Characterization of a GH3 family β-glucosidase from Dictyoglomus turgidum and its application to the hydrolysis of isoflavone glycosides in spent coffee grounds

Development of a Zn-Based Single-Atom Nanozyme for Efficient Hydrolysis of Glycosidic Bonds

Hydrolytic enzymes are essential components in second-generation biofuel technology and food fermentation processes. Nanozymes show promise for large-scale industrial applications as replacements for natural enzymes due to their distinct advantages. However, there remains a research gap concerning glycosidase nanozymes. In this study, a Zn-based single-atom nanozyme (ZnN4-900) is developed for efficient glycosidic bond hydrolysis in an aqueous solution. The planar structure of the class-porphyrin N4 material approximatively mimicked the catalytic centers of natural enzymes, facilitating oxidase-like (OXD-like) activity and promoting glycosidic bond cleavage. Theoretical calculations show that the Zn site can act as Lewis acids, attacking the C─O bond in glycosidic bonds. Additionally, ZnN4-900 has the ability to degrade starch and produce reducing sugars that increased yeast cell biomass by 32.86% and ethanol production by 14.56%. This catalyst held promising potential for enhancing processes in ethanol brewing and starch degradation industries.

Preparation of in vivo intermediate metabolites of soybean saponins with improved bioactivity by in vitro deacetylation and deglucosylation

Unlike natural soyasaponins and their aglycones formed by enzymatic hydrolysis in the human intestine, in vivo intermediate soyasaponin metabolites are difficult to prepare. Therefore, the pharmacological activities of in vivo intermediate soyasaponins remain uninvestigated. Herein, in vivo intermediate soyasaponins with purities of >90% were prepared by in vitro deacetylation (alkaline treatment) and deglucosylation (β-glucosidase treatment) of natural soyasaponins using preparative high-performance liquid chromatography. These compounds exhibited higher anti-inflammatory and antioxidant activities than natural soyasaponins in in vitro bioassays, suggesting that the intermediate soyasaponins can be used as improved bioactive food supplements. To the best of our knowledge, this is the first study reporting the in vitro preparation and bioassays of in vivo intermediate soyasaponin metabolites formed in the human intestine.

Exploring the diversity of β-glucosidase: Classification, catalytic mechanism, molecular characteristics, kinetic models, and applications

High-value chemicals and energy-related products can be produced from biomass. Biorefinery technology offers a sustainable and cost-effective method for this high-value conversion. β-glucosidase is one of the key enzymes in biorefinery processes, catalyzing the production of glucose from aryl-glycosides and cello-oligosaccharides via the hydrolysis of β-glycosidic bonds. Although β-glucosidase plays a critical catalytic role in the utilization of cellulosic biomass, its efficacy is often limited by substrate or product inhibitions, low thermostability, and/or insufficient catalytic activity. To provide a detailed overview of β-glucosidases and their benefits in certain desired applications, we collected and summarized extensive information from literature and public databases, covering β-glucosidases in different glycosidase hydrolase families and biological kingdoms. These β-glucosidases show differences in amino acid sequence, which are translated into varying degrees of the molecular properties critical in enzymatic applications. This review describes studies on the diversity of β-glucosidases related to the classification, catalytic mechanisms, key molecular characteristics, kinetics models, and applications, and highlights several β-glucosidases displaying high stability, activity, and resistance to glucose inhibition suitable for desired biotechnological applications.

Spent coffee grounds and its antioxidant dietary fiber promote different colonic microbiome signatures: Benefits for subjects with chronodisruption

