Herrmann Johannes M, Bonnefoy Nathalie
Institut für Physiologische Chemie, Universität München, Butenandtstrasse 5, München 81377, Germany.
J Biol Chem. 2004 Jan 23;279(4):2507-12. doi: 10.1074/jbc.M310468200. Epub 2003 Oct 30.
The biogenesis of mitochondria requires the insertion of both nuclear and mitochondrially encoded proteins into the inner membrane. The inner membrane protein Oxa1 plays an important role in this process. Translocation of the terminal intermembrane space domains of subunit 2 of the cytochrome oxidase complex, Cox2, strictly depends on Oxa1. In contrast, other Oxa1 substrates can be inserted independently of Oxa1 function, although at reduced efficiency. A Saccharomyces cerevisiae mutant containing a large deletion in its mitochondrial genome allowed us to analyze the insertion process of a fusion protein of cytochrome b and Cox2. In this mutant, the N-terminal domain of Cox2 is synthesized as a hairpin loop that is flanked by hydrophobic transmembrane segments on both sides. Both genetic and biochemical evidences indicate that translocation of this region across the inner membrane still requires Oxa1 function. Thus, the position of intermembrane space domains within protein sequences does not appear to determine their dependence on the Oxa1 translocase. Our observations rather suggest that the dependence on Oxa1 correlates with the net charge of the domain that has to be translocated across the lipid bilayer.
线粒体的生物合成需要将细胞核和线粒体编码的蛋白质都插入内膜。内膜蛋白Oxa1在此过程中起重要作用。细胞色素氧化酶复合体亚基2（Cox2）的跨膜空间末端结构域的转运严格依赖于Oxa1。相比之下，其他Oxa1底物可以独立于Oxa1功能进行插入，尽管效率较低。一个线粒体基因组中存在大片段缺失的酿酒酵母突变体使我们能够分析细胞色素b和Cox2融合蛋白的插入过程。在这个突变体中，Cox2的N端结构域被合成为一个发夹环，两侧均有疏水跨膜片段。遗传和生化证据均表明，该区域跨内膜的转运仍然需要Oxa1功能。因此，蛋白质序列中跨膜空间结构域的位置似乎并不能决定它们对Oxa1转位酶的依赖性。我们的观察结果反而表明，对Oxa1的依赖性与必须跨脂质双层转运的结构域的净电荷相关。
