Assembly Pathway of Hepatitis B Core Virus-like Particles from Genetically Fused Dimers

Background: We studied assembly of HBV capsids using a genetically-fused dimer. Results: Assembly intermediates composed of two, three and five copies of a fused dimer have been isolated. Conclusion: Capsid assembly could progress using dimeric, trimeric, and pentameric intermediates. Significance: The low abundance and transient nature of assembly intermediates make analysis challenging, however, the stability of the intermediates described here has overcome this. Macromolecular complexes are responsible for many key biological processes. However, in most cases details of the assembly/disassembly of such complexes are unknown at the molecular level, as the low abundance and transient nature of assembly intermediates make analysis challenging. The assembly of virus capsids is an example of such a process. The hepatitis B virus capsid (core) can be composed of either 90 or 120 dimers of coat protein. Previous studies have proposed a trimer of dimers as an important intermediate species in assembly, acting to nucleate further assembly by dimer addition. Using novel genetically-fused coat protein dimers, we have been able to trap higher-order assembly intermediates and to demonstrate for the first time that both dimeric and trimeric complexes are on pathway to virus-like particle (capsid) formation.