Crystallization, data collection and phasing of black-eyed pea trypsin/chymotrypsin inhibitor in complex with bovine β-trypsin

The black-eyed pea trypsin and chymotrypsin inhibitor (BTCI) is a Bowman–Birk-type inhibitor from Vigna unguiculata seeds. A complex of BTCI with bovine β-trypsin was crystallized by the hanging-drop vapour-diffusion method with ammonium sulfate as precipitant. Crystals belong to the orthorhombic space group P2₁2₁2₁, with unit-cell parameters a = 59.3, b = 61.8, c = 80.0 Å. Diffraction data were collected to 2.36 Å resolution and were processed to give an overall R_sym of 0.137. The Matthews coefficient for one complex per asymmetric unit is 2.2 ų Da⁻¹, with a corresponding solvent content of 43%. After molecular replacement and initial refinement, the model gives an R_cryst of 0.361 and an R_free of 0.432.