Crystals of PF-00835231 bound to SARS2/CoV-2 mature protease via cocrystallization: Freshly prepared SARS2/CoV-2 mature protease at 11.3 mg/mL was incubated with a 3-fold molar excess of PF-00835231 for 18 h at 4 °C. The complex was then passed through a 0.45 μM cellulose acetate spin filter and set up for crystallization using an NT-8 crystallization robot (Formulatrix). Using MRC-2 crystallization plates, wells containing 40 μL of 15% v/v 2-propanol, 0.1 M citric acid pH 5.0, and 10% w/v PEG 10 000 were dispensed, and then sitting drops consisting of 0.3 μL protein and a 0.3 μL well buffer were set up. Crystallization plates were incubated at 13 °C, and crystals shaped as rectangular blocks measuring 0.1 × 0.2 × 0.2 mm3 grew overnight. Crystals were flash-frozen in liquid nitrogen after being passed through a cryo consisting of a well buffer containing 20% glycerol.