In Vitro Refolding of Vault-like Protein Nanocapsules with a Novel Scaffolding Mechanism

We attempted the in vitro scaffold-coordinated refolding of denatured major vault protein monomers into assembled vault-like nanoparticles. DNA or hyaluronic acid-binding tags were added to the MVP monomers, allowing MVP to align rotationally and translationally along these linear molecules. This was proposed to mimic the polyribosome assembly in vivo. Tagged MVP variants were expressed in E. coli and purified under denaturing conditions. Dynamic light scattering showed the formation of nanoparticles with a hydrodynamic radius of ~26 nm, consistent with the formation of vault-like nanoparticles. This was confirmed by transmission electron microscopy, FRET analysis, and cargo loading of CFP-INT fusion. CFP- and YFP-tagged MVP showed FRET only in the presence of MVP with a DNA-binding tag. This is the first successful instance of bioengineering of homogenous and heterogeneous vault-like nanoparticles, and at a potentially much larger scale than current protocols.