The specific delivery of proteins to human liver cells by engineered bio-nanocapsules.

A bio-nanocapsule (BNC), composed of the surface antigen (sAg) of the hepatitis B virus, is an efficient nanomachine with which to accomplish the liver-specific delivery of genes and drugs. Approximately 110 molecules of sAg are associated to form a BNC particle with an average diameter of 130 nm. The L protein is an sAg peptide composed mainly of preS and S regions. The preS region, with specific affinity for human hepatocytes, is localized in the N-terminus. The S region following the preS has two transmembrane regions responsible for the formation of particles. In this study, the fusion of emerald green fluorescent protein (EGFP) at the C-terminus of the S region was designed to deliver proteins to human hepatocytes. Truncation of the C-terminus of the S region was required to obtain sufficient expression levels in Cos7 cells. The nanoparticles that were produced delivered EGFP to human hepatoma cells, displaying the EGFP moiety outside, or enclosing it inside. However, only a single orientation characterizes the particle, so that either type of L fusion particle could be effectively and independently separated by an antibody affinity column. The dual C-terminal topologies of the L fusion particles designed in this study could be applied to various proteins for the C-terminal moiety of the L fusion proteins, depending on the character of the proteins, such as cytoplasmic proteins, as well as cytokines or ligands to cell surface receptors. We suggest that this fusion design is the most efficient way to prepare a BNC that delivers proteins to specific cells or tissues.