Studies of structural proteins in packaging and maturation of flaviviruses

Flavivirus is a small spherical enveloped virus. Members of the flavivirus genus include yellow fever, dengue, Japanese encephalitis, and West Nile viruses. The flavivirus genome encodes three structural proteins, C, prM, and E, and seven non-structural proteins. The structural proteins, together with genomic RNA and a host-cell derived membrane, compose the flavivirus particle. The aim of this study is to understand the mechanism of genome packaging and virus assembly. Structures of the C protein revealed that it forms a homodimer in solution. The dimeric C protein has been proposed to be the building block of the nucleocapsid core (Ma, Jones et al. 2004). Genetic and biochemical evidence document the significance of the dimeric C proteins in the virus life cycle. In particular, the C-terminal hydrophobic sequence of the C protein was found to be involved in genome packaging and particle assembly. Study of the C-terminal hydrophobic sequence by a trans-packaging assay showed that the signal sequence retains the C proteins in the endoplasmic reticulum to facilitate the packaging of the genome into the virus particle. However, it is not known how the specificity of genome packaging is achieved. It is proposed that there is a determinant for specific packaging of the flavivirus genome into the virus particle. Identification of such determinants for specific genome packaging was pursued using heterologous packaging systems derived from yellow fever virus and West Nile virus. The newly budded flaviviruses in the endoplasmic reticulum are immature particles, and maturation of the virus takes place along the cellular secretory pathway. In the trans-Golgi network, the pr component of the prM protein is cleaved by a host protease. However, pr is retained at the viral surface until the particle is released outside of the cell, where there is a neutral pH environment. Based on the available structures of pr-E, residues that may be involved in the pr retention on the virus surface were investigated