Disparate Pathways for the Biogenesis of Cytochrome Oxidases in Bradyrhizobium japonicum
Disparate Pathways for the Biogenesis of Cytochrome Oxidases in Bradyrhizobium japonicum
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DOI：
10.1074/jbc.m109.085217
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发表时间：
2010-05-21
影响因子：
4.8
通讯作者：
Hennecke, Hauke
中科院分区：
文献类型：
--
作者：
Buehler, Doris;Rossmann, Reinhild;Hennecke, Hauke
这项工作解决了日本慢生根瘤菌（大豆固氮根瘤共生体）中血红素铜末端氧化酶的生物发生。 B. japonicum 有四种喹啉氧化酶和四种细胞色素氧化酶。后者包括 aa(3) 型和 cbb(3) 型氧化酶。尽管两者都在亚基 I 中具有 Cu-B 中心，但亚基 II 蛋白的不同之处在于具有 Cu-A 中心（在 aa(3) 中）或共价结合的血红素 c（在 cbb(3) 中）。这里对两个生物发生因子进行了遗传学研究，周质暴露的 CoxG 和 ScoI 蛋白，它们是线粒体铜转运伴侣 Cox11 和 Sco1 的同源物，用于形成细胞色素 aa(3) 亚基 I 中的 Cu-B 中心和 II 亚基中的 Cu-A 中心。我们可以在体外证明铜与 ScoI 的结合，ScoI 多肽中半胱氨酸残基 74 和 78 的硫醇对此过程至关重要。日本芽孢杆菌 coxG 和 scoI 基因的敲除突变导致细胞色素 aa(3) 组装和细胞质膜中活性的丧失，而 cbb(3) 型细胞色素氧化酶显然不受影响。这表明 cbb(3) 型氧化酶的亚基 I 通过与细胞色素 aa(3) 不同的途径获得铜辅因子。与 coxG 突变相反，scoI 突变导致共生固氮活性降低。我们假设，除了任何已鉴定的 Cu-A 蛋白之外，日本 B. japonicum 周质蛋白依赖于 ScoI，并且是有效共生所必需的。
This work addresses the biogenesis of heme-copper terminal oxidases in Bradyrhizobium japonicum, the nitrogen-fixing root nodule symbiont of soybean. B. japonicum has four quinol oxidases and four cytochrome oxidases. The latter include the aa(3)- and cbb(3)-type oxidases. Although both have a Cu-B center in subunit I, the subunit II proteins differ in having either a Cu-A center (in aa(3)) or a covalently bound heme c (in cbb(3)). Two biogenesis factors were genetically studied here, the periplasmically exposed CoxG and ScoI proteins, which are the respective homologs of the mitochondrial copper-trafficking chaperones Cox11 and Sco1 for the formation of the Cu-B center in subunit I and the Cu-A center in subunit II of cytochrome aa(3). We could demonstrate copper binding to ScoI in vitro, a process for which the thiols of cysteine residues 74 and 78 in the ScoI polypeptide were shown to be essential. Knock-out mutations in the B. japonicum coxG and scoI genes led to loss of cytochrome aa(3) assembly and activity in the cytoplasmic membrane, whereas the cbb(3)-type cytochrome oxidase apparently remained unaffected. This suggests that subunit I of the cbb(3)-type oxidase obtains its copper cofactor via a different pathway than cytochrome aa(3). In contrast to the coxG mutation, the scoI mutation caused a decreased symbiotic nitrogen fixation activity. We hypothesize that a periplasmic B. japonicum protein other than any of the identified Cu-A proteins depends on ScoI and is required for an effective symbiosis.