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β-Conglycinin is a major seed storage protein in soybeans, which are an important source of protein. The major subunits (α, α' and β) of β-conglycinin are sorted to protein-storage vacuoles in seed cells. Vacuolar sorting receptor (VSR) is an integral membrane protein that recognizes the sorting determinant of vacuolar proteins, including β-conglycinin, and regulates their sorting process. Vacuolar sorting determinants of the α' and β subunits of β-conglycinin exist in their C-terminal peptides. Here, the preliminary X-ray diffraction analysis of the binding domain of soybean VSR crystallized with the peptide responsible for the sorting determinant in β-conglycinin is reported. X-ray diffraction data were collected to a resolution of 3.5 Å. The crystals belonged to space group P3121, with unit-cell parameters a = b = 116.4, c = 86.1 Å.

Glycinin is one of the most abundant storage-protein molecules in soybean seeds and is composed of five subunits (A1aB1b, A1bB2, A2B1a, A3B4 and A5A4B3). A1bB2 was purified from a mutant soybean cultivar containing glycinin composed of only A5A4B3 and A1bB2. At 281 K the protein formed hexagonal, rectangular and rod-shaped crystals in the first [0.1 M imidazole pH 8.0, 0.2 M MgCl₂, 35%(v/v) MPD], second [0.1 M sodium citrate pH 5.6, 0.2 M ammonium acetate, 30%(v/v) MPD] and third (0.1 M phosphate-citrate pH 4.2, 2.0 M ammonium sulfate) crystallization conditions, respectively. X-ray diffraction data were collected to resolutions of 1.85, 1.85 and 2.5 Å from crystals of the three different shapes. The crystals belonged to space groups P6₃22, P2₁ and P1, with unit-cell parameters a = b = 143.60, c = 84.54 Å, a = 114.54, b = 105.82, c = 116.67 Å, β = 94.99° and a = 94.45, b = 94.96, c = 100.66 Å, α = 107.02, β = 108.44, γ = 110.71°, respectively. One, six and six subunits of A1bB2 were estimated to be present in the respective asymmetric units. The three-dimensional structure of the A1bB2 hexamer is currently being determined.

Amaranth is a crop known for its high quality proteins. 11S Globulin is one of the most abundant and important storage proteins of the amaranth grain. Here, we report the crystal structure of amaranth 11S proglobulin at a final resolution of 2.28 Å. It belonged to the space group P6(3) with cell dimensions a=b=96.6, c=75.0 Å. It contains one asymmetric unit consisting of 372 residues and 100 water molecules. Disordered regions in the model approximately correspond to the variable regions of the 11S globulins. The structure has an extended α-helix and β-barrel domains at both N-terminal and C-terminal regions, which are characteristic of the 11S and 7S globulins. The three dimensional structure suggests that its high thermal stability is due to the cumulative effects of many factors and its good emulsifying property depended on the balance between its surface hydrophobicity and hydrophilicity., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

11S globulin is one of the major seed storage proteins in amaranth. Recombinant protein was produced as up to approximately 80% of the total bacterial protein using Escherichia coli Rosetta-gami (DE3) containing pET21d with amaranth 11S globulin cDNA. The best expression condition was at 302 K for 20 h using LB medium containing 0.5 M NaCl. The recombinant protein was easily separated from most of the Escherichia coli proteins by precipitation with 0-40% ammonium sulfate solution. It formed aggregates at low temperature and at low salt concentrations. This behaviour may imply that it has a more hydrophobic nature than other 11S seed globulins. The crystals diffracted to 6 A resolution and belonged to space group P6(3), with unit-cell parameters a=b=97.6, c=74.8 A, gamma=120.0 degrees. One subunit of a trimer was estimated to be present in the asymmetric unit, assuming a Vsol of 41%. To obtain the complete structure solution, experiments to improve crystallization and flash-cooling conditions are in progress.

Basic 7S globulin, a cysteine-rich protein from soybean seeds, consists of subunits containing 27 kD and 16 kD chains linked by disulfide bonding. Three differently sized subunits of the basic 7S globulin were detected and partially separated by SP Sepharose chromatography. The basic 7S globulin was characterized as a member of a superfamily of structurally related but functionally distinct proteins descended from a specific group of plant aspartic proteinases.

The recombinant proteins Adzuki 7S1, Adzuki 7S2, and Adzuki 7S3 were prepared through the Escherichia coli expression systems of three kinds of adzuki bean cDNAs. The recombinant proteins exhibited intrinsic thermal stabilities, surface hydrophobicities, and solubilities, although the homology of their amino acid sequences ranged from 95-98%. To understand why these individual proteins exhibited different properties, their three-dimensional structures were elucidated. The three proteins were successfully crystallized, and the three-dimensional structures of Adzuki 7S1 and Adzuki 7S3 were determined. The properties and structures of these two proteins were comprehensively compared with those of recombinant 7S globulins (soybean beta-conglycinins beta and alpha'c and mungbean 8Salpha) reported previously. It was likely that cavity sizes, hydrogen bonds, salt bridges, hydrophobic interactions, and lengths of loops determine the thermal stabilities of 7S globulins, and results indicated that cavity sizes strongly contribute to such stability. Surface hydrophobicity was also found to be determined not only by distributions of hydrophobic residues on the molecular surface. Furthermore, solubility at neutral and weak alkaline pH values at mu = 0.08 was found to be dominantly influenced by the electrostatic surface potentials.

