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Title: Bioactive peptides from the skin secretion of the Mexican giant leaf frog, Pachymedusa dacnicolor
Author: Jiang , Yingchun
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2013
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Amphibian skin is a rich source of biologically-active compounds that are assumed to have diverse physiological and defence functions It has been known for a long time that the granular glands of amphibian skin produce these biologically-active compounds The glands are controlled by sympathetic nerves, and discharge their contents onto the dorsal surface of the animal in response to a variety of stimuli. The compounds secreted by the glands are thought to play various roles, either in the regulation of physiological functions of the skin, or in defence against predators or microorganisms Amphibian skin secretions contain four major categories of biochemical components which are: biogenic amines, steroids, alkaloids and peptides/proteins. It has been demonstrated that among the secretion components, peptides account for a major percentage. Many hundreds of bioactive peptides have been identified in the skin secretions of species from many families of frogs. They can be classified into two major classes: -- antimicrobial peptides and pharmacological peptides such as retroactive peptides, vasoactive peptides and anticancer peptides. Bioactive peptides are superior to many chemical drugs in several ways. For example, antimicrobial peptides have fewer side effects, have good thermal stability, a broad-spectrum antimicrobial action and, because of their non-specific antibacterial mechanism, are less inclined to induce drug resistance. To date, antimicrobial peptides, trypsin inhibitory peptides, bradykinins, tachykinins, caeruleins, litorins, opioids and tryptophyllins, have been discovered in the skin secretions of frogs from the genus, Phyllomedusa. However, species from other genera of phyllomedusine frogs remain relatively unstudied and thus this project aimed to more systematically-identify novel bioactive peptides from the skin secretion of the Mexican giant leaf frog, Pachymedusa dacnicolor , that is the only species within its genus. The focus of the research was to "shotgun" clone the skin peptide precursor -encoding cDNAs, to deduce the peptide structures prior to confirmation by sequencing and to evaluate their bioactivities following chemical synthesis. In this thesis, twelve skin peptides are described from the skin secretion of Pachymedusa dacnicolor. Chapter 3 describes seven of these peptides which were discovered through the ~shotgun " cloning approach. In Chapter 4, five of these peptides were synthesized and subjected to functional assays. In Chapter 5, four bradykinin-related peptides are described and characterized and Chapter 7 describes the isolation of a novel Kazal-type trypsin inhibitor peptide.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available