The thermostability of a Vaccine Delivery system X-Protein (VADEX-Pro) based protein nanoparticle

We have adapted split GFP technology into the protein nanoparticle platform, Vaccine Delivery system X (VADEX), created in previous study. To evaluate the capability of this new platform, a model protein, maltose binding protein (MBP), was fused to the β-strand 11 of sfGFP and co-expressed with VADEX-10 which was composed of LYRRLE peptide and N-terminal part up to β-strand 10 of sfGFP. When these two fusion proteins were expressed in a cell, they were assembled into PNP spontaneously with a dynamic light scattering (DLS) particle size of 26 nm. This nanoparticle platform was renamed as VADEX-Pro for its capacity of expressing large protein on PNP. The thermostability of the assembled PNP was verified by both SDS-PAGE and DLS analysis following treatment. This PNP was stable at 25 °C and at temperatures as high as 40 °C for at least two months. Mutations that replaced cysteine residue of the LYRRLE peptide with serine or alanine destabilized and induced degradation of the VADEX-based PNP. The results in this study showed that the non-covalent complementation of split sfGFP became irreversible when reconstituted sfGFP was assembled in a VADEX-Pro PNP. This platform may be applied in developing thermostable vaccines.