Polymerization of Several Proteins by Ca2+-Independent Transglutaminase Derived from Microorganisms

α_s1-Casein and soybean globulins were polymerized and gelatinized by Ca²⁺-independent transglutaminase that was isolated from the culture filtrate of a microorganism thought to belong to Streptoverticillium sp. of actinomycetes. This enzyme polymerized such albumins as bovine serum albumin, human serum albumin and conalbumin in the presence of dithiothreitol. Rabbit myosin was polymerized by the present emzyme but actin was not. An RP-HPLC analysis after enzymic digestion of the polymerized a_sl -casein showed existence of the £-(y-Glu)Lys bond. Thus, it was confirmed that the polymerization was formed by a catalytic reaction of the transglutaminase.     

Gelation of Casein and Soybean Globulins by Transglutaminase

Guinea pig liver transglutaminase is a Ca²⁺ dependent enzyme which catalyzes the formation of inter- and intramolecular ε-(γ-glutamyl)lysyl cross-links between protein molecules. We have found that solutions of several proteins (α_s1-casein, and soybean 11S and 7S globulins) were gelatinized firmly by transglutaminase. The gel formation depended on the protein concentration. In the case of α_s1-casein, a reaction mixture containing below 2% was incapable of gelation. However, above 3%, a firm gel was formed by transglutaminase. As to soybean 11S and 7S globulins, reaction mixtures containing below 5% did not form gels, while, above 8%, firm gels were formed. The protein solutions in the presence of EDTA, an inhibitor of transglutaminase, were not gelatinized on treatment with transglutaminase. Thus, transglutaminase and a higher concentration of a substrate protein are indispensable for firm gel formation. It is supposed that the protein gels are formed through covalent bonds with transglutaminase.     

Flavonoids in Poncirus Hybrids

α_sl-Casein can be made either soluble or insoluble by adjusting the concentration of coexisting calcium ions. In this study, we tried to make a soluble-insoluble interconvertible enzyme through the formation of a conjugate of an enzyme and α_sl-casein using a heterobifunctional crosslinking reagent, N-succinimidyl 3-(2-pyridyldithio)propionate. The conjugate of phosphoglyceromutase and native α_s1-casein did not exhibit sufficient calcium-dependent precipitation. However, conjugates of enzymes (phosphoglyceromutase, enolase or peroxidase) and α_sl-casein polymerized by transglutaminase precipitated almost completely in the presence of more than 50 mM CaCl₂. Most of the enzyme conjugates precipitated as calcium caseinates could be solubilized reversibly with EDTA, without a significant loss of activity. A mixture of the enzyme ? polymerized α_s1-casein conjugates prepared with phosphoglyceromutase, enolase and pyruvate kinase could catalyze sequential reactions which convert d-3-phosphoglycerate into pyruvate with the same efficiency as a mixture of free enzymes. These results indicate that conjugates of enzymes and polymerized α_s1-casein can be useful as soluble-insoluble interconvertible enzymes.     

Crosslinking of Soybean 7S and 11S Proteins by Transglutaminase

Transglutaminase catalyzes the formation of intermolecular and intramolecular ε-(γ-glutamyl)lysyl crosslinks in proteins. The study here examined the substrate effectiveness of soybean 7S and 11S proteins in the intermolecular-crosslinking reaction catalyzed by guinea pig liver transglutaminase.

Both 7S and 11S proteins could act as the substrate for the transglutaminase reaction. The reaction with 11S protein was faster than that of 7S protein. Analyses of the reaction products by sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that three main subunit groups of 7S protein and two acidic subunit groups of 11S protein were polymerized through the formation of intermolecular crosslinks by transglutaminase. Interestingly enough, no intermolecular crosslink was formed between the basic subunits of 11S protein. The possible significance of the intermolecular crosslinking catalyzed by transglutaminase is discussed, including the use of this enzyme reaction to improve the properties of food protein.     

Formation of Pseudo- and Hybrid-11S Globulins from Subunits of Soybean and Broad Bean 11S Globulins

Pseudo- and hybrid-11S globulins were reconstituted from native acidic and basic subunits of soybean and broad bean 11S globulins. The subunit structures of these two globulins are known to be similar to each other. Pseudo-11S globulins were formed in combinations between glycinin acidic subunit (G-AS_{1 + 2}) and glycinin basic subunit (G-BS) and between legumin acidic subunit (L-ASII) and legumin basic subunit (L-BS). Hybrid-11S globulins were formed in combinations between G-AS_{1 + 2} and L-BS and between L-ASII and G-BS. The yields of the reconstituted 11S components of G-AS_{1 +2} + G-BS and G-AS_{1 + 2} + L-BS were lower than those of L-ASII + G-BS and L-ASII + L-BS. These pseudo- and hybrid-11S globulins were similar to native 11S globulins; they all consisted of reconstituted intermediary subunits which were composed of acidic and basic subunits linked by disufide bridges and had molecular weights similar to those of native 11S globulins. However, the dissociation-association behaviors of pseudo-glycinin and hybrid-11S globulins were different from those of native 11S globulins.     