Chronodisruption, commonly displayed by people living with obesity (PLO), is linked to colonic microbiota dysbiosis, and may increase the risk of many chronic non-communicable diseases, whereas dietary interventions-called chrononutrition may mitigate it. We evaluated the in vitro effects of spent coffee grounds (SCG), and their antioxidant dietary fiber (SCG-DF) on the colonic microbiota of an obese donor displaying dysbiosis and chronodisruption. Basal microbiota pattern was associated with an increased risk of non-communicable chronic diseases. Both samples decrease species richness and increase microbiota diversity (p < 0.05; Chao and Shannon index, respectively), positively enhancing Firmicutes/Bacteroidetes index (SCG, p < 0.04; SCG-DF, p < 0.02). SCG and SCG-DF modulated the microbiota, but SCG-DF induced greater changes, significantly increasing. p_Actonobacterias (SCG p < 0.04; SCG-DF, p < 0.02), and reducing g_Alistipes; s_putredinis, g_Prevotella;s_copri. The highest increase was displayed by p_Proteobacteria (f_Desulfovibrionaceae and f_Alcanigenaceae, p < 0.05), while g_Haemophilus; s_parainfluenzae decreased (p < 0.05). However, neither SCG nor SCG-DF modulated g_Alistipes (evening-type colonic microbial marker) beneficially. SCG and SCG-DF reduced (p < 0.05) g_Lachnospira, a microbial evening-type marker, among other microbial populations, of an obese donor displaying chronodisruption and dysbiosis. SCG and SCG-DF displayed a prebiotic effect with the potential to mitigate diseases linked to chronodisruption.

Biochemical characteristics of Myceliophthora thermophila recombinant β-glucosidase (MtBgl3c) applicable in cellulose bioconversion

The GH3 β-glucosidase gene of Myceliophthora thermophila (MtBgl3c) has been cloned and heterologously expressed in E. coli for the first time. This study highlights the important characteristics of recombinant MtBgl3c (rMtBgl3c) which make it a promising candidate in industrial applications. Optimization of the production of rMtBgl3c led to 28,000 U L-1. On purification, it has a molecular mass of ∼100 kDa. It is a broad substrate specific thermostable enzyme that exhibits pH and temperature optima at 5.0 and 55 °C, respectively. The amino acid residues Asp287 and Glu514 act as nucleophile and catalytic acid/base, respectively in the enzyme catalysis. Its low Km value (1.28 mM) indicates a high substrate affinity as compared to those previously reported. The rMtBgl3c displays a synergistic action with the commercial enzyme cocktail in the saccharification of sugarcane bagasse suggesting its utility in the cellulose bioconversion. Tolerance to solvents, detergents as well as glucose make this enzyme applicable in wine, detergent, paper and textile industries too.

A review on applications of β-glucosidase in food, brewery, pharmaceutical and cosmetic industries

β-glucosidases hydrolyse glycosidic bonds to release non-reducing terminal glucosyl residues from glycosides and oligosaccharides via catalytic mechanisms. It is very well known that the β-glucosidase enzyme is used in biorefineries for cellulose degradation, where β-glucosidases is the rate-limiting enzyme for the final glucose production from cellobiose. The β-glucosidase enzyme is used as a catalyst in other industrial sectors, including pharmaceuticals, breweries, dairy, and food processing. With the aid of β-glucosidase enzymes, cyanogenic glycosides and plant glycosides are transformed into sugar moiety and aglycones. These aglycone compounds are employed as aromatic compounds in the food processing and brewing industries. They are also used as medications and dietary supplements based on their pharmacological qualities. Applications of aglycones and the microbiological sources of β-glucosidase in aglycone production have been discussed in this review.

Production of Daidzein and Genistein from Seed and Root Extracts of Korean Wild Soybean (Glycine soja) by Thermostable β-Galactosidase from Thermoproteus uzoniensis

Isoflavone glycosides are commonly biotransformed into isoflavone aglycones due to the superior biological activities of the latter. Wild soybeans contain a higher isoflavone content than domesticated soybeans due to their high level of genetic diversity. In this study, we cloned and characterized a thermostable β-galactosidase from the extreme thermophile Thermoproteus uzoniensis for potential application in isoflavone conversion in Korean wild soybeans. The purified recombinant enzyme exhibited a maximum specific activity of 1103 μmol/min/mg at pH 5.0 and 90 °C with a half-life of 46 h and exists as a homodimer of 113 kDa. The enzyme exhibited the highest activity for p-nitrophenyl (pNP)-β-D-galactopyranoside among aryl glycosides and it hydrolyzed isoflavone glycosides in the order genistin > daidzin > ononin > glycitin. The enzyme completely hydrolyzed 2.77 mM daidzin and 3.85 mM genistin in the seed extract of wild soybean after 80 and 70 min with productivities of 1.86 and 3.30 mM/h, respectively, and 9.89 mM daidzin and 1.67 mM genistin in the root extract after 180 and 30 min, with the highest productivities of 3.30 and 3.36 mM/h, respectively, compared to other glycosidases. Our results will contribute to the industrial production of isoflavone aglycone using wild soybean and this is the first report on the enzymatic production of isoflavone aglycones from isoflavone glycosides in wild soybeans.

