Crystallization and preliminary X-ray analysis of soybean proglycinins modified by protein engineering

Glycinin is one of the most abundant storage proteins in soybean seeds. We earlier reported the preparation of proglycinins modified by protein engineering to improve food functions. Crystals of the modified proglycinins (delta I, delta V8, IV + 4Met, V + 4Met, Gly12, and Ser88) expressed in Escherichia coli were grown, each under different suitable crystallization conditions. The crystals of delta I, V + 4Met, Gly12, and Ser88 diffracted X-rays sufficiently for crystallographic analysis. delta I, Gly12, and Ser88 crystals were tetragonal, space group P4(1) or P4(3), and with unit cell dimensions a = b = 114.3-115.9 A and c = 145.1-146.1 A. V + 4Met crystals were monoclinic, space group P2, and with unit cell dimensions a = 118.7 A, b = 78.1 A, c = 109.9 A, and beta = 119 degrees. The number of promoters per asymmetric unit of all of the crystals of these four modified proglycinins was about 3. This value is consistent with proglycinins being trimers. These data indicated that most of the modified proglycinin crystals examined here could be studied by X-ray crystallography to elucidate the relationships between the structure and the functional properties of glycinin at molecular level.