title: [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.
abstract: 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 ~2.7 Å Fe-Fe distances and additional longer vectors of ≥3.4 Å, 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-μO 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).
authors: Humboldt-Universität zu Berlin, Institut für Biologie/Mikrobiologie, 10115 Berlin, Germany.
authors: Johannes
authors: J
authors: Fritsch
authors: Simone
authors: S
authors: Löscher
authors: Oliver
authors: O
authors: Sanganas
authors: Elisabeth
authors: E
authors: Siebert
authors: Ingo
authors: I
authors: Zebger
authors: Matthias
authors: M
authors: Stein
authors: Marcus
authors: M
authors: Ludwig
authors: Antonio L
authors: AL
authors: De Lacey
authors: Holger
authors: H
authors: Dau
authors: Bärbel
authors: B
authors: Friedrich
authors: Oliver
authors: O
authors: Lenz
authors: Michael
authors: M
authors: Haumann