3C-like protease
The 3CLpro is present in homodimer form and has cys-his dyad on active site which shows protease activity.[27] If mutated on the Ser139 and phe140 positions, it abolishes the dimerization of 3CLPro (PDB ID: 3F9G).[76] This protease can cleave 11 sites in the p1 position of PP1a and PP1ab and can produce a mature protein that anchors the replication/transcription complex[377] and also releases the mature NSPs.[78]
N-(benzo[1,2,3]triazol-1-yl)-N-(benzyl) acetamido) phenyl) carboxamides are also found to be important inhibitors of CLPro. The structure of CLPro inhibitor is with ML188 (IC50 1.5 μM) is reported (CID: 46897844, PDB ID: 3V3M).[7980] Another structure with CLPro inhibitor ML300 (PDB ID: 4MDS, IC50: 6.2 μM) is reported.[79] Some metal-conjugated and peptidomimetic compounds showed inhibitory activity against 3CLpro.[77] Some of the small molecules also act as an inhibitor that is arylboronic acids, quinolinecarboxylate derivatives, thiophenecarboxylate, and phthalhydrazide-substituted ketoglutamine analogs.[77] Some flavonoids are also reported to inhibit Mpro.[75] GC376 also has protease inhibitor activity.[81] A crystal structure of Mpro with small molecule inhibitor N3 is also reported (PDB ID: 2AMQ).[82] Lopinavir and ritonavir, which are the inhibitors of HIV protease, also inhibit Mpro.[83] In silico studies directed that among commercially available drugs, colistin, valrubicin, icatibant, bepotastine, epirubicin, epoprostenol, vapreotide, aprepitant, caspofungin, and perphenazine also bind to the lopinavir/ritonavir-binding site on CoV.[83]