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.