REFINED 1.6-ANGSTROM RESOLUTION CRYSTAL-STRUCTURE OF THE COMPLEX FORMED BETWEEN PORCINE BETA-TRYPSIN AND MCTI-A, A TRYPSIN-INHIBITOR OF THE SQUASH FAMILY - DETAILED COMPARISON WITH BOVINE BETA-TRYPSIN AND ITS COMPLEX

The crystal structure of the complex formed by porcine β-trypsin with the MCTI-A inhibitor (Momordica charantia, Linn. Cucurbitaceae) has been determined at 1.6 Å resolution using the molecular replacement method. The sequence of MCTI-A was determined by recognizing the electron density, and shows that MCTI-A is a member of the squash family of trypsin inhibitors. We report the first high-resolution structure of porcine β-trypsin. Detailed comparisons have been made on the overall structure, solvent structure and active-site geometries between this complex and bovine β-trypsin and its complexes. On the basis of our results, we discuss the interaction patterns between inhibitor and trypsin. Unlike other complex structures formed by bovine trypsin with inhibitors, no out-of-plane distortion around the inhibitor's scissile peptide was observed. The role of the trypsin catalytic triad is also discussed on the basis of this structure.