Poster Title: 13C-NMR to monitor online the kinetics of intracellular metabolite pools in response to heat stress: input data for modeling the trehalose cycle in Saccharomyces cerevisiae 10th International Conference on Molecular Systems Biology February 25-28, 2008, University of the Philippines, Diliman, Quezon City Authors: L. Fonseca, C. Sanchez, J. Wu, H. Santos, and E.O. Voit Presentor: Luis Fonseca (Universidade Nova de Lisboa, Portugal)
Abstract: Trehalose is widely distributed in living cells where it plays a variety of roles that are generally associated with protection against stress. The disaccharide is frequently found in yeast, fungi, and plants, but also occurs in many bacteria and hyperthermophilic archaea. In Saccharomyces cerevisiae, the intracellular concentration of trehalose increases rapidly in response to many environmental stresses, including heat stress. The high trehalose levels have been correlated with tolerance to adverse conditions and led to the notion that trehalose functions as a chemical chaperone. The objective of the present work is to understand the design and operation of the trehalose cycle in S. cerevisiae through a combination of experimental and computational approaches. Here, we revisit earlier work, which assumed that trehalose production is transcriptionally controlled. In conflict with this assumption, newer metabolomics data from our lab show that trehalose increases much too fast to be driven by genomic mechanisms. Instead, our preliminary modeling analysis suggests that observed heat induced changes in the activity of key enzymes might be sufficient to evoke the observed responses. The data for this analysis came in part from published data and in part from new real-time metabolic time course studies using in vivo NMR methods. Specifically, a circulatory system was used to pump the yeast cell suspension between a mini-reactor and the NMR tube in a 500 MHz spectrometer. Temperature, pH, and pO2 were controlled in the bioreactor. A pulse of [1-13C]-glucose was added and the time courses of labeled metabolites were monitored under control conditions and also during heat stress (39ºC). Cells accumulated small amounts of trehalose (2-4 mM) under control conditions, while FBP reached 18 mM. Under heat stress (10 min 39ºC), trehalose accumulation reached 8 mM following a pulse of 65 mM glucose. When the duration of the stress was increased to one hour and 3 pulses of glucose were supplied, trehalose increased to 25 mM. The experimental system also allowed monitoring end-product formation (ethanol, glycerol and acetate). The time courses of FBP and trehalose build-up combined with data at the transcriptional and transductional level of relevant genes of the trehalose cycle were used as input data for a series of computational models. Source |