HBcAg (cAg) has been expressed in E.coli were it assembles in the bacterial cytoplasm into icosahedral capsids. Deletion of the polybasic C-terminal 34 residues (protamine domain) produces assembly competent protein (Cp149) which is suitable for structural analysis. The structure of the capsids has been previously determined by cryo-electron microscopy and by X-ray crystallography. Native HBeAg (eAg) is a secreted soluble protein which is thought to modulate both the innate and adaptive immune responses so as to favor persistent infection as well being an important clinical marker. This protein is truncated at position 149 and in addition contains a 10 residue N-terminal extension derived from partial processing of precursor protein. The structure of the eAg has not been determined. We have performed biophysical analysis on the eAg which have highlighted the importance of disulfide linkages in controlling conformation and solubility of the protein. Using a similar approach as for structural determination of the HIV-1 Rev, a specific antibody was used to mediate the successful crystallization of eAg. Structural determination is being performed by X-ray crystallography from which expect to obtain more detailed insight into the structural and conformation differences with the cAg. Previous structural determinations of nucleocapsid-antibody immune complexes by cryo-electron microscopy were performed with a panel of murine antibodies. This work has been extended to included human antibodies from clinical samples. The results indicate binding to distinct regions on the capsid surface (epitopes) which we had previously identified using the murine antibodies. This work, together our previous description of an immune complex of capsids and an antibody representative of the surface immunoglobulin from naive B-cells, provide one of the most complete pictures of the interaction of antibodies with a viral protein system related to an important human disease. Using a rabbit antibody library, monoclonal antibodies (mAbs) were selected then humanized to produce chimeric mAb fragment antigen binding portions (Fab). Fabs against the HBV capsid proteins were selected for high affinity binding to the capsid subunits. The binding of the antibodies prevent the assembly of the capsids (a central functional and structural component of the HBV virus) and may with development provide useful anti-HBV reagents.
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