SRPK2 Mediates HBV Core Protein Phosphorylation and Capsid Assembly via Docking Interaction

Members of the serine-arginine protein kinase (SRPK) family, SRPK1 and SRPK2, phosphorylate the hepatitis B core protein (Cp) and are crucial for pregenomic RNA encapsidation during viral nucleocapsid assembly. Among them, SRPK2 exhibits higher kinase activity toward Cp. In this study, we identified Cp sites that are phosphorylated by SRPK2 and demonstrated that the kinase utilizes an SRPK-specific docking groove to interact with and regulate the phosphorylation of the C-terminal arginine rich domain of Cp. We determined that direct interaction between the docking groove of SRPK2 and unphosphorylated Cp inhibited premature viral capsid assembly in vitro, whereas the phosphorylation of the viral protein reactivated the process. Pull-down assays together with the new cryo-electron microscopy structure of the HBV capsid in complex with SRPK2 revealed that the kinases decorate the surface of the viral capsid by interacting with the C-terminal domain of Cp, underscoring the importance of the docking interaction in regulating capsid assembly and pregenome packaging. Moreover, SRPK2-knockout in HepG2 cells suppressed Cp phosphorylation, indicating that SRPK2 is an important cellular kinase for HBV life cycle. Hepatitis B virus (HBV) is an enveloped DNA virus that causes hepatitis B, a common liver infection. HBV infection is highly associated with the development of both acute and chronic liver diseases, ranging from cirrhosis to liver cancer and liver failure. Like many viruses, HBV does not possess adequate endogenous factors for self-replication. Thus, it relies on host metabolism and machinery. Members of the SRPK family have been identified to the host cellular kinases that interact with HBV core protein during viral core assembly. Here we report the mechanism of how SRPK2 interacts with and phosphorylates HBV core protein. We also highlight the role of SRPK2 in the phosphorylation of HBV core protein in cells. Our research laid the foundation to targeting this host cellular kinase and developing new means to combat HBV infection.