Discovery of novel glycoside hydrolases from C-glycoside-degrading bacteria using sequence similarity network analysis

C-Glycosides are an important type of natural product with significant bioactivities, and the C-glycosidic bonds of C-glycosides can be cleaved by several intestinal bacteria, as exemplified by the human faeces-derived puerarin-degrading bacterium Dorea strain PUE. However, glycoside hydrolases in these bacteria, which may be involved in the C-glycosidic bond cleavage of C-glycosides, remain largely unknown. In this study, the genomes of the closest phylogenetic neighbours of five puerarin-degrading intestinal bacteria (including Dorea strain PUE) were retrieved, and the protein-coding genes in the genomes were subjected to sequence similarity network (SSN) analysis. Only four clusters of genes were annotated as glycoside hydrolases and observed in the genome of D. longicatena DSM 13814^T (the closest phylogenetic neighbour of Dorea strain PUE); therefore, genes from D. longicatena DSM 13814^T belonging to these clusters were selected to overexpress recombinant proteins (CG1, CG2, CG3, and CG4) in Escherichia coli BL21(DE3). In vitro assays indicated that CG4 efficiently cleaved the O-glycosidic bond of daidzin and showed moderate β-D-glucosidase and β-D-xylosidase activity. CG2 showed weak activity in hydrolyzing daidzin and pNP-β-D-fucopyranoside, while CG3 was identified as a highly selective and efficient α-glycosidase. Interestingly, CG3 and CG4 could be selectively inhibited by daidzein, explaining their different performance in kinetic studies. Molecular docking studies predicted the molecular determinants of CG2, CG3, and CG4 in substrate selectivity and inhibition propensity. The present study identified three novel and distinctive glycoside hydrolases, highlighting the potential of SSN in the discovery of novel enzymes from genomic data.

Characterization of a novel isoflavone glycoside-hydrolyzing β-glucosidase from mangrove soil metagenomic library

For the beneficial pharmacological properties of isoflavonoids and their related glycoconjugates, there is increasingly interest in their enzymatic conversion. In this study, a novel β-glucosidase gene isolated from metagenomic library of mangrove sediment was cloned and overexpressed in Escherichia coli BL21(DE3). The purified recombination β-glucosidase, designated as r-Bgl66, showed high catalytic activity for soy isoflavone glycosides. It converted soy isoflavone flour extract with the productivities of 0.87 mM/h for daidzein, 0.59 mM/h for genistein and 0.42 mM/h for glycitein. The kcat/Km values for daidzin, genistin and glycitin were 208.73, 222.37 and 288.07 mM-1 s-1, respectively. In addition, r-Bgl66 also exhibited the characteristic of glucose-tolerance, and the inhibition constant Ki was 471.4 mM. These properties make it a good candidate in the enzymatic hydrolysis of soy isoflavone glycosides. This study also highlights the utility of metagenomic approach in discovering novel β-glucosidase for soy isoflavone glycosides hydrolysis.

Unconventional β-Glucosidases: A Promising Biocatalyst for Industrial Biotechnology

β-Glucosidases primarily catalyze removal of terminal glucosyl residues from a variety of glucoconjugates and also perform transglycosylation and reverse hydrolysis. These catalytic properties can be readily exploited for degradation of lignocellulosic biomass as well as for pharmaceutical, food and flavor industries. β-Glucosidases have been either isolated in the native form from the producer organism or recombinantly expressed and gaged for their biochemical properties and substrate specificities. Although almond and Aspergillus niger have been instantly recognizable sources of β-glucosidases utilized for various applications, an intricate pool of novel β-glucosidases from different sources can provide their potent replacements. Moreover, one can envisage the better efficacy of these novel candidates in biofuel and biorefinery industries facilitating efficient degradation of biomass. This article reviews properties of the novel β-glucosidases such as glucose tolerance and activation, substrate specificity, and thermostability which can be useful for their applications in lignocellulose degradation, food industry, and pharmaceutical industry in comparison with the β-glucosidases from the conventional sources. Such β-glucosidases have potential for encouraging white biotechnology.

