Abstract
The efficient use of hemicellulose in the plant cell wall is critical for the economic conversion of plant biomass to renewable fuels and chemicals. Previously, the yeast Saccharomyces cerevisiae has been engineered to convert the hemicellulose-derived pentose sugars xylose and arabinose to d-xylulose-5-phosphate for conversion via the pentose phosphate pathway (PPP). However, efficient pentose utilization requires PPP optimization and may interfere with its roles in NADPH and pentose production. Here, we developed an alternative xylose utilization pathway that largely bypasses the PPP. In the new pathway, d-xylulose is converted to d-xylulose-1-phosphate, a novel metabolite to S. cerevisiae, which is then cleaved to glycolaldehyde and dihydroxyacetone phosphate. This synthetic pathway served as a platform for the biosynthesis of ethanol and ethylene glycol. The use of d-xylulose-1-phosphate as an entry point for xylose metabolism opens the way for optimizing chemical conversion of pentose sugars in S. cerevisiae in a modular fashion.
Highlights
Utilization of pentose sugars in hemicellulose is essential for economical biofuel and renewable chemical production from plant cell wall derived biomass [1,2]
We hypothesized that rat liver KHK might be used to catalyze the second step of the pathway–the conversion of D-xylulose to D-xylulose-1-phosphate (X1P)–due to its similarity to ketohexokinase from human liver (80% amino acid identity), which catalyzes this reaction [14], and the fact that rat liver KHK can phosphorylate fructose in S. cerevisiae cell lysates [15]
These results suggest that XKS1 deletion was necessary for driving metabolic flux through Dxylulose-1-phosphate to produce ethylene glycol
Summary
Utilization of pentose sugars in hemicellulose is essential for economical biofuel and renewable chemical production from plant cell wall derived biomass [1,2]. To broaden its substrate spectrum, heterologous enzymes from bacteria and fungi have been successfully engineered into S. cerevisiae to enable xylose and arabinose consumption [3,4,5]. These pathways deliver xylose and arabinose to the endogenous pentose phosphate pathway (PPP) via D-xylulose-5-phosphate (X5P). It has been found that to improve pentose utilization efficiency, expression of the endogenous PPP enzymes must be manipulated [6,7]. A systematic approach to PLOS ONE | DOI:10.1371/journal.pone.0158111 June 23, 2016
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