title: The crystal structure of Cupriavidus necator nitrate reductase in oxidized and partially reduced states.
abstract: The periplasmic nitrate reductase (NapAB) from Cupriavidus necator is a heterodimeric protein that belongs to the dimethyl sulfoxide reductase family of mononuclear Mo-containing enzymes and catalyzes the reduction of nitrate to nitrite. The protein comprises a large catalytic subunit (NapA, 91 kDa) containing the molybdenum active site plus one [4Fe-4S] cluster, as well as a small subunit (NapB, 17 kDa), which is a diheme c-type cytochrome involved in electron transfer. Crystals of the oxidized form of the enzyme diffracted beyond 1.5 Å at the European Synchrotron Radiation Facility. This is the highest resolution reported to date for a nitrate reductase, providing true atomic details of the protein active center, and this showed further evidence on the molybdenum coordination sphere, corroborating previous data on the related Desulfovibrio desulfuricans NapA. The molybdenum atom is bound to a total of six sulfur atoms, with no oxygen ligands or water molecules in the vicinity. In the present work, we were also able to prepare partially reduced crystals that revealed two alternate conformations of the Mo-coordinating cysteine. This crystal form was obtained by soaking dithionite into crystals grown in the presence of the ionic liquid [C(4)mim]Cl(-). In addition, UV-Vis and EPR spectroscopy studies showed that the periplasmic nitrate reductase from C. necator might work at unexpectedly high redox potentials when compared to all periplasmic nitrate reductases studied to date.
authors.affiliation: REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
authors.forename: Catarina
authors.initials: C
authors.lastname: Coelho
authors.forename: Pablo J
authors.initials: PJ
authors.lastname: González
authors.forename: Joséj G
authors.initials: JG
authors.lastname: Moura
authors.forename: Isabel
authors.initials: I
authors.lastname: Moura
authors.forename: José
authors.initials: J
authors.lastname: Trincão
authors.forename: Maria
authors.initials: M
authors.lastname: João Romão
mesh_terms: D000595:Amino Acid Sequence; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D020118:Cupriavidus necator / Q000201:enzymology*; D003545:Cysteine / Q000737:chemistry; D004227:Dithionite / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D052578:Ionic Liquids / Q000737:chemistry; D008969:Molecular Sequence Data; D008982:Molybdenum / Q000737:chemistry; D050901:Nitrate Reductase / Q000737:chemistry*; D019897:Periplasm / Q000201:enzymology; D011487:Protein Conformation
chemical_list: D052578:Ionic Liquids; D004227:Dithionite; D008982:Molybdenum; D050901:Nitrate Reductase; D003545:Cysteine