[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.
Biochemistry
; 50(26): 5858-69, 2011 Jul 05.
Article
in En
| MEDLINE
| ID: mdl-21618994
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).
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Oxygen
/
Cell Membrane
/
Coenzymes
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Cupriavidus necator
/
X-Ray Absorption Spectroscopy
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Hydrogen
/
Hydrogenase
Language:
En
Journal:
Biochemistry
Year:
2011
Document type:
Article
Affiliation country:
Germany