The zika virus genome produces a polyprotein with more than 3000 amino acids; this polyproptein is then cleaved into three structural and seven non-structural proteins.The flaviviral genome encodes (from 50 to 30 end, i.e. from N- to C-terminal of the polyprotein) the structural C (capsid, ~ 11 kDa), prM (precursor M protein, ~ 26 kDa, which is further cleaved into the M protein), and E(envelope,~ 53 kDa) proteins, and the non-structural NS1 (~ 46 kDa), NS2A (~ 22 kDa), NS2B (~ 14 kDa), NS3 (~ 70 kDa), NS4A (~ 16 kDa), NS4B (~ 27 kDa), and NS5 (~ 103 kDa) proteins.Structurally, the E and M proteins are located at the surface of the viral particles, while the nucleocapsid is made up of the C protein and the genomic RNA molecule.
|Table 2||Key proteins of flaviviruses and their functions.|
|Proteins||Functions||Possible effects on hosts|
|C||RNA binding to form the nucleocapsid.|
|prM, M||Stabilization, assisting the folding and secretion of E protein.||Antibodies towards prM enhances infectivity of immature virions, could be involved in pathogenesis of severe dengue in secondary infections.|
|E||Receptor binding, membrane fusion.|
|NS1||RNA replication.||Localization to host cell surface and secreted extracellularly; modulates signalling of innate immune system, possible damages to platelets and endothelial cells through anti-NS1 antibodies, antagonizes C4 complement.|
|NS2A||RNA synthesis and viral assembly.||Interferon antagonist, induces host cell apoptosis.|
|NS2B||Complexes with NS3 to function as serine protease.|
|NS3||Complexes with NS2B to function as serine protease; possess RNA helicase and triphosphatasae activities.||Induces apoptosis of host cells, modulates host microRNA, one of the targets of cytotoxic T cell response.|
|NS4A||RNA replication.||Blocks type I interferon signalling, induces autophagy and protects host cells from death during infection.|
|NS4B||RNA replication.||Blocks type I interferon signalling and RNA interference, modulator of stress granules in host cells.|
|NS5||Methytransferase and RNA guanylyltransferase activities; capping and synthesis of RNA; RNA-dependent RNA polymerase.||Blocks type I interferon signalling.|
The E protein (<53 kDa) is the major virion surface protein. E is involved in various aspects of the viral cycle, mediating binding and membrane fusion. Domain III of the Zika envelope protein is likely the main specific neutralizing domain. The NS5 protein (<103 kDa) is the largest viral protein whose C-terminal portion has RNA-dependent RNA polymerase (RdRP) activity and the Nterminus is involved in RNA capping by virtue of its processing due to methyl transferase activity.
Click here to see the amino acid sequence of those antigens of strain zikaSPH2015.