Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, 79104 Freiburg, Germany.
Cell. 2013 Aug 1;154(3):596-608. doi: 10.1016/j.cell.2013.06.033.
The mitochondrial outer membrane harbors two protein translocases that are essential for cell viability: the translocase of the outer mitochondrial membrane (TOM) and the sorting and assembly machinery (SAM). The precursors of β-barrel proteins use both translocases-TOM for import to the intermembrane space and SAM for export into the outer membrane. It is unknown if the translocases cooperate and where the β-barrel of newly imported proteins is formed. We established a position-specific assay for monitoring β-barrel formation in vivo and in organello and demonstrated that the β-barrel was formed and membrane inserted while the precursor was bound to SAM. β-barrel formation was inhibited by SAM mutants and, unexpectedly, by mutants of the central import receptor, Tom22. We show that the cytosolic domain of Tom22 links TOM and SAM into a supercomplex, facilitating precursor transfer on the intermembrane space side. Our study reveals receptor-mediated coupling of import and export translocases as a means of precursor channeling.
外膜转位酶（TOM）和分选和装配机器（SAM）。β桶状蛋白的前体使用这两种转运体——TOM 进行跨膜空间的导入和 SAM 进行外膜的导出。目前还不清楚这两种转运体是否合作，以及新导入的蛋白质的β桶在哪里形成。我们建立了一种用于在体内和体外监测β桶形成的位置特异性测定法，并证明β桶是在与 SAM 结合的同时形成和插入膜中的。β桶的形成受到 SAM 突变体和出人意料的中央导入受体 Tom22 突变体的抑制。我们表明，Tom22 的细胞质结构域将 TOM 和 SAM 连接成一个超级复合物，促进跨膜空间侧的前体转移。我们的研究揭示了导入和导出转运体的受体介导偶联作为前体通道化的一种手段。
