Department of Plant Biology, University of California Davis, CA, USA.
FEBS Lett. 2019 Mar;593(6):565-572. doi: 10.1002/1873-3468.13342. Epub 2019 Mar 5.
Protein import into chloroplasts is carried out by the protein translocons at the outer and inner envelope membranes (TOC and TIC). Detailed structures for these translocons are lacking, with only a low-resolution TOC complex structure available. Recently, we showed that the TOC/TIC translocons can import folded proteins, a rather unique feat for a coupled double membrane system. We also determined the maximum functional TOC/TIC pore size to be 30-35 Å. Here, we discuss how such large pores could form and compare the structural dynamics of the pore-forming Toc75 subunit to its bacterial/mitochondrial Omp85 family homologs. We put forward structural models that can be empirically tested and also briefly review the pore dynamics of other protein translocons with known structures.
蛋白质通过叶绿体的内外膜上的蛋白转位复合物（TOC 和 TIC）进行输入。这些转位复合物的详细结构尚不清楚，只有一个低分辨率的 TOC 复合物结构。最近，我们表明 TOC/TIC 转位复合物可以导入折叠的蛋白质，这对于一个偶联的双层膜系统来说是一个相当独特的功能。我们还确定了 TOC/TIC 转位复合物的最大功能孔大小为 30-35Å。在这里，我们讨论了如此大的孔如何形成，并比较了形成孔的Toc75 亚基的结构动力学与其细菌/线粒体 Omp85 家族同源物。我们提出了可以通过经验验证的结构模型，并简要回顾了具有已知结构的其他蛋白转位复合物的孔动力学。