Characterization of a GH3 halophilic β-glucosidase from Pseudoalteromonas and its NaCl-induced activity toward isoflavones

A novel β-glucosidase gene was isolated from Pseudoalteromonas sp. GXQ-1 and heterologously expressed in Escherichia coli. The activity of the encoded enzyme, PABGL, toward p-nitrophenyl-β-D-glucopyranoside was increased 8.74-fold by the presence of 3 M NaCl relative to the absence of added NaCl. PABGL hydrolyzed a variety of soy isoflavone substrates. For the conversion of daidzin to daidzein, the production rate was 1.44 mM/h. The addition of NaCl enhanced the hydrolytic activity of PABGL toward daidzin and genistein; the maximum activation by NaCl was 3.48- and 6.79-fold, respectively. This is the first report of a halophilic β-glucosidase from Pseudoalteromonas spp., and represents the β-glucosidase with the highest multiple of activation by NaCl. PABGL exhibits strong potential for applications in food processing and industrial production.

One-step purification of two novel thermotolerant β-1,4-glucosidases from a newly isolated strain of Fusarium chlamydosporum HML278 and their characterization

A newly identified cellulase-producing Fusarium chlamydosporum HML278 was cultivated under solid-state fermentation of sugarcane bagasse, and two new β-glucosides enzymes (BG FH1, BG FH2) were recovered from fermentation solution by modified non-denaturing active gel electrophoresis and gel filtration chromatography. SDS-PAGE analysis showed that the molecular weight of BG FH1 and BG FH2 was 93 kDa and 52 kDa, respectively, and the enzyme activity was 5.6 U/mg and 11.5 U/mg, respectively. The optimal reaction temperature of the enzymes was 60 ℃, and the enzymes were stable with a temperature lower than 70 ℃. The optimal pH of the purified enzymes was 6.0, and the enzymes were stable between pH 4–10. K_m and V_max values ​​were 2.76 mg/mL and 20.6 U/mg for pNPG, respectively. Thin-layer chromatography and high-performance liquid chromatography analysis showed that BG FH1and BG FH2 had hydrolysis activity toward cellobiose and could hydrolyze cellobiose into glucose. In addition, both enzymes exhibited transglycoside activity, which could use glucose to synthesize cellobiose and cellotriose, and preferentially synthesize alcohol. In conclusion, our study demonstrated that F. chlamydosporum HML278 produces heat-resistant β-glucosidases with both hydrolytic activity and transglycosidic activity, and these β-glucosidases have potential application in bioethanol and papermaking industries.

Cloning and characterization of the β-xylosidase from Dictyoglomus turgidum for high efficient biotransformation of 10-deacetyl-7-xylosltaxol

