Protein import into complex plastids

许多藻类在次生内共生中进化。在这里，一个单细胞的真核细胞含有一个由两层膜包围的质体，被另一个真核细胞内化。在这种胞中胞的共同进化过程中，光养细胞被还原成一个被三层或四层膜包围的复杂质体。从许多基因组计划中得知，复杂质体的基因组不具有编码所有质体定位蛋白的能力。因此，对于共生相互作用，建立了一个运输系统，以保证核编码的质体蛋白穿过质体周围膜的运输。在硅藻的质体，这是由四个膜包围的情况下，我们已经确定了第一次的第二个最外面的，并在一个合作项目中，第三个膜的易位。此外，我们已经表明，这些translocators存在于许多其他藻类以及在一些细胞内寄生虫。在这里应用的项目中，我们将专注于第二最外层膜中的转运蛋白复合物的相互作用因子及其结构。为此，我们将首先应用于二次进化的模式生物的策略。此外，计划确定重要的转运蛋白复合物组分的蛋白质结构。我们期望从我们的工作中深入了解易位复合体及其功能。由于这种复合物在其膜组分方面与真核细胞的ERAD机制同源，我们期望ERAD工作的社区也将从我们的工作中受益。

Many algae evolved in secondary endosymbiosis. Here a unicellular, eukaryotic cell harboring a plastid surrounded by two membranes was internalized by another eukaryote. In the course of the co-evolution of this cell-within-a-cell the phototrophic cell was reduced to a complex plastid surrounded by either three or four membranes. From many genome projects it is known that the genomes of complex plastids have not the capacity to encode all plastid-located proteins. Thus, for the symbiontic interaction a transport system was established to guarantee transport of nucleus-encoded plastid protein across the plastid surrounding membranes. In case of the plastids of diatoms, which are surrounded by four membranes, we have identified for the first time the translocators of the second outermost and, in a cooperation project, of the third membrane. Additionally we have shown that these translocators are present in many other algae as well as in some intracellular parasites. In the project applied here, we will focus on the translocator complex in the second outermost membrane in respect to interacting factors and its structure. For that we will apply strategies firstly used in a secondarily evolved model organism. In addition it is planned to determine the protein structure of important translocator complex components. We expect from our work in-depth insights into the translocator complex and its functions. As this complex is in respect to its membrane components homologous to the ERAD machinery of eukaryotic cells, we expect that the community working on ERAD will profit from our work as well.