The glycinin Gy3 gene from soybean

Structural and functional analysis of various globulin proteins from soy seed

Storage proteins of soybean mostly consist of globulins, which are classified according to their sedimentation coefficient. Among 4 major types: 2S, 7S, 11S, and 15S of globulins, 7S and 11S constitute major fraction. The 11S fraction consists only of glycinin and 7S fraction majorly consists of β-conglycinin, small amounts of γ-conglycinin and basic 7S globulin (Bg7S). Glycinin exist as a hexamer while β-conglycinin as a trimer and Bg7S as a tetramer. Glycinin subunits are coded by 5 genes of a family, whereas about 15 genes are present for β-conglycinin subunits. Bg7S gene is present in four copies in soybean genome. Synthesis of all proteins takes place as a single polypeptide chain, which is cleaved after folding to yield different chains or subunits. Glycinin and β-Conglycinin are made for storage purpose. However, Bg7S has potential xylanase inhibition activity and protein kinase activity. Primary structure of Bg7S reveals 12 conserved cysteine residues involved in forming 6 disulfide bonds, which provides appreciable stability to protein. Secondary structure is predominately rich in β-sheets with few alpha helices. Bg7S shares structural similarity with various aspartic-proteases. In this review, our aim is to discuss sequence, structure, and function of various globulins present in Glycine max.

In vitro and in situ antimicrobial action and mechanism of glycinin and its basic subunit

Glycinin, basic subunit and β-conglycinin were isolated from soybean protein isolate and tested for their antimicrobial action against pathogenic and spoilage bacteria as compared to penicillin. The three fractions exhibited antibacterial activities equivalent to or higher than penicillin in the next order; basic subunit>glycinin>β-conglycinin with MIC of 50, 100 and 1000 μg/mL, respectively. The IC(50%) values of the basic subunit, glycinin and β-conglycinin against Listeria\monocytogenes were 15, 16 and 695 μg/mL, against Bacillussubtilis were 17, 20, and 612 μg/mL, and against S. Enteritidis were 18, 21 and 526 μg/mL, respectively. Transmission electron microscopy images of L. monocytogenes and S. Enteritidis exhibited bigger sizes and separation of cell wall from cell membrane when treated with glycinin or basic subunit. Scanning electron microscopy of B. subtilis indicated signs of irregular wrinkled outer surface, fragmentation, adhesion and aggregation of damaged cells or cellular debris when treated with glycinin or the basic subunits but not with penicillin. All tested substances particularly the basic subunit showed increased concentration-dependent cell permeation assessed by crystal violet uptake. The antimicrobial action of glycinin and basic subunit was swifter than that of penicillin. The cell killing efficiency was in the following descending order; basic subunit>glycinin>penicillin>β-conglycinin and the susceptibility of the bacteria to the antimicrobial agents was in the next order: L. monocytogenes>B. Subtilis>S. Enteritidis. Adding glycinin and the basic subunit to pasteurized milk inoculated with the three bacteria; L. monocytogenes, B. Subtilis and S. Enteritidis (ca. 5 log CFU/mL) could inhibit their propagation after 16-20 days storage at 4 °C by 2.42-2.98, 4.25-4.77 and 2.57-3.01 log and by 3.22-3.78, 5.65-6.27 and 3.35-3.72 log CFU/mL, respectively.

Morphology and phase separation of hydrophobic clusters of soy globular protein polymers

Protein hydrophobic interaction has been considered the most important factor dominating protein folding, aggregation, gelling, self-assembly, adhesion, and cohesion properties. In this paper, morphology and phase separation of hydrophobic clusters, networks, and aggregates of soy globular protein polymers, induced by using a reducing agent (NaHSO3), are studied using microscopic instruments. The morphology and phase separation of these hydrophobic clusters are sensitive to protein structure and composition, pH, and ionic-strength (I(m)). Most of the clusters are in spherical-shape architecture and mainly consist of hydrophobic polypeptides. Rod-shape clusters were also observed at higher ionic strength, and mainly consist of hydrophilic polypeptides. The ratio of hydrophobic/hydrophilic (HB/HL) polypeptides is important to facilitate the formation of clusters in an environment with a certain pH value and ionic strength. At HB/HL 0.8, uniform spherical clusters were observed and diameters ranged from 30 to 70 nm. At HB/HL <0.8, large spherical clusters were formed with diameters ranging from 100 to 1,000 nm, and at HB/HL >or=1.8, large hydrophobic aggregates formed, and size of aggregates can be up to 2 500 nm. When solid content increased from 3% to 38%, at I(m) or= 0.115 mol x L(-1), HB/HL ratio >or=1.8, the large aggregates became very cohesive and viscoelastic. Clear phase separation was observed during curing between hydrophobic and hydrophilic protein polymers. Phase-separation degree increased as HB/HL ratio increased.

