Identification and rational design of Bowman-Birk type protease inhibitory peptides derived from Ranidae frogs

  • Xi Chen

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

In recent years, increasing numbers of complex trace components have become accessible to obtain pure products and determine their precise chemical structures from a wide variety of living organisms. Research on synthesis, semi-synthesis and biosynthesis of natural active compounds has provided more new drugs that are independent of natural resources. The catalogues of peptides in skin secretions of different species show incredible structural and functional diversity which have irreplaceable value in biomedical research and natural drug discovery.

In this research, two novel Bowman-Birk type peptides, QUB1875 and QUB1906, of the ranacyclin family, were identified by molecular biotechnologies from the skin secretions of Limnonectes fujianesis and Sylvirana latouchii, respectively. After chemical synthesis, biofunctional identification was carried out on the two wild trypsin inhibitory peptides and their modified analogues.
In chapter 3, the substitution of Trp by Ile in P2’ enhanced the trypsin inhibitory activity of QUB1801 more than parent QUB1875 and both could inhibit the up-regulation of pro-inflammatory cytokines induced by lipopolysaccharide (LPS) in THP-1 (TNF-α, IL-6 and IL-1β) and RAW264.7 cells (TNF-α and IL-6). At the same time, a significant decrease in mRNA levels of TLR4-related pathways was detected in LPS-induced THP-1 cells treated with QUB1801. After substitution of Lys in P1 by Phe, QUB1894 and QUB1820 exhibited chymotrypsin inhibitory effects and anti-proliferative activity against breast, prostate and lung cancer cell lines. Moreover, the P2’ substituted analogue QUB1820 also promoted chymotrypsin inhibition more than the parent. In chapter 4, QUB1906 and designed analogue, QUB1853, displayed trypsin inhibitory activity and antimicrobial activity. Meanwhile, QUB1873, the designed chymotrypsin inhibitor with anti-proliferative effect on a series of human cancer cell lines, was found to activate caspase 3/7 in H157 and H838 cells and induce cell apoptosis. In chapter 5, QUB1571 and QUB1590 were designed based on parent QUB1906 from the nine-residue active loop in plant-derived BBIs. However, the functional assessment indicated that they lost other bioactivities except protease inhibition, which meant the simplification of the structure of the ranacyclin family requires more research. Additionally, all of the peptides showed low cytotoxicity on horse erythrocytes and HMEC-1 cells.

In conclusion, the initially verified antimicrobial, anticancer and immunomodulatory effects not only prove that QUB1875 and QUB1906 can achieve the expected transformation and improvement of biological activity through structural modification, but also provide ideas for the design of multifunctional peptide drugs.
Date of AwardDec 2020
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SupervisorMei Zhou (Supervisor), Lei Wang (Supervisor), Chengbang Ma (Supervisor) & Tianbao Chen (Supervisor)

Keywords

  • Bowman–Birk type inhibitor
  • Ranacyclin family
  • antimicrobial
  • anticancer
  • anti-inflammatory

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