The main objective of this thesis was to study the effects of glucose on the regulation central carbon metabolic functions in the human fungal pathogen Candida albicans (C. albicans). The virulence of C. albicans is dependent upon fitness attributes as well as virulence factors. These attributes include robust stress responses and metabolic flexibility (Brown, 2005). The assimilation of carbon sources is fundamentally important for growth in all organisms and essential for the establishment of infections by pathogens, such as C. albicans in their human host. The C. albicans PCK1 and ICL1 genes, which encode the gluconeogenic and glyoxylate cycle enzymes phosphoenolpyruvate carboxykinase and isocitrate lyase are required for growth on non-fermentable carbon sources such as lactate and oleic acid. This thesis examines the impact of glucose upon the assimilation of secondary carbon sources such as lactate and oleic acid by C. albicans. The addition of 2% glucose repressed the CaPCK1 and CaICL1 genes. However, the enzymes CaIcl1 and CaPck1 were not destabilised by glucose and they retained at high levels following glucose addition. As a result, C. albicans cells continued to assimilate lactate and oleic acid in the presence of glucose. In contrast, the ScPck1 and ScIcl1 proteins were degraded rapidly in S. cerevisiae, and lactate and oleic acid assimilation was repressed in response to glucose. Therefore, while C. albicans and S. cerevisiae display similar responses to glucose at the transcriptional level, their responses at post-transcriptional and metabolic level diverge significantly. As a result, C. albicans can assimilate both glucose and alternative carbon sources at the same time. Next, the molecular apparatus that triggers the destabilisation of target proteins in response to glucose in C. albicans was studied. The expression of C. albicans the ICLI ORF in S. cerevisiae suggested that CaIcl1 has lost the molecular signal that triggers destabilisation in response to glucose, as CaIcl1 was not degraded in response to glucose in S. cerevisiae. However, when ScIcl1 was expressed in C. albicans ScIcl1 was rapidly degraded in response to glucose indicating that C. albicans has retained the molecular apparatus for glucose-accelerated degradation of target proteins. ScIcl1 degradation was slowed in C. albicans ubi4/ubi4 mutants. Furthermore, the addition of a putative of S. cerevisiae ubiquitination site carboxy terminus of CaIcl1 led to glucose-accelerated degradation of this protein in C. albicans cells. Therefore, glucose triggers accelerated degradation of target proteins in C. albicans via a ubiquitin-dependent process.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:540454 |
| Date | January 2011 |
| Creators | Sandai, Doblin Anak |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=203832 |
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