The major vault protein is related to the toxic anion resistance protein (TelA) family

Vaults are barrel-shaped ribonucleoprotein particles that are abundant in certain tumors and multidrug resistant cancer cells. Prokaryotic relatives of the major vault protein, MVP, have not been identified. We used sequence analysis and molecular modeling to show that MVP and the toxic anion resistance protein, TelA of Rhodobacter sphaeroides strain 2.4.1, share a novel fold that consists of a three-stranded antiparallelβ -sheet. Because of this strong structural correspondence, we examined whether mammalian cell vaults respond to tellurite treatment. In the presence of the oxyanion tellurite, large vault aggregates, or vaultosomes, appear at the cell periphery in 15 min or less. Vaultosome formation is temperature-dependent, reversible, and occurs in normal human umbilical vein endothelial cells as well as transformed HeLa cervical cancer cells. Vaultosome formation is not restricted to tellurite and occurs in the presence of other toxic oxyanions (selenate, selinite, arsenate, arsenite, vanadate). In addition, vaultosomes form independently from other stress-induced ribonucleoprotein complexes, stress granules and aggresomes. Vaultosome formation is therefore a unique cellular response to an environmental toxin.