Ssl3451 is Important for Accumulation of NDH-1 Assembly Intermediates in the Cytoplasm of Synechocystis sp. Strain PCC 6803

Two mutants sensitive to high light for growth and impaired in NDH-1 activity were isolated from a transposon-tagged library of Synechocystis sp. strain PCC 6803. Both mutants were tagged in the ssl3451 gene encoding a hypothetical protein, which shares a significant homology with the Arabidopsis ( Arabidopsis thaliana) CHLORORESPIRATORY REDUCTION 42 ( CRR42). In Arabidopsis, CRR42 associates only with an NDH-1 hydrophilic arm assembly intermediate ( NAI) of about 400 kDa ( NAI400), one of total three NAIs ( NAI800, NAI500 and NAI400), and its deletion has little, if any, effect on accumulation of any NAIs in the stroma. In comparison, the ssl3451 product was localized mainly in the cytoplasm and associates with two NAIs of about 300 kDa ( NAI300) and 130 kDa ( NAI130). Deletion of Ssl3451 reduced the abundance of the NAI300 complex to levels no longer visible on gels and of the NAI130 complex to a low level, thereby impeding the assembly process of NDH-1 hydrophilic arm. Further, Ssl3451 interacts with another assembly factor Ssl3829 and they have a similar effect on accumulation of NAIs and NdhI maturation factor Slr1097 in the cytoplasm. We thus propose that Ssl3451 plays an important role in accumulation of the NAI300 and NAI130 complexes in the cytoplasm via its interacting protein Ssl3829.

从集胞藻（Synechocystis sp.）PCC 6803的转座子标签文库中分离出了两株对高光生长敏感且NDH - 1活性受损的突变体。这两个突变体在ssl3451基因处被标记，该基因编码一种假定蛋白，它与拟南芥（Arabidopsis thaliana）的叶绿体呼吸还原42（CRR42）具有显著的同源性。在拟南芥中，CRR42仅与约400 kDa的NDH - 1亲水臂组装中间体（NAI400）相关联，NAI400是总共三个NAI（NAI800、NAI500和NAI400）中的一个，并且其缺失对基质中任何NAI的积累几乎没有影响（如果有的话）。相比之下，ssl3451产物主要定位于细胞质中，并与约300 kDa（NAI300）和130 kDa（NAI130）的两个NAI相关联。Ssl3451的缺失使NAI300复合物的丰度降低到在凝胶上不再可见的水平，使NAI130复合物的丰度降低到较低水平，从而阻碍了NDH - 1亲水臂的组装过程。此外，Ssl3451与另一个组装因子Ssl3829相互作用，并且它们对细胞质中NAI的积累以及NdhI成熟因子Slr1097具有相似的影响。因此，我们提出Ssl3451通过其相互作用蛋白Ssl3829在细胞质中NAI300和NAI130复合物的积累中起重要作用。