Soybean glycinin is a member of the 11 S globulin family. The crystal struc
ture of proglycinin was determined by X-ray crystallography at 2.8 Angstrom
resolution with an R-factor of 0.199 and a free X-factor of 0.250. A trime
r molecule was found in an asymmetric unit of crystals. The trimer model co
ntains three A1aB1b subunits and comprises 1128 amino acid residues and 34
water molecules. The constituent protomers of the homo-trimeric protein are
arranged around a 3-fold symmetry axis with dimensions of 95 Angstrom x 95
Angstrom x 40 A. The protomer model is composed of five fragments which co
rrespond roughly to conserved regions based on the sequence alignment of va
rious 11 S globulins. The core of the protomer consists of two jelly-roll b
eta -barrels and two extended helix domains. This structure of proglycinin
is similar to those of canavalin and phaseolin belonging to the 7 S globuli
n family, strongly supporting the hypothesis that both 7 S and 11S globulin
s are derived from a common ancestor. The inter and intra-chain disulfide b
onds conserved in the 11S globulin family are clearly observed. It is found
that the face with the inter-chain disulfide bond (IE face) contains more
hydrophobic residues than that with the intra-chain disulfide bond. This su
ggests that a mature hexamer is formed by the interaction between the IE fa
ces after processing. (C) 2001 Academic Press.