Profiling of Substrate Specificities of 3C-Like Proteases from Group 1, 2a, 2b, and 3 Coronaviruses

Chuck, Chi-Pang; Chow, Hak-Fun; Wan, David Chi-Cheong; Wong, Kam-Bo

At P3 position, the protease activities on Arg/Lys-substituting variants were 5 to 14 fold higher than that on Asp/Glusubstituting variants ( Figure 1 , Table S1 ). This observation suggests that P3 position prefers positively charged residues over negatively charged one. In the active site of 3CL pro , there is no substrate-binding pocket for P3 residue. Molecular modeling showed that there is an invariant Glu residue (Glu-166 in SARS-CoV 3CL pro ) in the active site of 3CL pro that may form favorable charge-charge interactions with a positively charged residue at the P3 position, which may explain why Arg/Lys are favored over Asp/Glu at this position ( Figure S1 ). Moreover, no cleavage was observed for substrate containing Pro-substitution at P3 position.