Reconstitution and substrate specificity for isopentenyl pyrophosphate of the antiviral radical SAM enzyme viperin [Immunology]

We report here that recombinant fungal and archaeal viperin enzymes catalyze the addition of the 5′-deoxyadenosyl radical (5′-dA•) to the double bond of isopentenyl pyrophosphate (IPP), producing a new compound we named adenylated isopentyl pyrophosphate (AIPP). The reaction is specific for IPP, as other pyrophosphate compounds involved in the mevalonate biosynthetic pathway did not react with 5′-dA•. Enzymatic reactions employing IPP derivatives as substrates revealed that any chemical change in IPP diminishes its ability to be an effective substrate of fungal viperin. Mutational studies disclosed that the hydroxyl group on the side chain of Tyr-245 in fungal viperin is the likely source of hydrogen in the last step of the radical addition, providing mechanistic insight into the...

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