Discovery and design of novel bioactive peptides from the skin secretion of Ranidae frogs

Abstract

Amphibians have developed numerous strategies to fight against their predators and intrusive microorganisms by producing noxious/toxic skin secretions. Amphibian skins have been targeted for different kinds of medicinal substances in Traditional Chinese Medicine since ancient times. With ever more pathogenic bacteria developing resistance to commercial antibiotics and novel putative antibiotics keep on failing during this battle with bacteria, there is an urgent need for new antibiotic resources and present efforts need to be doubled at least. From previous studies, the amphibian defensive skin secretions have proven to be a great treasury for novel functional peptide discovery and these have become attractive targets for novel drug development.

With miscellaneous physical and chemical properties related to their bio functions, transcriptomic and peptidomic studies of the lyophilised defensive skin secretions helped here in the study of five novel peptides. In Chapter 3, a novel potent antimicrobial peptide QUB 2282 was found in the skin secretion of the Fujian Large-headed Frog (Limnonectes fujianensis), displaying differential growth-inhibiting activity on different microorganisms, even multi-drug resistant bacteria. Most of the MIC values against Gram-positive bacteria like S. aureus, MRSA (NCTC 12493) and E. faecalis, were at 4 µM. Besides, QUB 2282 was also able to inhibit and eradicate S. aureus and E. coli biofilms at low concentrations. In further studies, this novel antimicrobial peptide was found to disrupt the bacterial membrane first at MIC and then completely at its MBC. The peptide possesses an α-helical segment and a typical heptapeptide loop - the rana box. In Chapter 4, three novel peptides with highly-conserved primary structures were found in three different species of frog: the Green Mountain Frog (Odorrana livida), the Wuyi Torrent Frog (Amolops wuyiensis) and Schmacker’s Frog (Odorrana schmackeri). Although so far, the bio-activities of these XIII three novel peptides are not clear, more possibilities might be explored in the future. In Chapter 5, a Bowman-Birk type trypsin inhibitory peptide (Ki=0.62±0.03 µM) was discovered from the skin secretion of Schmacker’s Frog (Odorrana schmackeri). It was compared in activity with its 11-amino-acid-residue novel cysteine inhibitory loop (C-LT-K-S-I-P-P-K-P-C) at the carboxyl terminal, which was also found to have a potent inhibition on trypsin (Ki=1.53 ± 0.12 µM)

Date of Award	12 Oct 2018
Original language	English
Awarding Institution	Queen's University Belfast
Supervisor	Christopher Shaw (Supervisor), Mei Zhou (Supervisor) & Tianbao Chen (Supervisor)