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Abstract: This thesis deals with the mechanisms of sensing and signalling of glucose/fructose in baker’s yeast, focusing on the Snf1 transduction pathway. In the first place, we approached the question of how a reduction in glucose transport leads to a decrease in glycolytic rate. Modelling of the experimental data indicated that phosphofructokinase (PFK) might control glycolysis in order to allow adaptation to reduced sugar availability. We hypothesises that this could be due to a mechanism involving Protein Kinase A (PKA) in the generation of the PFK activator fructose-2, 6-bisphosphate. Next we addressed the question of which transcriptional responses were triggered by sensors of extracellular glucose. In a strain where glucose transport is abolished the response to glucose pulse is limited to the expression of hexotransporters. Any other significant response requires internalisation of glucose. Snf1 is an essential protein kinase for growth on poor carbon sources. Catabolism of glucose generally leads to the downregulation of Snf1 activity. We were interested in understanding how Snf1 is turned on and off. To approach this question, we undertook an interdisciplinary approach covering physiology, molecular biology, bioinformatics and single cell microscopy. We have established that the inactivation of the SNF1 pathway after addition of glucose occurs very rapidly (in less than 1 min) and therefore is independent on transcriptional events. The detailed time-course data sets obtained were used to explore the regulation upstream of Snf1 by modelling. Simulations revealed a scenario indicating that regulation of the phosphatase complex Reg1/Glc7 is sufficient to explain the activation/deactivation profile of the pathway. Hence, this supports the hypothesis that the Snf1-activating kinases do not respond to changes in the abundance of glucose. The response to glucose has been shown to require the phosphorylation of internal glucose into glucose-6-P. Hxk2 is the predominant hexokinase during growth on glucose. In addition, to its enzymatic role it has been suggested to play part in controlling the activity of the main glucose-dependent transcription repressor, Mig1. We present data suggesting that Hxk2 affects the Mig1 activation state in a parallel pathway to the SNF1 signalling pathway. The proposed mechanism requires Hxk2 protection of Mig1 regulatory residues from the phosphorylation mediated by Snf1. In conclusion, this thesis dives into the different glucose signalling pathways of baker’s yeast and attempts to identify what is the molecular basis of sugar sensing. A deepened knowledge of these pathways behaviour in yeast may in turn be useful in understanding the development of Diabetes type II, an increasingly widespread disease in humans, which it is believed to be influenced by the failure of cells to recognise and internalise sugar.
Keywords: yeast, Snf1, sugar signalling
Published in DiRROS: 24.06.2026; Views: 66; Downloads: 34
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Keywords: free sugar, ultra-processed food, food composition, sales data, nutrition label, Slovenia
Published in DiRROS: 18.11.2025; Views: 564; Downloads: 317
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Keywords: beverages, reformulation, added sugar, food composition, HPLC, database
Published in DiRROS: 11.11.2025; Views: 561; Downloads: 304
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