Structure of spinach nitrite reductase:: Implications for multi-electron reactions by the iron-sulfur:siroheme cofactor
Structure of spinach nitrite reductase:: Implications for multi-electron reactions by the iron-sulfur:siroheme cofactor
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DOI：
10.1021/bi050981y
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发表时间：
2005-12-13
期刊：
影响因子：
2.9
通讯作者：
Allen, JP
中科院分区：
文献类型：
--
作者：
Swamy, U;Wang, MT;Allen, JP
用X射线衍射法测定了氮同化过程中的关键酶亚硝酸盐还原酶的结构，其分辨极限为2.8埃。该蛋白具有由3个α/β结构域组成的球状折叠，在三个结构域的界面处具有西罗血红素-铁硫辅因子。Fe 4S 4簇由半胱氨酸441、447、482和486配位。siroheme位于离簇4.2埃的距离处，并且中心铁原子与Cys 486配位。siroheme被几个可电离的氨基酸残基包围，这些氨基酸残基促进亚硝酸盐的结合和随后的还原。铁氧还蛋白的模型：提出了亚硝酸还原酶复合物，其中铁氧还蛋白与亚硝酸还原酶的带正电荷区域的结合导致辅因子不暴露于溶剂。亚硝酸盐还原酶的结构与亚硫酸盐还原酶的血红素蛋白亚基具有广泛的相似性，但在骨架位置上存在许多显著差异，这些差异可能反映了序列差异，也可能是由于亚硫酸盐还原酶结构的改变而引起的，亚硫酸盐还原酶结构的改变是由于亚硫酸盐还原酶亚基与天然复合物分离而引起的。亚硝酸盐还原酶结构的理解多电子过程的影响进行了讨论，在蛋白质环境中的辅因子的差异。
The structure of nitrite reductase, a key enzyme in the process of nitrogen assimilation, has been determined using X-ray diffraction to a resolution limit of 2.8 angstrom. The protein has a globular fold consisting of 3 alpha/beta 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 distance of 4.2 angstrom from the cluster, and the central iron atom is coordinated to Cys 486. The siroheme is surrounded by several ionizable amino acid residues that facilitate the binding and subsequent reduction of nitrite. A model for the ferredoxin: nitrite reductase complex is proposed in which the binding of ferredoxin to a positively charged region of nitrite reductase results in elimination of exposure of the cofactors to the solvent. The structure of nitrite reductase shows a broad similarity to the hemoprotein subunit of sulfite reductase but has many significant differences in the backbone positions that could reflect sequence differences or could arise from alterations of the sulfite reductase structure that arise from the isolation of this subunit from the native complex. The implications of the nitrite reductase structure for understanding multi-electron processes are discussed in terms of differences in the protein environments of the cofactors.