Interactions between Viperin, Vesicle-associated Membrane Protein A and Hepatitis C Virus Protein NS5A Modulate Viperin Activity and NS5A Degradation

The radical SAM enzyme, viperin, exerts a wide range of antiviral effects through both the synthesis of the antiviral nucleotide 3’-deoxy-3’, 4’-didehydro-CTP (ddhCTP) and through its interactions with various cellular and viral proteins. Here we investigate the interaction of viperin with hepatitis C virus non-structural protein 5A (NS5A) and the host sterol regulatory protein, vesicle-associated membrane protein A (VAP-33). NS5A and VAP-33 form part of the viral replication complex that is essential for replicating the RNA genome of hepatitis C virus. Using transfected enzymes in HEK293T cells, we show that viperin binds to both NS5A and the C-terminal domain of VAP-33 (VAP-33C) independently and that this interaction is dependent on the proteins being co-localized to the ER membrane. Co-expression of VAP-33C and NS5A resulted in changes to the catalytic activity of viperin that depended upon viperin being co-localized to the ER membrane. The viperin-NS5A-VAP-33 complex exhibited the lowest activity, in...