Plasmid dimerization increases the production of hepatitis B core particles in E. coli

Due to their icosahedral structure with a high density of B- and T-cell epitopes, hepatitis B virus (HBV) core (HBc) particles are used as components of novel anti-HBV vaccines. Previous experiments demonstrated that C-terminally truncated HBV core (HBcΔ) proteins, which lack the polyarginine domain, were produced more efficiently in E. coli compared with full-length HBc. We have established a tryptophan operon promoter-directed high-level production system of 145 amino acid HBcΔ (HBc145); however, the level of HBc145 synthesis varied among individual subclones. Further investigation revealed that the subclones exhibiting higher HBc145 synthesis also demonstrated plasmid dimerization, leading to HBc145 yields that were 60 ～ 65% (mg/g) or 25 ～ 30% (mg/L) higher compared to clones containing a monomeric plasmid. These data were confirmed in at least three independent expression and purification events. Although plasmid dimerization is generally considered to inhibit plasmid stability in a growing cell population, it was found to have a positive effect on HBc145 synthesis and production in both Trp-deficient and Trp-rich media. This finding should be considered when planning large-scale production of HBc145.