X‐ray crystal structure of the bovine α‐chymotrypsin/eglin c complex at 2.6 Å resolution

Publisher Website
Google Scholar
Abstract
The crystal structure of the molecular complex formed by bovine α‐chymotrypsin and the recombinant serine proteinase inhibitor eglin c from Hirudo medicinalis has been solved using monoclinic crystals of the complex, reported previously. Four circle diffractometer data at 3.0 Å resolution were employed to determine the structure by molecular replacement techniques. Bovine α‐chymotrypsin alone was used as the search model; it allowed us to correctly orient and translate the enzyme in the unit cell and to obtain sufficient electron density for positioning the eglin c molecule. After independent rigid body refinement of the two complex components, the molecular model yielded a crystallographic R factor of 0.39. Five iterative cycles of restrained crystallographic refinement and model building were conducted, gradually increasing resolution. The current R factor at 2.6 Å resolution (diffractometer data) is 0.18. The model includes 56 solvent molecules. Eglin c binds to bovine α‐chymotrypsin in a manner consistent with other known serine proteinase/inhibitor complex structures. The reactive site loop shows the expected conformation for productive binding and is in tight contact with bovine α‐chymotrypsin between subsites P3 and P′2; Leu 45I acts as the P1 residue, located in the primary specificity S1 site of the enzyme. Hydrogen bonds equivalent to those observed in complexes of trypsin(ogen) with the pancreatic basic‐ and secretory‐ inhibitors are found around the scissile peptide bond.