This web page examines some of the structural properties of chymotrypsin, and it's corresponding zymogen-precursor, chymotrypsinogen.
Chymotrypsin, a digestive enzyme becomes activated after the proteolysis of the peptide bond between Arg15 and Ile16 in chymotrypsinogen by trypsin. The cleavage of this single bond allows several structural modifications to occur that help form the substrate binding site.
The first step in the activation of the the enzyme is the cleavage of the Arg15-Ile16 peptide bond and the subsequent movement of Ile16 to a point in the protein where the amino nitrogen of Ile16 forms a hydrogen bond with the carboxylate side chain of Asp194. Click on the buttons over the images on the right to view the relative positions of Ile16 and Asp194 in the zymogen and the active enzyme structures.
Note that the interaction between Ile16 and Asp194 in active chymotrypsin enzyme causes several important structural shifts. One very important and profound effect of this electrostatic interaction is the re-orientation of Gly193. In both the zymogen and the active enzyme,the catalytic triad (Asp102, His57, and Ser195) is in a similar conformation but Gly193 is not.
The NH group of Gly193 forms a hydrogen bond with the substrate, which helps to correctly align the substrate with the catalytic residues. The fact that the catalytic residues are in the correct conformation in both the zymogen and the enzyme, indicate that the lack of catalytic activity in chymotrypsinogen is mainly due to an incomplete substrate binding site, and not necessarily the position of the catalytic residues alone.
Thus, Gly193 needs to be in the correct orientation to align the substrate with the catalytic residues and the interaction between Ile16 with Asp194 causes this re-alignment. Finally, note the distance the NH group of Gly193 moves relative to His57 as a reference point in the transition from chymotrypsinogne to chymotrypsin.