Structure of Spinach Nitrite Reductase: Implications for Multi-electron Reactions by the Iron-Sulfur:Siroheme Cofactor
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- 作者：Uma Swamy ; Meitian Wang ; Jatinda N. Tripathy ; Sung-Kun Kim ; Masakazu Hirasawa ; David B. Knaff ; and James P. Allen
- 刊名：Biochemistry
- 出版年：2005
- 出版时间：December 13, 2005
- 年：2005
- 卷：44
- 期：49
- 页码：16054 - 16063
- 全文大小：821K
- 年卷期：v.44,no.49(December 13, 2005)
- ISSN：1520-4995
文摘
The structure of nitrite reductase, a key enzyme in the process of nitrogen assimilation, hasbeen determined using X-ray diffraction to a resolution limit of 2.8 Å. The protein has a globular foldconsisting of 3 
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beta2.gif" BORDER=0 ALIGN="middle"> domains with the siroheme-iron sulfur cofactor at the interface of the three domains.The Fe4S4 cluster is coordinated by cysteines 441, 447, 482, and 486. The siroheme is located at a distanceof 4.2 Å from the cluster, and the central iron atom is coordinated to Cys 486. The siroheme is surroundedby several ionizable amino acid residues that facilitate the binding and subsequent reduction of nitrite. Amodel for the ferredoxin:nitrite reductase complex is proposed in which the binding of ferredoxin to apositively charged region of nitrite reductase results in elimination of exposure of the cofactors to thesolvent. The structure of nitrite reductase shows a broad similarity to the hemoprotein subunit of sulfitereductase but has many significant differences in the backbone positions that could reflect sequencedifferences or could arise from alterations of the sulfite reductase structure that arise from the isolationof this subunit from the native complex. The implications of the nitrite reductase structure for understandingmulti-electron processes are discussed in terms of differences in the protein environments of the cofactors.
/beta2.gif" BORDER=0 ALIGN="middle"> domains with the siroheme-iron sulfur cofactor at the interface of the three domains.The Fe4S4 cluster is coordinated by cysteines 441, 447, 482, and 486. The siroheme is located at a distanceof 4.2 Å from the cluster, and the central iron atom is coordinated to Cys 486. The siroheme is surroundedby several ionizable amino acid residues that facilitate the binding and subsequent reduction of nitrite. Amodel for the ferredoxin:nitrite reductase complex is proposed in which the binding of ferredoxin to apositively charged region of nitrite reductase results in elimination of exposure of the cofactors to thesolvent. The structure of nitrite reductase shows a broad similarity to the hemoprotein subunit of sulfitereductase but has many significant differences in the backbone positions that could reflect sequencedifferences or could arise from alterations of the sulfite reductase structure that arise from the isolationof this subunit from the native complex. The implications of the nitrite reductase structure for understandingmulti-electron processes are discussed in terms of differences in the protein environments of the cofactors.