In 2002 vault research went off in a completely new direction. The cryoEM structures of the vault particle showed that it was like a small hollow capsule and experiments of Dr. Andy Stephen indicated that this basic barrel-like structure could be formed from many copies of MVP. These findings led to new research direction at UCLA with many groups from different disciplines working together (this is called interdisciplinary research) This included groups in the David Geffen School of Medicine (Rome, Stewart, Eisenberg), the College of Letters and Science (Zink) and the School of Engineering and Applied Science (Dunn, Mobouquette).
The object of this new research was to change the vault structure so it could be used as a nano-capsule. We would like to change the vaults for interesting new uses like sending medicines to cells in the body.
In order to package things (proteins) inside of the vault we used a short piece of the vault VPARP protein called the INT domain. INT acts like a "zip code" to direct the VPARP protein into the inside of the vault. To determine whether INT could direct a non-vault protein into the vault, we attached the INT zip code to a protein from the firefly. This protein (called luciferase) is responsible for making the firefly glow. By putting the INT zip code on the firefly luciferase protein, this protein could be sent into the vault. Thus we had made vaults into little nano-sized light bulbs that could cause the vaults to glow! Cryo EM studies showed that the firefly protein was packaged inside the vault resulting in two rings in the interior of the particle (Figure).
(A) The VPARP protein has a "zip code" shown by the orange box that can send this protein into the vault. If this zip code is put on the end of the firefly luciferase protein (shown by the purple box) it can send the firefly protein into the vault. The firefly protein is seen inside the vault in panel C as two yellow rings.
In addition to sending the firefly protein into vaults, we have also used the INT zip code to send other proteins into vaults.)
Vaults have been produced with tags (extra bits of protein) hanging on their outside surface at the top and bottom. These tags allow the vault to bind to the surface of certain kinds of cells that have proteins on their surface (called receptors). The receptors like to stick to the tags.