Purification, characterization, and crystallization of single molecular species of beta-conglycinin from soybean seeds.

Four major molecular species of beta-conglycinin, alpha 3, alpha 2 beta, alpha beta 2, and beta 3, were isolated and purified from seeds of an alpha' subunit-deficient strain of soybeans (Glycine max). All components were found to be homogeneous by high pressure liquid chromatography, SDS-polyacrylamide gel electrophoresis, and amino acid and amino terminal sequence analyses. The amino acid compositions of the alpha 3 and beta 3 components agreed fairly well with the compositions deduced from the cDNA sequences, and all of the components were highly glycosylated. The alpha 3 and beta 3 components were compared regarding their secondary structures. The secondary structure of the alpha 3 component deduced from CD measurements showed a higher alpha-helix content than that of the beta 3 component. The beta 3 component was crystallized by decreasing the ionic strength from 0.5 to 0.14 in phosphate buffer, pH 7.3, and the crystals grew to a size (1.0 mm x 0.2 mm x 0.2 mm) suitable for X-ray crystallographic analysis. A preliminary X-ray analysis showed that the crystal belonged to an orthorhombic crystal system having the space group P2(1)2(1)2(1) and unit cell dimensions of a = 185.1 A, b = 107.9 A, and c = 97.6 A.