Peptidomic and genomic analyses on bioactive peptides from the amphibian skin

Thus, the modified peptide might provide favourable prospects for novel biomedicine design and antibiotics substitution.<br>In Chapter 4, a bradykinin-related peptide (BRP), QUB1315 (RAA-Val1, Thr6-bradykinin), was isolated from the skin secretion of Odorrana schmackeri with the defined primary sequence of RAAVPPGFTPFR. After bioactivity studies, QUB1351 revealed a dose-dependent contractile property on rat bladder. The analogue peptide, QUB1281 (RAA-Val1, Thr6, Leu8-bradykinin), was modified based on QUB1315 by replacing a single amino acid from Phe8 to Leu8 to test the antagonistic activity.

However, the results showed that the modified peptide, QUB1281, was still an agonist. QUB1281 expressed less potency on bladder contraction than the wild-type QUB1315. It was also found that Thr6 and Leu8 might contribute to agonist effects and the substitution at position 8 could affect the affinity between peptides and bradykinin receptors. <br>In Chapter 5, two novel peptides from Odorrana schmackeri, QUB1517 and QUB2025, were found to exhibit antibacterial potency against Gram-positive (Staphylococcus aureus) bacteria, Gram-negative (Escherichia coli) bacteria and yeast (Candida albicans).

Their similar antimicrobial effects against these three microbes assumed that the same sequence domain might contribute to the antimicrobial activity. However, they both showed higher inhibitory activity on Gram-positive bacteria than Gram-negative bacteria.<br>It is expected that the novel data described in this thesis will contribute to the burgeoning database of biologically-active peptides from amphibian skin secretions and may ultimately provide a basis for the development of new classes of peptide drugs for both major diseases and for orphan indications.<br>