Correlation of gene expression and protein production rate - a system wide study.

BACKGROUND: Growth rate is a major determinant of intracellular function. However its effects can only be properly dissected with technically demanding chemostat cultivations in which it can be controlled. Recent work on Saccharomyces cerevisiae chemostat cultivations provided the first analysis on genome wide effects of growth rate. In this work we study the filamentous fungus Trichoderma reesei (Hypocrea jecorina) that is an industrial protein production host known for its exceptional protein secretion capability. Interestingly, it exhibits a low growth rate protein production phenotype. RESULTS: We have used transcriptomics and proteomics to study the effect of growth rate and cell density on protein production in chemostat cultivations of T. reesei. Use of chemostat allowed control of growth rate and exact estimation of the extracellular specific protein production rate (SPPR). We find that major biosynthetic activities are all negatively correlated with SPPR. We also find that expression of many genes of secreted proteins and secondary metabolism, as well as various lineage specific, mostly unknown genes are positively correlated with SPPR. Finally, we enumerate possible regulators and regulatory mechanisms, arising from the data, for this response. CONCLUSIONS: Based on these results it appears that in low growth rate protein production energy is very efficiently used primarly for protein production. Also, we propose that flux through early glycolysis or the TCA cycle is a more fundamental determining factor than growth rate for low growth rate protein production and we propose a novel eukaryotic response to this i.e. the lineage specific response (LSR).

Proteome analysis of recombinant xylose-fermenting Saccharomyces cerevisiae.

Introduction of an active xylose utilization pathway into Saccharomyces cerevisiae, which does not naturally ferment pentose sugars, is likely to have a major impact on the overall cellular metabolism as the carbon introduced to the cells will now flow through the pentose phosphate pathway. The metabolic responses in the recombinant xylose-fermenting S. cerevisiae were studied at the proteome level by comparative two-dimensional gel electrophoresis of cellular proteins within a pH range of 3-10. Glucose-limited chemostat cultivations and corresponding chemostat cultivations performed in media containing xylose as the major carbon source were compared. The cultivations were studied in aerobic and anaerobic metabolic steady states and in addition at time points 5, 30 and 60 min after the switch-off of oxygen supply. We identified 22 proteins having a significant abundance difference on xylose compared to glucose, and 12 proteins that responded to change from aerobic to anaerobic conditions on both carbon sources. On xylose in all conditions studied, major changes were seen in the abundance of alcohol dehydrogenase 2 (Adh2p), acetaldehyde dehydrogenases 4 and 6 (Ald4p and Ald6p), and DL-glycerol 3-phosphatase (Gpp1p). Our results give indications of altered metabolic fluxes especially in the acetate and glycerol pathways in cells growing on xylose compared to glucose.