Glutamine in commercial liquid nutritional products

Total glutamine concentrations in commercial nutritional products have been determined by enzymatic hydrolysis followed by HPLC quantification of free glutamine and free pyroglutamic acid. Hydrolysis was accomplished by a published three-enzyme (Pronase, leucine aminopeptidase, prolidase), 20-h/37 degrees C digestion. Glutamine was determined as its FMOC derivative by reverse phase HPLC-fluorescence, and pyroglutamic acid was determined directly by organic acid HPLC-UV. Approximately 4.11% of the released glutamine is converted to pyroglutamic acid during the 20-h digestion. Experimental ratios of enzyme hydrolysis glutamine to acid hydrolysis glutamic acid + glutamine + pyroglutamic acid (GLX) indicate that the method recovers >90% of the protein-bound glutamine. The nutritional products with casein dominant intact protein systems typically deliver >9 g of glutamine/100 g of protein, or approximately 40 g of glutamine/100 g of GLX.

Differences in denaturation of genetic variants of soy glycinin

In heat denaturation studies conducted in the past the genetic variants of glycinin have been considered as a homogeneous group of proteins. In this work the validity of this assumption was tested. It was found by calorimetric studies that glycinin denatures heterogeneously at pH 7.6. When the temperature of isothermal treatment is increased from 70 to 82 degrees C the proportion of glycinin remaining native progressively decreases from 95% to 5% while the denaturation temperature of the glycinin remaining native increases from 88.5 to 95 degrees C. Similar trends were found for pH 3.8. Fractionation and subsequent analysis (MALDI-TOF and CE) of isothermally treated samples demonstrated that at pH 7.6 the heterogeneous denaturation is caused by differences in thermal stability of the genetic variants of glycinin. The stability increases in the order G2/G3/G1< A(4)< G5 < G4.

Introduction of a low molecular weight agonist peptide for complement C3a receptor into soybean proglycinin A1aB1b subunit by site-directed mutagenesis

LPLPR, a complement C3a agonist peptide, with hypocholesterolemic activity was introduced into the homologous site of soybean proglycinin A1aB1b subunit by site-directed mutagenesis. This modified proglycinin was expressed in E. coli and recovered from the insoluble fraction. LPLPR was released by the action of chymotrypsin and trypsin as expected. Furthermore, two peptides (RPSYLPLPR and PSYLPLPR) with extended sequence at the amino-terminus of LPLPR were obtained. Their ileum-contracting activity was 9 to approximately 13 times stronger than that of LPLPR. The overall yields of purified LPLPR, RPSYLPLPR and PSYLPLPR were 25%, 12%, and 0.7% respectively.

Introduction of enterostatin (VPDPR) and a related sequence into soybean proglycinin A1aB1b subunit by site-directed mutagenesis

Enterostatin (VPDPR), having anoretic and hypocholesterolemic activities, and its homologue LPYPR, a hypocholesterolemic peptide found in the glycinin A5A4B3 subunit, were introduced into the corresponding site (TNGPQ) of the proglycinin A1aB1b subunit by site-directed mutagenesis. Modified proglycinins were expressed in E. coli and recovered from the insoluble fraction. VPDPR and LPYPR were released by the action of chymotrypsin and trypsin as expected. The overall yields of purified VPDPR and LPYPR were 40% and 62%, respectively.

Soy glycinin: influence of pH and ionic strength on solubility and molecular structure at ambient temperatures

This study describes the relationship between the solubility of glycinin, a major soy protein, and its structural properties at a quaternary, tertiary, and secondary folding level under conditions representative for food products. When the ionic strength is lowered from 0.5 to 0.2 or 0.03, the basic polypeptides shift more to the exterior of the glycinin complex, as determined at pH 7.6 by labeling solvent-exposed lysines, supported by the study of the proteolytic action of clostripain on glycinin. This structural reorganization caused the pH of minimal solubility to shift to higher values. Ultracentrifugational analysis shows that at pH 7.6 and an ionic strength of 0.5 glycinin forms hexameric complexes (11S), whereas at pH 3.8 and at an ionic strength of 0.03 glycinin exists as trimers (7S). Intermediate situations are obtained by modulation of pH and ionic strength. The observed quaternary dissociation correlates with an increased amount of nonstructured protein at a secondary level and with changes in tertiary folding as determined using circular dichroism. Tryptophan fluorescence shows no significant structural changes for different ionic strengths but demonstrates a more tightly packed fluorophore environment when the pH is lowered from 7.6 to 3.8.