3.1.1  Structure and function of CoV Mpro
Mpro is a homodimeric cysteine protease. The SARS‐CoV‐1 Mpro consists of three domains: I (residues 8–101), and II (residues 102–184), which are β‐barrel domains that shape the chymotrypsin‐like structure, while domain III (residues 201–306) is made up by α‐helices. 124  The CoV Mpro active site uses a catalytic dyad (Cys145‐His41), in which cysteine acts as the nucleophile in the proteolysis while histidine behaves as general acid‐base. The peptide substrate or inhibitor binds in a cleft between domains I and II. 125
As far as the development of new therapeutics against SARS‐ and MERS‐CoV infection is concerned, efforts have mainly focused on protease inhibitors. These enzymes are highly attractive drug targets because they are so essential to the virus. Peptides, peptidomimetics, and even small molecules can inhibit them, which leads to markedly reduced viral transmission and pathogenicity. Although most of the reported molecules display only weak anti‐CoV activity, several of studies elucidated structure–activity relationships that can be used to further improve their activity. 100 ,  126 ,  127 ,  128