Zara V, Palmisano I, Rassow J, Palmieri F
Dipartimento di Biologia, Università di Lecce, Italy.
J Mol Biol. 2001 Jul 27;310(5):965-71. doi: 10.1006/jmbi.2001.4833.
The mitochondrial inner membrane of Saccharomyces cerevisiae contains a group of homologous carrier proteins that mediate the exchange of several metabolites. The members of this protein family are synthesized in the cytosol and reach their final topology after translocation across the mitochondrial outer membrane. Using the ADP/ATP carrier (AAC) as a model protein, previous studies have established four distinct steps of the import pathway (stages I-IV). In the absence of the mitochondrial membrane potential (deltapsi), the AAC accumulates at the inner surface of the outer membrane (stage IIIa) and remains bound to the outer membrane import channel. Only in the presence of the membrane potential, can a complex of small Tim proteins mediate transfer of the AAC to the inner membrane. In this study, we characterized the import pathway of the dicarboxylate carrier (DIC). Different from the AAC, the DIC showed complete deltapsi-independent translocation across the outer membrane, release from the import pore, and mainly accumulated in a soluble state in the intermembrane space, thus defining a new translocation intermediate (stage III*). The DIC should be a suitable model protein for the characterization of deltapsi-independent functions of the intermembrane space Tim proteins.
酿酒酵母的线粒体内膜含有一组同源载体蛋白，它们介导几种代谢物的交换。该蛋白家族的成员在细胞质中合成，并在穿过线粒体外膜后达到其最终拓扑结构。以前的研究以ADP/ATP载体（AAC）作为模型蛋白，确定了导入途径的四个不同步骤（阶段I-IV）。在没有线粒体膜电位（Δψ）的情况下，AAC聚集在线粒体外膜的内表面（阶段IIIa），并与外膜导入通道结合。只有在存在膜电位的情况下，小Tim蛋白复合物才能介导AAC向内膜的转移。在本研究中，我们对二羧酸载体（DIC）的导入途径进行了表征。与AAC不同，DIC在外膜上表现出完全不依赖于Δψ的转运、从导入孔释放，并且主要以可溶状态积聚在膜间隙中，从而定义了一种新的转运中间体（阶段III*）。DIC应该是用于表征膜间隙Tim蛋白不依赖于Δψ功能的合适模型蛋白。
