Metabolic Engineering of a Pentose Metabolism Pathway in Ethanologenic
            <i>Zymomonas mobilis</i>

Zhang, Min; Eddy, C K; Deanda, K; Finkelstein, Mark; Picataggio, Stephen

doi:10.1126/science.267.5195.240

Cited by 643 publications

(354 citation statements)

References 20 publications

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“…D-xylose occurs abundantly in nature; however, attempts to construct an industrial fermentation system for the large-scale production of ethanol from this carbohydrate have not been very successful [e.g. 168,186]. A recombinant yeast strain expressing spinach TK may improve D-xylose fermentation signi®cantly.…”

Section: Substrate Speci®citymentioning

confidence: 99%

Properties and functions of the thiamin diphosphate dependent enzyme transketolase

Schenk

Duggleby

Nixon

1998

The International Journal of Biochemistry & Cell Biology

221

164

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This review highlights recent research on the properties and functions of the enzyme transketolase, which requires thiamin diphosphate and a divalent metal ion for its activity. The transketolase-catalysed reaction is part of the pentose phosphate pathway, where transketolase appears to control the non-oxidative branch of this pathway, although the overall¯ux of labelled substrates remains controversial. Yeast transketolase is one of several thiamin diphosphate dependent enzymes whose three-dimensional structures have been determined. Together with mutational analysis these structural data have led to detailed understanding of thiamin diphosphate catalysed reactions. In the homodimer transketolase the two catalytic sites, where dihydroxyethyl groups are transferred from ketose donors to aldose acceptors, are formed at the interface between the two subunits, where the thiazole and pyrimidine rings of thiamin diphosphate are bound. Transketolase is ubiquitous and more than 30 full-length sequences are known. The encoded protein sequences contain two motifs of high homology; one common to all thiamin diphosphate-dependent enzymes and the other a unique transketolase motif. All characterised transketolases have similar kinetic and physical properties, but the mammalian enzymes are more selective in substrate utilisation than the nonmammalian representatives. Since products of the transketolase-catalysed reaction serve as precursors for a number of synthetic compounds this enzyme has been exploited for industrial applications. Putative mutant forms of transketolase, once believed to predispose to disease, have not stood up to scrutiny. However, a modi®cation of transketolase is a marker for Alzheimer's disease, and transketolase activity in erythrocytes is a measure of thiamin nutrition. The cornea contains a particularly high transketolase concentration, consistent with the proposal that pentose phosphate pathway activity has a role in the removal of light-generated radicals. #

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Section: Substrate Speci®citymentioning

confidence: 99%

Properties and functions of the thiamin diphosphate dependent enzyme transketolase

Schenk

Duggleby

Nixon

1998

The International Journal of Biochemistry & Cell Biology

221

164

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“…Despite this, wild Z. mobilis strains cannot use xylose, the major component of hemicellulose [4]. Hence, many efforts have been devoted to develop efficient xylose-fermenting Z. mobilis, and at present, several recombinant strains capable of fermenting xylose to ethanol have been engineered [5,6]. However, the ability of engineered strains to metabolize xylose is lower than their ability to metabolize glucose.…”

mentioning

confidence: 99%

Optimization of a synthetic medium for ethanol production by xylose-fermenting Zymomonas mobilis using response surface methodology

Dong

Zhao

et al. 2012

Chin. Sci. Bull.

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A synthetic medium for ethanol production by recombinant xylose-fermenting Zymomonas mobilis was optimized using Plackett-Burman (PB) design and response surface methodology (RSM). The effects of 19 medium components were investigated by PB design. Eight of these components were determined to have significant effects on ethanol production. The statistical model was constructed via central composite design (CCD) using five selected variables, including xylose, trisodium citrate, choline chloride, pyridoxine, and thiamine. The validity of the developed model was verified. The ethanol concentration in the optimized medium was 6.7% higher than in the RM medium. The optimized medium was then simplified to give the final synthetic medium (S2), in which the ethanol concentration was 20.7% higher than in the RM medium. Xylose and trisodium citrate were the key medium components influencing ethanol production, while calcium pantothenate was the only growth factor required by recombinant Z. mobilis. Ethanol production and growth response were directly proportional to the logarithm of the concentration of trisodium citrate in the range of 0.1-1.6 g/L.recombinant Zymomonas mobilis, synthetic medium, ethanol production, response surface methodology, trisodium citrate, xylose Citation:Dong H N, Zhao X M, Ma Y Y, et al. Optimization of a synthetic medium for ethanol production by xylose-fermenting Zymomonas mobilis using response surface methodology.

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“…Although the sugar content in lignocellulosic materials (e.g., agricultural wastes such as corn stover) is higher than 50% of their dry weight, the heterogeneous nature of lignocellulosic sugars inhibits efficient microbial catabolism and thus decreases production (2,3). Industrial microbes such as S. cerevisiae and Zymomonas mobilis do not natively metabolize xylose, and a foreign xylose catabolic pathway must be integrated into these hosts for xylose utilization (4,5). Even for bacteria like E. coli that natively contain the xylose catabolic pathway, xylose utilization rates and growth rates on xylose are low (6).…”

mentioning

confidence: 99%

Experimental evolution reveals an effective avenue to release catabolite repression via mutations in XylR

Sievert

Nieves

Panyon

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Microbial production of fuels and chemicals from lignocellulosic biomass provides promising biorenewable alternatives to the conventional petroleum-based products. However, heterogeneous sugar composition of lignocellulosic biomass hinders efficient microbial conversion due to carbon catabolite repression. The most abundant sugar monomers in lignocellulosic biomass materials are glucose and xylose. Although industrial Escherichia coli strains efficiently use glucose, their ability to use xylose is often repressed in the presence of glucose. Here we independently evolved three E. coli strains from the same ancestor to achieve high efficiency for xylose fermentation. Each evolved strain has a point mutation in a transcriptional activator for xylose catabolic operons, either CRP or XylR, and these mutations are demonstrated to enhance xylose fermentation by allelic replacements. Identified XylR variants (R121C and P363S) have a higher affinity to their DNA binding sites, leading to a xylose catabolic activation independent of catabolite repression control. Upon introducing these amino acid substitutions into the E. coli D-lactate producer TG114, 94% of a glucose–xylose mixture (50 g⋅L−1 each) was used in mineral salt media that led to a 50% increase in product titer after 96 h of fermentation. The two amino acid substitutions in XylR enhance xylose utilization and release glucose-induced repression in different E. coli hosts, including wild type, suggesting its potential wide application in industrial E. coli biocatalysts.

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Metabolic Engineering of a Pentose Metabolism Pathway in Ethanologenic Zymomonas mobilis

Cited by 643 publications

References 20 publications

Properties and functions of the thiamin diphosphate dependent enzyme transketolase

Properties and functions of the thiamin diphosphate dependent enzyme transketolase

Optimization of a synthetic medium for ethanol production by xylose-fermenting Zymomonas mobilis using response surface methodology

Experimental evolution reveals an effective avenue to release catabolite repression via mutations in XylR

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