Bacterial major vault protein homologs form divergent vault structures

Vaults are large, enigmatic macromolecular protein complexes composed of symmetrically arranged major vault protein (MVP) subunits with a wide variety of proposed functions. While MVP is conserved in most eukaryotes, its prevalence in other domains of life has not been well studied. Furthermore, whether bacterial MVP homologs assemble into vaults remains unknown. Here, we identify and examine a subset of bacterial MVP homologs and report cryoEM structures of an intact vault from Corallococcus praedator and a half-vault from a Deltaproteobacteria bacterium. Both bacterial vault complexes exhibit architectures unlike any other previously characterized vault with barrel/cap symmetries of D35/C13 and C48/C16, respectively. These data demonstrate that bacterial MVP homologs can assemble into vault structures and highlight the structural diversity of vaults across domains of life.