Crystallization and preliminary X-ray studies on the trypsin inhibitor I-2 from wheat germ and its complex with trypsin

Abstract

A Bowman-Birk type trypsin inhibitor I-2, M(r) = 14 000, 123 amino-acid residues, isolated from wheat germ, and its complex with trypsin have been crystallized. For I-2 two morphologically different crystal forms were obtained. Crystal form 1 is tetragonal, P4(1)22 or P4(3)22, with a = 55.45 (2), c = 129.1 (2) A and V = 3.97 (2) x 10(5) A(3). The crystals diffract X-rays very anisotropically, to less than 6 A resolution normal to the c* direction, but up to 3 A resolution in the other directions. Crystal form 2 is monoclinic, space group C2. The cell parameters show significant variation even for crystals in the same batch. The median parameters are: a = 83.9, b = 41.5, c = 45.7 A, beta = 95.9 degrees and V = 1.58 x 10(5) A(3). The diffraction pattern is isotropic and reflections up to 2.2 A resolution were observed. The crystals of the complex between bovine trypsin and I-2 (2:1) belong to the orthorhombic space group P2(1)2(1)2(1) with a = 73.49 (2), b = 120.56 (3), c = 70.04 (2) A and V = 6.206 (5) x 10(5) A(3). The crystals diffract up to 2.3 A resolution, and contain one complex of 60 100 Da in an asymmetric unit.