Integrative approaches for studying pentose metabolism in Saccharomyces cerevisiae

We are interested in broadening the substrate utilisation range of the yeast Saccharomyces cerevisiae and in connection to this to study nutritional responses and signalling at a global level. S.cerevisiae does not naturally utilise pentose sugars unlike most other fungi, and recombinant S.cerevisiae strains have been constructed that contain the xylose utilisation pathway from other yeasts. The recombinant xylose pathway is believed to create a redox imbalance in the cells, due to different cofactor requirements of the enzymes of the pathway, and limit xylose fermentation. In order to understand redox and nutrient regulation in general, and the physiology of xylose utilising S.cerevisiae, we carried out chemostat and batch cultures at various oxygenation levels on xylose as a carbon source, and compared those with glucose cultures. Transcriptional profiling, total proteomics and metabolite analyses were carried out, as well as metabolix flux analysis (MFA) and measurements of metabolic fluxes with 13C-NMR. New responses towards xylose as a carbon source were discovered such as the upregulation of pathways for alternative carbon source utilisation and responses for nutritional control and starvation. The physiology of the recombinant yeast appears to be neither fully repressed (fermentative) nor derepressed (gluconeogenic). Own references [1] H. Maaheimo, J. Fiaux, Z. P. Cakar, J. E. Bailey, U. Sauer, T. Szyperski, Eur J Biochem. 268, 2464-2479 (2001). [2] J. P. Pitkänen, A. Aristidou, L. Salusjärvi, L. Ruohonen, M. Penttilä, Metab Eng. 5, 16-31 (2003). [3] L. Salusjärvi, M. Poutanen, J. P. Pitkänen, H. Koivistoinen, A. Aristidou, N. Kalkkinen, L. Ruohonen, M. Penttilä, Yeast 20, 295-314 (2003). [4] Salusjärvi, L., Pitkänen, J.-P., Aristidou, A., Ruohonen, L. and Penttilä, M. (2003a) (in preparation). [5] Toivari, M.H., Aristidou, A., Ruohonen, L. & Penttilä, M. 2001. Metab. Eng. 3, 236-249.