A naturally occurring antiviral ribonucleotide encoded by the human genome

Abstract

Viral infections continue to represent major challenges to public health, and an enhanced mechanistic understanding of the processes that contribute to viral life cycles is necessary for the development of new therapeutic strategies . Viperin, a member of the radical S-adenosyl-L-methionine (SAM) superfamily of enzymes, is an interferon-inducible protein implicated in the inhibition of replication of a broad range of RNA and DNA viruses, including dengue virus, West Nile virus, hepatitis C virus, influenza A virus, rabies virus and HIV. Viperin has been suggested to elicit these broad antiviral activities through interactions with a large number of functionally unrelated host and viral proteins. Here we demonstrate that viperin catalyses the conversion of cytidine triphosphate (CTP) to 3'-deoxy-3',4'-didehydro-CTP (ddhCTP), a previously undescribed biologically relevant molecule, via a SAM-dependent radical mechanism. We show that mammalian cells expressing viperin and macrophages stimulated with IFNα produce substantial quantities of ddhCTP. We also establish that ddhCTP acts as a chain terminator for the RNA-dependent RNA polymerases from multiple members of the Flavivirus genus, and show that ddhCTP directly inhibits replication of Zika virus in vivo. These findings suggest a partially unifying mechanism for the broad antiviral effects of viperin that is based on the intrinsic enzymatic properties of the protein and involves the generation of a naturally occurring replication-chain terminator encoded by mammalian genomes.

Viperin inhibits classical swine fever virus replication by interacting with viral nonstructural 5A protein

“…18 For flaviviruses, viperin has been shown to alter the chain terminating cytidine triphosphate (CTP) motif to a ddhCTP form. 38 In this report, we determined that the SAM and N-terminal viperin domains were most important for CSFV inhibition, whereas the C-terminal domain was dispensable for this activity (Figures 12 and 13), although the Nterminal domain demonstrated the strongest binding affinity. We observed distinct antiviral activity for different viperin truncation mutants when transfected into cells together with NS5A-N or alone.…”

“…A recent report has also described SAM domain‐dependent inhibition of TBEV RNA replication . For flaviviruses, viperin has been shown to alter the chain terminating cytidine triphosphate (CTP) motif to a ddhCTP form . In this report, we determined that the SAM and N‐terminal viperin domains were most important for CSFV inhibition, whereas the C‐terminal domain was dispensable for this activity (Figures and ), although the N‐terminal domain demonstrated the strongest binding affinity.…”

Temperature controlled high-throughput magnetic tweezers show striking difference in activation energies of replicating viral RNA-dependent RNA polymerases

“…Briefly, the HRV-C and PV RdRps coding region was amplified using respectively the HRV-C15 cDNA (Accession# GU219984.1) and the PV type 1 cDNA (Accession# V01149.1) as template, as described in Ref. (41). The PCR product of HRV-C RdRp was gel purified and cloned into the pSUMO plasmid using BsaI and SalI sites.…”

BK polyomavirus evades innate immune sensing by disrupting the mitochondrial network and membrane potential and by promoting mitophagy

“…Although structurally unrelated to agnoprotein, the 247aa-long cytomegalovirus 22 (CMV) US9 glycoprotein appears to suppress both MAVS and STING pathways, TBK-1 activation and IFN-β expression by disrupting the mitochondrial membrane potential in the late CMV replication phase (Choi et al, 2018;Mandic et al, 2009). Given the association of agnoprotein with LD, we were intrigued by the similarity to the antiviral host cell protein viperin, which is expressed following RNA-and DNA-virus infections (Gizzi et al, 2018;Hee and Cresswell, 2017). The antiviral effects of viperin have been attributed to a perplexing variety of functions including interference with lipid metabolism and formation of detergentresistant lipid rafts at the sites of influenza budding (Wang et al, 2007).…”