University of Osnabrück, Faculty of Biology and Chemistry, Department of Biophysics, Barbarastr. 13, 49076 Osnabrück, Germany.
Eur J Cell Biol. 2011 Sep;90(9):721-30. doi: 10.1016/j.ejcb.2011.04.012.
Proteins of living cells carry out their specialized functions within various subcellular membranes or aqueous spaces. Approximately half of all the proteins of a typical cell are transported into or across membranes. Targeting and transport to their correct subcellular destinations are essential steps in protein biosynthesis. In eukaryotic cells secretory proteins are transported into the endoplasmic reticulum before they are transported in vesicles to the plasma membrane. Virtually all proteins of the endosymbiotic organelles, chloroplasts and mitochondria, are synthesized on cytosolic ribosomes and posttranslationally imported. Genetic and biochemical techniques led to rather detailed knowledge on the subunit composition of the various protein transport complexes which carry out the membrane transport of the preproteins. Conclusive concepts on targeting and cytosolic transport of polypeptides emerged, while still few details on the molecular nature and mechanisms of the channel moieties of protein translocation complexes have been achieved. In this paper we will describe the history of how the individual subunits forming the channel pores of the chloroplast, mitochondrial and endoplasmic reticulum protein import machineries were identified and characterized by single channel electrophysiological techniques in planar bilayers. We will also highlight recent developments in the exploration of the molecular properties of protein translocating channels and the regulation of the diverse protein translocation systems using the planar bilayer technique.
活细胞中的蛋白质在各种亚细胞膜或水相中执行其专门功能。典型细胞中的大约一半蛋白质被运输到膜内或穿过膜。靶向和运输到其正确的亚细胞目的地是蛋白质生物合成的关键步骤。在真核细胞中，分泌蛋白在被运输到质膜之前先被运输到囊泡中进入内质网。实际上，共生细胞器叶绿体和线粒体的所有蛋白质都是在胞质核糖体上合成的，并经过翻译后被导入。遗传和生化技术使我们对执行前蛋白膜运输的各种蛋白质运输复合物的亚基组成有了相当详细的了解。虽然关于多肽的靶向和胞质运输的概念已经很明确，但对于蛋白质易位子复合物的通道部分的分子性质和机制仍知之甚少。在本文中，我们将描述如何通过平面双层单通道电生理技术鉴定和表征形成叶绿体、线粒体和内质网蛋白输入机制的通道孔的各个亚基的历史。我们还将重点介绍使用平面双层技术探索蛋白质易位子通道的分子特性和调节各种蛋白质易位子系统的最新进展。
