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Title: Regulation of the Rsr1 GTPase during polarized growth in Candida albicans
Author: Bedekovic, Tina
ISNI:       0000 0004 7226 0776
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 2018
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Candida albicans is an opportunistic fungal pathogen that can cause systemic infections in immunocompromised patients, where the formation of invasive hyphal filaments contributes to fatal levels of sepsis and organ failure. Hypha-mediated tissue damage depends on directional growth responses that are regulated by the small NRas-like GTPase, Rsr1. In S. cerevisiae, Rsr1 is K-Ras-like and specifies the yeast bud site where it is activated by its guanine-nucleotide exchange factor (GEF), Bud5, and de-activated by its GTPase activating protein (GAP), Bud2. However, its role in C. albicans hyphae is less understood. To elucidate the role of Rsr1 in hyphae, we generated mutant strains expressing a single copy of Rsr1 in a GDP-locked (Rsr1K16N) or GTP-locked (Rsr1G12V) form and compared their phenotypes with those of the rsr1?/?, bud5?/? and bud2?/? null strains. Deletion or dysregulation of Rsr1 caused large, rounded yeast cells and shorter hyphae that were unable to steer round obstacles or penetrate agar. Strikingly, these defects were seen in the strain expressing Rsr1K16N but not in the bud5?/? null, suggesting that Rsr1 may be regulated by a second GEF. Deletion and mis-regulation of Rsr1 caused abnormal intracellular organization in yeast and hyphae, and cells were multinucleate and exhibited vacuolar fusion defects. The site of Rsr1 activity is thought to be regulated by the localization of the Bud5 and Bud2 regulators at the tip and subapical region of hyphae, respectively. Here we show that YFP-Rsr1K16N and YFP-Rsr1G12V were differentially localized. YFPRsr1K16N appeared as patches on the plasma membrane whereas YFP-Rsr1G12V was uniformly localized to the plasma membrane, similar to WT. Proteomics results using heterologously-expressed GST-tagged mutant proteins with yeast and hyphal lysates showed that activity state and cell morphology differentially determined the binding partners of Rsr1. These findings suggest a more complex role for the N-Ras Rsr1 GTPase in C. albicans than has been described for the K-Ras Rsr1 GTPase in the yeast, S. cerevisiae.
Supervisor: Not available Sponsor: Society for Experimental Biology
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Candida albicans ; Guanosine triphosphatase