The large family of serine proteases (almost one-third of all proteases; EC 3.4.21.-) is characterized by its general mechanism of action to cleave peptide bonds in proteins, in which serine serves as the nucleophilic amino acid at the (enzyme's) active site. The members of this family  can be divided roughly into four sub-groups based on their structure, being chymotrypsin-like (trypsin-like), subtilisin-like, carboxypeptidase Y-like, and Clp-like[1].