Stability of the recombinant hepatitis B core antigen

The recombinant gene for hepatitis B core antigen (HBcAg) was cloned and expressed, and the protein was purified from Escherichia coli cultures. Purified HBcAg was tested for the effects of various physical and chemical agents on its immunoreactivity by a paramagnetic particle-based enzyme immunoassay. Recombinant HBcAg retained its immunoreactivity when heated at 70 degrees C for 60 min but was inactivated at 85 degrees C in 10 min. It was stable between pHs 5 and 10.5 but not at pHs 2 and 13.5. Treatment with sodium dodecyl sulfate (SDS), ethanol, and methanol caused a significant loss in HBcAg reactivity. The proteolytic enzymes papain and bacterial protease (type VIII from Bacillus licheniformis) degraded HBcAg significantly, but trypsin and chymotrypsin did not. The effect of combined SDS and 2-mercaptoethanol on recombinant HBcAg was an immediate loss in immunoreactivity, followed by rapid recovery to about 50% of the initial level. This level was maintained for 24 to 48 h and was followed by an almost total loss of HBcAg in about 120 h.