title: Characterization of a nitrite reductase involved in nitrifier denitrification.
abstract: Nitrifier denitrification is the conversion of nitrite to nitrous oxide by ammonia-oxidizing organisms. This process, which is distinct from denitrification, is active under aerobic conditions in the model nitrifier Nitrosomonas europaea. The central enzyme of the nitrifier dentrification pathway is a copper nitrite reductase (CuNIR). To understand how a CuNIR, typically inactivated by oxygen, functions in this pathway, the enzyme isolated directly from N. europaea (NeNIR) was biochemically and structurally characterized. NeNIR reduces nitrite at a similar rate to other CuNIRs but appears to be oxygen tolerant. Crystal structures of oxidized and reduced NeNIR reveal a substrate channel to the active site that is much more restricted than channels in typical CuNIRs. In addition, there is a second fully hydrated channel leading to the active site that likely acts a water exit pathway. The structure is minimally affected by changes in pH. Taken together, these findings provide insight into the molecular basis for NeNIR oxygen tolerance.
authors.affiliation: From the Departments of Molecular Biosciences and of Chemistry, Northwestern University, Evanston, Illinois 60208 and.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Lawton
authors.affiliation: From the Departments of Molecular Biosciences and of Chemistry, Northwestern University, Evanston, Illinois 60208 and.
authors.forename: Kimberly E
authors.initials: KE
authors.lastname: Bowen
authors.affiliation: Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331.
authors.forename: Luis A
authors.initials: LA
authors.lastname: Sayavedra-Soto
authors.affiliation: Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Arp
authors.affiliation: From the Departments of Molecular Biosciences and of Chemistry, Northwestern University, Evanston, Illinois 60208 and. Electronic address: amyr@northwestern.edu.
authors.forename: Amy C
authors.initials: AC
authors.lastname: Rosenzweig
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D058440:Denitrification; D009572:Nitrite Reductases / Q000737:chemistry* / Q000378:metabolism; D009573:Nitrites / Q000737:chemistry / Q000378:metabolism; D043370:Nitrosomonas europaea / Q000201:enzymology*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D009573:Nitrites; D009572:Nitrite Reductases; D010100:Oxygen
keywords: Copper; Crystal Structure; Denitrification; Electron Transfer; Nitrifier; Nitrite Reductase; Nitrogen Metabolism; Nitrosomonas europaea; Oxygen Binding