On the other hand, NC could be suggested by observing that: (i) some ligand/protein complex X-ray structures do exhibit asymmetry: namely, one subunit is not be obtained by a symmetry operator on the other one, and the crystallographic unit contains the whole functional dimer(s). However, the overall number of such structures is very small (1.8%). (ii) A symmetry-breaking process of apo-Mpro occurs once passing from the solid state to aqueous solution, as seen by long-time-scale molecular dynamics simulations . Such symmetry-breaking has not been discussed for the doubly occupied enzyme. (iii) The enzymatic activity increases with the addition of catalytically-inactive monomers in solution for SARS-CoV Mpro, which shares 96% sequence identity . However, one has to be careful in drawing conclusions from one protein to the other, as they exhibit significant catalytic differences .