With the aim of finding an extracellular biocatalyst that can efficiently remove the C-7 xylose group from 10-deacetyl-7-xylosltaxol, a Dictyoglomus turgidum β-xylosidase was cloned and expressed in Escherichia coli BL21 (DE3). The molecular mass of purified Dt-Xyl3 was approximately 84 kDa. The recombinant Dt-Xyl3 was most active at pH 5.0 and 75 °C, retaining 88% activity at 65 °C for 1 h, and displaying excellent stability over pH 4.0-7.5 for 24 h. In terms of kinetic parameters, the K_m and V_max values for pNPX were 0.8316 mM and 5.0178 μmol/mL·min, respectively. Moreover, Dt-Xyl3 was activated by Mn²⁺ and Ba²⁺ and inhibited by Cu²⁺, Ni⁺ and Al³⁺. In particular, it displayed high tolerance to salts with 60.8% activity in 20% (w/v) NaCl. Ethanol and methanol at 5-15% showed little effect on the enzymatic activity. Dt-Xyl3 demonstrated multifunctional activities followed by pNPX, pNPAraf and pNPG and had a high selectivity for cleaving the outer xylose moieties of 10-deacetyl-7-xylosltaxol with K_cat/K_m 110.87 s^-1/mM, which produced 10-deacetyl-taxol to semi-synthesize paclitaxel. Under the optimized conditions (60 °C, pH 4.5, enzyme dosage of 0.5 U/mL), 1 g of 10-deacetyl-7-xylosltaxol was transformed to its corresponding aglycone 10-deacetyl-taxol within 30 min, with a molar conversion of 98%. This is the first report that Dictyoglomus turgidum can produce extracellular GH3 β-xylosidase with highly specific activity for 10-deacetyl-7-xylosltaxol biotransformation, thus leading to the application of β-xylosidase Dt-Xyl3 as a biocatalyst in biopharmaceutics.

Identification and molecular characterization of a psychrophilic GH1 β-glucosidase from the subtropical soil microorganism Exiguobacterium sp. GXG2

The products of bacterial β-glucosidases with favorable cold-adapted properties have industrial applications. A psychrophilic β-glucosidase gene named bglG from subtropical soil microorganism Exiguobacterium sp. GXG2 was isolated and characterized by function-based screening strategy. Results of multiple alignments showed that the derived protein BglG shared 45.7% identities with reviewed β-glucosidases in the UniProtKB/Swiss-Prot database. Functional characterization of the β-glucosidase BglG indicated that BglG was a 468 aa protein with a molecular weight of 53.2 kDa. The BglG showed the highest activity in pH 7.0 at 35 °C and exhibited consistently high levels of activity within low temperatures ranging from 5 to 35 °C. The BglG appeared to be a psychrophilic enzyme. The values of K_m, V_max, k_cat, and k_cat/K_m of recombinant BglG toward ρNPG were 1.1 mM, 1.4 µg/mL/min, 12.7 s⁻¹, and 11.5 mM/s, respectively. The specific enzyme activity of BglG was 12.14 U/mg. The metal ion of Ca²⁺ and Fe³⁺ could stimulate the activity of BglG, whereas Mn²⁺ inhibited the activity. The cold-adapted β-glucosidase BglG displayed remarkable biochemical properties, making it a potential candidate for future industrial applications.

Biotransformation of Food-Derived Saponins, Platycosides, into Deglucosylated Saponins Including Deglucosylated Platycodin D and Their Anti-Inflammatory Activities

The Platycodon grandiflorum root, Platycodi radix, a common vegetable, and its extract with glycosylated saponins, platycosides, have been used as food items and food health supplements for pulmonary diseases and respiratory disorders. Enzymes convert glycosylated saponins into deglycosylated saponins, which exhibit higher biological activity than glycosylated saponins. In this study, β-glucosidase from the hyperthermophilic bacterium Dictyoglomus turgidum converted platycosides in the Platycodi radix extract into deglucosylated platycosides. In addition, the enzyme completely converted platycoside E (PE), platycodin D₃ (PD₃), and platycodin D (PD) in Platycodi radix extract into deglucosylated platycodin D (deglu PD), which was first identified by nuclear magnetic resonance. The anti-inflammatory activities of deglu PD and deglucosylated Platycodi radix extract were higher than those of PE, PD₃, PD, Platycodi radix extract, and baicalein, an anti-inflammatory agent. Therefore, deglucosylated Platycodi radix extract is expected to be used as improved functional food supplements.

