Capsid protein, Hepatitis B Virus (His)

The Capsid Protein plays a crucial role in the assembly of icosahedral capsids, forming large particles with T=4 icosahedral symmetry composed of 240 capsid protein copies, while a fraction assembles into smaller T=3 particles with 180 capsid proteins. These capsids are transported along microtubules to the nucleus, where phosphorylation of the capsid induces the exposure of a nuclear localization signal in its C-terminal portion, facilitating binding to the nuclear pore complex via importin (karyopherin-) alpha and beta. The intact capsids are imported through the nuclear pore into the nuclear basket, likely binding to NUP153. Only mature capsids containing the viral genome can release viral DNA and capsid protein into the nucleoplasm, while immature capsids remain stuck in the basket. Capsids encapsulate pre-genomic RNA and the P protein, with the RNA reverse-transcribed into DNA in the cytoplasm. The capsid, post-reverse transcription, can be directed to the nucleus for additional transcription or bud through the endoplasmic reticulum to produce new virions. The Capsid Protein homodimerizes, then multimerizes, and interacts with cytosol-exposed regions of viral L glycoprotein in the reticulum-to-Golgi compartment. Moreover, it interacts with human FLNB and, in its phosphorylated form, interacts with host importin alpha, dependent on NLS exposure influenced by genome maturation and/or capsid protein phosphorylation. The Capsid Protein also interacts with host NUP153 in the intricate process of viral assembly and genome release.