Fig. 5. pro-ISG15 in Natural biflavones are potent inhibitors against SARS-CoV-2 papain-like protease

Fig. 5. pro-ISG15 cleavage assays for the biflavones. (A) Initial screening of all nine biflavones for the inhibitory activities against PLpro-mediated deISGylation at a 20 μM concentration. (B–D) Active biflavones were further evaluated at serially diluted concentrations of 20, 10, 5 and 2.5 μM. (E) Inhibition rates for all 9 biflavones against PLpro-mediated deISGylation at 20 μM. (F) Inhibition rates for C–C-type biflavones (2–4) at concentrations of 20, 10, 5 and 2.5 μM. (G) Inhibition rates for C–O–C-type biflavones (7–9) at concentrations of 20, 10, 5 and 2.5 μM. w/o inb. = without inhibitors.