Proteases are a family of enzymes that conducts proteolysis by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain of proteins. These enzymes are involved in a multitude of physiological reactions from simple digestion of food proteins to highly regulated cascades (e.g., the blood-clotting cascade, the complement system, and the apoptosis pathways). Viral protease inhibitors are successful antiviral drugs that are widely used to treat HIV and HCV infections.