Rapaport D, Künkele K P, Dembowski M, Ahting U, Nargang F E, Neupert W, Lill R
Institut für Physiologische Chemie, Physikalische Biochemie und Zellbiologie der Universität München, 80336 Munich, Germany.
Mol Cell Biol. 1998 Sep;18(9):5256-62. doi: 10.1128/MCB.18.9.5256.
Translocation of preproteins across the mitochondrial outer membrane is mediated by the TOM complex. This complex consists of receptor components for the initial contact with preproteins at the mitochondrial surface and membrane-embedded proteins which promote transport and form the translocation pore. In order to understand the interplay between the translocating preprotein and the constituents of the TOM complex, we analyzed the dynamics of the TOM complex of Neurospora crassa and Saccharomyces cerevisiae mitochondria by following the structural alterations of the essential pore component Tom40 during the translocation of preproteins. Tom40 exists in a homo-oligomeric assembly and dynamically interacts with Tom6. The Tom40 assembly is influenced by a block of negatively charged amino acid residues in the cytosolic domain of Tom22, indicating a cross-talk between preprotein receptors and the translocation pore. Preprotein binding to specific sites on either side of the outer membrane (cis and trans sites) induces distinct structural alterations of Tom40. To a large extent, these changes are mediated by interaction with the mitochondrial targeting sequence. We propose that such targeting sequence-induced adaptations are a critical feature of translocases in order to facilitate the movement of preproteins across cellular membranes.
前体蛋白穿过线粒体外膜的转运是由TOM复合体介导的。该复合体由用于在线粒体表面与前体蛋白进行初始接触的受体组分以及促进转运并形成转运孔的膜嵌入蛋白组成。为了了解转运中的前体蛋白与TOM复合体各组分之间的相互作用，我们通过追踪前体蛋白转运过程中关键孔道组分Tom40的结构变化，分析了粗糙脉孢菌和酿酒酵母线粒体TOM复合体的动力学。Tom40以同寡聚体形式存在，并与Tom6动态相互作用。Tom40组装受到Tom22胞质结构域中一段带负电荷氨基酸残基的阻断影响，这表明前体蛋白受体与转运孔之间存在相互作用。前体蛋白与外膜两侧（顺式和反式位点）的特定位点结合会诱导Tom40发生明显的结构变化。在很大程度上，这些变化是由与线粒体靶向序列的相互作用介导的。我们提出，这种靶向序列诱导的适应性变化是转运酶的一个关键特征，以便促进前体蛋白穿过细胞膜的移动。
