Mechanistic insights into 1-deoxy-D-xylulose 5-phosphate reductoisomerase, a key enzyme of the MEP terpenoid biosynthetic pathway.

The binding mode of 1-deoxy-D-xylulose 5-phosphate (DXP) to 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) (EC 1.1.1.267) from Escherichia coli was investigated via (18) O isotope exchange experiments and determination of the kinetic parameters of the reaction. The results support a C3-C4 substrate binding mode in which DXP chelates a DXR-bound divalent cation via its hydroxyl groups at C3 and C4. Based on this binding mode and the early results, a catalytic cycle for the conversion of DXP to 2-methyl-D-erythritol 4-phosphate mediated by DXR including a pseudo-single molecule transition state of the retro-aldol intermediates is proposed. Taking into account the binding mode of DXP and the catalytic cycle of DXR, the mechanistic insights of DXR are disclosed and the current discrepancies concerning the catalysis of this enzyme are interpreted within the accepted retro-aldol/aldol sequence.