Disruption of a licorice cellulose synthase-derived glycosyltransferase gene demonstrates its in planta role in soyasaponin biosynthesis

KEY MESSAGE

CRISPR-Cas9-mediated disruption of a licorice cellulose synthase-derived glycosyltransferase gene, GuCSyGT, demonstrated the in planta role of GuCSyGT as the enzyme catalyzing 3-O-glucuronosylation of triterpenoid aglycones in soyasaponin biosynthesis. Triterpenoid glycosides (saponins) are a large, structurally diverse group of specialized metabolites in plants, including the sweet saponin glycyrrhizin produced by licorice (Glycyrrhiza uralensis) and soyasaponins that occur widely in legumes, with various bioactivities. The triterpenoid saponin biosynthetic pathway involves the glycosylation of triterpenoid sapogenins (the non-sugar part of triterpenoid saponins) by glycosyltransferases (GTs), leading to diverse saponin structures. Previously, we identified a cellulose synthase-derived GT (CSyGT), as a newly discovered class of triterpenoid GT from G. uralensis. GuCSyGT expressed in yeast, which could transfer the sugar glucuronic acid to the C3 position of glycyrrhetinic acid and soyasapogenol B, which are the sapogenins of glycyrrhizin and soyasaponin I, respectively. This suggested that GuCSyGT is involved in the biosynthesis of glycyrrhizin and soyasaponin I. However, the in planta role of GuCSyGT in saponin biosynthesis remains unclear. In this study, we generated GuCSyGT-disrupted licorice hairy roots using CRISPR-Cas9-mediated genome editing and analyzed the saponin content. This revealed that soyasaponin I was completely absent in GuCSyGT-disrupted lines, demonstrating the in planta role of GuCSyGT in saponin biosynthesis.

The discovery of novel SNPs associated with group A soyasaponin biosynthesis from Korea soybean core collection

Soyasaponin is a type of glycoside such as steroids, steroidal alkaloids or triterpenes, which enhance the body immunity. In order to efficiently identify genes and markers related to the soyasaponin, we used a 180K Axiom® SoyaSNP array and whole genome resequencing data from the Korean soybean core collection. As a result of conducting GWAS for group A soyasaponin (Aa and Ab derivatives), 16 significant common markers associated with Aa and Ab derivatives were mapped to chromosome 7, and three candidate genes including Glyma.07g254600 were detected. The functional haplotypes for candidate genes showed that Aa and Ab contents were mainly determined by alleles of AX-90322128, the marker of Glyma.07g254600. In addition, 14 novel SNPs variants closely associated with Aa and Ab derivatives were discovered for Glyma.07g254600. Therefore, the results of this study that identified soyasaponin-associated markers and useful genes utilizing various genomic information could provide insight into functional soybean breeding.

Mechanism of interactions between soyasaponins and soybean 7S/11S proteins

In this study, the proteins glycinin (11S) and β-conglycinin (7S) were mixed with soyasaponin (Ssa) Ab/Bb to form a composite system. We used fluorescence and synchronous fluorescence spectra to demonstrate the changes in the surrounding environment and the structure of the proteins. Dynamic interface behavior analysis showed the possible interface behavior induced by the composite system. The interactions between Ssa and the proteins, along with the mode of action, were analyzed by molecular docking. The interactions between Ssa and soy protein increased with the change in concentration. The interactions between the two proteins were mediated by tryptophan (Trp) and primarily involved hydrogen bonds, which changed the microenvironment and loosened the protein structure. These results helped in understanding the mechanism underlying the interactions between Ssa Ab/Bb and 7S/11S. Furthermore, these results highlighted the theoretical fundamentals for the future applications of composite systems as surfactants in the food industry.

