DXP Reductoisomerase: Reaction of the Substrate in Pieces Reveals a Catalytic Role for the Nonreacting Phosphodianion Group

Abstract

The role of the nonreacting phosphodianion group of 1-deoxy-d-xylulose-5-phosphate (DXP) in catalysis by DXP reductoisomerase (DXR) was investigated for the reaction of the “substrate in pieces”. The truncated substrate 1-deoxy-l-erythrulose is converted by DXR to 2-<i>C</i>-methylglycerol with a <i>k</i>_cat/<i>K</i>_m that is 10⁶-fold lower than that for DXP. Phosphite dianion was found to be a nonessential activator, providing 3.2 kcal/mol of transition state stabilization for the truncated substrate. These results implicate a phosphate-driven conformational change involving loop closure over the DXR active site to generate an environment poised for catalysis