Covalent structure of a group-specific protease from rat small intestine. Appendix: Crystallographic data for a group specific protease from rat intestine

Publisher Website
Google Scholar
Abstract
Group-specific protease (GSP) is a serine protease, obtained from rat small intestine, which preferentially inactivates the apo forms of certain pyridoxal phosphate requiring enzymes. The enzyme contains 224 amino acid residues in a single polypeptide chain and 3 disulfide bonds. The covalent structure was determined and its homologous relationship to those of chymotrypsin, trypsin and elastase was established (approximately 33% identity with each). The residues forming the charge-relay system of the active site of chymotrypsin (His-57, Asp-102 and Ser-195) are found in corresponding regions in GSP, whereas an alanyl residue at position 176 of GSP corresponds to a residue which participates in the primary substrate binding site in serine proteases (Asp-177 in trypsin; Ser-189 in chymotrypsin). Three disulfide bonds in GSP occur in similar positions in chymotrypsin, trypsin and elastase. GSP lacks a disulfide bond which is present in all known serine proteases (linking Cys-191 to Cys-220 in chymotrypsin). In view of the close proximity of this bond to both the primary and the anti-parallel binding sites of various serine proteases, it is likely that its absence in GSP is related to the substrate specificity of this enzyme. GSP probably diverged from a common ancestor preceding chymotrypsin but following trypsin.