Synthesis and assembly of Hepatitis B virus envelope protein-derived particles in Escherichia coli

Hepatitis B virus (HBV) envelope particles have been synthesized in eukaryotic cells (e.g., mammalian cells, insect cells, and yeast cells) as an HB vaccine immunogen and drug delivery system (DDS) nanocarrier. Many researchers had made attempts to synthesize the particles in Escherichia coli for minimize the cost and time for producing HBV envelope particles, but the protein was too deleterious to be synthesized in E. coli. In this study, we generated deletion mutants of HBV envelope L protein (389 amino acid residues (aa)) containing three transmembrane domains (TM1, TM2, TM3). The ΔNC mutant spanning from TM2 to N-terminal half of TM3 (from 237 aa to 335 aa) was found as a shortest form showing spontaneous particle formation. After the N-terminal end of ΔNC mutant was optimized by the N-end rule for E. coli expression, the modified ΔNC mutant (mΔNC) was efficiently expressed as particles in E. coli. The molecular mass of mΔNC particle was approx. 670 kDa, and the diameter was 28.5 ± 6.2 nm (mean ± SD, N = 61). The particle could react with anti-HBV envelope S protein antibody, indicating the particles exhibited S antigenic domain outside as well as HBV envelope particles. Taken together, the E. coli-derived mΔNC particles could be used as a substitute of eukaryotic cell-derived HBV envelope particles for versatile applications.