Figure 1.
Tannic acid is a promising direct inhibitor of Mpro. A. Screening of previously identified bioactive compounds in fruits that were effective in inhibiting Mpro of SARS-CoV-2. 50 μM bioactive compounds were pre-incubated with 1 μM of SARS-CoV-2 Mpro for 30 min at room temperature. The fluorescent substrates (20 μM) were then added to initiate the reaction. The first 15 min of the reaction was used to calculate initial velocity (V0) and then normalized to control. Tannic acid was dissolved in water, other compounds were dissolved in DMSO. Both water and DMSO were used as negative control as indicated. Data are shown as mean ± SEM from experiments performed in triplicate. Statistical significance was calculated using Student t-test, *P < 0.05, **P < 0.01. B. Inhibition of peptide cleavage activity of SARS-CoV-2 Mpro by tannic acid. M, marker. Lane 1, the fluorescent substrate (CFP-TSAVLQSGFRKM-YFP, 57.5 kDa) only. Lane 2, SARS-CoV-2 Mpro was incubated with the fluorescent substrate at 30°C for 1 hour. Two separate bands correspond to CFP-TSAVLQ (30 kDa) and SGFRKM-YFP (27.5 kDa) were detected. Lane 3, SARS-CoV-2 Mpro was incubated with the fluorescent substrate plus 50 μM tannic acid at 30°C for 1 hour. The fluorescent substrate remains uncleaved. C. Dose-effect course of tannic acid in inhibiting SARS-CoV-2 Mpro. The IC50 was calculated by plotting the initial velocity against different concentrations of tannic acid as shown by a dose-response curve generated with the Prism 8 software.