Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
Faculty of Biology, University of Freiburg, Freiburg, Germany.
Nature. 2023 Sep;621(7979):627-634. doi: 10.1038/s41586-023-06477-8. Epub 2023 Aug 1.
The presequence translocase of the mitochondrial inner membrane (TIM23) represents the major route for the import of nuclear-encoded proteins into mitochondria. About 60% of more than 1,000 different mitochondrial proteins are synthesized with amino-terminal targeting signals, termed presequences, which form positively charged amphiphilic α-helices. TIM23 sorts the presequence proteins into the inner membrane or matrix. Various views, including regulatory and coupling functions, have been reported on the essential TIM23 subunit Tim17 (refs. ). Here we mapped the interaction of Tim17 with matrix-targeted and inner membrane-sorted preproteins during translocation in the native membrane environment. We show that Tim17 contains conserved negative charges close to the intermembrane space side of the bilayer, which are essential to initiate presequence protein translocation along a distinct transmembrane cavity of Tim17 for both classes of preproteins. The amphiphilic character of mitochondrial presequences directly matches this Tim17-dependent translocation mechanism. This mechanism permits direct lateral release of transmembrane segments of inner membrane-sorted precursors into the inner membrane.
线粒体内膜的前导序列转位酶（TIM23）代表了核编码蛋白进入线粒体的主要途径。大约 1000 多种不同的线粒体蛋白中有 60%以上是用氨基末端靶向信号（称为前导序列）合成的，这些信号形成带正电荷的两亲性α-螺旋。TIM23 将前导序列蛋白分拣到内膜或基质中。已经报道了 TIM23 亚基 Tim17 的各种观点，包括调节和偶联功能（参考文献）。在这里，我们在天然膜环境中对跨膜转运过程中 Tim17 与基质靶向和内膜分拣的前体蛋白的相互作用进行了作图。我们表明，Tim17 在靠近双层膜的膜间隙侧含有保守的负电荷，对于这两类前体蛋白，这些负电荷对于启动前导序列蛋白沿着 Tim17 的独特跨膜腔的转运是必需的。线粒体前导序列的两亲性直接与这种依赖 Tim17 的转运机制相匹配。这种机制允许将内膜分拣前体的跨膜片段直接横向释放到内膜中。
