The MERS coronavirus (MERS-CoV) is a highly pathogenic, emerging virus that produces accessory proteins to antagonize the host innate immune response. The MERS-CoV ORF4b protein has been shown to bind preferentially to the nuclear import adapter IMPα3 in infected cells, thereby inhibiting NF-κB-dependent innate immune responses. Here, we report high-resolution structures of ORF4b bound to two distinct IMPα family members. Each exhibit highly similar binding mechanisms that, in both cases, lack a prototypical Lys bound at their P2 site. Mutations within the NLS region dramatically alter the mechanism of binding, which reverts to the canonical P2 Lys binding mechanism. Mutational studies confirm that the novel binding mechanism is important for its nuclear import, IMPα interaction, and inhibition of innate immune signaling pathways. In parallel, we determined structures of the nuclear binding domain of NF-κB component p50 bound to both IMPα2 and α3, demonstrating that p50 overlaps with the ORF4b binding sites, suggesting a basis for inhibition. Our results provide a detailed structural basis that explains how a virus can target the IMPα nuclear import adapter to impair immunity, and illustrate how small mutations in ORF4b, like those found in closely related coronaviruses such as HKU5, change the IMPα binding mechanism. MERS-CoV ORF4b antagonizes host innate immune response, partially via blocking nuclear import adapter IMPα activity and preventing nuclear translocation of NF-κB. Here, Munasinghe and Edwards et al. biochemically and structurally define the interaction between ORF4b and IMPα-family members and find a non-canonical interaction between ORF4b NLS and IMPα2 and IMPα3.
【저자키워드】 viral infection, X-ray crystallography, Virus-host interactions, 【초록키워드】 Structure, Mutation, innate immune response, Immunity, virus, MERS-CoV, Protein, signaling pathways, mechanism, accessory protein, binding, NF-κB, innate immune, Interaction, MERS coronavirus, overlap, infected cells, nuclear translocation, binding domain, binding mechanism, innate immune responses, adapter, nuclear, highly pathogenic, Host, Alter, P50, high-resolution structure, shown, lack, coronavirus, biochemically, ORF4b, inhibiting, explain, impair, NLS, canonical, Edward, 【제목키워드】 Innate immunity, MERS-CoV, binding mechanism, ORF4b,