Disparate Pathways for the Biogenesis of Cytochrome Oxidases in Bradyrhizobium japonicum

作者：Buehler Doris; Rossmann Reinhild; Landolt Sarah; Balsiger Sylvia; Fischer Hans Martin; Hennecke Hauke^*

来源：JOURNAL OF BIOLOGICAL CHEMISTRY, 2010, 285(21): 15704-15713.

DOI：10.1074/jbc.M109.085217

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.

• 出版日期2010-5-21