Flavivirus genus, belong to the family Flaviviridae, comprises numerous medically important mosquito-borne viruses such as Dengue virus (DENV), West Nile virus (WNV)and Japanese Encephalitis virus (JEV). Due to the incomplete understanding of flavivirus pathogenesis, anti-viral drugs are still not commercially available. Flavivirus capsid protein was known to localize in the nucleus in the early phase of the infection. As infection progressed there was an accumulation of the capsid proteins in the cytoplasm.
The entry of the capsid protein into the nucleus was found to be a key step in establishing infections. Transportation was actively driven through phosphorylation of the capsid protein allowing interaction with the importin-α and importin-β protein complex. Inhibition of protein kinase C (PKC) activity also retarded the nuclear translocation of capsid protein.
An optimized platform was developed to engineer, express and purify biotinylated full-length capsid protein for high-throughput screening of novel interacting partners via ProtoArray® platform. While in the nuclear phase, the capsid protein was found to initiate cell cycle arrest at S- and G2-/M phases. This provided an environment conducive for virus replication. Numerous cell cycle-related genes and proteins were found up-regulated and interacting with capsid protein. The capsid protein was also observed to manipulate host transcriptional and translational activities. SRP19 protein which is involved in protein biogenesis was found to reduce DENV viral RNA replication resulting in lower virus production. Over-expression of capsid protein was found to degrade the SRP19 protein.
At late phase of the virus replication, less newly synthesize capsid proteins are phosphorylated. The non-phosphorylation capsid proteins became the source for interaction with the progeny viral RNA starting the assembly process of the infectious virus particles. This completes the replication process of the virus.