Novel Ethanol- and 5-Hydroxymethyl Furfural-Stimulated β-Glucosidase Retrieved From a Brazilian Secondary Atlantic Forest Soil Metagenome

Beta-glucosidases are key enzymes involved in lignocellulosic biomass degradation for bioethanol production, which complete the final step during cellulose hydrolysis by converting cellobiose into glucose. Currently, industry requires enzymes with improved catalytic performance or tolerance to process-specific parameters. In this sense, metagenomics has become a powerful tool for accessing and exploring the biochemical biodiversity present in different natural environments. Here, we report the identification of a novel β-glucosidase from metagenomic DNA isolated from soil samples enriched with decaying plant matter from a Secondary Atlantic Forest region. For this, we employed a functional screening approach using an optimized and synthetic broad host-range vector for library production. The novel β-glucosidase – named Lfa2 – displays three GH3-family conserved domains and conserved catalytic amino acids D283 and E487. The purified enzyme was most active in pH 5.5 and at 50°C, and showed hydrolytic activity toward several pNP synthetic substrates containing β-glucose, β-galactose, β-xylose, β-fucose, and α-arabinopyranose, as well as toward cellobiose. Lfa2 showed considerable glucose tolerance, exhibiting an IC₅₀ of 300 mM glucose and 30% of remaining activity in 600 mM glucose. In addition, Lfa2 retained full or slightly enhanced activity in the presence of several metal ions. Further, β-glucosidase activity was increased by 1.7-fold in the presence of 10% (v/v) ethanol, a concentration that can be reached in conventional fermentation processes. Similarly, Lfa2 showed 1.7-fold enhanced activity at high concentrations of 5-hydroxymethyl furfural, one of the most important cellulase inhibitors in pretreated sugarcane bagasse hydrolysates. Moreover, the synergistic effect of Lfa2 on Bacillus subtilis GH5-CBM3 endoglucanase activity was demonstrated by the increased production of glucose (1.6-fold). Together, these results indicate that β-glucosidase Lfa2 is a promissory enzyme candidate for utilization in diverse industrial applications, such as cellulosic biomass degradation or flavor enhancement in winemaking and grape processing.

Cellulases from Thermophiles Found by Metagenomics

Cellulases are a heterogeneous group of enzymes that synergistically catalyze the hydrolysis of cellulose, the major component of plant biomass. Such reaction has biotechnological applications in a broad spectrum of industries, where they can provide a more sustainable model of production. As a prerequisite for their implementation, these enzymes need to be able to operate in the conditions the industrial process requires. Thus, cellulases retrieved from extremophiles, and more specifically those of thermophiles, are likely to be more appropriate for industrial needs in which high temperatures are involved. Metagenomics, the study of genes and gene products from the whole community genomic DNA present in an environmental sample, is a powerful tool for bioprospecting in search of novel enzymes. In this review, we describe the cellulolytic systems, we summarize their biotechnological applications, and we discuss the strategies adopted in the field of metagenomics for the discovery of new cellulases, focusing on those of thermophilic microorganisms.

Carbohydrate-binding module assisted purification and immobilization of β-glucosidase onto cellulose and application in hydrolysis of soybean isoflavone glycosides

Complicated purification steps, together with the fact that β-glucosidase has to be tolerant to ethanol restricts the application of β-glucosidase in isoflavone aglycone hydrolyzing process. β-Glucosidase Bgl1A(A24S/F297Y) is a promising enzyme in hydrolyzing isoflavones. In this work, six different carbohydrate-binding modules (CBMs), which were from 3 families, were fused to the C-terminal of Bgl1A(A24S/F297Y), respectively, to simplify the enzyme preparation process. The fusion proteins were expressed in Escherichia coli and adsorbed onto cellulose. The Bgl-CBM24 was found to have the highest immobilization efficiency at room temperature within 1 h adsorption. Notably, 1-g cellulose absorbs up to 254.9±5.7 U of Bgl-CBM24. Interestingly, the immobilized Bgl-CBM24 showed improved ethanol tolerance ability, with the IC50 of 35% (v/v) ethanol. Bgl-CBM24 effectively hydrolyze soybean isoflavone glycosides. The hydrolysis rate of daidzin and gemistin was 85.22±3.24% and 82.14±3.82% within 10 min, with the concentrations of daidzein and genistein increased by 6.36±0.18 mM and 3.98±0.22 mM, respectively. In the repetitive hydrolytic cycles, the concentrations of daidzein and genistein still increased by 3.07±0.24 mM and 1.94±0.34 mM in the fourth cycle with 20% (v/v) ethanol. These results suggest that the immobilized Bgl-CBM24 has excellent potential in the preparation of isoflavone aglycones.

