Tick-transmitted thogotovirus gains high virulence by a single MxA escape mutation in the viral nucleoprotein

Tick-borne thogotoviruses are highly sensitive to the human interferon-induced restriction factor myxovirus resistance protein A (MxA), which limits their zoonotic potential. Here, Fuchs et al. systematically evaluated the MxA sensitivity of ten globally distributed thogotovirus isolates using cell culture, viral minigenome assays, and mouse infection models. While all THOV-like viruses were potently inhibited by MxA, the Nigerian isolate Jos virus (JOSV) showed complete resistance in MxA-expressing cells and in MxA-transgenic mice. Polymerase reconstitution assays identified the viral nucleoprotein (NP) as the determinant of MxA sensitivity. Chimeric NP analysis and targeted mutagenesis mapped MxA escape to two adjacent NP residues (G327 and R328). Introduction of a single substitution, R328V, into the otherwise MxA-sensitive SiAr126 strain fully abolished MxA-mediated restriction without compromising viral replication or fitness. Recombinant SiAr126-NP(R328V) replicated efficiently in MxA-expressing cells and caused lethal infection in MxA-transgenic mice, whereas wild-type virus was completely restricted. Mechanistically, co-immunoprecipitation and imaging studies demonstrated that the R328V mutation disrupts NP–MxA interaction, permitting nuclear import of viral ribonucleoproteins. Collectively, these data provide direct experimental evidence that a single amino acid change enables thogotoviruses to evade human innate immunity, substantially increasing their virulence and zoonotic potential
(TMR)