Thousands of nuclear-encoded proteins are transported into chloroplasts through the TOC–TIC translocon that spans the chloroplast envelope membranes. A motor complex pulls the translocated proteins out of the TOC–TIC complex into the chloroplast stroma by hydrolyzing ATP. The Orf2971–FtsHi complex has been suggested to serve as the ATP-hydrolyzing motor in Chlamydomonas reinhardtii, but little is known about its architecture and assembly. Here, we report the 3.2-Å resolution structure of the Chlamydomonas Orf2971–FtsHi complex. The 20-subunit complex spans the chloroplast inner envelope, with two bulky modules protruding into the intermembrane space and stromal matrix. Six subunits form a hetero-hexamer that potentially provides the pulling force through ATP hydrolysis. The remaining subunits, including potential enzymes/chaperones, likely facilitate the complex assembly and regulate its proper function. Taken together, our results provide the structural foundation for a mechanistic understanding of chloroplast protein translocation.

中文翻译：

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用于将蛋白质导入叶绿体的 ATP 驱动电机的结构


数以千计的核编码蛋白通过跨越叶绿体包膜的 TOC-TIC 转位子转运到叶绿体中。马达复合物通过水解 ATP 将易位的蛋白质从 TOC-TIC 复合物中拉出到叶绿体基质中。Orf2971-FtsHi 复合物被认为在莱茵衣藻中用作 ATP 水解马达，但对其结构和组装知之甚少。在这里，我们报道了衣藻 Orf2971–FtsHi 复合物的 3.2-Å 分辨率结构。20 个亚基复合物跨越叶绿体内膜，两个笨重的模块突出到膜间隙和基质基质中。六个亚基形成异六聚体，可能通过 ATP 水解提供拉力。其余的亚基，包括潜在的酶/伴侣，可能促进复合物组装并调节其正常功能。综上所述，我们的结果为叶绿体蛋白易位的机制理解提供了结构基础。