Fig. 4: Inhibitory activity profiles of RBC against SARS-CoV-2 helicase.
a–d, Inhibition of the ATPase activity of the SARS-CoV-2 helicase by CBS (a), RBC (b), Bi(TPP) (c) and Bi(TPyP) (d), at varying concentrations as indicated. e–h, Titration of the DNA-unwinding activity of the SARS-CoV-2 helicase by CBS (e), RBC (f), Bi(TPP) (g) and Bi(TPyP) (h), at varying concentrations, as indicated by a FRET-based assay. In a–h, the data are expressed as a percentage of the control reaction in the absence of inhibitors. Dose–response curves for half-maximum inhibitory concentration (IC50) values were determined by nonlinear regression. i,j, Restoration of the activity of ATPase (i) and the DNA-unwinding activity of Bi-SARS-CoV-2 helicase (j) following supplementation with various ratios of zinc(ii) as indicated. All assays in a–j were performed in triplicate and the data are presented as mean ± s.d. k,l, Lineweaver–Burk plots showing the kinetics of inhibition on ATPase activity (k) and DNA-unwinding activity of SARS-CoV-2 helicase (l) by RBC. The effect of the inhibitors on the enzyme was determined from the double reciprocal plot of 1/rate (1/V) versus 1/substrate concentration in the presence of varying concentrations of RBC. The Ki values were calculated by the intersection of the curves obtained by plotting 1/V versus inhibitor concentration for each substrate concentration. In a–i, measures of drug concentration are based on metal content. The mean value of three replicates is shown and error bars indicate ± s.d. of n = 3 independent replicates. Statistical significance was calculated using an unpaired two-tailed Student’s t-test. All experiments were repeated twice for confirmation.
