The origin of the eukaryotic cell is unresolved1,2. Metagenomics sequencing has recently identified several potential eukaryotic gene homologues in Asgard archaea3,4, consistent with the hypothesis that the eukaryotic cell evolved from within the Archaea domain. However, many of these eukaryotic-like sequences are highly divergent and the organisms have yet to be imaged or cultivated, which brings into question the extent to which these archaeal proteins represent functional equivalents of their eukaryotic counterparts. Here we show that Asgard archaea encode functional profilins and thereby establish that this archaeal superphylum has a regulated actin cytoskeleton, one of the hallmarks of the eukaryotic cell5. Loki profilin-1, Loki profilin-2 and Odin profilin adopt the typical profilin fold and are able to interact with rabbit actin—an interaction that involves proteins from species that diverged more than 1.2 billion years ago6. Biochemical experiments reveal that mammalian actin polymerizes in the presence of Asgard profilins; however, Loki, Odin and Heimdall profilins impede pointed-end elongation. These archaeal profilins also retard the spontaneous nucleation of actin filaments, an effect that is reduced in the presence of phospholipids. Asgard profilins do not interact with polyproline motifs and the profilin–polyproline interaction therefore probably evolved later in the Eukarya lineage. These results suggest that Asgard archaea possess a primordial, polar, profilin-regulated actin system, which may be localized to membranes owing to the sensitivity of Asgard profilins to phospholipids. Because Asgard archaea are also predicted to encode potential eukaryotic-like genes involved in membrane-trafficking and endocytosis3,4, imaging is now necessary to elucidate whether these organisms are capable of generating eukaryotic-like membrane dynamics that are regulated by actin, such as are observed in eukaryotic cell movement, podosomes and endocytosis.Asgard archaea encode functional profilins that can interact with mammalian actin, which suggests that—similar to eukaryotic cells—they possess a regulated actin cytoskeleton.

中文翻译：

---

Asgard 古细菌的基因组编码调节肌动蛋白的 profilins

真核细胞的起源尚未解决1,2。宏基因组学测序最近在 Asgard 古细菌 3,4 中确定了几个潜在的真核基因同源物，这与真核细胞从古细菌域内进化的假设一致。然而，这些真核样序列中的许多是高度分化的，并且生物体尚未被成像或培养，这使得这些古细菌蛋白在多大程度上代表其真核生物对应物的功能等价物成为问题。 .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 在这里，我们展示了 Asgard 古细菌编码功能性 profilins，从而确定这种古细菌超门具有受调节的肌动蛋白细胞骨架，这是真核细胞的标志之一。Loki profilin-1，Loki profilin-2 和 Odin profilin 采用典型的 profilin 折叠，能够与兔肌动蛋白相互作用——这种相互作用涉及来自超过 12 亿年前分化的物种的蛋白质6。生化实验表明，哺乳动物肌动蛋白在 Asgard profilins 存在下聚合；然而，Loki、Odin 和 Heimdall profilins 会阻碍尖端伸长。这些古细菌 profilins 还阻碍了肌动蛋白丝的自发成核，这种作用在磷脂存在的情况下会减弱。Asgard profilins 不与聚脯氨酸基序相互作用，因此 profilin-聚脯氨酸相互作用可能在 Eukarya 谱系中进化较晚。这些结果表明 Asgard 古细菌拥有原始的、极性的、由 profilin 调节的肌动蛋白系统，由于 Asgard profilins 对磷脂的敏感性，它可能位于膜上。由于 Asgard 古细菌也被预测编码参与膜运输和内吞作用的潜在真核样基因 3,4，现在需要成像来阐明这些生物是否能够产生受肌动蛋白调节的真核样膜动力学，例如在真核细胞运动、足小体和内吞作用中观察到。Asgard 古细菌编码可与哺乳动物肌动蛋白相互作用的功能性谱蛋白，这表明与真核细胞类似，它们具有受调节的肌动蛋白细胞骨架。