title: The substrate-binding site in Cu nitrite reductase and its similarity to Zn carbonic anhydrase.
abstract: Here we investigate the structure of the two types of copper site in nitrite reductase from Alcaligenes xylosoxidans, the molecular organisation of the enzyme when the type-2 copper is absent, and its mode of substrate binding. X-ray absorption studies provide evidence for a fourth ligand at the type-2 Cu, that substrate binds to this site and indicates that this binding does not change the type-1 Cu centre. The substrate replaces a putative water ligand and is accommodated by a lengthening of the Cu-histidine bond by approximately 0.08 A. Modelling suggests a similarity between this unusual type-2 Cu site and the Zn site in carbonic anhydrase and that nitrite is anchored by hydrogen bonds to an unligated histidine present in the type-2 Cu cavity.
authors.affiliation: Molecular Biophysics Group, Daresbury Laboratory, Warrington, Cheshire, UK.
authors.forename: R W
authors.initials: RW
authors.lastname: Strange
authors.forename: F E
authors.initials: FE
authors.lastname: Dodd
authors.forename: Z H
authors.initials: ZH
authors.lastname: Abraham
authors.forename: J G
authors.initials: JG
authors.lastname: Grossmann
authors.forename: T
authors.initials: T
authors.lastname: Brüser
authors.forename: R R
authors.initials: RR
authors.lastname: Eady
authors.forename: B E
authors.initials: BE
authors.lastname: Smith
authors.forename: S S
authors.initials: SS
authors.lastname: Hasnain
mesh_terms: D015502:Absorptiometry, Photon; D000421:Alcaligenes / Q000201:enzymology; D001665:Binding Sites; D002256:Carbonic Anhydrases / Q000737:chemistry* / Q000378:metabolism*; D003300:Copper / Q000378:metabolism*; D008958:Models, Molecular; D009572:Nitrite Reductases / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D013482:Superoxide Dismutase / Q000737:chemistry / Q000378:metabolism; D015032:Zinc / Q000378:metabolism*
chemical_list: D003300:Copper; D013482:Superoxide Dismutase; D009572:Nitrite Reductases; D002256:Carbonic Anhydrases; D015032:Zinc