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。