Cryo-EM structure of the vault from human brain reveals symmetry mismatch at its caps.

The vault protein is expressed in most eukaryotic cells, where it is assembled on polyribosomes into large hollow barrel-shaped complexes. Despite its widespread and abundant presence in cells, the biological function of the vault remains unclear. In this study, we describe the cryo-EM structure of vault particles that were imaged as a contamination of a preparation to extract tau filaments from brain tissue of an individual with progressive supranuclear palsy (PSP). We identify a mechanism of symmetry mismatch at the caps of the vault, from 39-fold to 13-fold symmetry, where two out of three monomers are sequentially excluded from the cap, resulting in a narrow, greasy pore at the tip of the vault. Our structure offers valuable insights for engineering carboxy-terminal modifications of the major vault protein (MVP) for potential therapeutic applications.