Dietmeier K, Hönlinger A, Bömer U, Dekker P J, Eckerskorn C, Lottspeich F, Kübrich M, Pfanner N
Institut für Biochemie und Molekularbiologie, Universität Freiburg, Germany.
Nature. 1997 Jul 10;388(6638):195-200. doi: 10.1038/40663.
Most mitochondrial proteins are synthesized as preproteins on cytosolic polysomes and are subsequently imported into the organelle. The mitochondrial outer membrane contains a multisubunit preprotein translocase (Tom) which has receptors on the cytosolic side and a general import pore (GIP) in the membrane. Tom20-Tom22 and Tom70-Tom37 function as import receptors with a preference for preproteins that have amino-terminal presequences or internal targeting information, respectively. Tom40 is an essential constituent of the GIP, whereas Tom6 and Tom7 modulate the assembly and dissociation of the Tom machinery. Here we report the identification of Tom5, a small subunit that has a crucial role importing preproteins destined for all four mitochondrial subcompartments. Tom5 has a single membrane anchor and a cytosolic segment with a negative net charge, and accepts preproteins from the receptors and mediates their insertion into the GIP. We conclude that Tom5 represents a functional link between surface receptors and GIP, and is part of an 'acid chain' that guides the stepwise transport of positively charged mitochondrial targeting sequences.
大多数线粒体蛋白作为前体蛋白在胞质多核糖体上合成，随后被导入该细胞器。线粒体外膜含有一种多亚基前体蛋白转位酶（Tom），其在胞质侧有受体，膜上有一个通用导入孔（GIP）。Tom20 - Tom22和Tom70 - Tom37分别作为导入受体，前者偏好具有氨基末端前导序列的前体蛋白，后者偏好具有内部靶向信息的前体蛋白。Tom40是GIP的重要组成部分，而Tom6和Tom7调节Tom机制的组装和解离。在此，我们报告了Tom5的鉴定，它是一个小亚基，在导入定位于所有四个线粒体亚区室的前体蛋白中起关键作用。Tom5有一个单一的膜锚定结构和一个带负净电荷的胞质区段，从受体接受前体蛋白并介导它们插入GIP。我们得出结论，Tom5代表表面受体和GIP之间的功能联系，并且是引导带正电荷的线粒体靶向序列逐步运输的“酸性链”的一部分。
