In Vivo Self-Assembly of Chimeric Ferritin for Multi-Functional Nanoparticle

Protein-based nanoparticles are attractive materials as carriers or templates in various fields because of several advantages: high biocompatibility and stability, uniform size, easy surface modification, and low immunogenicity. In particular, ferritin, one of the valuable nanoparticles, is an iron storage protein with a hollow form of a diameter of inner 8nm and outer 12nm. In ferritin, 24 monomers are arranged with 4-3-2 axial symmetry to form eight three-fold channels (N-terminal interface) and six four-fold channels (C-terminal interface), the diameter of 3~5 Å, which can make material diffusion between the outside and the inside. This structure formation is self-assembly and reversible assembly so that various materials such as drugs, dye, or metals can load inside. In addition, it can manufacture mixed forms with diversely modified monomers or control the number of functional monomers for a degree of activity. However, methods of reversible assembly-disassembly are often harsh enough to cause damage or incomplete assembly by applying extreme pH. Although most studies induce disassembly in pH 2 or 11 conditions, some researchers reported that it could not form intact at reassembly. This study produced a chimeric form without damage by simultaneously expressing two monomers using a dual expression vector. This method can make the chimeric form more easily without an additional purification process and loss of protein yield during manufacture. In order to check the ratio of each monomer and the difference in function according to it, silica forming peptide (SFP)-fused human ferritin monomer was used. The double expression confirmed that ferritin and SFP fusion ferritin were expressed at a constant ratio and gathered to form chimeric ferritin. The chimeric protein showed different sizes and functional properties than ferritins (non or SFP-fused form) composed of single monomers. This study showed that the form with two different monomers could be expressed intact in vivo to confer different functionalities on ferritin. Also, intact fabrication of protein-based nanoparticles combined with various functional tags will be applied more actively in nanotechnology.