Tris ion induces conformational change and crystal-packing contraction of porcine pancreatic elastase

Graduate School of Science, Osaka Prefecture University
â—‹Asako Yamaguchi Takayoshi Kinoshita Toshiji Tada

Porcine pancreatic elastase (PPE) was crystallized under the new sulphate-free conditions containing 0.3 M NaCl and 50 mM tris(hydroxymethyl)aminomethane (TRIS)/HCl at pH 7.0. The crystal structure determined at 1.5 Å resolution had a unique conformation in four regions which contained loop portions. A chloride ion bound near the catalytic triad instead of a sulphate ion in 1QNJ, a typical PPE crystal structure. However, the chloride ion did not affect the configuration of the catalytic triad. A TRIS molecule bound to the S4 and S5 subsites in the place of the adjacent molecule in the 1QNJ crystal and played a significant role in the structural change of the region. Subsequently, the distortion in this region may have induced the conformational changes in the other three regions. The fact that TRIS and these four regions made a diagonal line in the ac plane may have affected the crystal-packing contraction along the a and c axes in the crystal compared to the typical crystal.