Institute of Chemistry, University of Campinas (UNICAMP), 13083-970 Campinas, SP, Brazil.
Arch Biochem Biophys. 2011 Sep 15;513(2):119-25. doi: 10.1016/j.abb.2011.06.015. Epub 2011 Jul 14.
A large majority of the 1000-1500 proteins in the mitochondria are encoded by the nuclear genome, and therefore, they are translated in the cytosol in the form and contain signals to enable the import of proteins into the organelle. The TOM complex is the major translocase of the outer membrane responsible for preprotein translocation. It consists of a general import pore complex and two membrane import receptors, Tom20 and Tom70. Tom70 contains a characteristic TPR domain, which is a docking site for the Hsp70 and Hsp90 chaperones. These chaperones are involved in protecting cytosolic preproteins from aggregation and then in delivering them to the TOM complex. Although highly significant, many aspects of the interaction between Tom70 and Hsp90 are still uncertain. Thus, we used biophysical tools to study the interaction between the C-terminal domain of Hsp90 (C-Hsp90), which contains the EEVD motif that binds to TPR domains, and the cytosolic fragment of Tom70. The results indicate a stoichiometry of binding of one monomer of Tom70 per dimer of C-Hsp90 with a K(D) of 360±30nM, and the stoichiometry and thermodynamic parameters obtained suggested that Tom70 presents a different mechanism of interaction with Hsp90 when compared with other TPR proteins investigated.
线粒体中的 1000-1500 种蛋白质绝大多数都由核基因组编码，因此，它们以细胞质中的形式翻译，并包含将蛋白质导入细胞器的信号。TOM 复合物是负责前体蛋白转运的外膜主要转运体。它由一个通用的输入孔复合物和两个膜输入受体 Tom20 和 Tom70 组成。Tom70 包含一个特征性的 TPR 结构域，这是 Hsp70 和 Hsp90 伴侣蛋白的对接位点。这些伴侣蛋白参与保护细胞质前体蛋白不聚集，然后将它们递送到 TOM 复合物。尽管这一点非常重要，但 Tom70 和 Hsp90 之间相互作用的许多方面仍然不确定。因此，我们使用生物物理工具研究了包含与 TPR 结构域结合的 EEVD 基序的 Hsp90（C-Hsp90）的 C 末端结构域与 Tom70 的细胞质片段之间的相互作用。结果表明，Tom70 与 C-Hsp90 二聚体的结合比为 1:1，K(D)为 360±30nM，获得的结合比和热力学参数表明，与其他研究的 TPR 蛋白相比，Tom70 与 Hsp90 具有不同的相互作用机制。
