Molybdenum site structure of Escherichia coli YedY, a novel bacterial oxidoreductase

We report a structural characterization using X-ray absorption spectroscopy of the molybdenum site of Escherichia coli YedY, a novel oxidoreductase related to be the sulfite oxidase family of molybdenum enzymes. We find that the enzyme can exist in Mo(V) and Mo(IV) oxidation states but cannot be readily oxidized to the Mo(VI) form. Mo(V) YedY has molybdenum coordination similar to that of sulfite oxidase, with one Mo═O at 1.71 Å, three Mo-S at 2.39 Å, and one Mo-OH at 2.09 Å, which elongates to 2.20 Å upon reduction to Mo(IV), indicating Mo-OH(2) coordination. The Mo(V) enzyme also possesses a long Mo-O coordination at 2.64 Å, which may be due to oxygen coordination by Asn-45 O(δ), with Mo-O(δ) approximately trans to the Mo═O group. A comparison with sulfite oxidase indicates that YedY possesses a much more uniform Mo-S coordination, with a maximum permitted deviation of less than 0.05 Å. Our results indicate that the YedY active site shows considerable similarity to but also important differences from that of reduced forms of sulfite oxidase.