Crystallization and Preliminary X-ray Analysis of Complexes of Porcine Pancreatic Elastase with two Natural Inhibitors

Two different natural protease inhibitors, the squash inhibitor MCEI III and the third domain of turkey ovomucoid inhibitor OMTKY3, were crystallized in complexes with porcine pancreatic elastase (PPE). About 700 conditions were screened altogether. Crystals of the complex between MCEI III and PPE were grown in citrate buffer with and without ammonium acetate. X-ray diffraction data were collected to 1.9 Å resolution at room temperature using synchrotron radiation. The crystals belong to space group P21, with unit-cell parameters a = 49.17, β = 44.59, c = 67.08 Å, β = 110.97° . Crystals of the OMTKY3 / PPE complex were obtained in the presence of ammonium sulfate, MES buffer and polyethylene glycol monomethylether (PEG). These crystals of this complex diffracted to 2.1 Å resolution and belongs to space group I222, with unit-cell parameters a = 84.58, b = 84.61, c = 89.92 Å and diffracted to 2.2 Å resolution. The diffraction data were collected using a conventional rotating anode X-ray generator at room temperature. In both cases the presence of inhibitor in the crystals was confirmed by crystallography.