ABSTRACT
Proteases are enzymes catalyzing the hydrolysis of peptide bonds. They form one of the largest enzyme families encoded by the human genome, with more than 500 active members. Based on the different catalytic mechanisms of substrate hydrolysis, these enzymes are divided into four major classes: serine/threonine, cysteine, metallo, and aspartic proteases. In serine, cysteine, and threonine proteases, the nucleophile of the catalytic site is a side chain of an amino acid in the protease (covalent catalysis). In metallo and aspartic proteases, the nucleophile is a water molecule activated through the interaction with amino acid side chains in the catalytic site (non-covalent catalysis) (Gerhartz et al., 2002).
