Structure, Assembly, and Antigenicity of Hepatitis B Virus Capsid Proteins

This chapter reviews current information pertaining to the structure and assembly properties of hepatitis B virus (HBV) capsid protein, as well as the insights into its antigenicity and other interactions. HBV has a small (3.2 kb) DNA genome, although this modest genetic endowment is amplified by a variety of strategies, including alternative expression products of the same gene. In the replication cycle of HBV, the genome is initially incorporated into the assembling virus particle as a single-stranded RNA molecule—the pregenome—that is subsequently retrotranscribed in situ by the viral reverse transcriptase (RT). The DNA-containing nucleocapsid subsequently becomes enveloped by a membrane containing the viral glycoprotein—surface antigen (sAg), of which there are three size variants called S, M, and L, respectively—to yield the completely assembled and infectious virion. The capsid protein of HBV has several unexpected properties. It was found to have a novel fold, rich in a helix, and quite distinct from the eight-stranded b barrel that was common to the first dozen or so capsid proteins to be solved (from plant, animal, and bacterial viruses) and the other capsid protein folds that have been determined more recently.