ABSTRACT
The first structure of an intradiol dioxygenase was the structure of PCD, determinedo at 2.1 A [47]. The functional common denominator for the intradiol dioxygenases, an ap-Fe(III) unit that is present in different oligomeric forms in the different enzymes, was shown to consist of a and p subunits with similar structures. The subunits are each formed by a sandwich of mixed p sheets (Fig. 6) and are related by a pseudotwofold axis, suggesting that they have evolved through a gene duplication event. The active site of PCD is found close to the subunit interface and is formed by a solventaccessible crevice. The Fe(III) ion in PCD is coordinated by Tyr447, Tyr408, His460, and His462 (Fig. 7a). A solvent molecule, which is most likely a hydroxide, completes the trigonal bipyrimidal coordination. The ligands of Fe(III), and other residues of the active site, are contributed from loops of the end regions of p strands of the p sand wich of the p subunit.
