Arpita Chakravarti, Kiruthika Selvadurai, Rezvan Shahoei, Hugo Lee, Shirin
Fatma, Emad Tajkhorshid, and Raven H. Huang.
Reconstitution and substrate specificity for isopentenyl
pyrophosphate of the antiviral radical SAM enzyme viperin.
Journal of Biological Chemistry, 293:14122-14133, 2018.
(PMC: PMC6130951)
CHAK2018-ET
Viperin is a radical SAM enzyme that has been shown to possess antiviral
activity against a broad spectrum of viruses; however, its molecular
mechanism is unknown. We report here that recombinant fungal and
archaeal viperin enzymes catalyzes 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 radical
reaction catalyzed by fungal viperin. Structure-based molecular dynamics
(MD) simulations of viperin interacting with IPP revealed a good fit of the
isopentenyl motif of IPP to the active site cavity of viperin, unraveling the
molecular basis of substrate specificity of viperin for IPP. Collectively, our
findings indicate that IPP is an effective substrate of fungal and archaeal
viperin enzymes and provide critical insights into the reaction mechanism.
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