Porcine Mx1 protein inhibits porcine deltacoronavirus replication in vitro by disturbing the N-Nsp12 interaction

Porcine deltacoronavirus (PDCoV) is an emerging enteric pathogen with significant economic impact and potential zoonotic risk. The interplay between PDCoV and host innate immunity, particularly involving interferon-stimulated genes (ISGs), remains incompletely understood. Porcine myxovirus resistance 1 (pMx1) protein, an ISG with broad-spectrum antiviral activity, has not been characterized for its role against PDCoV up to now. This study demonstrates that PDCoV infection upregulates endogenous pMx1 expression in porcine intestinal epithelial cells (IPEC-J2 and IPI-2I) through an IFN-α-dependent mechanism. Functional assays confirmed pMx1 protein has significant antiviral activity against PDCoV. Mechanistically, we confirmed a direct interaction between the pMx1 protein and the PDCoV nucleocapsid (N) protein, and the GTPase domain of the pMx1 protein was identified as the critical binding region. This result is strongly supported by a predicted interaction complex structural model generated using AlphaFold 3, and this domain is indispensable for pMx1's antiviral function. We further revealed a crucial synergistic interaction between the PDCoV N protein and the viral RNA-dependent RNA polymerase Nsp12, a core component of the replication-transcription complex (RTC), and demonstrated that pMx1 protein effectively disrupts this interaction, thereby impeding viral genome replication. In summary, this study elucidates the mechanism by which the pMx1 protein, as a host antiviral factor, inhibits PDCoV infection. These findings provide novel insights into the innate immune defense against coronaviruses and highlight the pMx1 gene as a promising host-derived immune factor with potential as a therapeutic target or gene editing tool for combating PDCoV.