Viperin inhibits coronavirus replication by targeting non-structural protein 8 to disrupt replication-transcription complex assembly and RNA-dependent RNA polymerase activity.

Virus inhibitory protein, endoplasmic reticulum-associated, interferon-inducible (Viperin), an interferon-stimulated gene (ISG) product, restricts the replication of a broad spectrum of viruses through its radical S-adenosyl methionine (SAM) enzymatic activity, which converts cytidine triphosphate (CTP) to 3'-deoxy-3',4'-didehydro-CTP (ddhCTP). This conversion leads to premature termination of RNA synthesis by the RNA-dependent RNA polymerase (RdRp) of certain RNA viruses. Coronaviruses, being RNA viruses, can be suppressed by viperin; certain strains, such as porcine epidemic diarrhea virus (PEDV), are directly influenced by ddhCTP, while others, such as Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), are inhibited by different pathways. In this study, we describe a previously unrecognized anti-coronavirus mechanism of viperin. Using Porcine Deltacoronavirus (PDCoV) as a model, we observed that viperin is strongly induced upon PDCoV infection and significantly inhibits viral replication. Furthermore, we found that viperin directly interacts with the viral non-structural protein 8 (nsp8) protein, disrupting the formation of the replication-transcription complex (RTC) and reducing RdRp activity. Our results further indicate that the central domain (residues 43-184) of viperin and the lysine 82 (K82) residue in the N-terminal domain of nsp8 are critical for this interaction and its antiviral function. We illustrate that the viperin-nsp8 interaction is preserved across all genera of α-, β-, γ-, and δ-coronaviruses. These findings reveal a unique anti-coronavirus mechanism of viperin and offer new insights into its potential as a target for inhibiting viral nsp8 function.