Immunoabsorbent nanoparticles based on a tobamovirus displaying protein A

Earlier attempts to express peptides longer than 20 aa on the surface of tobamoviruses such as tobacco mosaic virus have failed. Surprisingly, we found that a functional fragment of protein A (133 aa) can be displayed on the surface of a tobamovirus as a C-terminal fusion to the coat protein via a 15-aa linker. The macromolecular nature of these nanoparticles allowed the design of a simple protocol for purification of mAbs with a recovery yield of 50% and > 90% product purity. The extremely dense packing of protein A on the nanoparticles (> 2,100 copies per viral particle) results in an immunoadsorbent with a binding capacity of 2 g mAb per g. This characteristic, combined with the high level of expression of the nanoparticles (> 3 g adsorbent per kg of leaf biomass), provides a very inexpensive self-assembling matrix that could meet the criteria for a single-use industrial immunoadsorbent for antibody purification.