Crystal Structure of a Trapped Phosphate Intermediate in Vanadium Apochloroperoxidase Catalyzing a Dephosphorylation Reaction

The crystal structure of the apo form of vanadium chloroperoxidase from Curvularia inaequalis reacted with para-nitrophenylphosphate was determined at a resolution of 1.5 A. The aim of this study was to solve structural details of the dephosphorylation reaction catalyzed by this enzyme. Since the chloroperoxidase is functionally and evolutionary related to several acid phosphatases including human glucose-6-phosphatase and a group of membrane-bound lipid phosphatases, the structure sheds light on the details of the dephosphorylation catalyzed by these enzymes as well. The trapped intermediate found is bound to the active site as a metaphosphate anion PO3-, with its phosphorus atom covalently attached to the Nepsilon2 atom of His496. An apical water molecule is within hydrogen-bonding distance to the phosphorus atom of the metaphosphate, and it is in a perfect position for a nucleophilic attack on the metaphosphate-histidine intermediate to form the inorganic phosphate. This is, to our knowledge, the first structural characterization of a real reaction intermediate of the inorganic phosphate group release in a dephosphorylation reaction.