Simultaneous Determination of Patulin and Penicillic Acid in Grains by Gas Chromatographic Method

Changes in aggregation and properties of alkali-treated soybean 7S and 11S globulins depend upon protein concentration during alkali-treatment. Such variables were investigated by viscosity, electrophoresis, circular dichroism, pulsed NMR, emulsion capacity and CaCl₂ precipitation measurements. In lower protein concentrations, the intrinsic viscosity decreased and the penetrative fractions into electrophoresis gel increased. The reduced contacts of proteins during neutralization resulted in smaller aggregates. Also specific fractions which were more sensitive to protein concentration on aggregation were observed for 11S globulin. The quantity of bound water depended only on pH at 7% concentration treatment. When the gel was formed, the bound water of protein increased, e.g., 0.085 g and 0.135 g/g protein at pH 10.6 and 13.2 treatment, respectively, whereas at 1% treatment, bound water showed almost no pH dependence (about 0.13 g/g protein). Furthermore, proteins prepared at higher protein concentrations were characterized by higher emulsion capacity and CaCI₂ precipitation ability. However, no protein concentration dependence was seen in the secondary structure of the aggregates.     

7S Globulins from Phaseolus vulgaris L.: Impact of Structural Aspects on the Nutritional Quality

7S globulins were extracted from common bean (Phaseolus vulgaris L.) seeds and characterized. SDS–PAGE showed major bands corresponding to the phaseolin subunits (43–53 kDa). An amino acid analysis indicated that, in spite of the limited amounts of sulphur amino acids and tryptophan, the globulins contained very high levels of essential amino acids. The protein solubility profiles of native and denatured (120 °C for 20 min) 7S globulins in water and in 0.5 M NaCl showed that NaCl had a limited effect on increasing the solubility of either the native or denatured proteins. The in vivo small intestinal digestibility of the 7S globulins was 90%, this being decreased to 86% after a thermal treatment. Fourier transform infrared spectroscopy revealed a high content of β-sheet and β-turn structures, together with a contribution at 1687 cm^?1 that was assigned to intramolecular β-sheets. These features are diagnostic of a high propensity to irreversible aggregation that may be related to an adverse effect on the protein quality.     

Isolation and Characterization of the Multiple 7S Globulins of Soybean Proteins

Two major proteins (the 7S and 11S globulins) of soybean (Glycine max) were simultaneously isolated by a simple method based on their different solubilities in dilute tris (hydroxymethyl) aminomethane buffers. The purified 7S globulins, which represented essentially the entire 7S soybean protein fraction capable of dimerization at 0.1 ionic strength, were fractionated into five components by diethylaminoethyl Sephadex A-50 column chromatography. The five 7S components were characterized by disc-electrophoresis.     

Whipping and Emulsifying Properties of Soybean Products

Both whipping and emulsifying properties, the characteristic functional properties of soybean products, were investigated by using the commercial products in Japan. Whipping properties of the soybean products, expressed by foam expansion and foam stability, were found to correlate with water dispersible nitrogen, and the resultant foams were stable when the dissolved proteins were native. Thus, the native defatted soybean flour which contained native and soluble protein exhibited excellent whipping property. Emulsifying properties correlated positively with protein and negatively with fiber contents. As soybean protein isolate and soybean protein extract are rich in protein and poor in fiber contents, both of them show good emulsifying functions.     

Acetylation of Amino Groups and Its Effect on the Structure of Soybean Glycinin

Purified soybean glycinin (11S globulin) was acetylated at three degrees; low (21-51%), middle (60-81%) and high (90-92%) acetylation in lysine residues. With increasing the acetyl content, the β-structure gradually decreased and the random structure increased resulting in the exposure of tyrosine residue. These were determined from the results of optical rotatory dispersion, intrinsic viscosity, ultraviolet and fluorescence measurement. Gel filtration, ultracentrifugation and gel electrophoresis studies showed drastic conformational changes of highly acetylated 11S (over 90%), in which most of the modified protein (75%) polymerized, and the other dissociated into 3S protein. The close relation between the conformation of acetylated 11S and its emulsifying properties was discussed.     

