Structural evidence for a functional actin cytoskeleton in Asgard archaea
The origin of the eukaryotic cell is unresolved. Metagenomics sequencing recently provided evidence for several potential eukaryotic gene homologs in the Asgard archaea. However, many of these eukaryotic-like sequences are highly divergent and the organisms have yet to be imaged or cultivated, bringing in to question whether these archaea exhibit eukaryotic characteristics. Here we explore the properties of putative cytoskeletal proteins from Asgard archaea. We determine that the Asgard genomes encode functional profilins and gelsolins, establishing that these archaea have a regulated actin cytoskeleton, one of the hallmarks of the eukaryotic cell. Thus, Asgard archaea possess an ancient polar and regulated actin system, which is likely to integrate force into membrane remodeling processes through directed polymerization. Since Asgard archaea are also predicted to encode potential eukaryotic-like genes involved in membrane trafficking and endocytosis, it is probable that actin polymerization drives membrane perturbations and organization.