Chapter 3 Galactose Metabolism in Yeast—Structure and Regulation of the Leloir Pathway Enzymes and the Genes Encoding Them

Sellick, Christopher A.; Campbell, Robert N.; Reece, Richard J.

doi:10.1016/s1937-6448(08)01003-4

Cited by 126 publications

(133 citation statements)

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“…Exceptions were ribose, galactose, and lactose, on which conidiation was strongly reduced but biomass formation occurred. Ribose may rely on a special ribokinase for activation, whereas galactose and lactose may rely on a galactokinase for activation, leading to glucose-6-phosphate via the Leloir pathway (44). However, we were surprised by the negative effect of glucose in the presence of alternative gluconeogenic carbon sources.…”

Section: Vol 9 2010mentioning

confidence: 82%

“…This mutant failed to grow on glucose, fructose, mannose, glucosamine, sorbose, and saccharose. Some growth on galactose and lactose (galactose containing) was observed, which may be due mainly to the Leloir pathway, which generates glucose-6-phosphate from galactose-1-phosphate in several steps (44). Some very minor growth on starch was also observed.…”

Section: Downloaded Frommentioning

confidence: 99%

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Aspergillus fumigatus Catalytic Glucokinase and Hexokinase: Expression Analysis and Importance for Germination, Growth, and Conidiation

Fleck

Brock

2010

Eukaryot Cell

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Fungi contain several hexokinases, which are involved either in sugar phosphorylation or in carbon source sensing. Glucose and fructose phosphorylations appear to rely exclusively on glucokinase and hexokinase. Here, we characterized the catalytic glucokinase and hexokinase from the opportunistic human pathogen Aspergillus fumigatus and showed that both enzymes display different biochemical properties and play different roles during growth and development. Glucokinase efficiently activates glucose and mannose but activates fructose only to a minor extent. Hexokinase showed a high efficiency for fructose activation but also activated glucose and mannose. Transcript and activity determinations revealed high levels of glucokinase in resting conidia, whereas hexokinase was associated mainly with the mycelium. Consequentially, a glucokinase mutant showed delayed germination at low glucose concentrations, whereas colony growth was not overly affected. The deletion of hexokinase had only a minor impact on germination but reduced colony growth, especially on sugar-containing media. Transcript determinations from infected mouse lungs revealed the expression of both genes, indicating a contribution to virulence. Interestingly, a double-deletion mutant showed impaired growth not only on sugars but also on nonfermentable nutrients, and growth on gluconeogenic carbon sources was strongly suppressed in the presence of glucose. Furthermore, the glkA hxkA deletion affected cell wall integrity, implying that both enzymes contribute to the cell wall composition. Additionally, the absence of either enzyme deregulated carbon catabolite repression since mutants displayed an induction of isocitrate lyase activity during growth on glucose-ethanol medium. Therefore, both enzymes seem to be required for balancing carbon flux in A. fumigatus and are indispensable for growth under all nutritional conditions.

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Section: Vol 9 2010mentioning

confidence: 82%

Section: Downloaded Frommentioning

confidence: 99%

Aspergillus fumigatus Catalytic Glucokinase and Hexokinase: Expression Analysis and Importance for Germination, Growth, and Conidiation

Fleck

Brock

2010

Eukaryot Cell

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“…Although the precise molecular role(s) for the .30,000 eukaryotic lncRNAs identified thus far is not well defined, an emerging theme is that lncRNAs fine tune transcriptional switches in gene expression (Fatica and Bozzoni 2014). The GAL cluster genes are part of the galactose metabolic switch that allows budding yeast to rapidly adapt to the availability of galactose as an alternative to glucose as a carbon source (Lohr et al 1995;Sellick et al 2008). This switch involves a number of carbon source sensors, sugar transporters, signaling cascades, and transcriptional effectors to globally alter the metabolic program for energy production (Gancedo 1998;Johnston and Kim 2005;Traven et al 2006;Broach 2012).…”

