Asgard Arf GTPases can act as membrane-associating molecular switches with the potential to function in organelle biogenesis.

Inward membrane budding, i.e., the bending of membrane towards the cytosol, is essential for forming and maintaining eukaryotic organelles. In eukaryotes, Arf GTPases initiate this inward budding. Our research shows that Asgard archaea genomes encode putative Arf proteins (AArfs). AArfs possess structural elements characteristic of their eukaryotic counterparts. When expressed in yeast and mammalian cells, some AArfs displayed GTP-dependent membrane targeting. In vitro, AArf associated with both eukaryotic and archaeal membranes. In yeast, AArfs interacted with and were regulated by key organelle biogenesis players. Expressing an AArf led to a massive proliferation of endomembrane organelles including the endoplasmic reticulum and Golgi. This AArf interacted with Sec23, a COPII vesicle coat component, in a GTP-dependent manner. These findings suggest certain AArfs are membrane-associating molecular switches with the functional potential to initiate organelle biogenesis, and the evolution of a functional coat could be the next critical step towards establishing eukaryotic cell architecture.