The unassembled flavoprotein subunits of human and bacterial complex II have impaired catalytic activity and generate only minor amounts of ROS
The unassembled flavoprotein subunits of human and bacterial complex II have impaired catalytic activity and generate only minor amounts of ROS
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DOI：
10.1074/jbc.ra118.001977
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发表时间：
2018-05-18
影响因子：
4.8
通讯作者：
Cecchini, Gary
中科院分区：
文献类型：
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作者：
Maklashina, Elena;Rajagukguk, Sany;Cecchini, Gary
复合物 II (SdhABCD) 是线粒体和细菌电子传递链以及 TCA 循环的膜结合成分。以此能力，它催化琥珀酸的可逆氧化。 SdhABCD 包含具有共价结合的 FAD 氧化还原中心的 SDHA 蛋白和包含三个不同铁硫中心的铁硫蛋白 SDHB。当该复合物的组装受到损害时，黄素蛋白 SDHA 可能会在线粒体基质或细菌细胞质中积聚。未组装的 SDHA 是否具有任何催化活性，例如在琥珀酸氧化、富马酸还原、活性氧 (ROS) 生成或其他旁路反应中，尚不清楚。因此，我们在此研究未组装的大肠杆菌SdhA黄素蛋白、其同源物富马酸还原酶(FrdA)和人SDHA蛋白是否具有琥珀酸氧化酶或富马酸还原酶活性并可以产生ROS。使用大肠杆菌中的重组表达，我们发现来自这些不同生物来源的游离黄素蛋白具有固有的低催化活性并且产生很少的ROS。这些结果表明复合物 II 中的铁硫蛋白 SDHB 对于强大的催化活性是必需的。我们的研究结果与报道的与铁硫或血红素伴侣蛋白无关的单亚基黄素蛋白同系物的结果一致。
Complex II (SdhABCD) is a membrane-bound component of mitochondrial and bacterial electron transport chains, as well as of the TCA cycle. In this capacity, it catalyzes the reversible oxidation of succinate. SdhABCD contains the SDHA protein harboring a covalently bound FAD redox center and the iron-sulfur protein SDHB, containing three distinct iron-sulfur centers. When assembly of this complex is compromised, the flavoprotein SDHA may accumulate in the mitochondrial matrix or bacterial cytoplasm. Whether the unassembled SDHA has any catalytic activity, for example in succinate oxidation, fumarate reduction, reactive oxygen species (ROS) generation, or other off-pathway reactions, is not known. Therefore, here we investigated whether unassembled Escherichia coli SdhA flavoprotein, its homolog fumarate reductase (FrdA), and the human SDHA protein have succinate oxidase or fumarate reductase activity and can produce ROS. Using recombinant expression in E. coli, we found that the free flavoproteins from these divergent biological sources have inherently low catalytic activity and generate little ROS. These results suggest that the iron-sulfur protein SDHB in complex II is necessary for robust catalytic activity. Our findings are consistent with those reported for single-subunit flavoprotein homologs that are not associated with iron-sulfur or heme partner proteins.