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confidence: 99%

Regulation of Glucose-Dependent Gene Expression by the RNA Helicase Dbp2 in Saccharomyces cerevisiae

et al. 2014

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Cellular homeostasis requires a fine balance between energy uptake, utilization, and growth. Dbp2 is a member of the DEAD-box protein family in Saccharomyces cerevisiae with characterized ATPase and helicase activity in vitro. DEAD-box RNA helicases are a class of enzymes that utilize ATP hydrolysis to remodel RNA and/or RNA-protein (RNP) composition. Dbp2 has been proposed to utilize its helicase activity in vivo to promote RNA-protein complex assembly of both messenger (m)RNAs and long noncoding (lnc)RNAs. Previous work from our laboratory demonstrated that loss of DBP2 enhances the lncRNA-dependent transcriptional induction of the GAL genes by abolishing glucose-dependent repression. Herein, we report that either a carbon source switch or glucose deprivation results in rapid export of Dbp2 to the cytoplasm. Genome-wide RNA sequencing identified a new class of antisense hexose transporter transcripts that are specifically upregulated upon loss of DBP2. Further investigation revealed that both sense and antisense hexose transporter (HXT) transcripts are aberrantly expressed in DBP2-deficient cells and that this expression pathway can be partially mimicked in wild-type cells by glucose depletion. We also find that Dbp2 promotes ribosome biogenesis and represses alternative ATP-producing pathways, as loss of DBP2 alters the transcript levels of ribosome biosynthesis (snoRNAs and associated proteins) and respiration gene products. This suggests that Dbp2 is a key integrator of nutritional status and gene expression programs required for energy homeostasis.

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“…3b). This is probably due to the fact that yeast maintains a strict hierarchy in terms of sugar utilization and glucose is at the top [23]. In the present study, the glucose consumption rate was not affected by the engineering of XYL1 or XYL2, and free glucose in the fermentation medium was depleted after 30 h fermentation.…”

Section: Discussionmentioning

confidence: 42%

Metabolic engineering of Saccharomyces cerevisiae for increased bioconversion of lignocellulose to ethanol

Cai

2012

Indian J Microbiol

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The absence of pentose-utilizing enzymes in Saccharomyces cerevisiae is an obstacle for efficiently converting lignocellulosic materials to ethanol. In the present study, the genes coding xylose reductase (XYL1) and xylitol dehydrogenase (XYL2) from Pichia stipitis were successfully engineered into S. cerevisae. As compared to the control transformant, engineering of XYL1 and XYL2 into yeasts significantly increased the microbial biomass (8.1 vs. 3.4 g/L), xylose consumption rate (0.15 vs. 0.02 g/h) and ethanol yield (6.8 vs. 3.5 g/L) after 72 h fermentation using a xylose-based medium. Interestingly, engineering of XYL1 and XYL2 into yeasts also elevated the ethanol yield from sugarcane bagasse hydrolysate (SUBH). This study not only provides an effective approach to increase the xylose utilization by yeasts, but the results also suggest that production of ethanol by this recombinant yeasts using unconventional nutrient sources, such as components in SUBH deserves further attention in the future.

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Chapter 3 Galactose Metabolism in Yeast—Structure and Regulation of the Leloir Pathway Enzymes and the Genes Encoding Them

Cited by 126 publications

References 139 publications

Aspergillus fumigatus Catalytic Glucokinase and Hexokinase: Expression Analysis and Importance for Germination, Growth, and Conidiation

Aspergillus fumigatus Catalytic Glucokinase and Hexokinase: Expression Analysis and Importance for Germination, Growth, and Conidiation

Regulation of Glucose-Dependent Gene Expression by the RNA Helicase Dbp2 in Saccharomyces cerevisiae

Metabolic engineering of Saccharomyces cerevisiae for increased bioconversion of lignocellulose to ethanol

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