Crystal structures of recombinant and native soybean β‐conglycinin β homotrimers

Abstract

The crystal structures of recombinant and native b homotrimers of soybean b-conglycinin were determined by X-ray crystallography at 2.7 and 2.8 A Ê resolutions, respectively. The crystals of the recombinant and native b homotrimers belong to space group P2 1 with cell parameters a 80. Keywords: b-conglycinin; crystal structure; N-linked glycan; soybean; vicilin.Soybean proteins are one of the most attractive plant food proteins for man, as they exhibit a hypocholesterolemic effect [1,2] and have good nutritional and physicochemical properties (such as gel-forming and emulsifying abilities required for food systems) [3,4]. Soybean proteins are composed of two major components, b-conglycinin (vicilin class) and glycinin (legumin class), which account for about 30% and 40% of the total seed proteins, respectively. These two components are responsible for the nutritional, physicochemical and physiological properties of soybean proteins.b-Conglycinin has a trimeric structure analogous to that of other 7S globulins [4,5] and is composed of three kinds of subunit a, a H and b. Many molecular species with different subunit compositions, including homotrimers with almost random combinations, are present in soybean seeds [6,7]. The amino-acid sequences of these subunits deduced from their nucleotide sequences indicate that the a and a H subunits contain extension regions in addition to core regions common to all subunits, and that the core regions exhibit high absolute homologies (90.4, 76.2 and 75.5% between a and a H , a and b, and a H and b, respectively [8]). However, it is known that the contributions of individual subunits to physicochemical and physiological properties and allergenicity differ as follows: (a) the orders of thermal stabilities, which are one of the structural features related to food processing and conferred by the core regions, are b . a H . a [8]; (b) b-conglycinin mainly contributes to the up-regulation of low-density lipoprotein receptors, which is one of the mechanisms of the hypocholesterolemic effect of soybean proteins [2,9], and only the a H subunit is responsible for the up-regulation activity of b-conglycinin [10]; (c) b-conglycinin is the third main allergen responsible for soybean allergy, and only the a subunit is identified as having a reactivity with soybean-sensitive-patients H sera [11].In order to investigate why individual subunits of b-conglycinin have different properties as described above, it is necessary to elucidate their crystal structures by means of X-ray crystallography. Although a large amount of homogeneous homotrimers is required for X-ray crystallography, they are very difficult to obtain from natural soybean seeds because of molecular heterogeneity [6,7] and the high homologies of their amino-acid sequences [8]. Recently, a mutant soybean cultivar has been developed which contains b-conglycinin composed of only the b subunit [12]. Therefore, b homotrimers can be purified easily using the mutant soybean. Alternatively, the Escherichia coli expression systems we cons...

Crystal structure of soybean 11S globulin: Glycinin A3B4 homohexamer

“…Although the quaternary structures of the 7S and 11S globulins are different from each other (the former being a trimeric protein and the latter a hexameric protein), they are believed to be derived from a common ancestor because of the partial homologies in their amino acid sequences and limited proteolysis patterns (3). This assumption has been confirmed by x-ray crystallography of 7S globulins from kidney bean (4), jack bean (5), and soybean (6) and of the trimeric soybean 11S globulin precursor (7).…”

C-Terminal 23�kDa polypeptide of soybean Gly�m�Bd 28�K is a potential allergen

“…3D-PSSM was the only automated modeling program that preserved the alignment of Gly m Bd 28 K with known cupin domains. Of the models generated by 3D-PSSM, we chose the one based upon the b-conglycinin structure (PDB identifier 1ipj; Berman et al 2000;Maruyama et al 2001). We used percent identity and similarity to infer homology, and utilized the power of the 3D-PSSM server to model distant homologs of proteins.…”

Phosphorylation of the 12 S globulin cruciferin in wild-type and abi1-1 mutant Arabidopsis thaliana (thale cress) seeds

“…Salt-soluble globulins are widely distributed in dicotyledons, monocotyledons and gymnosperms, and comprise the trimeric and predominantly glycosylated 7 S vicilins and the hexameric and generally non-glycosylated 11-12 S legumins [1]. The three-dimensional structures of several vicilin-type proteins, namely phaseolin [2], canavalin [3], β-conglycinin [4] and germin [5], and the legumin-type proglycinin A1aB1b homotrimer [6] and glycinin A3B4 homohexamer [7], have revealed that seed storage globulins share striking similarities in secondary and tertiary structure with the cupin superfamily of prokaryotic and eukaryotic proteins [8,9]. Proteins in this family have been ascribed a wide variety of functions [8,9].…”