The antiviral protein, viperin, localizes to lipid droplets via its N-terminal amphipathic alpha-helix.

Lipid droplets are intracellular lipid-storage organelles that are thought to be derived from the endoplasmic reticulum (ER). Several pathogens, notably hepatitis C virus, use lipid droplets for replication. Numerous questions remain about how lipid droplets are generated and used by viruses. Here we show that the IFN-induced antiviral protein viperin, which localizes to the cytosolic face of the ER and inhibits HCV, localizes to lipid droplets. We show that the N-terminal amphipathic alpha-helix of viperin that is responsible for ER localization is also necessary and sufficient to localize both viperin and the fluorescent protein dsRed to lipid droplets. Point mutations in the alpha-helix that prevent ER association also disrupt lipid droplet association, and sequential deletion mutants indicate that the same number of helical turns are necessary for ER and lipid droplet association. Finally, we show that the N-terminal amphipathic alpha-helix of the hepatitis C viral protein NS5A can localize dsRed and viperin to lipid droplets. These findings indicate that the amphipathic alpha-helices of viperin and NS5A are lipid droplet-targeting domains and suggest that viperin inhibits HCV by localizing to lipid droplets using a domain and mechanism similar to that used by HCV itself.