Functional optimisation and mechanistic studies of helical antimicrobial peptides from the skin secretion of the frog, Phyllomedusa tarsius

Abstract

A novel dermaseptin family peptide was isolated from the skin secretion of the leaf frog phyllomedusa tarsius, and named dermaseptin-SS1 (SS1, accession number: OR265763). The amino acid sequence of the peptide was obtained using a shotgun' cloning strategy, and solid-phase peptide synthesis was used to provide sufficient material for extensive functional studies. Several analogues were likewise designed and synthesized to study structure-activity relationships and to improve the therapeutic index. It was found that addition of a lysine residue with a positive charge at position 5, enhanced both anti-planktonic activity against tested microorganisms and swimming motility inhibitory effects against two strains of Escherichia coli. The analogue 14V5K also improved the antimicrobial effects in a salt environment and improved time-killing kinetics against Escherichia coli strains. It was found that SS1 utilised the membrane-targeting mechanism to kill Escherichia coli cells, including binding lipopolysaccharide on the surface of the cell wall and causing the disturbance of the outer and inner membranes. Moreover, SS1 exhibited anti-proliferative activity against several cancer cell lines. A natural peptide from the dermatoxin family was likewise discovered in the skin secretion of Phyllomedusa tarsius, and named dermatoxin-TA1 (DRT-T1, accession number: P84928). DRT-T1 possessed a broad-spectrum antibacterial activity against lung, breast and brain cancer cell lines. The results illustrated that the N-terminal of this peptide sequence provided antibacterial and antifungal efficacies using the membrane-damaging mechanism, and the modification of incorporating a positively charged arginine residue at position 11, significantly improved the anti-planktonic activity and salt sensitivity. Overall, this study indicated the rational design and modification of an N-terminal active fragment is ideal for optimizing the dual activities of dermatoxin peptides and it is proposed that N16-11R could be a promising agent for further pharmaceutical research.

Thesis is embargoed until 31 July 2029.

Date of Award	Jul 2024
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Lei Wang (Supervisor) & Tianbao Chen (Supervisor)