title: Hydrogen-induced structural changes at the nickel site of the regulatory [NiFe] hydrogenase from Ralstonia eutropha detected by X-ray absorption spectroscopy.
abstract: For the first time, the nickel site of the hydrogen sensor of Ralstonia eutropha, the regulatory [NiFe] hydrogenase (RH), was investigated by X-ray absorption spectroscopy (XAS) at the nickel K-edge. The oxidation state and the atomic structure of the Ni site were investigated in the RH in the absence (air-oxidized, RH(ox)) and presence of hydrogen (RH(+H2)). Incubation with hydrogen is found to cause remarkable changes in the spectroscopic properties. The Ni-C EPR signal, indicative of Ni(III), is detectable only in the RH(+H2) state. XANES and EXAFS spectra indicate a coordination of the Ni in the RH(ox) and RH(+H2) that pronouncedly differs from the one in standard [NiFe] hydrogenases. Also, the changes induced by exposure to H(2) are unique. A drastic modification in the XANES spectra and an upshift of the K-edge energy from 8339.8 (RH(ox)) to 8341.1 eV (RH(+H2)) is observed. The EXAFS spectra indicate a change in the Ni coordination in the RH upon exposure to H(2). One likely interpretation of the data is the detachment of one sulfur ligand in RH(+H2) and the binding of additional (O,N) or H ligands. The following Ni oxidation states and coordinations are proposed: five-coordinated Ni(II)(O,N)(2)S(3) for RH(ox) and six-coordinated Ni((III))(O,N)(3)X(1)S(2) [X being either an (O,N) or H ligand] for RH(+H2). Implications of the structural features of the Ni site of the RH in relation to its function, hydrogen sensing, are discussed.
authors.affiliation: Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany. haumann@physik.fu-berlin.de
authors.forename: Michael
authors.initials: M
authors.lastname: Haumann
authors.forename: Antje
authors.initials: A
authors.lastname: Porthun
authors.forename: Thorsten
authors.initials: T
authors.lastname: Buhrke
authors.forename: Peter
authors.initials: P
authors.lastname: Liebisch
authors.forename: Wolfram
authors.initials: W
authors.lastname: Meyer-Klaucke
authors.forename: Bärbel
authors.initials: B
authors.lastname: Friedrich
authors.forename: Holger
authors.initials: H
authors.lastname: Dau
mesh_terms: D002384:Catalysis; D020118:Cupriavidus necator / Q000201:enzymology*; D004578:Electron Spin Resonance Spectroscopy; D005583:Fourier Analysis; D006859:Hydrogen / Q000737:chemistry*; D006864:Hydrogenase / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D015233:Models, Statistical; D009532:Nickel / Q000737:chemistry*; D017785:Photons; D011487:Protein Conformation; D013052:Spectrometry, X-Ray Emission
chemical_list: D008024:Ligands; D009532:Nickel; D006859:Hydrogen; C043296:nickel-iron hydrogenase; D006864:Hydrogenase