Soy glycinin-soyasaponin mixtures at oil-water interface: Interfacial behavior and O/W emulsion stability

Soy glycinin (11S) was mixed with soyasaponin (Ssa) to elucidate the mechanism(s) involved in the stabilization of emulsions by mixed systems based on dynamic interfacial tension and dilatational rheology at the oil-water interface. The short/long-term properties of oil-in-water emulsions stabilized by 11S-Ssa mixtures included droplet-size distribution, droplet ζ-potential, microstructure, and Turbiscan stability index. The combination of Ssa (0.05%) with 11S significantly affected the interfacial dilatational and emulsion properties although the interfacial properties were still dominated by the protein. Higher concentrations (0.1% and 0.2%) of Ssa combined with 11S synergistically decreased the interfacial tension, which was attributed to the interaction between 11S and Ssa. Using high Ssa concentrations (0.25%-0.5%) enhanced the long-term stability of emulsions (in response to external deformations) after 42 d. These results will aid the basic understanding of protein-Ssa interfacial adsorption during emulsion formation and can help prepare natural food additives for designing emulsions.

Soyasaponins reduce inflammation by downregulating MyD88 expression and suppressing the recruitments of TLR4 and MyD88 into lipid rafts

Background

Previous studies indicate that soyasaponins may reduce inflammation via modulating toll-like receptor 4 (TLR4)/myeloid differentiation factor 88 (MyD88) signaling. However, its underlying mechanisms are still not fully understood.

Methods

Lipopolysaccharide (LPS)-challenged inflamed male ICR mice were intervened by intragastrical administration with 10 and 20 μmol/kg·BW of soyasaponin A₁, A₂ or I for 8 weeks. The serum inflammatory markers were determined by commercial kits and the expression of molecules in TLR4/MyD88 signaling pathway in liver by real-time PCR and western blotting. The recruitments of TLR4 and MyD88 into lipid rafts of live tissue lysates were detected by sucrose gradient ultracentrifugation and western blotting. LPS-stimulated RAW264.7 macrophages were treated with 10, 20 and 40 μmol/L of soyasaponin A₁, A₂ or I for 2 h. MyD88-overexpressed HEK293T cells were treated with 20 and 40 μmol/L of soyasaponins (A₁, A₂ or I) or 20 μmol/L of ST2825 (a MyD88 inhibitor) for 6 h. The expression of molecules in TLR4/MyD88 signaling pathway were determined by western blotting. Data were analyzed by using one way analysis of variance or t-test by SPSS 20.0 statistical software.

Results

Soyasaponins A₁, A₂ or I significantly reduced the levels of tumor necrosis factor alpha (TNFα), interleukin (IL)-6 and nitric oxide (NO) in serum (p < 0.05), and decreased the mRNA levels of TNFα, IL-6, IL-1β, cyclooxygenase 2 (COX-2) and inducible nitric oxide synthase (iNOS) (p < 0.05), the protein levels of myeloid differentiation protein 2 (MD-2), TLR4, MyD88, toll-interleukin1 receptor domain containing adaptor protein (TIRAP), phosphorylated interleukin-1 receptor-associated kinase 4 (p-IRAK-4), phosphorylated interleukin-1 receptor-associated kinase 1 (p-IRAK-1) and TNF receptor associated factor 6 (TRAF6) (p < 0.05), and the recruitments of TLR4 and MyD88 into lipid rafts in liver (p < 0.05). In LPS-stimulated macrophages, soyasaponins A₂ or I significantly decreased MyD88 (p < 0.05), soyasaponins A₁, A₂ or I reduced p-IRAK-4 and p-IRAK-1 (p < 0.05), and soyasaponin I decreased TRAF6 (p < 0.05). In MyD88-overexpressed HEK293T cells, soyasaponins (A₁, A₂ or I) and ST2825 significantly decreased MyD88 and TRAF6 (p < 0.05).

Conclusion

Soyasaponins can reduce inflammation by downregulating MyD88 expression and suppressing the recruitments of TLR4 and MyD88 into lipid rafts. This study provides novel understanding about the anti-inflammatory mechanism of soyasaponins.

Interaction between soyasaponin and soy β-conglycinin or glycinin: Air-water interfacial behavior and foaming property of their mixtures

The interaction between soyasaponin and soy β-conglycinin (7S) or glycinin (11S), adsorption of their mixtures at air-water interface, and foaming properties of the mixed system were investigated in this study. Fluorescence spectroscopy results showed that there was a weak binding of soyasaponin with 7S or 11S in bulk solutions, leading to the conformational changes of protein by nonspecific hydrophobic interactions. Dynamic surface properties of soyasaponin-7S/11S mixtures indicated that the composite layers formed via their weak interactions due to the synergy of reducing surface tension and the plateau of elasticity at the interface. Most mixtures represented high foam forming ability and stability except 0.2 % soyasaponin mixture, which could be a consequence that the surface behavior was dominated by soyasaponin under this concentration, and low surface elasticity lead to a less stable interfacial film. Overall, foamability of soyasaponin-7S mixtures were better than 11S ones. All data of this work was helpful to understand air-water behaviors of soyasaponin-7S/11S mixtures. This mixed system has shown good potential for further foam related industrial applications.

