Assembly of hepatitis B virus core protein through distinct cellular compartments into complete and incomplete viral particles

• Applicant: Professor Dr. Mengji Lu
• Subject Area: Virology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 546849318

The hepatitis B virus (HBV) infection cycle in hepatocytes includes receptor binding, entry, disassembly and uncoating of capsids at the nuclear pore complex, covalently closed circular DNA (cccDNA) synthesis, transcription and translation, assembly of capsids and secretion of viral particles. In addition to the rcDNA containing complete virion, several types of viral particles are generated and released from the HBV replicating hepatocytes, including subviral particles (SVPs), genome-free viral particles and naked capsids, through different secretory pathways. Previous studies already indicated the critical role of cellular vesicle trafficking system, including ER-Golgi apparatus, early endosome, late endosome/MVBs, autophagosome and amphisomes, in assembly and secretion of different types of viral particles. However, the process of recruitment of HBV replication intermediates to these compartments for assembly and release of specific viral particles is not yet clearly investigated. This study focused on HBc capsids, which have been found to be associated with autophagosomes and late endosomes and could be exported as enveloped particles or naked capsids. The main aim of this collaborative project is to combine the expertise of both Taiwan and German sides for elucidating the process for assembly of HBV capsids and viral particles, in association with distinct cellular compartments. HBcAg is produced as monomers and forms dimers and multimers that then assemble to capsids together with HBV polymerase and pgRNAs. In the assembly process, HBc undergoes modification for productive HBV biogenesis, from phosphorylation to dephosphorylation at the pgRNA encapsidation step. The specific HBc intermediates as phosphorylated or dephosphorylated form in mediating the interaction with HBsAg and assembly to complete virions in specific cellular compartments will be addressed. The potential role of specific viral proteins, including HBsAg, polymerase and the newly discovered protein encoded by splicing RNA SP1 (which lacks the last amino acid of HBc), in recruitment of HBc replication intermediates to the endosomes/MVB and autophagosomes will also be addressed in this project. Meanwhile, the effects of current antiviral HBV core protein allosteric modulators (CpAMs) and interferon treatment on the assembly and release of those viral particles through distinct compartments will be addressed in this project. Three specific aims are proposed in this project to answer the questions: (1) how HBc assembles into viral particles through distinct cellular compartments? (2) how HBcAg targets to distinct cellular compartments and assemble into different capsids and viral particles, through HBc modification or specific viral proteins and their cellular transporting molecules? (3) what are the effects of CpAMs, interferon or new antivirals developed by current project on HBc assembly at distinct compartments?

• DFG Programme: Research Grants
• International Connection: Taiwan
• Partner Organisation: National Science and Technology Council (NSTC)
• Cooperation Partner: Professor Dr. Pei-Jer Chen