Photolysis of Aryl Glycosides with Ultraviolet Irradiation

Bovine casein components (α_sl-, β-, and κ-caseins) were chemically phosphorylated and the properties of the modified components were compared with those of the native to clarify the function of the intrinsic phosphate groups of casein components in casein micelle formation. The calcium binding ability of casein components increased after chemical phosphorylation. The concentrations of calcium chloride required to precipitate modified α_sl- and β-caseins were higher than those for native components. However, phosphorylation of α_sl- and β-caseins did not affect their properties of forming micelles through interaction with κ-casein. The stabilizing ability of κ-casein for α_sl- and β caseins was impaired by its phosphorylation, but the stability was recovered by treating phosphorylated κ-casein with phosphoprotein phosphatase. The results show that the phosphate content of κ-casein must be low to form a stable casein micelle. The results also explain why the specific phosphorylation of casein components in the mammary gland is required.     

Factors Influencing Conformation Changes in a 7S Protein of Soybean Globulins by Ultracentrifugal Investigations

Effects of pH, ionic strength, kind of salts and disulfide bond cleaving agent (2-mercaptoethanol) on conformation changes revealed on ultracentrifugal patterns of a 7S protein in soybean globulins were investigated. In the solution with lower pH than isoelectric point, this protein dissociated into two components in low ionic strength, but showed a 7S sedimentation pattern in higher ionic strength than 0.1. On the other hand, in the solution with higher pH than isoelectric point, this protoin showed aggregation to a 9S isomer in lower ionic strength than 0.1. Between ionic strength of 0.1 and 0.5, the mixture of 7S and 9S forms existed and in higher ionic strength than 0.5, the protein kept a 7S form stablely. These reactions were reversible and effect of 2-mercaptoethanol was scarcely observed but those of salts were observed.

The molecular weight of the 9S isomer was approximately 370,000 and the s_20,w value was 12.30S. Therefore, the 9S isomer was considered to be a dimer of the 7S protein.     

A Comparison of Soybean Globulins and the Protein Bodies in the Protein Composition

The protein compositions between soybean globulins and the protein bodies were compared by gel filtration with Sephadex G-200, sedimentation analyses and disc isoelectric focusing.

From the results of the three comparisons, it was difficult to find an essential difference in the protein compositions of the both. And, the 7S and the 11S globulins were the main components in the both. This fact was more strongly suggested that these globulins were the typical reserve proteins.     

Enzymatic Modification of Protein Functionality: Implantation of Potent Amphiphilicity to Succinylated Proteins by Covalent Attachment of Leucine Alkyl Esters

This work is a new attempt to modify the functionality of food proteins by the use of a potential activity of papain. Fish protein concentrate, soy protein isolate, casein, ovalbumin and gelatin were succinylated prior to using them as substrates. Each of the L-leucine n-alkyl esters with different alkyl-chain lengths was covalently incorporated into each substrate by applying the unusual papain-catalyzed reaction [Agric. Biol. Chem., 43, 1065 (1979)]. The resulting products posessed high whippability and/or emulsifying activity. The highest whippability was observed when leucine butyl ester or hexyl ester was incorporated, while the incorporation of higher alkyl esters generally caused an increase in emulsifying activity.     

Properties and applications of microbial transglutaminase

Some properties and applications of the transglutaminase (TGase) referred to as microbial TGase (MTGase), derived from a variant of Streptomyces mobaraensis (formerly classified as Streptoverticillium mobaraense), are described. MTGase cross-linked most food proteins, such as caseins, soybean globulins, gluten, actin, myosins, and egg proteins, as efficiently as mammalian TGases by forming an -(-glutamyl)lysine bond. However, unlike many other TGases, MTGase is calcium-independent and has a relatively low molecular weight. Both of these properties are of advantage in industrial applications; a number of studies have illustrated the potential of MTGase in food processing and other areas. The crystal structure of MTGase has been solved. It provides basic structural information on the MTGase and accounts well for its characteristics. Moreover, an efficient method for producing extracellular MTGase has been established using Corynebacterium glutamicum. MTGase may be expected to find many uses in both food and non-food applications.     

Ultrastructural localization of glycinin and β-conglycinin in Glycine max (soybean) cv. Maple Arrow by the immunogold method

Summary -Conglycinin (7S globulin) and glycinin (11S globulin) are the major reserve proteins of soybean. They were localized by the protein A immunogold method in thin sections of glycine max (soybean) cv. Maple Arrow. In cotyledons, both globulins were simultaneously present in all protein bodies. Statistical analysis of marking intensities indicated no correlation between globulin concentration and size of protein bodies. The immunogold method failed to detect either globulin in the embryonic axis and in cotyledons of four-day-old seedlings. Similar observations were made with cotyledons of two soy varieties lacking either the lectin or the Kunitz trypsin inhibitor. In another variety (T-102) lacking the lectin, the 7S globulin could not be detected.     

