Purification and Observation of the Recombinant Hepatitis B Virus Core Antigen (rHBcAg) Particles Produced in the Yeast

Hepatitis B virus core antigen protein gene (C gene) was expressed in Saccharomyces cerevisiae and the products (rHBcAg particles) were purified from crude lysate of the yeast by three steps: Sephrose CL-4B chromatography, sucrose step-gradient ultracentrifugation, and CsCl-isopycnic ultracentrifugation. rHBcAg was synthesized in yeast cells as a particle consisting of polypeptides which have a molecular weight of 21.5 kDa (p21.5). ELISA and CsCl- isopycnic ultracentrifugation purification products (rHBcAg particles) in each fraction indicated that the particle densities of the fraction with higher rHBcAg antigenicity mainly distributed at the densities of 1.27g•mL-1 and 1.40 g•mL-1, respectively. Observation of the purified products (rHBcAg particles) by TEM indicated that rHBcAg peptides could self-assemble into two kinds of different sizes of rHBcAg particles (core particles); the large particle was about 30.1±2.4 nm in diameter and the small particle about 21.5±3.3 nm. This indicated that the rHBcAg particles displayed dimorphism, but the biological significance of this dimorphism is not clear and needs to be studied further.