Gastricsins, asparate proteases produced in gastric mucosa.
Gastricsin is also called pepsinogen C. Gastricsins are produced in gastric mucosa of mammals. It is synthesized by the chief cells in the stomach as an inactive zymogen. It is self-converted to a mature enzyme under acidic conditions. Human gastricsin is distributed throughout all parts of the stomach. Gastricsin is synthesized as an inactive progastricsin that has an approximately 40 residue prosequence. It is self-converting to a mature enzyme being triggered by a drop in pH from neutrality to acidic conditions. Like other aspartic proteases, gastricsin are characterized by two catalytic aspartic residues at the active site, and display optimal activity at acidic pH. Mature enzyme has a pseudo-2-fold symmetry that passes through the active site between the catalytic aspartate residues. Structurally, aspartic proteases are bilobal enzymes, each lobe contributing a catalytic aspartate residue, with an extended active site cleft localized between the two lobes of the molecule. One lobe may be evolved from the other through ancient gene-duplication event. Although the three-dimensional structures of the two lobes are very similar, the amino acid sequences are more divergent, except for the conserved catalytic site motif. This family of aspartate proteases is classified by MEROPS as the peptidase family A1 (pepsin A, clan AA).