Crystallization of porcine pancreatic elastase and a preliminary neutron diffraction experiment

To investigate the structural characteristics of a covalent inhibitor bound to porcine pancreatic elastase (PPE), including H atoms and hydration by water, a crystal of porcine pancreatic elastase with its inhibitor was grown to a size of 1.6 mm³ for neutron diffraction study. The crystal diffracted to 2.3 Å resolution with sufficient quality for further structure determination owing to the similar atomic scattering properties of deuterium and carbon. Porcine pancreatic elastase (PPE) resembles the attractive drug target leukocyte elastase, which has been implicated in a number of inflammatory disorders. In order to investigate the structural characteristics of a covalent inhibitor bound to PPE, including H atoms and the hydration by water, a single crystal of PPE for neutron diffraction study was grown in D₂O containing 0.2 M sodium sulfate (pD 5.0) using the sitting-drop vapour-diffusion method. The crystal was grown to a size of 1.6 mm³ by repeated macroseeding. Neutron diffraction data were collected at room temperature using a BIX-3 diffractometer at the JRR-3 research reactor of the Japan Atomic Energy Agency (JAEA). The data set was integrated and scaled to 2.3 Å resolution in space group P2₁2₁2₁, with unit-cell parameters a = 51.2, b = 57.8, c = 75.6 Å