Deoxy-D-xylulose 5-Phosphate Synthase DXS

Although the purified enzyme is much less active than transketolase (3 U mg versus 80-100 U mg ), it could be utilized as a tool in a one-pot multi-enzyme asymmetric synthesis yielding about 700 mg of the barium salt of DXP [21]. 

Our original paper on DXS has up to now been quoted in more than 200 articles. Purified DXS can be used further for the chemoenzymatic syntheses of various 1-deoxysugars and 1-deoxysugar phosphates, as shown by our group and others [22]. 

Attempts to crystallize DXS with the aim of determining the enzyme s 3D structure have failed so far. In the absence of a 3D structure, yeast transketolase structure was used as a model for DXS. Amino acid residues which are conserved 

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This thermodynamic driving force is particularly useful tvith multienzyme equilibrium systems such as that used in the gram-scale synthesis of tv ro equivalents ofo-xylulose 5-phosphate (104) from (26) (Figure 10.38) [171,172]. Similarly, the corresponding 1-deoxy-D-xylulose 5-phosphate tvas efficiently produced from pyruvate and (34) by the catalytic action of the thiamine diphosphate-dependent 1-deoxy-D-xylulose 5-phosphate synthase (DXS) (EC 2.2.1.7) from E. coli [173]. 

The CPPase substrate DMAPP (15) is formed from isopentenyl pyrophosphate (IPP) (14) via the IPP isomerase reaction. It had been assumed that IPP was generated only via mevalonic acid (12) (Fig. 2), but Rohmer discovered another route, 2-C-methyl-D-erythritol 4-phosphate (13) (MEP) pathway (Fig. 2) [22, 23]. A key step in the MEP pathway is the reaction catalyzed by 1-deoxy-D-xylulose 5-phosphate synthase (DXS), which combines hydroxyethyl thiamine pyrophosphate (hydroxyethyl TPP) generated from pyruvic acid (17) and TPP with glyceral-dehyde 3-phosphate (18) to yield 1-deoxy-D-xylulose 5-phosphate (19) containing five carbons. The mevalonate pathway operates in the cytosol of plants and animals, whereas the MEP pathway is present in the plastid of plants or in eubacteria [24-27]. 

From the many enzymes that are known to make and break C-C bonds, we first chose the two transferases, transketolase (TKT) and transaldolase (TAL), both from the Gram-negative bacterium Escherichia coli. While project B21 evolved, we learned that this microorganism holds other and so far unknown enzymes which are of interest for asymmetric syntheses. One transketolase-like enzyme, 1-deoxy-D-xylulose 5-phosphate synthase (DXS), turned out to be the first enzyme of a novel biosynthetic pathway leading to isoprenoids in bacteria, algae, and plants. The other, fructose 6-phosphate aldolase (ESA) - while similar to transaldolase - allows the direct use of the inexpensive dihydroxyacetone in aldol condensations. 

C-C-Bonding Microbial Enzymes 317 2.2.2.2.2 1-Deoxy-D-xylulose 5-Phosphate Synthase (DXS)... 

Colonization of barley, wheat and maize and rice roots by Glomus intraradices resulted in strong induction of transcript levels of the pivotal enzymes of methylerythritol phosphate pathway of isoprenoid biosynthes i.e., 1 -deoxy-D-xylulose 5-phosphate synthase (DXS) and 1 -deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) (Walter et al., 2000). At the same time six cyclohexenone derivatives were characterized from mycorrhizal wheat and maize roots. DXS2 transcript levels are low in most tissues but are strongly stimulated in roots upon colonization by mycorrhizal fungi, correlated with accumulation of carotenoids and apocarotenoids (Walter et al., 2002). Some reports show that the AM symbiosis may cause an increase, decrease, or no change in the plant defense reactions (Guenoune et al., 2001 Mohr et al., 1998). 

In the first path, the PLP precursor pyridoxine 5-phosphate (PNP) is biosynthesized from 3-hydroxy-1-aminoacetone phosphate 1 and DXP 2 (Figure 6.1). DXP 2 is formed from pyruvate 3 and glyceraldehyde 3-phosphate 4, catalyzed by deoxy-D-xylulose 5-phosphate synthase (DXS). The 3-hydroxy-1-aminoacetone phosphate 1 is obtained from the erythrose 4-phosphate 5 in four steps. The first step involves the oxidation of erythrose 4-phosphate 5, mediated by erythrose 4-phosphate dehydrogenase (GapB), to erythronate 4-phosphate 6. The latter is further oxidized by D-erythronate 4-phosphate dehydrogenase (PdxB) to 3-hydroxy-4-phosphohydroxy-a-ketobutyrate 7. Transamination reaction between... 

In spike lavender, an additional copy of the l-deoxy-D-xylulose-5-phosphate synthase gene (DXS), the first enzymatic step in the methylerythritol phosphate (MEP) pathway leading to the precursors of monoterpenes, from Arabidopsis thaliam was introduced and led to an increase of the essential oil of the leaves of up to 360% and of the essential oil of flowers of up to 74% (Munoz-Bertomeu et al., 2006). 

Battilana, J., Costantini, L., EmanueUi, F., Sevini, F., Segala, C., Moser, S., Velasco, R., Versini, G., Grando, M.S., 2009. The 1-deoxy-d-xylulose 5-phosphate synthase gene co-localizes with a major QTL affecting monoterpene content in grapevine. Theor. Appl. Genet. 118, 653-669. http //dx.doi.Org/10.1007/s00122-008-0927-8. 

Fig. 117.9 An overview of the cytosolic mevalonate pathway and plastidial mevalonate-independent pathway for the biosynthesis of terpenoids (isoprenoids) in plant cells [99] (DMAPP, dimethylallyl diphosphate DXP, l-deoxy-D-xylulose-5-phosphate DXS, DXP synthase DXR, DXP reductoisomerase MEP, 2-C-methyl-D-erythritol 4-phosphate GASP, gfyc-eraldehyde-3-phosphate HMG-CoA, 3-hydroxy-3-methylglutaryl-CoA HMGR, HMGR-CoA reductase IPP, isopentenyl diphosphate. Mevinolin and fosmidomycin are inhibitors of HMGR and DXR, respectively)...

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