[NiFe] and [FeS] Cofactors in the Membrane-Bound Hydrogenase of Ralstonia eutropha Investigated by X-ray Absorption Spectroscopy: Insights into O2-Tolerant H2 Cleavage

详细信息    查看全文

• 作者：Johannes Fritsch ; Simone Lo虉scher ; Oliver Sanganas ; Elisabeth Siebert ; Ingo Zebger ; Matthias Stein ; Marcus Ludwig ; Antonio L. De Lacey ; Holger Dau ; Ba虉rbel Friedrich ; Oliver Lenz ; Michael Haumann
• 刊名：Biochemistry
• 出版年：2011
• 出版时间：July 5, 2011
• 年：2011
• 卷：50
• 期：26
• 页码：5858-5869
• 全文大小：1058K
• 年卷期：v.50,no.26(July 5, 2011)
• ISSN：1520-4995

文摘

Molecular features that allow certain [NiFe] hydrogenases to catalyze the conversion of molecular hydrogen (H₂) in the presence of dioxygen (O₂) were investigated. Using X-ray absorption spectroscopy (XAS), we compared the [NiFe] active site and FeS clusters in the O₂-tolerant membrane-bound hydrogenase (MBH) of Ralstonia eutropha and the O₂-sensitive periplasmic hydrogenase (PH) of Desulfovibrio gigas. Fe-XAS indicated an unusual complement of iron鈥搒ulfur 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 脜 Fe鈥揊e distances and additional longer vectors of 鈮?.4 脜, 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鈭捨糘 bonds due to Ni鈥揊e 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 O₂ 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 H₂ and O₂.