The new coronavirus SARS-CoV-2 expresses two proteases, the papain-like protease (PLpro) and 3C-like protease (3CLpro). Both belong to the group of cysteine proteases, as they have a cysteine residue at their catalytic site. Their main function is the processing of the viral polyprotein, that contains two cleavage sites to build up the viral replicase complex. Additionally, PLpro has the ability of removing ISG15 and ubiquitin from viral proteins expressed in the cell, this enables evasion from the innate immune response by the host. This represents an interesting target for drug development. This is because it not only would inhibit viral replication, but would also prevent the massive immunological response that results from the over-activation of the host’s immune system. Such an over-activation can lead to damage of the uninfected cells and thus to a worsening of the patient’s condition. N-terminal His-Tag was removed to restore protease activity.
