Transaldolase TAL

TAL B mutant proteins were characterized biochemically and their 3D structures were determined [34], 

TAL B samples from E. coli as well as from yeast were assayed successfully with fluorogenic chemical probes that contained (3S,4R)-dihydroxy compounds [35]. 

This should open the search for novel stereospecificities for transaldolase mutant proteins. 

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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. 

Fig. 2.2.2.S Three-dimensional structures of transaldolase B (TAL B) and fructose 6-phosphate aldolase (FSA) from E. coli. a) TAL B forms a dimer structure b), c) FSA is a decameric enzyme consisting of two pentamer rings (right) one on top of the other, b) Two adjacent subunits of FSA showing the C-terminal extension of one...

Fig. 5. A simplified metabolic scheme of ethanol formation from glucose and xylose. Enzyme abbreviations GPDH Glucose 6-phosphate 1-dehydrogenase, PGDH Phosphogluconate dehydrogenase, PGI Glucose 6-phosphate-isomerase, RKI Ribose 5-phosphate isomerase, RPE Ribulose phosphate 3-epimerase, TAL Transaldolase, TKL Transketolase, XDH Xylitol dehydrogenase, XK-. Xylulokinase, XR Xylose reductase...

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