ERAD-Derived Preprotein Transport across the Second Outermost Plastid Membrane of Diatoms
ERAD-Derived Preprotein Transport across the Second Outermost Plastid Membrane of Diatoms
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DOI：
10.1093/molbev/msp079
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发表时间：
2009-08-01
影响因子：
10.7
通讯作者：
Maier, Uwe G.
中科院分区：
文献类型：
--
作者：
Hempel, Franziska;Bullmann, Lars;Maier, Uwe G.
三角褐指藻（Phaeodactylum tricornutum）的质体由四层膜包围，通过次生内共生进化。与陆地植物一样，其质体蛋白质大多数编码为宿主细胞核基因组上的前体蛋白，并最终重定向到细胞器中。由于硅藻中存在的两个膜比围绕初级质体的一对膜多，因此靶向情况明显不同且更复杂。在这项工作中，我们专注于前蛋白质运输的第二个最外层的质体膜，一个问题，是实验上无法访问到现在。我们提供的第一个迹象表明，我们的假设ERAD（ER相关降解）衍生的前蛋白转运系统可能是正确的。我们的数据表明，共生体特异性Der 1蛋白，sDer 1 -1和sDer 1 -2，形成一个寡聚复合物内的第二个最外层膜的复杂质体。此外，我们提出的第一个证据表明，该复合物与转运肽的前体蛋白被运送穿过这一膜的periplastidid室，但不与转运肽的基质靶向蛋白。因此，sDer 1复合物可能在区分跨最外两层膜运输的前蛋白与直接跨复合质体所有四层膜的前蛋白方面具有额外的作用。总而言之，我们的研究共生体特定的ERAD样机制的硅藻表明，一个预先存在的细胞机器被回收，以履行一个新的功能，在过渡的前自由生活的真核生物到二级内共生体。
The diatom Phaeodactylum tricornutum harbors a plastid that is surrounded by four membranes and evolved by way of secondary endosymbiosis. Like land plants, most of its plastid proteins are encoded as preproteins on the nuclear genome of the host cell and are resultantly redirected into the organelle. Because two more membranes are present in diatoms than the one pair surrounding primary plastids, the targeting situation is obviously different and more complex. In this work, we focus on preprotein transport across the second outermost plastid membrane-an issue that was experimentally inaccessible until now. We provide first indications that our hypothesis of an ERAD (ER-associated degradation)-derived preprotein transport system might be correct. Our data demonstrate that the symbiont-specific Der1 proteins, sDer1-1 and sDer1-2, form an oligomeric complex within the second outermost membrane of the complex plastid. Moreover, we present first evidence that the complex interacts with transit peptides of preproteins being transported across this membrane into the periplastidal compartment but not with transit peptides of stromal-targeted proteins. Thus, the sDer1 complex might have an additional role in discriminating preproteins that are transported across the two outermost membranes from preproteins directed across all four membranes of the complex plastid. Altogether, our studies of the symbiont-specific ERAD-like machinery of diatoms suggest that a preexisting cellular machinery was recycled to fulfill a novel function during the transition of a former free-living eukaryote into a secondary endosymbiont.