Type 1 Cu Structure of Blue Nitrite Reductase from Alcaligenes xylosoxidans GIFU 1051 at 2.05 Å Resolution: Comparison of Blue and Green Nitrite Reductases

The crystal structure of the blue nitrite reductase from Alcaligenes xylosoxidans GIFU 1051 (AxgNIR) has been determined at 2.05 Å resolution. AxgNIR contains both type 1 and 2 Cu sites, the geometry of the former being distorted tetrahedral. The superpositioning of the type 1 Cu sites in the blue enzyme and a green nitrite reductase revealed that the orientation of the Met160 side chain differed. The deviation of the S3(Met150) atom from the axial position of the NNS plane formed by two N3(His95 and His145) and one Sβ(Cysl36) atom caused the difference in the colors of the enzymes, i.e. blue and green.