Biopeptides are synthesised as large pro-protein precursors that have to undergo proteolytic cleavage at positively charged amino acids (Lys and Arg) in order to become active. This cleavage is mediated by a family of subtilin/kexin related calcium dependent serine endoproteinases named prohormone convertases. The present thesis focuses on the endocrine member of the family named PC1/3. PC1/3 is expressed in the regulated secretory pathway of endocrine and neuroendocrine cells, where it was shown to activate various peptide hormones such as proopiomelanocortin (POMC), pro-insulin and pro-glucagon. PC1/3 is synthesized as a large precursor containing a signal peptide, a propeptide, a catalytic domain, a P domain and a C-terminal domain. The activation of the enzyme requires the sequential removal of the signal peptide, the propeptide and ultimately the C-terminal domain. / The structural characterisation of the enzyme is compromised by the difficulty in producing a sufficient amount of recombinant PC1/3. In this thesis it is clearly demonstrated that the production of PC1/3 using Baculovirus technology can be greatly improved by modifying the expression vector in insect cells (Spodoptera frugiperda). In addition, the intracoelemic injection of insect larvae (Tricoplusia ni) with the Baculovirus encoding the recombinant PC1/3 is shown to be a very efficient method for the production of a large amount of prohormone convertases. / It was previously demonstrated that the propeptide is essential for the folding of the enzyme and act as a tight binding inhibitor of the enzyme until the latter reaches the appropriate compartment for substrate cleavage. To assess the role of certain residues within the propeptide in the inhibition of the cognate enzyme, a mutational analysis by alanine scan was conducted. The results demonstrate that the substitution of a single amino acid can affect markedly the inhibition behavior, potency and selectivity of the propeptide towards the enzyme. Moreover, this mutational analysis allowed the first experimental mapping of the sequence involved in propeptide degradation once its function is achieved. / However, PC1/3 also possesses a C-terminal domain which must also be cleaved to allow the full activation of the enzyme. Previous studies showed that this domain is implicated in the sorting of the enzyme to secretory granules. In addition, over expression experiments showed that the C-terminal domain can inhibit the cleavage of certain substrates by PC1/3. The results, presented here, suggest that the CT-peptide acts as a non-essential activator of PC1/3, in vitro, which adds a supplementary level of complexity to the activation process of the enzyme. / Finally, based upon our results, it can be proposed that PC1/3 is a very complex enzyme capable of controlling its enzymatic activity through the coordinate action of its various domains. This exceptional mode of self-regulation is unique among all protease families.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.103282 |
| Date | January 2007 |
| Creators | Rabah, Nadia. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | French |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Division of Experimental Medicine.) |
| Rights | © Nadia Rabah, 2007 |
| Relation | alephsysno: 002652501, proquestno: AAINR38632, Theses scanned by UMI/ProQuest. |
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