LAUSR

Significance The 2′-O methyl group in Cap-1 is essential to protect viral RNA from host interferon-induced response. We determined crystal structures of SARS-CoV-2 Nsp10/16 heterodimer in complex with substrates (Cap-0 analog and S-adenosyl methionine) and products (Cap-1 analog and S-adenosyl-L-homocysteine) at room temperature using synchrotron serial crystallography. Analysis of these structures will aid structure-based drug design against 2′-O-methyltransferase from SARS-CoV-2. The genome of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) coronavirus has a capping modification at the 5′-untranslated region (UTR) to prevent its degradation by host nucleases. These modifications are performed by the Nsp10/14 and Nsp10/16 heterodimers using S-adenosylmethionine as the methyl donor. Nsp10/16 heterodimer is responsible for the methylation at the ribose 2′-O position of the first nucleotide. To investigate the conformational changes of the complex during 2′-O methyltransferase activity, we used a fixed-target serial synchrotron crystallography method at room temperature. We determined crystal structures of Nsp10/16 with substrates and products that revealed the states before and after methylation, occurring within the crystals during the experiments. Here we report the crystal structure of Nsp10/16 in complex with Cap-1 analog (m7GpppAm2′-O). Inhibition of Nsp16 activity may reduce viral proliferation, making this protein an attractive drug target.