Improve ethanol tolerance of β-glucosidase Bgl1A by semi-rational engineering for the hydrolysis of soybean isoflavone glycosides

A β-glucosidase Bgl1A variant (A24S/F297Y) with improved ethanol tolerance was obtained by semi-rational engineering. At 30-40°C, IC50 values (the amount required for inhibiting 50% enzyme activity) of the variant for ethanol were 17-30% (v/v), 1.4- to 2.4-fold of Bgl1A. When incubating in 15% (v/v) ethanol at 30°C, the half-life of A24S/F297Y was 13min; whereas Bgl1A lost all enzyme activity within 5min. A24S/F297Y was more stable at pH 7.5 than at pH 6.5, and more than 50% of the original activity remained after incubation at 30°C for 10h. At 35°C and pH 7.5, the half-life of A24S/F297Y was 80min, 4.3 times longer than that of Bgl1A. When converting isoflavone glycosides to aglycones using A24S/F297Y as catalyst, the hydrolysis rates were 99% for daidzin and 98% for genistin. The concentrations of daidzein and genistein rapidly increased by 7.02mM and 4.35mM within 10min, respectively. These results showed that A24S/F297Y was a promising candidate for the enzymatic hydrolysis of soybean isoflavone glycosides.

Heterologous expression of a GH3 β-glucosidase from Neurospora crassa in Pichia pastoris with high purity and its application in the hydrolysis of soybean isoflavone glycosides

Previous studies have shown isoflavone aglycones to have more biological effects than their counterparts, isoflavone glycones. Some β-glucosidases can hydrolyze isoflavone glucosides to release aglycones, and discovery of these has attracted great interest. A glycoside hydrolase (GH) family 3 β-glucosidase (bgl2) gene from Neurospora crassa was heterologously expressed in Pichia pastoris with high purity. The recombinant BGL2 enzyme displayed its highest activity at pH 5.0 and 60 °C, and had its maximum activity against p-nitrophenyl-β-d-glucopyranoside (pNPG) (143.27 ± 4.79 U/mg), followed by cellobiose (74.99 ± 0.78 U/mg), gentiobiose (47.55 ± 0.15 U/mg), p-nitrophenyl-β-d-cellobioside (pNPC) (40.07 ± 0.87 U/mg), cellotriose (12.31 ± 0.36 U/mg) and cellotetraose (9.04 ± 0.14 U/mg). The kinetic parameters of Km and Vmax were 0.21 ± 0.01 mM and 147.93 ± 2.77 μM/mg/min for pNPG. The purified enzyme showed a heightened ability to convert the major soybean isoflavone glycosides (daidzin, genistin and glycitin) into their corresponding aglycone forms (daidzien, genistein and glycitein). With this activity against soybean isoflavone glycosides, BGL2 shows great potential for applications in the food, animal feed, and pharmaceutical industries.

Overexpression and characterization of a Ca2+ activated thermostable β-glucosidase with high ginsenoside Rb1 to ginsenoside 20(S)-Rg3 bioconversion productivity

The thermostable β-glucosidase gene from Thermotoga petrophila DSM 13995 was cloned and overexpressed in Escherichia coli. The activity of the recombinant β-glucosidase was 21 U/mL in the LB medium. Recombinant β-glucosidase was purified, and its molecular weight was approximately 81 kDa. The optimal activity was at pH 5.0 and 90 °C, and the thermostability of the enzyme was improved by Ca2+. The β-glucosidase had high selectivity for cleaving the outer and inner glucopyranosyl moieties at the C-20 carbon of ginsenoside Rb1, which produced the pharmacologically active minor ginsenoside 20(S)-Rg3. In a reaction at 90 °C and pH 5.0, 10 g/L of ginsenoside Rb1 was transformed into 6.93 g/L of Rg3 within 90 min, with a corresponding molar conversion of 97.9 %, and Rg3 productivity of 4620 mg/L/h. This study is the first report of a GH3-family enzyme that used Ca2+ to improve its thermostability, and it is the first report on the high substrate concentration bioconversion of ginsenoside Rb1 to ginsenoside 20(S)-Rg3 by using thermostable β-glucosidase under high temperature.

