Bioactive peptides from the defensive skin secretions of selected Australian and Asian frogs

• Main Author: Gan, Tian
• Published: Queen's University Belfast 2017
• Subjects: 615.3
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.726349

Frog skin secretions are recognised as an extraordinarily rich source of antimicrobial and pharmacological peptides, which are adapted to serve as the first-line defences against microorganisms and predators. To date, a wide variety of antimicrobial peptides and pharmacological peptides have been identified in frog skin secretions and some are significant as therapeutic leads. In this thesis, several bioactive peptides have been studied in the secretions of the Australian frog, Litoria infrafrenata and the Asian frog, Odorrana livida, by using genomic and proteomic techniques. The cDNAs encoding novel peptide biosynthetic precursors were each cloned from respective cDNA libraries of the frog skin secretions using a “shotgun” cloning strategy employing a degenerate primer designed to the highly-conserved domain of 5’-untranslated regions of previously known peptide precursor cDNAs from Rana and Litoria. Mature peptides were identified in respective species skin secretion reverse phase HPLC fractions using MALDI-TOF MS and their sequences were confirmed using tandem MS/MS fragmentation sequencing. Replicates of the novel peptides and their analogues were synthesised and analysed by RP-HPLC and MALDI-TOF MS to establish their degree of purity and authenticity of structure. The synthetic peptides were used in several biological assays, such as antimicrobial assays, a haemolysis assay and smooth muscle assays. The peptides described in this study could be divided into antimicrobial peptides and bradykinin-related peptides. All the antimicrobial peptides possessed broad-spectrum antimicrobial activity and a relatively low cytotoxicity. The bradykinin-related peptides exhibited significant and selective activities on different mammalian smooth muscle preparations. These discoveries enrich the diversity of the bioactive peptides in these frogs. These data indicate that the skin secretions of amphibians can continue to provide novel peptide templates for the rational design of analogues with possible therapeutic utility.