Table 1. 3CL^pro activities against doubly- and triply-substituted substrate variants. WT substrate was substituted at P3 to P5 positions to generate doubly- and triply-substituted variants. The relative activities of 3CL^pro on these substrate variants are reported.

Variant sequence	HCoV-NL63	HCoV-OC43	SARS-CoV	IBV
VAVLQ↓SGF	1.23±0.40	1.55±0.30	1.80±0.31	1.58±0.27
SARLQ↓SGF	1.14±0.24	1.36±0.17	0.97±0.12	1.72±0.22
VARLQ↓SGF	1.70±0.07	1.87±0.17	1.70±0.17	3.24±0.37
SPVLQ↓SGF	0.06±0.01	0.29±0.07	0.61±0.10	1.09±0.24
VPRLQ↓SGF	0.15±0.04	0.91±0.12	0.99±0.12	4.33±0.98
SVVLQ↓SGF	0.76±0.10	0.59±0.07	1.39±0.19	0.59±0.09
VVVLQ↓SGF	1.23±0.06	0.60±0.05	1.97±0.19	0.86±0.05
VVRLQ↓SGF	1.63±0.07	0.55±0.04	2.50±0.51	2.19±0.13