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Cellobionic acid utilization: from Neurospora crassa to Saccharomyces cerevisiae.

Li X, Chomvong K, Yu VY, Liang JM, Lin Y, Cate JH - Biotechnol Biofuels (2015)

Bottom Line: Intracellular cellobionic acid was further cleaved to glucose 1-phosphate and gluconic acid by CAP.However, it remains unclear how N. crassa utilizes extracellular gluconic acid.The aldonic acid pathway was successfully implemented in Saccharomyces cerevisiae when N. crassa gluconokinase was co-expressed, resulting in cellobionic acid consumption in both aerobic and anaerobic conditions.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, CA USA.

ABSTRACT

Background: Economical production of fuels and chemicals from plant biomass requires the efficient use of sugars derived from the plant cell wall. Neurospora crassa, a model lignocellulosic degrading fungus, is capable of breaking down the complex structure of the plant cell wall. In addition to cellulases and hemicellulases, N. crassa secretes lytic polysaccharide monooxygenases (LPMOs), which cleave cellulose by generating oxidized sugars-particularly aldonic acids. However, the strategies N. crassa employs to utilize these sugars are unknown.

Results: We identified an aldonic acid utilization pathway in N. crassa, comprised of an extracellular hydrolase (NCU08755), cellobionic acid transporter (CBT-1, NCU05853) and cellobionic acid phosphorylase (CAP, NCU09425). Extracellular cellobionic acid could be imported directly by CBT-1 or cleaved to gluconic acid and glucose by a β-glucosidase (NCU08755) outside the cells. Intracellular cellobionic acid was further cleaved to glucose 1-phosphate and gluconic acid by CAP. However, it remains unclear how N. crassa utilizes extracellular gluconic acid. The aldonic acid pathway was successfully implemented in Saccharomyces cerevisiae when N. crassa gluconokinase was co-expressed, resulting in cellobionic acid consumption in both aerobic and anaerobic conditions.

Conclusions: We successfully identified a branched aldonic acid utilization pathway in N. crassa and transferred its essential components into S. cerevisiae, a robust industrial microorganism.

No MeSH data available.


Related in: MedlinePlus

Aldonic acid consumption pathway. Schematic of aldonic acid utilization in N. crassa and S. cerevisiae. Enzymes are abbreviated as follows: LPMOs lytic polysaccharide monooxygenases, CDHs cellobiose dehydrogenases, BGs β-glucosidases, CBT-1 cellobionic transporter, HXTs hexose transporters, CAP cellobionic acid phosphorylase, GnK gluconokinase.
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Fig6: Aldonic acid consumption pathway. Schematic of aldonic acid utilization in N. crassa and S. cerevisiae. Enzymes are abbreviated as follows: LPMOs lytic polysaccharide monooxygenases, CDHs cellobiose dehydrogenases, BGs β-glucosidases, CBT-1 cellobionic transporter, HXTs hexose transporters, CAP cellobionic acid phosphorylase, GnK gluconokinase.

Mentions: Although S. cerevisiae was capable of utilizing cellobionic acid in aerobic conditions, its consumption in anaerobic conditions was poor. We hypothesized that co-utilization of cellobionic acid with other sugars might improve the anaerobic consumption rates, similar to the phenomenon observed in cellobiose–xylose and xylodextrin–xylose co-consumption experiments [3, 20, 21]. To test this hypothesis, either glucose or xylose was provided in addition to cellobionic acid for anaerobic fermentations of the engineered yeast strains expressing CBT-1, CAP and GnK. The rate of cellobionic acid consumption improved ~5.5-fold in the presence of xylose (Fig. 5d). Although the rate of cellobionic acid consumption remained unchanged when glucose was provided, the lag phase of cellobionic consumption was shortened by ~12 h (Fig. 5d). These results suggest that the addition of other sugars, particularly xylose, can have positive effects on anaerobic consumption of cellobionic acid in S. cerevisiae. This may be because cellobionic acid consumption was previously limited by the rate of gluconic acid utilization via 6-phosphogluconate and the pentose phosphate pathway (Fig. 6). Addition of xylose may improve flux through the pentose phosphate pathway, increasing the ability of S. cerevisiae to utilize gluconic acid.Fig. 6


Cellobionic acid utilization: from Neurospora crassa to Saccharomyces cerevisiae.

