Identification, characterization and bioevaluation of a bioactive peptide from the skin secretion of the Chinese forest frog

Abstract

The emergence of multi-drug resistant bacteria has made many traditional antibiotics lose their clinical efficacy, which has become a public health problem that needs to be solved in the world. Antimicrobial peptides are considered to be a new treatment scheme that is difficult to form drug resistance due to their special membrane antibacterial mechanism. Amphibian skin secretion was found to be an ideal source of antimicrobial peptides, which is worthy of further study.

In this study, the skin secretions of the Chinese forest frog (Rana chensinensis) were collected in a mitigating stimulation method. Then the natural antimicrobial peptide QUB-1735 was identified by molecular cloning, chromatographic analysis and mass spectrometry. Through the study of structure and biological activity, it was found that QUB-1735 was a helical peptide belonging to the Temporin family, and possessed good anti-Gram-positive bacteria activity through the mechanism of membrane destruction. However, its strong haemolytic ability and antimicrobial activity was easily affected by physiological conditions making it difficult to be further studied.

In order to provide a better modification basis, the structure-activity relationship of the C-terminal and N-terminal of QUB-1735 was studied. It was found that the hydrophobic region of the C-terminus affected its haemolytic ability and antibacterial activity at the same time, while increasing the net charge number and hydrophobicity of the N-terminus only increased its antibacterial activity without changing its haemolytic activity. At the same time, the addition of proline and tryptophan into the N-terminus improved the flexibility of the N-terminal and the chelating ability to the bacterial cell membrane.

Finally, QUB-1623, which was obtained from the structure-activity relationship study, was modified by introducing cyclohexylalanine (Cha) or a branched structure to obtain a peptide with stable antimicrobial activity in different physiological environments. For the removal of part of the hydrophobic region at the C terminal and the addition of Cha, the reduction of peptide length showed a decrease in membrane breaking ability. The use of a branched structure allowed the active units of the peptide to accumulate, and even though the haemolytic activity increased, the stable antibacterial activity made it possible to enter the next step of in vivo experiments.

Thesis embargoed until 31 December 2026.

Date of Award	Dec 2021
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Mei Zhou (Supervisor), Lei Wang (Supervisor), Tianbao Chen (Supervisor) & Xinping Xi (Supervisor)