Molecular characterization of a highly-active thermophilic β-glucosidase from Neosartorya fischeri P1 and its application in the hydrolysis of soybean isoflavone glycosides

Isoflavone occurs abundantly in leguminous seeds in the form of glycoside and aglycone. However, isoflavone glycoside has anti-nutritional effect and only the free type is beneficial to human health. In the present study we identified a β-glucosidase from thermophilic Neosartorya fischeri P1, termed NfBGL1, capable of efficiently converting isoflavone glycosides into free isoflavones. The gene, belonging to glycoside hydrolase family 3, was successfully overexpressed in Pichia pastoris at high cell density in a 3.7-l fermentor. Purified recombinant NfBGL1 had higher specific activity (2189 ± 1.7 U/mg) and temperature optimum (80 °C) than other fungal counterparts when using p-nitrophenyl β-D-glucopyranoside as the substrate. It retained stable at temperatures up to 70 °C and over a broad pH range of 3.0-10.0. NfBGL1 had broad substrate specificity including glucosidase, cellobiase, xylanase and glucanase activities, and displayed preference for hydrolysis of β-1,2 glycosidic bond rather than β-1,3, β-1,4, β-1,6 bonds. The enzyme showed high bioconversion ability for major soybean isoflavone glycosides (daidin, gensitin and glycitin) into free forms. These properties make NfBGL1 potential for the wide use in the food, feed, pharmacy and biofuel industries.

Deglycosylation of isoflavones in isoflavone-rich soy germ flour by Aspergillus oryzae KACC 40247

Aspergillus oryzae KACC 40247 was selected as an efficient daidzein-producing fungus from strains of the genus Aspergillus by using 5% (w/v) soy germ flour (SGF) as an isoflavone-glycoside-rich medium. The culture conditions, including SGF concentration, agitation speed, initial pH, temperature, and time, were optimized as follows: 7% (w/v) SGF, initial pH 6.0, 33 °C, 300 rpm, and 24 h in a 100 mL baffled flask. The determined amount of isoflavone aglycons in SGF using 50% ethyl acetate was the highest among the solvent systems tested and it was 3.7-fold higher than that using 70% methanol. Under the optimized conditions, the content and concentration of daidzein were 134 mg/g of SGF and 9.4 g/L, respectively, with a productivity of 391 ± 2.8 mg/L/h, and those of isoflavone aglycons were 165 mg/g of SGF and 11.5 g/L, respectively, with a productivity of 479 mg/L/h. Optimization of culture conditions increased the content, concentration, and productivity of isoflavone aglycons by 3.1-, 3.0-, and 3.7-fold, respectively. To our knowledge, this is the highest production of isoflavone aglycons reported to date.

Hydrolysis of isoflavone glycosides by a thermostable β-glucosidase from Pyrococcus furiosus

The recombinant β-glucosidase from the hyperthermophilic archaeon Pyrococcus furiosus was purified with a specific activity of 330 U/mg for genistin by His-trap chromatography. The specific activity of the purified enzyme followed the order genistin > daidzin > glycitin> malonyl glycitin > malonyl daidzin > malonyl genistin. The hydrolytic activity for genistin was highest at pH 6.0 and 95 °C with a half-life of 59 h, a K(m) of 0.5 mM, and a k(cat) of 6050 1/s. The enzyme completely hydrolyzed 1.0 mM genistin, daidzin, and glycitin within 100, 140, and 180 min, respectively. The soybean flour extract at 7.5% (w/v) contained 1.0 mM genistin, 0.9 mM daidzin, and 0.3 mM glycitin. Genistin, daidzin, and glycitin in the soybean flour extract were completely hydrolyzed after 60, 75, and 120 min, respectively. Of the reported β-glucosidases, P. furiosusβ-glucosidase exhibited the highest thermostability, k(cat), k(cat)/K(m), yield, and productivity for hydrolyzing genistin. These results suggest that this enzyme may be useful for the industrial hydrolysis of isoflavone glycosides.