Qbadou Soumya, Becker Thomas, Bionda Tihana, Reger Katharina, Ruprecht Maike, Soll Jürgen, Schleiff Enrico
Botanik, LMU München, Menzinger Str. 67, 80638 München, Germany.
J Mol Biol. 2007 Apr 13;367(5):1330-46. doi: 10.1016/j.jmb.2007.01.047. Epub 2007 Jan 24.
Protein translocation across membranes is assisted by translocation machineries present in the membrane targeted by the precursor proteins. Translocon subunits can be functionally divided into receptor proteins warranting the specificity of this machine and a translocation channel. At the outer envelope of chloroplasts two sets of receptor proteins regulate protein translocation facing the cytosol or acting in the intermembrane space. One, Toc64 is a receptor of the translocon at the outer envelope of chloroplasts (Toc complex) with dual function. Toc64 recognizes Hsp90 delivered precursor proteins via a cytosolic exposed domain containing three tetratrico-peptide repeat motifs and as demonstrated in here, Toc64 functions also as a major component of a complex facing the intermembrane space. The latter complex is composed of an Hsp70 localized in the intermembrane space, its interaction partner Toc12, a J-domain containing protein and the intermembrane space protein Tic22. We analyzed the intermembrane space domain of Toc64. This domain is involved in preprotein recognition and association with the Toc-complex independent of the cytosolic domain of the Toc64 receptor. Therefore, Toc64 is involved in preprotein translocation across the outer envelope at both sites of the membrane.
蛋白质跨膜转运由前体蛋白靶向的膜中存在的转运机制协助。转运体亚基在功能上可分为保证该机制特异性的受体蛋白和转运通道。在叶绿体的外膜上，两组受体蛋白调节面向细胞质或在膜间隙中起作用的蛋白质转运。其中，Toc64是叶绿体外膜转运体（Toc复合体）的一种具有双重功能的受体。Toc64通过一个含有三个四三肽重复基序的胞质暴露结构域识别Hsp90传递的前体蛋白，如本文所示，Toc64还作为面向膜间隙的复合体的主要成分发挥作用。后者的复合体由定位在膜间隙中的Hsp70、其相互作用伙伴Toc12、一个含J结构域的蛋白和膜间隙蛋白Tic22组成。我们分析了Toc64的膜间隙结构域。该结构域。该结构域参与前体蛋白的识别以及与Toc复合体的结合，且不依赖于Toc64受体的胞质结构域。因此，Toc64在膜的两个位点参与前体蛋白跨外膜的转运。
