Fig. 4. A MOLSCRIPT diagram (Kraulis, 1991) showing the overall fold of TGEV Mpro (A) with the two β-barrel domains and the α-helical C-terminal domain. β-strands and helices are represented as arrows and cylinders, respectively. The β-barrels of each domain I and II are composed of six-stranded β-sheets (green). Domain III is composed mainly of α-helices (red). The structures of HAV 3Cpro (PDB code: 1HAV) (B) and α-chymotrypsin (4CHA, residues 12–15 and 147–148 are excised) (C) are shown for comparison.