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PublicationBiochemistry
Year2011
Volume50
Pages5858-5869
International

[NiFe] and [FeS] Cofactors in the Membrane-Bound Hydrogenase of Ralstonia eutropha Investigated by X-ray Absorption Spectroscopy: Insights into O(2)-Tolerant H(2) Cleavage

Authors:Johannes Fritsch , Simone Loescher , Oliver Sanganas , Elisabeth Siebert , Ingo Zebger , Matthias Stein , Marcus Ludwig , Antonio López de Lacey, Holger Dau , Baerbel Friedrich , Oliver Lenz , Michale Haumann
Groups of research:BioElectroCatalysis
Molecular features that allow certain [NiFe] hydrogenases to catalyze the conversion of molecular hydrogen (H(2)) in the presence of dioxygen (O(2)) were investigated. Using X-ray absorption spectroscopy (XAS), we compared the [NiFe] active site and FeS clusters in the O(2)-tolerant membrane-bound hydrogenase (MBH) of Ralstonia eutropha and the O(2)-sensitive periplasmic hydrogenase (PH) of Desulfovibrio gigas. Fe-XAS indicated an unusual complement of iron-sulfur centers in the MBH, likely based on a specific structure of the FeS cluster proximal to the active site. This cluster is a [4Fe4S] cubane in PH. For MBH, it comprises less than similar to 2.7 angstrom Fe-Fe distances and additional longer vectors of >= 3.4 angstrom, consistent with an Fe trimer with a more isolated Fe ion. Ni-XAS indicated a similar architecture of the [NiFe] site in MBH and PH, featuring Ni coordination by four thiolates of conserved cysteines, i.e., in the fully reduced state (Ni-SR). For oxidized states, short Ni-mu O bonds due to Ni-Fe bridging oxygen species were detected in the Ni-B state of the MBH and in the Ni-A state of the PH. Furthermore, a bridging sulfenate (CysSO) is suggested for an inactive state (Ni(ia)-S) of the MBH. We propose that the O(2) tolerance of the MBH is mainly based on a dedicated electron donation from a modified proximal FeS cluster to the active site, which may favor formation of the rapidly reactivated Ni-B state instead of the slowly reactivated Ni-A state. Thereby, the catalytic activity of the MBH is facilitated in the presence of both H(2) and O(2).
Keywords:DESULFOVIBRIO-GIGAS HYDROGENASE; OXYGEN-TOLERANT HYDROGENASE; BACTERIUM AQUIFEX-AEOLICUS; NICKEL-IRON HYDROGENASE; LOW-LEVEL H-2; ACTIVE-SITE; METAL CENTERS; ELECTRONIC-STRUCTURE; FTIR SPECTROSCOPY; REDOX PROPERTIES
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