Hydride Binding to the Active Site of [FeFe]-Hydrogenase

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• 作者：Petko Chernev ; Camilla Lambertz ; Annika Br眉nje ; Nils Leidel ; Kajsa G. V. Sigfridsson ; Ramona Kositzki ; Chung-Hung Hsieh ; Shenglai Yao ; Rafael Schiwon ; Matthias Driess ; Christian Limberg ; Thomas Happe ; Michael Haumann
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：November 17, 2014
• 年：2014
• 卷：53
• 期：22
• 页码：12164-12177
• 全文大小：1022K
• ISSN：1520-510X

文摘

[FeFe]-hydrogenase from green algae (HydA1) is the most efficient hydrogen (H₂) producing enzyme in nature and of prime interest for (bio)technology. Its active site is a unique six-iron center (H-cluster) composed of a cubane cluster, [4Fe4S]_H, cysteine-linked to a diiron unit, [2Fe]_H, which carries unusual carbon monoxide (CO) and cyanide ligands and a bridging azadithiolate group. We have probed the molecular and electronic configurations of the H-cluster in functional oxidized, reduced, and super-reduced or CO-inhibited HydA1 protein, in particular searching for intermediates with iron-hydride bonds. Site-selective X-ray absorption and emission spectroscopy were used to distinguish between low- and high-spin iron sites in the two subcomplexes of the H-cluster. The experimental methods and spectral simulations were calibrated using synthetic model complexes with ligand variations and bound hydride species. Distinct X-ray spectroscopic signatures of electronic excitation or decay transitions in [4Fe4S]_H and [2Fe]_H were obtained, which were quantitatively reproduced by density functional theory calculations, thereby leading to specific H-cluster model structures. We show that iron-hydride bonds are absent in the reduced state, whereas only in the super-reduced state, ligand rotation facilitates hydride binding presumably to the Fe鈥揊e bridging position at [2Fe]_H. These results are in agreement with a catalytic cycle involving three main intermediates and at least two protonation and electron transfer steps prior to the H₂ formation chemistry in [FeFe]-hydrogenases.