Spectroscopic Evidence for Site Specific Chemistry at a Unique Iron Site of the [4Fe-4S] Cluster in Ferredoxin:Thioredoxin Reductase

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• 作者：Guy N. L. Jameson ; Elizabeth M. Walters ; Wanda Manieri ; Peter Schü ; rmann ; Michael K. Johnson ; and Boi Hanh Huynh
• 刊名：Journal of the American Chemical Society
• 出版年：2003
• 出版时间：February 5, 2003
• 年：2003
• 卷：125
• 期：5
• 页码：1146 - 1147
• 全文大小：53K
• 年卷期：v.125,no.5(February 5, 2003)
• ISSN：1520-5126

文摘

Ferredoxin:thioredoxin reductase (FTR) catalyzes the reduction of the disulfide in thioredoxin in two one-electron steps using an active site comprising a [4Fe-4S] in close proximity to a redox active disulfide. Mössbauer spectroscopy has been used to investigate the ligation and electronic properties of the [4Fe-4S] cluster in as-prepared FTR which has the active-site disulfide intact and in the N-ethylmaleimide (NEM)-modified form which provides a stable analogue of the one-electron-reduced heterodisulfide intermediate and has one of the cysteines of the active-site disulfide alkylated with NEM. The results reveal novel site-specific cluster chemistry involving weak interaction of the active-site disulfide with a unique Fe site of the [4Fe-4S]²⁺ cluster in the resting enzyme and cleavage of the active-site disulfide with concomitant coordination of one of the cysteines to yield a [4Fe-4S]³⁺ cluster with a five-coordinate Fe site ligated by two cysteine residues in the NEM-modified enzyme. The results provide molecular-level insight into the catalytic mechanism of FTR and other Fe-S-cluster-containing disulfide reductases, and suggest a possible mechanism for the reductive cleavage of S-adenosylmethionine by the radical SAM family of Fe-S enzymes.