(A) The crystal structure of SARS-CoV-2 Mpro (PDB ID: 6LU7). The active site of Mpro is between two distinct domains termed domain I and domain II that forms two β-barrel folds that is linked to domain III that forms five α helices. Substrate binding site is located in deep cleft between domain I and domain II and is capable of cleaving multiple sites on the target polyprotein encoded by viral RNA. (B) Serpin conformation: native (PDB ID: 3FGQ) serpin structure showing RCL and strand 3A and 5A of β-sheet A, where RCL inserts as strand 4A after protease cleavage inactivating it in the process. Picture was created by using PyMOL molecular graphic system.