Acta Crystallographica Section D

Biological Crystallography

Volume 58, Part 9 (September 2002)

research papers

Acta Cryst. (2002). D58, 1407-1412 [ doi:10.1107/S0907444902010934 ]

Metal binding to porcine pancreatic elastase: calcium or not calcium

M. S. Weiss, S. Panjikar, E. Nowak and P. A. Tucker

Abstract: Porcine pancreatic elastase has been crystallized at slightly acidic pH under two similar but slightly different conditions. Diffraction data were collected at a wavelength of 1.5 Å to a maximum resolution of 1.7 Å. Both difference electron-density maps and anomalous difference electron-density maps suggest that in crystals grown from a sodium sulfate solution PPE binds Na⁺ in its metal-binding site. In contrast, PPE binds Ca²⁺ in crystals grown from a solution containing sodium citrate and calcium chloride. This observation is in contradiction to most PPE structures reported in the PDB. In addition to the metal-binding site, up to three other binding sites, which appear to be anion-binding sites, could be identified based on the observed anomalous intensity differences.

PDB references: 1lka and 1lkb

Keywords: porcine pancreatic elastase; metal-binding sites; serine proteases; anomalous dispersion.