Anti-inflammatory effects of soyasapogenol I-αa via downregulation of the MAPK signaling pathway in LPS-induced RAW 264.7 macrophages

The crude extract of soyasaponins was reported to possess anti-inflammatory activity. We determined the new purity group I saponin, I-αa and I-γa that was isolated from wild soybean (Glycine soja) in terms of its efficacy in protecting RAW 264.7 macrophages from lipopolysaccharide (LPS)-stimuli. Cells were treated with soyasaponin I-αa/I-γa (30-300 μΜ) and LPS (0.1 μg/mL) for 24 h. Soyasaponin I-αa inhibited nitric oxide (NO) production at 100 μg/mL, while soyasaponin I-γa demonstrated this effect at a higher concentration (200 μg/mL). The expression levels of iNOS and COX-2 enzymes were downregulated by both soyasaponins. Soyasaponin I-αa exerted its effect via the TNF-α and IL-1β cytokines. However, soyasaponin I-γa only inhibited the expression of TNF-α. The inflammatory effect of group I soyasaponin was mainly mediated via the phosphorylation of the p38 and JNK proteins. Collectively, these results suggested the potential anti-inflammatory effects of soyasaponins.

Rapid characterization of metabolites in soybean using ultra high performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (UPLC-ESI-Q-TOF-MS/MS) and screening for α-glucosidase inhibitory and antioxidant properties through different solvent systems

This work was the first to investigate on the simultaneous characterization of metabolite profiles in soybean using UPLC-ESI-Q-TOF-MS/MS. Twenty two compositions were observed within 14 min from the methanol extract and confirmed as twelve isoflavones of three types and ten soyasaponins (Ab, Af, I-III, αg, βg, βa, γg, and γa). Moreover, the patterns of two chemicals showed considerable differences in seven solvent systems by HPLC analysis and their optimal extraction was achieved by 70% methanol (isoflavone: 4102.69 μg/g; soyasaponin: ten peaks). The second abundant isoflavones were detected in 50% methanol (4054.39 μg/g), followed by 30% methanol, 100% methanol, 10% methanol, CH2Cl2, and acetone extracts with 3134.03, 2979.49, 1681.33, 366.19, and 119.00 μg/g, respectively. Soyasaponins exhibited similar tendencies as those of isoflavones. The highest total phenolic was found as 2.10 ± 0.05 mg GAE/g in 70% methanol with remarkable differences by comparing other extracts. Specifically, this extract showed potent α-glucosidase inhibitory (81%) and antioxidant capacities (DPPH: 93% and ABTS: 95%) at a concentration of 1.0 mg/mL. Our results may be contributed to enhancing the value to functional foods and evaluating the secondary metabolites concern to antioxidant properties using solvent system in soybean.

Effects of fermentation on the phytochemical composition and antioxidant properties of soy germ

Soy germ is a remarkable source of bioactive phytochemicals offering an interesting alternative as starting ingredient for fermented food. This work aimed to determine whether lactic acid bacteria fermentation of soy germ induces changes on its phytochemical composition. The antioxidant properties of fermented soy germ samples periodically taken during the fermentation process were evaluated and correlated with the concentration and structural modifications of isoflavones, saponins, phytosterols and tocopherols. Fermented soy germ extracts exhibited a higher inhibition effect against the superoxide anion radical, and lesser but significant ferric-reducing and DPPH radical scavenging effects compared with raw soy germ. By comparison to the traditional whole seed-based products, soy germ exhibits higher levels of isoflavones, saponins, phytosterols and tocopherols. All these phytochemicals contributed to the antioxidant capacity of soy germ and were conserved under lactic acid bacteria fermentation.