1-deoxy-D-xylulose 5-phosphate synthase (DXS) catalyzes the initial step of the 2-C-methyl-D- erythritol 4-phosphate (MEP) pathway consisting in the condensation of (hydroxiethyl)thiamin derived from pyruvate with D-glyceraldehyde 3-phosphate (GAP) to yield 1-deoxy-D-xylulose 5-phosphate (DXP). The role of the conserved residues H49, E370, D427 and H431 of E. coli DXS was examined by site-directed mutagenesis and kinetic analysis of the purified recombinant enzyme mutants. Mutants at position H49 showed a severe reduction in their specific activities with a decrease of the kcat/KM ratio by two orders of magnitude lower than the wild-type DXS. According to available structural data residue H49 is perfectly positioned to abstract a proton from the donor substrate. Mutations in DXS E370 showed that this residue is also essential for catalytic activity. Three-dimensional structure supports its involvement in cofactor deprotonation, the first step in enzymatic thiamin catalysis. Results obtained with H431 mutant enzymes indicate that this residue plays a role contributing to transition state stabilization. Finally, mutants at position D427 also showed a severe specific activity decrease with a reduction of the kcat/KM ratio. A role in binding the substrate and selecting the stereoisomer is proposed for D427.
 Chappell, J. (2002) The Genetics and Molecular Genetics of Terpene and Sterol Origami. Current Opinion in Plant Biology, 5, 151-157. http://dx.doi.org/10.1016/S1369-5266(02)00241-8
 Zhao, L.S., Chang, W.C., Xiao, Y.L., Liu, H.W. and Liu, P.H. (2013) Methylerythritol Phosphate Pathway of Isopre- noid Biosynthesis. Annual Review of Bio-chemistry, 82, 497-530. http://dx.doi.org/10.1146/annurev-biochem-052010-100934
 Rohmer, M., Knani, M., Simonin, P., Sutter, B. and Sham, H. (1993) Isoprenoid Biosynthesis in Bacteria: A Novel Pathway for Early Steps Leading to Isopentenyl Di-phosphate. The Biochemical Journal, 295, 517-524.
 Eubanks, L.M. and Poulter C.D. (2003) Rhodobacter capsu-latus 1-Deoxy-D-Xylulose 5-Phosphate Synthase: Steady- State Kinetics and Substrate Binding. Biochemistry, 42, 1140-1149. http://dx.doi.org/10.1021/bi0205303
 Sprenger, G.A., Sch?rken, U., Wiegert, T., Grolle, S., De Graaf, A., Taylor, S., Begley, T., Bringer-Meyer, S. and Sahm, H. (1997) Identification of a Novel Thiamin-Dependent Synthase in Escherichia coli Required for the Formation of the 1-Deoxy-D-Xylulose 5-Phosphate Precursor to Isoprenoids, Thiamin, and Pyridoxol. Proceedings of the National Academy of Sciences of the USA, 94, 12857-12862.