 | Acta Crystallographica Section D Acta Crystallographica Section D BIOLOGICAL CRYSTALLOGRAPHY |
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![[Figure 3]](dw5075fig3mag.jpg)
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Figure 3
Substrates, products and intermediates in the TAL reaction. (a) Overall transformation of sedoheptulose 7-phosphate (S7P) and glyceraldehyde 3-phosphate (G3P) to fructose 6-phosphate (F6P) and erythrose 4-phosphate (E4P). The carbon–carbon bond involved in the TAL-catalyzed tandem retroaldol/aldol sequence is highlighted in red. The remaining panels show the covalent enzymic intermediates involved: (b) carbinolamine I1, initially formed by nucleophilic attack of the TAL active-site lysine on the S7P ketone carbonyl, (c) the subsequent imine I2, formed by dehydration of the carbinolamine, and (d) hydroxy-enamine (dihydroxyacetone) intermediate I3, the result of the retroaldol reaction of the preceding intermediate, shown with the departing E4P product. After departure of E4P and binding of G3P, the subsequent aldol reaction between I3 and G3P yields F6P; upon F6P release, the free enzyme is regenerated. F6P-type intermediates generated in this direction correspond to structures I1, I2 and I3, but lack the hydroxymethine [–CH(OH)–] unit underscored in the intermediates by a blue bracket. See Supplementary Fig. S1 for a more detailed representation of reaction mechanism. |
![[Figure 3]](dw5075fig3.jpg)
| BIOLOGICAL CRYSTALLOGRAPHY |
ISSN: 1399-0047
