Dihanich M
Friedrich-Miescher-Institute, Basel, Switzerland.
Experientia. 1990 Feb 15;46(2):146-53. doi: 10.1007/BF02027310.
Like most other mitochondrial proteins porin is synthesized in the cytosol and imported posttranslationally into the outer mitochondrial membrane. This transport follows the general rules for mitochondrial protein import with a few aberrations: a) porin contains an uncleaved NH2-terminal signal sequence, b) also its carboxyterminus might be involved in the import process, and c) this transport does not seem to require a membrane potential delta psi, although it is ATP-dependent. Most likely the actual import step occurs at contact sites between the outer and the inner mitochondrial membrane and involves at least one receptor protein. Although porin is known to be the major gate through the outer mitochondrial membrane, its absence only causes transient respiratory problems in yeast cells. This could mean a) that there is a bypass for some mitochondrial functions in the cytosol and/or b) that there are alternative channel proteins in the outer membrane. The first idea is supported by the overexpression of cytosolic virus-like particles in yeast cells lacking porin and the second by the occurrence of residual pore activity in mitochondrial outer membrane purified from porinless mutant cells.
与大多数其他线粒体蛋白一样，孔蛋白在胞质溶胶中合成，翻译后被导入线粒体外膜。这种转运遵循线粒体蛋白导入的一般规则，但有一些偏差：a）孔蛋白含有未切割的NH2末端信号序列，b）其羧基末端可能也参与导入过程，c）这种转运似乎不需要膜电位Δψ，尽管它依赖于ATP。最有可能的是，实际的导入步骤发生在线粒体外膜和内膜之间的接触位点，并且至少涉及一种受体蛋白。尽管已知孔蛋白是穿过线粒体外膜的主要通道，但其缺失仅在酵母细胞中引起短暂的呼吸问题。这可能意味着a）胞质溶胶中存在一些线粒体功能的旁路和/或b）外膜中存在替代通道蛋白。第一个想法得到了缺乏孔蛋白的酵母细胞中胞质病毒样颗粒过表达的支持，第二个想法得到了从无孔蛋白突变细胞纯化的线粒体外膜中残留孔活性的出现的支持。
