An Evolutionarily Conserved Strategy for Ribosome Binding and Host Translation Inhibition by b-coronavirus Non-structural Protein 1

An important pathogenicity factor of SARS-CoV-2 and related coronaviruses is Non-structural protein 1 (Nsp1), which suppresses host gene expression and stunts antiviral signaling. SARS-CoV-2 Nsp1 binds the ribosome to inhibit translation through mRNA displacement and induces degradation of host mRNAs. Here we show that Nsp1-dependent host shutoff is conserved in diverse coronaviruses, but only Nsp1 from f3-Coronaviruses (f3-CoV) inhibits translation through ribosome binding. The C-terminal domain (CTD) of all f3-CoV Nsp1s confers high-affinity ribosome binding despite low sequence conservation. Modeling of interactions of four Nsp1s with the ribosome identified the few absolutely conserved amino acids that, together with an overall conservation in surface charge, form the f3-CoV Nsp1 ribosome -binding domain. Contrary to previous models, the Nsp1 ribosome-binding domain is an inefficient trans-lation inhibitor. Instead, the Nsp1-CTD likely functions by recruiting Nsp10s N-terminal effector domain. Finally, we show that a cis-acting viral RNA element has co-evolved to fine-tune SARS-CoV-2 Nsp1 func-tion, but does not provide similar protection against Nsp1 from related viruses. Together, our work pro-vides new insight into the diversity and conservation of ribosome-dependent host-shutoff functions of Nsp1, knowledge that could aid future efforts in pharmacological targeting of Nsp1 from SARS-CoV-2 and related human-pathogenic f3-CoVs. Our study also exemplifies how comparing highly divergent Nsp1 variants can help to dissect the different modalities of this multi-functional viral protein.(c) 2023 Elsevier Ltd. All rights reserved.

Automated summary

Non-structural protein 1 (Nsp1) is an important pathogenicity factor of SARS-CoV-2 and related coronaviruses. It inhibits host gene expression and antiviral signaling. Nsp1 binds the ribosome and suppresses translation, and its C-terminal domain (CTD) has high-affinity ribosome binding capability. However, the Nsp1 ribosome-binding domain is not an efficient translation inhibitor. A viral RNA element has co-evolved to fine-tune SARS-CoV-2 Nsp1 function, but does not provide similar protection against Nsp1 from related viruses.