Abstract：
In all domains of life, the ribosome-translocon complex inserts nascent transmembrane proteins into, and processes and transports signal peptide-containing proteins across, membranes. Eukaryotic translocons are anchored in the endoplasmic reticulum, while the prokaryotic complexes reside in cell membranes. Phylogenetic analyses indicate inheritance of eukaryotic Sec61/OST/TRAP translocon subunits from an Asgard archaea ancestor. However, the mechanism for translocon migration from a peripheral membrane to an internal cellular compartment (the proto-endoplasmic reticulum) during eukaryogenesis is unknown. Here we show compatibility between the eukaryotic ribosome-translocon complex and Asgard signal peptides and transmembrane proteins. We find that Asgard translocon proteins from Candidatus Prometheoarchaeum syntrophicum strain MK-D1, a Lokiarchaeon confirmed to contain no internal cellular membranes, are targeted to the eukaryotic endoplasmic reticulum on ectopic expression. Furthermore, we show that the cytoplasmic domain of MK-D1 OST1 (ribophorin I) can interact with eukaryotic ribosomes. Our data indicate that the location of existing ribosome-translocon complexes, at the protein level, determines the future placement of yet to be translated translocon subunits. This principle predicts that during eukaryogenesis, under positive selection pressure, the relocation of a few translocon complexes to the proto-endoplasmic reticulum will have contributed to propagating the new translocon location, leading to their loss from the cell membrane.
摘要：
在生活的所有领域，核糖体-转位复合物将新生的跨膜蛋白插入，处理和运输含信号肽的蛋白质，膜。真核转环体锚定在内质网中，而原核复合物存在于细胞膜中。系统发育分析表明，真核生物Sec61/OST/TRAP转位子亚基从Asgard古细菌祖先遗传。然而,真核发生过程中从外周膜向内部细胞区室（原内质网）转移的机制尚不清楚。在这里，我们显示了真核核糖体-转位子复合物与Asgard信号肽和跨膜蛋白之间的相容性。我们发现，来自念珠菌原发菌菌株MK-D1的Asgard转位蛋白，Lokiarchaear被证实不含内部细胞膜，定位于真核内质网上的异位表达。此外，我们表明，MK-D1OST1（病毒蛋白I）的细胞质结构域可以与真核核糖体相互作用。我们的数据表明，现有核糖体-转位复合物的位置，在蛋白质水平上，确定尚未翻译的转位子亚基的未来位置。这个原理预测在真核发生过程中，在积极的选择压力下，一些转位复合物重新定位到原内质网将有助于传播新的转位位置，导致它们从细胞膜上丢失。
