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Flavivirus NS1 Structures Reveal Surfaces for Associations with Membranes and the Immune System

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Science  21 Feb 2014:
Vol. 343, Issue 6173, pp. 881-885
DOI: 10.1126/science.1247749

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Two-Faced Viral Protein

Flaviviruses cause human diseases such as West Nile fever and dengue fever. The flavivirus nonstructural protein 1 (NS1) has multiple functions in flavivirus biology and is a target for vaccine development. Dimeric NS1 is essential for replication of the viral genome inside host cells, while hexameric NS1 is secreted and plays a role in evasion of the immune system. Akey et al. (p. 881, published online 6 February; see the Perspective by Shi) report crystal structures for full-length glycosylated NS1 from West Nile and dengue viruses. The structures show a hexamer comprised of three dimers. The structural analysis together with liposome and mutational studies identify a membrane interacting surface on one face of the dimer and an immune evasion surface on the other.

Abstract

Flaviviruses, the human pathogens responsible for dengue fever, West Nile fever, tick-borne encephalitis, and yellow fever, are endemic in tropical and temperate parts of the world. The flavivirus nonstructural protein 1 (NS1) functions in genome replication as an intracellular dimer and in immune system evasion as a secreted hexamer. We report crystal structures for full-length, glycosylated NS1 from West Nile and dengue viruses. The NS1 hexamer in crystal structures is similar to a solution hexamer visualized by single-particle electron microscopy. Recombinant NS1 binds to lipid bilayers and remodels large liposomes into lipoprotein nanoparticles. The NS1 structures reveal distinct domains for membrane association of the dimer and interactions with the immune system and are a basis for elucidating the molecular mechanism of NS1 function.

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