Comparison of three different recombinant hepatitis B virus core particles expressed in Escherichia coli

The properties of three different recombinant hepatitis B virus core proteins expressed in Escherichia coli were compared: an N-terminal fusion protein, a C-terminally truncated protein and a sequence-authentic protein. All three proteins assembled into capsid-like particles with typical HBc-antigenicity, sedimentation behavior and distinctive electron microscopical images. Apart from this, however, variant HBc proteins displayed properties different from sequence-authentic HBc protein p21.4. Unlike p21.4, the particles of the N-terminal fusion protein p22.2 were sensitive to proteolytic attack by trypsin at variable sites within its arginine-rich C-terminus but not in its extended N-terminus. We therefore conclude that the C-terminal region is located on the surface of the p22.2 particle. These particles also showed increased HBe-antigenicity, as did the C-terminally truncated core particles p17.6, and to an even greater extent p18* particles which were derived from p22.2 by tryptic digestion. This might be interpreted as evidence for an--albeit minor--structural change. All variant core particles were less stable and contained less RNA. Electron microscopic indication for DNA binding of C-terminal deleted p17.6 particles was obtained using an aqueous spreading technique.