X-ray crystal structure of a dipeptide-chymotrypsin complex in an inhibitory interaction.Kashima, A., Inoue, Y., Sugio, S., Maeda, I., Nose, T., Shimohigashi, Y.
(1998) Eur.J.Biochem. 255: 12-23
- PubMed: 9692896
- Primary Citation of Related Structures:  1AFQ
- PubMed Abstract:
- Gamma-Chymotrypsin is a Complex of Alpha-Chymotrypsin with its Own Autolysis Products
Harel, M.,Su, C.T.,Frolow, F.,Silman, I.,Sussman, J.L.
(1991) Biochemistry 30: 5217
- Is Gamma-Chymotrypsin a Tetrapeptide Acyl-Enzyme Adduct of Alpha-Chymotrypsin?
Dixon, M.M.,Matthews, B.W.
(1989) Biochemistry 28: 7033
- Structure of Gamma-Chymotrypsin in the Range Ph 2.0 To Ph 10.5 Suggests that Gamma-Chymotrypsin is a Covalent Acyl-Enzyme Adduct at Low Ph
Dixon, M.M.,Brennan, R.G.,Matthews, B.W.
(1991) Int.J.Biol.Macromol. 13: 89
The dipeptide D-leucyl-L-phenylalanyl p-fluorobenzylamide (D-Leu-Phe-NH-BzlF) inhibits chymotrypsin strongly in a competitive manner with the Ki value of 0.61 microM [Shimohigashi, Y., Maeda, I., Nose, T., Ikesue, K., Sakamoto, H., Ogawa, T., Ide, Y. ...
The dipeptide D-leucyl-L-phenylalanyl p-fluorobenzylamide (D-Leu-Phe-NH-BzlF) inhibits chymotrypsin strongly in a competitive manner with the Ki value of 0.61 microM [Shimohigashi, Y., Maeda, I., Nose, T., Ikesue, K., Sakamoto, H., Ogawa, T., Ide, Y., Kawahara, M., Nezu, T., Terada, Y., Kawano, K. & Ohno, M. (1996) J. Chem. Soc. Perkin Trans. 1, 2479-2485]. The structure/activity studies have suggested a unique inhibitory conformation, in which the C-terminal benzyl group fits the chymotrypsin S1 site and the hydrophobic core constructed by the side chains of D-Leu-Phe fits the S2 or S1' site. To verify this assumption, the molecular structure of the complex between the dipeptide and gamma-chymotrypsin has been determined crystallographically. Gamma-chymotrypsin itself was first crystallized and refined at 1.6-A resolution. The refined structure was virtually identical to the conformation reported and the electron density at the active site was interpreted as a pentapeptide Thr-Pro-Gly-Val-Tyr derived from autolysis of the enzyme (residues 224-228). The chymotrypsin-dipeptide complex was obtained by soaking the crystals of gamma-chymotrypsin in a solution saturated with the dipeptide inhibitor. The crystal structure of the complex has been refined at 1.8-A resolution to a crystallographic R-factor of 18.1%. The structure of gamma-chymotrypsin in the complex agreed fairly well with that of gamma-chymotrypsin per se with a rmsd of 0.13 A for all the C alpha carbons. Two inhibitor molecules were assigned in an asymmetric unit, i.e. one in the active site and the other at the interface of two symmetry-related enzyme molecules. In both sites dipeptides adopted very similar folded conformations, in which side chains of D-Leu-Phe are spatially proximal. In the active site where the binding of dipeptide was judged to be a direct cause of inhibition, C-terminal p-fluorobenzylamide group of the dipeptide, NH-BzlF, was found in the S1 hydrophobic pocket. At the bottom of this pocket, the p-fluorine atom hydrogen bonded with a water molecule, probably to enhance the inhibitory activity. The stereospecific interaction of R and S isomers of the dipeptide with C-terminal NH-C*H(CH3)-C6H5 was well explained by the space available for methyl replacement in the complex. The hydrophobic core constructed by side chains of D-Leu-Phe was found at the broad S2 site. Interestingly, a novel interaction was found between the inhibitor Phe residue and chymotrypsin His57, the phenyl of Phe and the imidazole of His being in a pi-pi stacking interaction at a distance 3.75 A.
Research Division, The Green Cross Corp., Hirakata, Japan.