The 8S globulins of mung bean [Vigna radiata (L.) Wilczek] are vicilin-type seed storage globulins which consist of three isoforms: 8Salpha, 8Salpha' and 8Sbeta. The three isoforms have high sequence identities with each other (around 90%). The structure of 8Salpha globulin has been determined for the first time by X-ray crystallographic analysis and refined at 2.65 A resolution with a final R factor of 19.6% for 10-2.65 A resolution data. The refined 8Salpha globulin structure consisted of 366 of the 423 amino-acid residues (one subunit of the biological trimer). With the exception of several disordered regions, the overall 8Salpha globulin structure closely resembled those of other seed storage 7S globulins. The 8Salpha globulin exhibited the highest degree of sequence identity (68%) and structural similarity (a root-mean-square deviation of 0.6 A) with soybean beta-conglycinin beta (7S globulin). Their surface hydrophobicities are also similar to each other, although their solubilities differ under alkaline conditions at low ionic strength. This difference seems to be a consequence of charge-charge interactions and not hydrophobic interactions of the surfaces, based on a comparison of the electrostatic potentials of the molecular surfaces. The thermal stability of 8Salpha globulin is lower than that of soybean beta-conglycinin beta. This correlates with the cavity size derived from the crystal structure, although other structural features also have a small effect on the protein's thermal stability.

The crystal structure of the core region of the alpha' subunit (alpha(c')) of soybean beta-conglycinin has been determined at 2.3 A resolution. alpha(c') was superimposed on the known crystal structure of the beta-conglycinin beta subunit with a small root-mean square deviation of 0.77 A, which is consistent with the high sequence identity of 75.5% between alpha(c') and the beta subunit. It is known that the thermal stability of the beta subunit is higher than that of the alpha' subunit and that their thermal stabilities are conferred by highly homologous core regions. Comparisons of the three-dimensional structures and primary sequences between alpha(c') and the beta subunit suggest that five factors account for this difference between subunits as regards the difference in thermal stability: (i) the total cavity volume is larger in alpha(c'), (ii) the cluster of charged residues at the intermonomer interface is smaller in alpha(c') and alpha(c') lacks the intermonomer salt bridge of the beta subunit, (iii) the solvent-accessible surface is more hydrophobic in alpha(c'), (iv) there are fewer proline residues in alpha(c') and (v) a loop region between helix 3 and strand J' in alpha(c') is more flexible owing to the insertion of five additional residues. Although more hydrogen bonds were found in alpha(c'), this difference should be more than compensated for by the combined contributions of these other factors.

Most plant seeds contain 11S globulins as major storage proteins for their nutrition. Soybean glycinin belongs to the 11S globulin family and consists of five kinds of subunits. We determined the crystal structure of a homohexamer of the glycinin A3B4 subunit at 2.1-A resolution. The crystal structure shows that the hexamer has 32-point group symmetry formed by face-to-face stacking of two trimers. The interface buries the highly conserved interchain disulfide. Based on the structure, we propose that an ingenious face-to-face mechanism controls the hexamer formation of the 11S globulin by movement of a mobile disordered region to the side of the trimer after posttranslational processing. Electrostatic analysis of the faces suggests that the interchain disulfide-containing face has high positive potential at acidic pH, which induces dissociation of the hexamer into trimers that may be susceptible to proteinases after seed imbibition. This dissociation might result in the degradation and mobilization of 11S globulins as storage proteins in embryos during germination and seedling growth.

Abstract: Ara h 1, a 7S globulin, is one of the three major peanut allergens. We previously reported the crystallization of the core region of recombinant Ara h 1. Here, we present the crystal structure of the Ara h 1 core at a resolution of 2.43Å. We also assayed the Ara h 1 core thermal stability and compared its final structure against other 7S globulins. The Ara h 1 core has a thermal denaturation temperature of 88.3°C and a structure that is very similar to other 7S globulins. Previously identified linear IgE epitopes were also mapped on the three-dimensional structure. Most linear epitopes were found in the extended loop domains and the coils between the N- and C-terminal modules, while others were found in the less accessible β-sheets of the C-terminal core β-barrel domain of each monomer. Most of these epitopes become either slightly or significantly buried upon trimer formation, implying that allergen digestion in the gut is required for these epitopes to be accessible to immunoglobulins. Our findings also suggest that both intact and partially degraded allergens should be employed in future diagnostic and immunotherapeutic strategies. [Copyright &y& Elsevier]

Abstract: The crystal structures of two pro-11S globulins namely: rapeseed procruciferin and pea prolegumin are presented here. We have extensively compared them with the other known structures of plant seed 11S and 7S globulins. In general, the disordered regions in the crystal structures among the 11S globulins correspond to their five variable regions. Variable region III of procruciferin is relatively short and is in a loop conformation. This region is highly disordered in other pro-11S globulin crystals. Local helical and strand variations also occur across the group despite general structure conservation. We showed how these variations may alter specific physicochemical, functional and physiological properties. Aliphatic hydrophobic residues on the molecular surface correlate well with T m values of the globulins. We also considered other structural features that were reported to influence thermal stability but no definite conclusion was drawn since each factor has additive or subtractive effect. Comparison between proA3B4 and mature A3B4 revealed an increase in r.m.s.d. values near variable regions II and IV. Both regions are on the IE face. Secondary structure based alignment of 11S and 7S globulins revealed 16 identical residues. Based on proA3B4 sequence, Pro60, Gly128, Phe163, Phe208, Leu213, Leu227, Ile237, Pro382, Val404, Pro425 and Val 466 are involved in trimer formation and stabilization. Gly28, Gly74, Asp135, Gly349 and Gly397 are involved in correct globular folding. [Copyright &y& Elsevier]