Mitochondrial Aconitase is a Transglutaminase 2 Substrate: Transglutamination is a Probable Mechanism Contributing to High-Molecular-Weight Aggregates of Aconitase and Loss of Aconitase Activity in Huntington Disease Brain

Transglutaminase activity was found to be present in highly purified non-synaptosomal rat brain mitochondria. A 78-kDa protein in these organelles was shown to be a transglutaminase 2 substrate, and incubation of a non-synaptosomal mitochondrial lysate with transglutaminase 2 yielded high-M_r proteins. The 78-kDa protein was identified as mitochondrial aconitase by MALDI-TOF analysis. Aconitase activity was decreased in a dose-dependent manner when non-synaptosomal rat brain mitochondria were incubated with transglutaminase 2. Transglutaminase activity is increased about 2-fold in the mitochondrial fraction of HD caudate. Moreover, Western blotting of the mitochondrial fraction revealed that most of the mitochondrial aconitase in HD caudate is present as high-M_r aggregates. Aconitase activity was previously shown to be decreased in Huntington disease (HD) caudate (a region severely damaged by the disease). The present findings suggest that an increase of transglutaminase activity in HD caudate may contribute to mitochondrial dysfunction by incorporating aconitase into inactive polymers.     

Identification of the 7S and 11S globulins as percutaneously sensitizing soybean allergens as demonstrated through epidermal application of crude soybean extract

Cutaneous exposure to food allergens can predispose individuals to food allergies. Soybean, a major allergenic food, is an ingredient in various cosmetic products. However, the types of soybean proteins that are percutaneously sensitizing in humans or animal models remain unknown. In this study, BALB/c mice were dorsally shaved and epicutaneously exposed to a crude soybean extract including sodium dodecyl sulfate or distilled water alone. Specific IgEs secreted in response to 7S globulin (Gly m 5), 11S globulin (Gly m 6), Gly m 3, and Gly m 4 were measured using enzyme-linked immunosorbent assays or immunoblots. Exposure to soybean extract elicited the secretion of soybean-specific IgEs. Of the soybean proteins, 7S and 11S globulins acted as percutaneous sensitizers in 6/9 mice (67%). Additionally, IgE bound specifically and preferentially to the 7S globulin β subunit. In conclusion, this is the first report to identify percutaneously sensitizing soybean allergens in a mouse model.     

Genetic mapping and validation of the loci controlling 7S α′ and 11S A-type storage protein subunits in soybean [<Emphasis Type="Italic">Glycine max</Emphasis> (L.) Merr.]

Key message

Four soybean storage protein subunit QTLs were mapped using bulked segregant analysis and an F₂ population, which were validated with an F₅ RIL population.

Abstract

The storage protein globulins β-conglycinin (7S subunit) and glycinin (11S subunits) can affect the quantity and quality of proteins found in soybean seeds and account for more than 70% of the total soybean protein. Manipulating the storage protein subunits to enhance soymeal nutrition and for desirable tofu manufacturing characteristics are two end-use quality goals in soybean breeding programs. To aid in developing soybean cultivars with desired seed composition, an F₂ mapping population (n = 448) and an F₅ RIL population (n = 180) were developed by crossing high protein cultivar ‘Harovinton’ with the breeding line SQ97-0263_3-1a, which lacks the 7S α′, 11S A₁, 11S A₂, 11S A₃ and 11S A₄ subunits. The storage protein composition of each individual in the F₂ and F₅ populations were profiled using SDS-PAGE. Based on the presence/absence of the subunits, genomic DNA bulks were formed among the F₂ plants to identify genomic regions controlling the 7S α′ and 11S protein subunits. By utilizing polymorphic SNPs between the bulks characterized with Illumina SoySNP50K iSelect BeadChips at targeted genomic regions, KASP assays were designed and used to map QTLs causing the loss of the subunits. Soybean storage protein QTLs were identified on Chromosome 3 (11S A₁), Chromosome 10 (7S α′ and 11S A₄), and Chromosome 13 (11S A₃), which were also validated in the F₅ RIL population. The results of this research could allow for the deployment of marker-assisted selection for desired storage protein subunits by screening breeding populations using the SNPs linked with the subunits of interest.

     

Purification and Properties of meso-α,∊-Diaminopimelate Decarboxylase from Bacillus sphaericus

Soybean 7S and 11S globulins were stored at relative humidities (RHs) of 11% and 96% at 50°C. The redispersibility of the proteins at RH 96% decreased in a short time. However, it did not decrease, when stored for 45 days at RH 11%. Gel filtration showed that the proteins polymerized during storage. The effects of urea, sodium dodecyl sulfate (SDS) and 2-mercaptoethanol (2-ME) on the redispersibilities of the proteins at RH 96% showed that the hydrogen, hydrophobic and disulfide bonds participate in the polymerization of 7S globulin, and that the disulfide bond is strongly related to the polymerization of 11S globulin. Redispersibility was restored with 2-ME in both the 7S and 11S globulins and some of the proteins in the supernatant redispersed with 2-ME were observed to be similar to the native ones with respect to the gel filtration, electrophoretic behavior and circular dichroism spectrum.