective in Kas-2 design. Besides, the first helix was ineffective in the sequence when interacting with bacterial cell membranes. Four designed cell-penetrating peptides with a special motif with tryptophan and arginine residues, displayed potent antimicrobial and anticancer activities but high haemolysis. These data may provide some ideas to improve the bioactivities of AMPs from Kassina species in further studies.

Under the studies on the identification and bioactivity evaluation of this two novel peptides Kas-4 and Kas-2, from the skin secretion of two different African frogs, Kassina senegalensis and Kassina maculate, respectively, we found that the positions of two prolines had a great influence on the bioactivities of peptides from Kassina species rather than cationicity and hydrophobicity. Also, through rational design, activities and haemolysis of Kas-4 and Kas-2 were well improved. This study provided a fresh perspective on the creation of antimicrobial derivatives.

Thesis is embargoed until 31 July 2028.

Date of Award	Jul 2023
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Mei Zhou (Supervisor), Tianbao Chen (Supervisor) & Yangyang Jiang (Supervisor)