West Nile (WNV) is a member of the Flavivirus genus of the Flaviviridae family. The Flavivirus genus includes other important human pathogens such as yellow fever (YFV), Dengue vius (DENV), Japanese encephalitis (JEV), and tick borne encephalitis (TBEV). Flaviviruses are enveloped viruses with a single stranded, <11 kb, positive-sense RNA genome, which encodes a single long open reading frame (ORF), The virus enters the host cell by receptor mediated endocytosis. Upon internalization and acidification of the endosome, fusion of viral and vesicular membranes allows release of the genomic RNA into the cytoplasm, which serves as mRNA. Translation of the single ORF at the rough ER produces a large polyprotein that is cleaved co- and posttranslationally into the mature proteins. The N-terminal of the polyprotein encodes the three structural proteins (C-prM-E), followed by at least seven non-structural (NS) proteins (NS1-NS2A-NS2B-NS3-NS4A-NS4B-NS5). Viral NS1 is a glycosylated 48-kD protein that plays a role in both viral replication and immune evasion. Secreted soluble WNV NS1 is found in patient serum during acute illness and is used as a diagnostic indicator of acute WNV infection. High levels of sNS1 are associated with increased disease severity.

Full-length West Nile virus NS1 (351aa) encoding gene was constructed with codon optimization and expressed with a small T7-His-TEV cleavage site Tag (29aa) fusion at its N-terminal. This protein is expressed in E.coli as inclusion bodies. The final product was refolded using our unique “temperature shift inclusion body refolding” technology and chromatographically purified.