Four major classes of proteases are known and are designated by the principal functional group in their active site: serine, thiol, carboxyl, and metallo. Serine proteases are characterized by the presence of a unique serine residue that functions as a nucleophile to cleave peptide bonds. In some cases, the serine forms covalent adducts with substrates and inhibitors. The serine functions with two other principal residues of the active site, a histidine, and an acid, frequently aspartic acid. Together these three residues compose the catalytic triad which is a signature of the family. Serine proteases are divided into two major evolutionary families. One family is represented by the bacterial protease subtilisin. The other family is the trypsin-chymotrypsin family and includes chymotrypsin, trypsin, and elastase. Other members of the trypsin-chymotrypsin family include thrombin, plasmin, kallikrein, and acrosin. Members of the trypsin-chymotrypsin serine protease family are involved in a range of diverse cellular functions including, cell motility, cell growth and differentiation, hormone production, organogenesis, extracellular matrix regulation, blood clotting, and complementation activation.
These proteases catalyze the hydrolysis of peptide bonds in proteins and peptides. While the various serine proteases catalyze this reaction in very similar ways, they differ in their preference for the amino acid side chains immediately C-terminal to the cleave site. Trypsin cleaves bonds only after lysine and arginine residues, whereas chymotrypsin cleaves bonds after large hydrophobic residues. Other proteases of this family have less distinct preferences for this position, but also depend to varying extents on the residues at neighboring positions.
Some members of the trypsin serine protease family play critical roles in a variety of important biological events including regulating cell proliferation, tumor growth, tumor invasion, metastasis, development, and tissue remodeling. Accordingly, there is a need for identifying and characterizing novel trypsin serine proteases.