亚硫酸盐还原酶
化学
亚硫酸盐
钼辅因子
铁氧还蛋白
硫黄
立体化学
辅因子
催化循环
无机化学
还原酶
催化作用
生物化学
有机化学
酶
作者
Brian R. Crane,Lewis M. Siegel,Elizabeth D. Getzoff
出处
期刊:Science
[American Association for the Advancement of Science (AAAS)]
日期:1995-10-06
卷期号:270 (5233): 59-67
被引量:318
标识
DOI:10.1126/science.270.5233.59
摘要
Fundamental chemical transformations for biogeochemical cycling of sulfur and nitrogen are catalyzed by sulfite and nitrite reductases. The crystallographic structure of Escherichia coli sulfite reductase hemoprotein (SiRHP), which catalyzes the concerted six-electron reductions of sulfite to sulfide and nitrite to ammonia, was solved with multiwavelength anomalous diffraction (MAD) of the native siroheme and Fe4S4 cluster cofactors, multiple isomorphous replacement, and selenomethionine sequence markers. Twofold symmetry within the 64-kilodalton polypeptide generates a distinctive three-domain α/ β fold that controls cofactor assembly and reactivity. Homology regions conserved between the symmetry-related halves of SiRHP and among other sulfite and nitrite reductases revealed key residues for stability and function, and identified a sulfite or nitrite reductase repeat (SNiRR) common to a redox-enzyme superfamily. The saddle-shaped siroheme shares a cysteine thiolate ligand with the Fe4S4 cluster and ligates an unexpected phosphate anion. In the substrate complex, sulfite displaces phosphate and binds to siroheme iron through sulfur. An extensive hydrogen-bonding network of positive side chains, water molecules, and siroheme carboxylates activates S-O bonds for reductive cleavage.
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