Purification crystallization and preliminary crystallographic studies of SPCI–chymotrypsin complex at 2.8 Å resolution

摘要

A binary complex of the Schizolobium parahyba chymotrypsin inhibitor (SPCI) with chymotrypsin was purified by size-exclusion chromatography and crystallized by the sitting-drop vapour-diffusion method with 100 mM MES–NaOH pH 5.5, 20%(w/v) PEG 6000, 200 mM LiCl as precipitant and 200 mM nondetergent sulfobetaine molecular weight 201 Da (NDSB-201) as an additive. SPCI is a small protein with 180 amino-acid residues isolated from S. parahyba seeds and is able to inhibit chymotrypsin at a 1:1 molar ratio by forming a stable complex. X-ray data were collected to 2.8 Å resolution from a single crystal of the SPCI–chymotrypsin binary complex under cryogenic conditions. The crystal belongs to space group P212121, with unit-cell parameters a = 45.28, b = 64.57, c = 169.23 Å, and the R merge is 0.122 for 11 254 unique reflections. A molecular-replacement solution was found using the preliminary crystal structure of SPCI and the structure of chymotrypsin (PDB code ) independently as search models.