Interfering with mRNA Methylation by the 2′O-Methyltransferase (NSP16) from SARS-CoV-2 to Tackle the COVID-19 Disease

The pandemic associated to Severe Acute Respiratory Syndrome Coronavirus type 2 (SARS-CoV-2) has resulted in a huge number of deaths and infected people. Although several vaccine programmes are currently underway and have reached phase 3, and a few small size drugs repurposed to aid treatment of severe cases of COVID-19 infections, effective therapeutic options for this disease do not currently exist. NSP16 is a S-adenosyl-L-Methionine (SAM) dependent 2 ' O-Methyltransferase that converts mRNA cap-0 into cap-1 structure to prevent virus detection by cell innate immunity mechanisms. NSP16 methylates the ribose 2 ' O-position of the first nucleotide of the mRNA only in the presence of an interacting partner, the protein NSP10. This feature suggests that inhibition of the NSP16 may represent a therapeutic window to treat COVID-19. To test this idea, we performed comparative structural analyses of the NSP16 present in human coronaviruses and developed a sinefungin (SFG) similarity-based virtual screening campaign to assess the druggability of the SARS-CoV-2 NSP16 enzyme. Through these studies, we identified the SFG analogue44601604as a promising more potent inhibitor of NSP16 to limit viral replication in infected cells, favouring viral clearance.