Purification and characterization of a novel ginsenoside Rc-hydrolyzing β-glucosidase from Armillaria mellea mycelia

Advancements in enzymatic biotransformation and bioactivities of rare ginsenosides：A Review

Ginsenoside, the principal active constituent of ginseng, exhibits enhanced bioavailability and medicinal efficacy in rare ginsenosides compared to major ginsenosides. Current research is focused on efficiently and selectively removing sugar groups attached to the major ginsenoside sugar chains to convert them into rare ginsenosides that meet the demands of medical industry and functional foods. The methods for preparing rare ginsenosides encompass chemical, microbial, and enzymatic approaches. Among these, the enzyme conversion method is highly favored by researchers due to its exceptional specificity and robust efficiency. This review summarizes the biological activities of different rare ginsenosides, explores the various glycosidases used in the biotransformation of different major ginsenosides as substrates, and elucidates their respective corresponding biotransformation pathways. These findings will provide valuable references for the development, utilization, and industrial production of ginsenosides.

β-Glucosidase and Its Application in Bioconversion of Ginsenosides in Panax ginseng

Ginsenosides are a group of bioactive compounds isolated from Panax ginseng. Conventional major ginsenosides have a long history of use in traditional medicine for both illness prevention and therapy. Bioconversion processes have the potential to create new and valuable products in pharmaceutical and biological activities, making them both critical for research and highly economic to implement. This has led to an increase in the number of studies that use major ginsenosides as a precursor to generate minor ones using β-glucosidase. Minor ginsenosides may also have useful properties but are difficult to isolate from raw ginseng because of their scarcity. Bioconversion processes have the potential to create novel minor ginsenosides from the more abundant major ginsenoside precursors in a cost-effective manner. While numerous bioconversion techniques have been developed, an increasing number of studies have reported that β-glucosidase can effectively and specifically generate minor ginsenosides. This paper summarizes the probable bioconversion mechanisms of two protopanaxadiol (PPD) and protopanaxatriol (PPT) types. Other high-efficiency and high-value bioconversion processes using complete proteins isolated from bacterial biomass or recombinant enzymes are also discussed in this article. This paper also discusses the various conversion and analysis methods and their potential applications. Overall, this paper offers theoretical and technical foundations for future studies that will be both scientifically and economically significant.

Production of Minor Ginsenosides C-K and C-Y from Naturally Occurring Major Ginsenosides Using Crude β-Glucosidase Preparation from Submerged Culture of Fomitella fraxinea

Minor ginsenosides, such as compounds (C)-K and C-Y, possess relatively better bioactivity than those of naturally occurring major ginsenosides. Therefore, this study focused on the biotransformation of major ginsenosides into minor ginsenosides using crude β-glucosidase preparation isolated from submerged liquid culture of Fomitella fraxinea (FFEP). FFEP was prepared by ammonium sulfate (30–80%) precipitation from submerged culture of F. fraxinea. FFEP was used to prepare minor ginsenosides from protopanaxadiol (PPD)-type ginsenoside (PPDG-F) or total ginsenoside fraction (TG-F). In addition, biotransformation of major ginsenosides into minor ginsenosides as affected by reaction time and pH were investigated by TLC and HPLC analyses, and the metabolites were also identified by UPLC/negative-ESI-Q-TOF-MS analysis. FFEP biotransformed ginsenosides Rb1 and Rc into C-K via the following pathways: Rd → F2 → C-K for Rb1 and both Rd → F2→ C-K and C-Mc1 → C-Mc → C-K for Rc, respectively, while C-Y is formed from Rb2 via C-O. FFEP can be applied to produce minor ginsenosides C-K and C-Y from PPDG-F or TG-F. To the best of our knowledge, this study is the first to report the production of C-K and C-Y from major ginsenosides by basidiomycete F. fraxinea.

Two Key Amino Acids Variant of α-l-arabinofuranosidase from Bacillus subtilis Str. 168 with Altered Activity for Selective Conversion Ginsenoside Rc to Rd

α-l-arabinofuranosidase is a subfamily of glycosidases involved in the hydrolysis of l-arabinofuranosidic bonds, especially in those of the terminal non-reducing arabinofuranosyl residues of glycosides, from which efficient glycoside hydrolases can be screened for the transformation of ginsenosides. In this study, the ginsenoside Rc-hydrolyzing α-l-arabinofuranosidase gene, BsAbfA, was cloned from Bacilus subtilis, and its codons were optimized for efficient expression in E. coli BL21 (DE3). The recombinant protein BsAbfA fused with an N-terminal His-tag was overexpressed and purified, and then subjected to enzymatic characterization. Site-directed mutagenesis of BsAbfA was performed to verify the catalytic site, and the molecular mechanism of BsAbfA catalyzing ginsenoside Rc was analyzed by molecular docking, using the homology model of sequence alignment with other β-glycosidases. The results show that the purified BsAbfA had a specific activity of 32.6 U/mg. Under optimal conditions (pH 5, 40 °C), the kinetic parameters K_m of BsAbfA for pNP-α-Araf and ginsenoside Rc were 0.6 mM and 0.4 mM, while the K_cat/K_m were 181.5 s^-1 mM^-1 and 197.8 s^-1 mM^-1, respectively. More than 90% of ginsenoside Rc could be transformed by 12 U/mL purified BsAbfA at 40 °C and pH 5 in 24 h. The results of molecular docking and site-directed mutagenesis suggested that the E173 and E292 variants for BsAbfA are important in recognizing ginsenoside Rc effectively, and to make it enter the active pocket to hydrolyze the outer arabinofuranosyl moieties at C₂₀ position. These remarkable properties and the catalytic mechanism of BsAbfA provide a good alternative for the effective biotransformation of the major ginsenoside Rc into Rd.

