Porcine Deltacoronavirus Nsp13 Suppresses the Assembly of the MAVS-TBK1-IRF3 Complex and IRF9 Nuclear Translocation.

Porcine deltacoronavirus (PDCoV) is an emerging enteric coronavirus that causes substantial morbidity in swine and may pose a zoonotic risk because of its cross-species transmission potential. Type I interferon (IFN-I) signaling is central to antiviral defense, initiated through the mitochondrial antiviral signaling (MAVS)-TBK1-IFN regulatory factor 3 (IRF3) axis and executed by the downstream JAK-STAT1-STAT2-IRF9 (ISGF3) pathway; however, how PDCoV circumvents both the induction and effector arms of this cascade remains incompletely understood. Here, we identify PDCoV nonstructural protein 13 (Nsp13) as a potent antagonist of IFN-I responses. Ectopic expression of Nsp13 markedly reduces IFN-β production and the expression of IFN-stimulated genes (ISGs, such as ISG56 and CXCL10). Mechanistically, Nsp13 directly binds the C-terminal domain (CTD) of TBK1 and competitively disrupts TBK1 interactions with IRF3 and MAVS. In addition, Nsp13 preferentially binds IRF9 and impairs its nuclear translocation, thereby inhibiting IFN-α-induced signaling. Notably, PDCoV Nsp13 exhibits a host-target binding profile similar to that of SARS-CoV-2 Nsp13, yet it does not alter TBK1 ubiquitination or protein stability. Collectively, these findings reveal a dual-layer immune evasion strategy whereby PDCoV Nsp13 suppresses both IFN induction and downstream signaling, and highlighting Nsp13 as a potential target for antiviral intervention.