Asgard archaea genomes contain potential eukaryotic-like genes that provide intriguing insight for the evolution of eukaryotes. The eukaryotic actin polymerization/depolymerization cycle is critical for providing force and structure in many processes, including membrane remodeling. In general, Asgard genomes encode two classes of actin-regulating proteins from sequence analysis, profilins and gelsolins. Asgard profilins were demonstrated to regulate actin filament nucleation. Here, we identify actin filament severing, capping, annealing and bundling, and monomer sequestration activities by gelsolin proteins from Thorarchaeota (Thor), which complete a eukaryotic-like actin depolymerization cycle, and indicate complex actin cytoskeleton regulation in Asgard organisms. Thor gelsolins have homologs in other Asgard archaea and comprise one or two copies of the prototypical gelsolin domain. This appears to be a record of an initial preeukaryotic gene duplication event, since eukaryotic gelsolins are generally comprise three to six domains. X-ray structures of these proteins in complex with mammalian actin revealed similar interactions to the first domain of human gelsolin or cofilin with actin. Asgard two-domain, but not one-domain, gelsolins contain calcium-binding sites, which is manifested in calcium-controlled activities. Expression of two-domain gelsolins in mammalian cells enhanced actin filament disassembly on ionomycin-triggered calcium release. This functional demonstration, at the cellular level, provides evidence for a calcium-controlled Asgard actin cytoskeleton, indicating that the calcium-regulated actin cytoskeleton predates eukaryotes. In eukaryotes, dynamic bundled actin filaments are responsible for shaping filopodia and microvilli. By correlation, we hypothesize that the formation of the protrusions observed from Lokiarchaeota cell bodies may involve the gelsolin-regulated actin structures.

Asgard古细菌基因组包含潜在的真核生物样基因，为真核生物的进化提供了有趣的见解。真核肌动蛋白的聚合/解聚循环对于在许多过程（包括膜重塑）中提供力和结构至关重要。一般而言，Asgard基因组编码来自序列分析的两类肌动蛋白调节蛋白，分别是profilins和凝溶胶蛋白。事实证明，Asgard profilins可调节肌动蛋白丝的成核。在这里，我们确定了肌动蛋白丝的切断，加帽，退火和捆绑以及来自Thorarchaeota（Thor）的凝溶胶蛋白的单体螯合活性，这些蛋白完成了真核样肌动蛋白解聚循环，并表明了Asgard生物体中复杂的肌动蛋白细胞骨架调控。雷神凝溶胶蛋白在其他阿斯加德古细菌中具有同源物，并包含一或两个拷贝的典型凝溶胶蛋白结构域。由于真核凝溶胶蛋白通常包含三至六个结构域，因此这似乎是最初的真核生物基因复制事件的记录。这些蛋白质与哺乳动物肌动蛋白复合的X射线结构揭示了与人凝溶胶蛋白或cofilin与肌动蛋白的第一个结构域相似的相互作用。Asgard两域而非单域凝溶胶蛋白含有钙结合位点，这表现在钙控制的活动中。两域凝溶胶蛋白在哺乳动物细胞中的表达增强了肌动蛋白丝对离子霉素触发的钙释放的分解。这种在细胞水平上的功能演示为钙控制的Asgard肌动蛋白细胞骨架提供了证据，表明钙调节的肌动蛋白细胞骨架早于真核生物。在真核生物中，动态捆绑的肌动蛋白丝负责塑造丝状伪足和微绒毛。通过相关性，我们假设从Lokiarchaeota细胞体观察到的突起的形成可能涉及凝溶胶蛋白调节的肌动蛋白结构。