Hepatitis B virus (HBV) is a significant global health concern, causing both acute and chronic liver infections. The virus is a member of the Hepadnaviridae family and is known for its unique replication strategy, which involves reverse transcription of its pregenomic RNA (pgRNA) into DNA. One of the critical components of HBV is the core protein, also known as HBcAg (Hepatitis B core antigen), which plays a vital role in the virus’s life cycle.
The HBV core protein is a structural protein that forms the nucleocapsid, encapsulating the viral DNA and polymerase. The full-length core protein consists of 183 amino acids (a.a.), with the first 149 amino acids forming the assembly domain responsible for capsid formation, and the remaining C-terminal region (a.a. 150-183) being rich in arginine residues, which are crucial for nucleic acid binding .
The recombinant HBV core protein (1-183 a.a.) is typically expressed in Escherichia coli (E. coli) and purified using chromatographic techniques. This recombinant protein retains the immunodominant regions of the native core protein, making it useful for various research and diagnostic applications .
The HBV core protein is essential for the virus’s replication and assembly. After the virus enters a hepatocyte, the core protein assembles into a capsid around the pgRNA and viral polymerase. This capsid then undergoes reverse transcription to produce relaxed circular (RC) DNA, which can either be enveloped and secreted as a virion or transported back to the nucleus to form covalently closed circular DNA (cccDNA), serving as a template for further viral replication .
Phosphorylation of the HBV core protein, particularly in the C-terminal domain, plays a crucial role in regulating its interactions with nucleic acids. Specific phosphorylation sites have been identified, and their occupancy can significantly impact RNA binding and capsid structure. For instance, phosphorylation by serine-arginine protein kinase 1 (SRPK1) has been shown to reduce non-specific RNA encapsidation, thereby facilitating the selective packaging of the pgRNA/polymerase complex .
The recombinant HBV core protein (1-183 a.a.) is widely used in research to study the virus’s structure, replication, and interactions with host cells. It is also employed in diagnostic assays to detect antibodies against HBV in infected individuals. The high purity and immunoreactivity of the recombinant protein make it a valuable tool for these purposes .