From the Department of Structural Biology, Zoological Institute, Christian-Albrechts-University Kiel, 24118 Kiel, Germany,; the Department of Biophysics-Structural Biology, Saarland University, 66421 Homburg, Germany.
From the Department of Structural Biology, Zoological Institute, Christian-Albrechts-University Kiel, 24118 Kiel, Germany.
J Biol Chem. 2011 Mar 11;286(10):8349-8360. doi: 10.1074/jbc.M110.193631. Epub 2010 Dec 8.
The sulfur cycle enzyme sulfane dehydrogenase SoxCD is an essential component of the sulfur oxidation (Sox) enzyme system of Paracoccus pantotrophus. SoxCD catalyzes a six-electron oxidation reaction within the Sox cycle. SoxCD is an α(2)β(2) heterotetrameric complex of the molybdenum cofactor-containing SoxC protein and the diheme c-type cytochrome SoxD with the heme domains D(1) and D(2). SoxCD(1) misses the heme-2 domain D(2) and is catalytically as active as SoxCD. The crystal structure of SoxCD(1) was solved at 1.33 Å. The substrate of SoxCD is the outer (sulfane) sulfur of Cys-110-persulfide located at the C-terminal peptide swinging arm of SoxY of the SoxYZ carrier complex. The SoxCD(1) substrate funnel toward the molybdopterin is narrow and partially shielded by side-chain residues of SoxD(1). For access of the sulfane-sulfur of SoxY-Cys-110 persulfide we propose that (i) the blockage by SoxD-Arg-98 is opened via interaction with the C terminus of SoxY and (ii) the C-terminal peptide VTIGGCGG of SoxY provides interactions with the entrance path such that the cysteine-bound persulfide is optimally positioned near the molybdenum atom. The subsequent oxidation reactions of the sulfane-sulfur are initiated by the nucleophilic attack of the persulfide anion on the molybdenum atom that is, in turn, reduced. The close proximity of heme-1 to the molybdopterin allows easy acceptance of the electrons. Because SoxYZ, SoxXA, and SoxB are already structurally characterized, with SoxCD(1) the structures of all key enzymes of the Sox cycle are known with atomic resolution.
硫循环酶磺酰脱氢酶 SoxCD 是泛养副球菌硫氧化（Sox）酶系统的必需组成部分。SoxCD 催化 Sox 循环中的六电子氧化反应。SoxCD 是一种含有钼辅因子的 SoxC 蛋白和二血红素 c 型细胞色素 SoxD 的 α(2)β(2)异四聚体复合物，具有血红素域 D(1)和 D(2)。SoxCD(1)缺失血红素-2 结构域 D(2)，并且具有与 SoxCD 相同的催化活性。SoxCD(1)的晶体结构在 1.33 Å 处得到解决。SoxCD 的底物是 SoxY 的 C 末端肽摆动臂上位于 Cys-110-过硫化物的外（磺酰）硫。SoxCD(1)的底物通向钼喋呤的通道狭窄，并且部分被 SoxD(1)的侧链残基屏蔽。为了进入 SoxY-Cys-110 过硫化物的磺酰硫，我们提出（i）通过与 SoxY 的 C 末端相互作用，打开 SoxD-Arg-98 的阻塞，（ii）SoxY 的 C 末端肽 VTIGGCGG 与入口路径相互作用，使得半胱氨酸结合的过硫化物最佳定位于钼原子附近。随后的磺酰硫氧化反应由过硫化物阴离子对钼原子的亲核攻击引发，钼原子继而被还原。血红素-1 与钼喋呤的紧密接近允许电子的容易接受。由于 SoxYZ、SoxXA 和 SoxB 已经具有结构特征，因此 SoxCD(1)的结构已知具有原子分辨率的 Sox 循环的所有关键酶。
