Structural basis for translational shutdown and immune evasion by the Nsp1 protein of SARS-CoV-2

Thoms, Matthias; Buschauer, Robert; Ameismeier, Michael; Koepke, Lennart; Denk, Timo; Hirschenberger, Maximilian; Kratzat, Hanna; Hayn, Manuel; Mackens-Kiani, Timur; Cheng, Jingdong; Straub, Jan H.; Stürzel, Christina M.; Fröhlich, Thomas; Berninghausen, Otto; Becker, Thomas; Kirchhoff, Frank; Sparrer, Konstantin M. J.; Beckmann, Roland

SARS-CoV-2 is the causative agent of the current COVID-19 pandemic. A major virulence factor of SARS-CoVs is the nonstructural protein 1 (Nsp1) which suppresses host gene expression by ribosome association. Here, we show that Nsp1 from SARS-CoV-2 binds to the 40S ribosomal subunit, resulting in shutdown of mRNA translation both in vitro and in cells. Structural analysis by cryo-electron microscopy (cryo-EM) of in vitro reconstituted Nsp1-40S and various native Nsp1-40S and -80S complexes revealed that the Nsp1 C terminus binds to and obstructs the mRNA entry tunnel. Thereby, Nsp1 effectively blocks RIG-I-dependent innate immune responses that would otherwise facilitate clearance of the infection. Thus, the structural characterization of the inhibitory mechanism of Nsp1 may aid structure-based drug design against SARS-CoV-2.