Divalent cations govern the activity of coronavirus nsp15

Coronavirus nsp15 is an endoribonuclease that limits the accumulation of viral dsRNA in cytosol and plays a crucial role in the evasion of host immunity. Here, we show that Co ²⁺ or Ni ²⁺ potently activates nsp15 of human and animal coronaviruses, including SARS-CoV-2, SARS-CoV, MERS-CoV, HCoV-229E, MHV-A59, and PEDV. Whereas Zn ²⁺ strongly inhibits nsp15 of these coronaviruses. Cryo-EM structures of the Co ²⁺ -bound SARS-CoV-2 nsp15/dsRNA complexes reveal that Co ²⁺ binds to the nsp15 active site and is coordinated by three catalytic residues H234, H249, K289, and the 2’ hydroxyl of the flipped base from dsRNA, suggesting that Co ²⁺ stabilizes the catalytic core and increases substrate binding. Although our data indicated that Ni ²⁺ and Zn ²⁺ bind to the same site as Co ²⁺ , Zn ²⁺ lacks the catalytic capability and inhibits nsp15. These findings reveal that divalent cations govern coronavirus nsp15’s activity and provide basis for new therapeutic strategies.