Department of Cell and Molecular Biology, Science for Life Laboratory, Uppsala University, SE-75123 Uppsala, Sweden.
Department of Marine Science, University of Texas-Austin, Marine Science Institute, Port Aransas, Texas 78373, USA.
Nature. 2017 Jan 19;541(7637):353-358. doi: 10.1038/nature21031. Epub 2017 Jan 11.
The origin and cellular complexity of eukaryotes represent a major enigma in biology. Current data support scenarios in which an archaeal host cell and an alphaproteobacterial (mitochondrial) endosymbiont merged together, resulting in the first eukaryotic cell. The host cell is related to Lokiarchaeota, an archaeal phylum with many eukaryotic features. The emergence of the structural complexity that characterizes eukaryotic cells remains unclear. Here we describe the 'Asgard' superphylum, a group of uncultivated archaea that, as well as Lokiarchaeota, includes Thor-, Odin- and Heimdallarchaeota. Asgard archaea affiliate with eukaryotes in phylogenomic analyses, and their genomes are enriched for proteins formerly considered specific to eukaryotes. Notably, thorarchaeal genomes encode several homologues of eukaryotic membrane-trafficking machinery components, including Sec23/24 and TRAPP domains. Furthermore, we identify thorarchaeal proteins with similar features to eukaryotic coat proteins involved in vesicle biogenesis. Our results expand the known repertoire of 'eukaryote-specific' proteins in Archaea, indicating that the archaeal host cell already contained many key components that govern eukaryotic cellular complexity.
真核生物的起源和细胞复杂性是生物学中的一个主要谜团。目前的数据支持以下情景：古菌宿主细胞与α变形菌（线粒体）内共生体融合在一起，形成了第一个真核细胞。宿主细胞与 Lokiarchaeota 有关，后者是一个具有许多真核特征的古菌门。真核细胞的结构复杂性的出现仍然不清楚。在这里，我们描述了“Asgard”超门，这是一组未培养的古菌，除了 Lokiarchaeota 外，还包括 Thor-, Odin- 和 Heimdallarchaeota。Asgard 古菌在系统基因组分析中与真核生物有关联，其基因组富含以前被认为是真核生物特有的蛋白质。值得注意的是，thorarchaeal 基因组编码了几种真核膜运输机制成分的同源物，包括 Sec23/24 和 TRAPP 结构域。此外，我们还鉴定了具有类似于真核囊泡生物发生中涉及的囊泡蛋白的特征的 thorarchaeal 蛋白。我们的结果扩展了古菌中“真核生物特异性”蛋白质的已知范围，表明古菌宿主细胞已经包含了许多控制真核细胞复杂性的关键成分。