Li X, Chomvong K, Yu VY, Liang JM, Lin Y, Cate JH - Biotechnol Biofuels (2015)

Aldonic acid consumption pathway. Schematic of aldonic acid utilization in N. crassa and S. cerevisiae. Enzymes are abbreviated as follows: LPMOs lytic polysaccharide monooxygenases, CDHs cellobiose dehydrogenases, BGs β-glucosidases, CBT-1 cellobionic transporter, HXTs hexose transporters, CAP cellobionic acid phosphorylase, GnK gluconokinase.
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4537572&req=5

Fig6: Aldonic acid consumption pathway. Schematic of aldonic acid utilization in N. crassa and S. cerevisiae. Enzymes are abbreviated as follows: LPMOs lytic polysaccharide monooxygenases, CDHs cellobiose dehydrogenases, BGs β-glucosidases, CBT-1 cellobionic transporter, HXTs hexose transporters, CAP cellobionic acid phosphorylase, GnK gluconokinase.
Mentions: Although S. cerevisiae was capable of utilizing cellobionic acid in aerobic conditions, its consumption in anaerobic conditions was poor. We hypothesized that co-utilization of cellobionic acid with other sugars might improve the anaerobic consumption rates, similar to the phenomenon observed in cellobiose–xylose and xylodextrin–xylose co-consumption experiments [3, 20, 21]. To test this hypothesis, either glucose or xylose was provided in addition to cellobionic acid for anaerobic fermentations of the engineered yeast strains expressing CBT-1, CAP and GnK. The rate of cellobionic acid consumption improved ~5.5-fold in the presence of xylose (Fig. 5d). Although the rate of cellobionic acid consumption remained unchanged when glucose was provided, the lag phase of cellobionic consumption was shortened by ~12 h (Fig. 5d). These results suggest that the addition of other sugars, particularly xylose, can have positive effects on anaerobic consumption of cellobionic acid in S. cerevisiae. This may be because cellobionic acid consumption was previously limited by the rate of gluconic acid utilization via 6-phosphogluconate and the pentose phosphate pathway (Fig. 6). Addition of xylose may improve flux through the pentose phosphate pathway, increasing the ability of S. cerevisiae to utilize gluconic acid.Fig. 6

Bottom Line: Intracellular cellobionic acid was further cleaved to glucose 1-phosphate and gluconic acid by CAP.However, it remains unclear how N. crassa utilizes extracellular gluconic acid.The aldonic acid pathway was successfully implemented in Saccharomyces cerevisiae when N. crassa gluconokinase was co-expressed, resulting in cellobionic acid consumption in both aerobic and anaerobic conditions.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, CA USA.

ABSTRACT

Background: Economical production of fuels and chemicals from plant biomass requires the efficient use of sugars derived from the plant cell wall. Neurospora crassa, a model lignocellulosic degrading fungus, is capable of breaking down the complex structure of the plant cell wall. In addition to cellulases and hemicellulases, N. crassa secretes lytic polysaccharide monooxygenases (LPMOs), which cleave cellulose by generating oxidized sugars-particularly aldonic acids. However, the strategies N. crassa employs to utilize these sugars are unknown.

Results: We identified an aldonic acid utilization pathway in N. crassa, comprised of an extracellular hydrolase (NCU08755), cellobionic acid transporter (CBT-1, NCU05853) and cellobionic acid phosphorylase (CAP, NCU09425). Extracellular cellobionic acid could be imported directly by CBT-1 or cleaved to gluconic acid and glucose by a β-glucosidase (NCU08755) outside the cells. Intracellular cellobionic acid was further cleaved to glucose 1-phosphate and gluconic acid by CAP. However, it remains unclear how N. crassa utilizes extracellular gluconic acid. The aldonic acid pathway was successfully implemented in Saccharomyces cerevisiae when N. crassa gluconokinase was co-expressed, resulting in cellobionic acid consumption in both aerobic and anaerobic conditions.

Conclusions: We successfully identified a branched aldonic acid utilization pathway in N. crassa and transferred its essential components into S. cerevisiae, a robust industrial microorganism.

No MeSH data available.


Related in: MedlinePlus