CRYSTAL STRUCTURE OF THE COMPLEX OF PORCINE PANCREATIC TRYPSIN WITH KUNITZ-TYPE SOYBEAN TRYPSIN INHIBITOR. Hyun Kyu Song and SeWon Suh, Department of Chemistry and Center for Molecular Catalysis, Seoul National University, Seoul 151-742, Korea.

The crystal structure of the complex formed between the procine pancreatic trypsin and Kuntiz-type soybean trypsin inhibitor has been determined at 1.75 Å resolution (R-factor of 18.9 % for 31,038 unique reflections with Fo > 2 [[sigma]]F in the range 8.0-1.75 Å). The root mean square deviations from ideal stereochemistry are 0.013 Å for bond lengths and 1.32deg. for bond angles. Moleculare replacement models for porcine pancreatic trypsin and Kunitz-type soybean trypsin inhibitor were porcine, ß-trypsin complexed with Momordica charantia trypsin inhibitor [Hunag et al. (1993) J. Mol. Biol. 229, 1022-1036, pdb ID code: lsmf] and Erythrina caffra trypsin inhibitor [Onesti et al. (1991) J. Mol. Biol. 217, 153-176, pdb ID code: 1tie], respectively. This study at high resolution significantly improved the model of the complex, previously determined at 2.6 Å resolution by multiple isomorphous replacement method [Sweet et al. (1974) Biochemistry 13, 4212-4228]. The improved resolution has enabled positioning of the protein atoms with greater accuracy as well as locating solvent atoms, including water molecules near the catalytic residues.