Crystals of PF-00835231 bound to SARS2/CoV-2 DC2 protease via soaking: Freshly prepared SARS2/CoV-2 DC2 protease at 25.8 mg/mL was passed through a 0.45 mM cellulose acetate spin filter and set up for crystallization using an NT-8 crystallization robot (Formulatrix). Using MRC-2 crystallization plates, wells containing 40 mL of 0.2 M potassium sodium tartrate tetrahydrate and 20% w/v PEG 3350 were dispensed, and then sitting drops consisting of 0.3 μL protein were set up in a 1:1 ratio with a well buffer. Crystallization plates were incubated at 13 °C, and large crystals shaped as beveled plates measuring 0.35 × 0.2 × 0.025 mm3 grew after 48 h. PF-00835231 (in 100% DMSO solution) was introduced to the drop (in situ), at a final concentration of 1 mM, and then incubated at 13 °C for 24 h. Soaked crystals were flash-frozen in liquid nitrogen after being passed through a cryo consisting of a well buffer containing 20% glycerol. Structure determination.