Spork Simone, Hiss Jan A, Mandel Katharina, Sommer Maik, Kooij Taco W A, Chu Trang, Schneider Gisbert, Maier Uwe G, Przyborski Jude M
Department of Parasitology, Philipps University Marburg, Germany.
Eukaryot Cell. 2009 Aug;8(8):1134-45. doi: 10.1128/EC.00083-09. Epub 2009 Jun 5.
Many apicomplexan parasites, including Plasmodium falciparum, harbor a so-called apicoplast, a complex plastid of red algal origin which was gained by a secondary endosymbiotic event. The exact molecular mechanisms directing the transport of nuclear-encoded proteins to the apicoplast of P. falciparum are not well understood. Recently, in silico analyses revealed a second copy of proteins homologous to components of the endoplasmic reticulum (ER)-associated protein degradation (ERAD) system in organisms with secondary plastids, including the malaria parasite P. falciparum. These proteins are predicted to be endowed with an apicoplast targeting signal and are suggested to play a role in the transport of nuclear-encoded proteins to the apicoplast. Here, we have studied components of this ERAD-derived putative preprotein translocon complex in malaria parasites. Using transfection technology coupled with fluorescence imaging techniques we can demonstrate that the N terminus of several ERAD-derived components targets green fluorescent protein to the apicoplast. Furthermore, we confirm that full-length PfsDer1-1 and PfsUba1 (homologues of yeast ERAD components) localize to the apicoplast, where PfsDer1-1 tightly associates with membranes. Conversely, PfhDer1-1 (a host-specific copy of the Der1-1 protein) localizes to the ER. Our data suggest that ERAD components have been "rewired" to provide a conduit for protein transport to the apicoplast. Our results are discussed in relation to the nature of the apicoplast protein transport machinery.
许多顶复门寄生虫，包括恶性疟原虫，都含有一种所谓的顶质体，它是一种起源于红藻的复杂质体，是通过次生内共生事件获得的。目前尚不清楚指导核编码蛋白转运至恶性疟原虫顶质体的确切分子机制。最近，计算机分析揭示，在包括疟原虫恶性疟原虫在内的具有次生质体的生物中，存在与内质网（ER）相关蛋白降解（ERAD）系统组分同源的蛋白的第二个拷贝。这些蛋白预计具有顶质体靶向信号，并被认为在核编码蛋白向顶质体的转运中发挥作用。在此，我们研究了疟原虫中这种源自ERAD的假定前体蛋白转运体复合物的组分。利用转染技术结合荧光成像技术，我们可以证明几种源自ERAD的组分的N末端将绿色荧光蛋白靶向至顶质体。此外，我们证实全长的PfsDer1-1和PfsUba1（酵母ERAD组分的同源物）定位于顶质体，其中PfsDer1-1与膜紧密结合。相反，PfhDer1-1（Der1-1蛋白的宿主特异性拷贝）定位于内质网。我们的数据表明，ERAD组分已被“重新布线”，以提供一条将蛋白质转运至顶质体的通道。我们结合顶质体蛋白转运机制的性质对结果进行了讨论。
