Figure 3.

a) Native mass spectrum for 5 μM M^Pro with 50 μM of the 11‐mer substrate at t=30 s. Peaks labelled TSAVLQ and +substrate indicate acyl‐enzyme complex and the non‐covalent enzyme‐substrate complex, respectively. b) mass spectra for the 15+ charge state at three representative times along the substrate cleavage reaction. Satellite peaks adjacent to the 15+ charge state are consistent with oxidation of between 4 and 8 of the ten methionine residues (+16 Da,). Peaks marked with asterisk corresponds to an impurity (+1042 Da). Inset: plot of the relative abundance of the enzyme‐substrate complex as a function of time. Solid line indicates the fit to a unimolecular kinetics model. c) Bar plot summarizing half‐lives of the enzyme‐substrate complex in the presence of different small molecules. Error bars represent standard deviation (n=3 independent replicates). *p<0.05, **p<0.001 (to M^Pro values). Representative mass spectra and kinetic plots for each dataset are shown in Figure S4.