2.8 Data analysis
The MS RAW files were converted to mgf format by MSconvert and output by pLabel v2.4.1. GraphPad Prism 7.0 was used to calculate the IC50 and KI values.
Results
3.1 Screening the antiviral herbs with strong anti-SARS-CoV-2 Mproeffect
First of all, the anti-SARS-CoV-2 Mpro potentials of 60 antiviral herbs were assessed, while the residual activity of the protease was measured by a FRET-based assay. As shown inFig.2 , LJ exhibited potent inhibitory effects on Mpro at a final concentration of 100 μg/mL, resulting in a residual activity of 6.55%. Subsequent assays revealed that LJ could block the activity of SARS-CoV-2 Mpro in a time- and dose- dependent manner. The IC50 value for preincubation of 63 minutes was determined as 37.82±1.038 μg/mL(Fig. 2). Moreover, we used DTT sensitivity analysis to verify the inactivation mechanism of Mpro by Lonicera japonica . In the absence of DTT, the residual activity of 100 ug/mL LJ on Mpro was close to 0. In contrast, the addition of 1 mM DTT resulted in almost no inhibition of Mpro(Fig. S2) . These results suggested that LJ could potently and time-dependently inhibit Mpro mainly through the interactions with cysteines of this viral enzyme.