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

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)