Wagner Karina, Gebert Natalia, Guiard Bernard, Brandner Katrin, Truscott Kaye N, Wiedemann Nils, Pfanner Nikolaus, Rehling Peter
Institut für Biochemie und Molekularbiologie, ZBMZ, Universität Freiburg, D-79104 Freiburg, Germany.
Mol Cell Biol. 2008 Jul;28(13):4251-60. doi: 10.1128/MCB.02216-07. Epub 2008 May 5.
The mitochondrial inner membrane contains preprotein translocases that mediate insertion of hydrophobic proteins. Little is known about how the individual components of these inner membrane preprotein translocases combine to form multisubunit complexes. We have analyzed the assembly pathway of the three membrane-integral subunits Tim18, Tim22, and Tim54 of the twin-pore carrier translocase. Tim54 displayed the most complex pathway involving four preprotein translocases. The precursor is translocated across the intermembrane space in a supercomplex of outer and inner membrane translocases. The TIM10 complex, which translocates the precursor of Tim22 through the intermembrane space, functions in a new posttranslocational manner: in case of Tim54, it is required for the integration of Tim54 into the carrier translocase. Tim18, the function of which has been unknown so far, stimulates integration of Tim54 into the carrier translocase. We show that the carrier translocase is built via a modular process and that each subunit follows a different assembly route. Membrane insertion and assembly into the oligomeric complex are uncoupled for each precursor protein. We propose that the mitochondrial assembly machinery has adapted to the needs of each membrane-integral subunit and that the uncoupling of translocation and oligomerization is an important principle to ensure continuous import and assembly of protein complexes in a highly active membrane.
线粒体内膜含有介导疏水蛋白插入的前体蛋白转位酶。关于这些内膜前体蛋白转位酶的各个组分如何结合形成多亚基复合物，我们了解甚少。我们分析了双孔载体转位酶的三个膜整合亚基Tim18、Tim22和Tim54的组装途径。Tim54展示了最复杂的途径，涉及四种前体蛋白转位酶。前体在内外膜转位酶的超复合物中跨膜间隙转运。将Tim22的前体转运穿过膜间隙的TIM10复合物以一种新的转位后方式发挥作用：对于Tim54而言，它是Tim54整合到载体转位酶中所必需的。到目前为止功能未知的Tim18刺激Tim54整合到载体转位酶中。我们表明载体转位酶是通过模块化过程构建的，并且每个亚基遵循不同的组装途径。每个前体蛋白的膜插入和组装到寡聚复合物中是解偶联的。我们提出线粒体组装机制已适应每个膜整合亚基的需求，并且转位和寡聚化的解偶联是确保在高活性膜中蛋白质复合物持续导入和组装的重要原则。
