Fig. 2.

Structural heterogeneity of the main protease of SARS-CoV and SARS-CoV-2. (a) Overlay of representative ligand-free structures and complexes of SARS-CoV and SARS-CoV-2 main protease in ribbon form to show variation in the segments containing Met49 and Gln189. Color code: 6Y2E in light purple, 6Y2F in light blue, 6Y2G in purple, 6M0K in blue, 7BRO in dark cyan, 1UK3 in cyan, 2C3S in light orange, 2GT7 in orange, 2GTB in tan, 4MDS in yellow, 2VJ1 in grey, 2DUC in light green. Structures 6Y2E, 7BRO, 2C3S, 1UK3, 2GT7, and 2DUC are ligand-free structures. (b) Zoomed-in view of the backbone flexibility in Gly143 at the oxyanion loop. Same color code is used as in section (a).