Complete Bioconversion of Protopanaxadiol-Type Ginsenosides to Compound K by Extracellular Enzymes from the Isolated Strain Aspergillus tubingensis

A compound K-producing fungus was isolated from meju (fermented soybean brick) and identified as the generally recognized as safe (GRAS) strain Aspergillus tubingensis. The extracellular enzymes obtained after the cultivation of 6 days in the medium with 20 g/L citrus pectin as an inducer showed the highest compound K-producing activity among the inducers tested. Under the optimized conditions of 0.05 mM MgSO₄, 55 °C, pH 4.0, 13.4 mM protopanaxadiol (PPD)-type ginsenosides, and 11 mg/mL enzymes, the extracellular enzymes from A. tubingensis completely converted PPD-type ginsenosides in the ginseng extract to 13.4 mM (8.35 mg/mL) compound K after 20 h, with the highest concentration and productivity among the results reported so far. As far as we know, this is the first GRAS enzyme to completely convert all PPD-type ginsenosides to compound K.

Biotransformation of Protopanaxadiol-Type Ginsenosides in Korean Ginseng Extract into Food-Available Compound K by an Extracellular Enzyme from Aspergillus niger

Compound K (C-K) is one of the most pharmaceutically effective ginsenosides, but it is absent in natural ginseng. However, C-K can be obtained through the hydrolysis of protopanaxadiol-type ginsenosides (PPDGs) in natural ginseng. The aim of this study was to obtain the high concentration of food-available C-K using PPDGs in Korean ginseng extract by an extracellular enzyme from Aspergillus niger KACC 46495. A. niger was cultivated in the culture medium containing the inducer carboxymethyl cellulose (CMC) for 6 days. The extracellular enzyme extracted from A. niger was prepared from the culture broth by filtration, ammonium sulfate, and dialysis. The extracellular enzyme was used for C-K production using PPDGs. The glycoside-hydrolyzing pathways for converting PPDGs into C-K by the extracellular enzyme were Rb1 → Rd → F2 → C-K, Rb2 → Rd or compound O → F2 or compound Y → C-K, and Rc → Rd or compound Mc1 → F2 or compound Mc → C-K. The extracellular enzyme from A. niger at 8.0 mg/ml, which was obtained by the induction of CMC during the cultivation, converted 6.0 mg/ml (5.6 mM) PPDGs in Korean ginseng extract into 2.8 mg/ml (4.5 mM) food-available C-K in 9 h, with a productivity of 313 mg/l/h and a molar conversion of 80%. To the best of our knowledge, the productivity and concentration of C-K of the extracellular enzyme are the highest among those by crude enzymes from wild-type microorganisms.

Preparation and Characterization of β-glucosidase Films for Stabilization and Handling in Dry Configurations

BACKGROUND

Although the stability of proteins is of significance to maintain protein function for therapeutical applications, this remains a challenge. Herein, a general method of preserving protein stability and function was developed using gelatin films.

METHODS

Enzymes immobilized onto films composed of gelatin and Ethylene Glycol (EG) were developed to study their ability to stabilize proteins. As a model functional protein, β-glucosidase was selected. The tensile properties, microstructure, and crystallization behavior of the gelatin films were assessed.

RESULTS

Our results indicated that film configurations can preserve the activity of β-glucosidase under rigorous conditions (75% relative humidity and 37°C for 47 days). In both control films and films containing 1.8 % β-glucosidase, tensile strength increased with increased EG content, whilst the elongation at break increased initially, then decreased over time. The presence of β-glucosidase had a negligible influence on tensile strength and elongation at break. Scanning electron-microscopy (SEM) revealed that with increasing EG content or decreasing enzyme concentrations, a denser microstructure was observed.

CONCLUSION

In conclusion, the dry film is a promising candidate to maintain protein stabilization and handling. The configuration is convenient and cheap, and thus applicable to protein storage and transportation processes in the future.

Preparative separation of minor saponins from Panax notoginseng leaves using biotransformation, macroporous resins, and preparative high-performance liquid chromatography

Background

Ginsenosides with less sugar moieties may exhibit the better adsorptive capacity and more pharmacological activities.

Methods

An efficient method for the separation of four minor saponins, including gypenoside XVII, notoginsenoside Fe, ginsenoside Rd2, and notoginsenoside Fd, from Panax notoginseng leaves (PNL) was established using biotransformation, macroporous resins, and subsequent preparative high-performance liquid chromatography.

Results

The dried PNL powder was immersed in the distilled water at 50°C for 30 min for converting the major saponins, ginsenosides Rb1, Rc, Rb2, and Rb3, to minor saponins, gypenoside XVII, notoginsenoside Fe, ginsenoside Rd2, and notoginsenoside Fd, respectively, by the enzymes present in PNL. The adsorption characteristics of these minor saponins on five types of macroporous resins, D-101, DA-201, DM-301, X-5, and S-8, were evaluated and compared. Among them, D-101 was selected due to the best adsorption and desorption properties. Under the optimized conditions, the fraction containing the four target saponins was separated by D-101 resin. Subsequently, the target minor saponins were individually separated and purified by preparative high-performance liquid chromatography with a reversed-phase column.

Conclusion

Our study provides a simple and efficient method for the preparation of these four minor saponins from PNL, which will be potential for industrial applications.

Highly regioselective biotransformation of ginsenoside Rb2 into compound Y and compound K by β-glycosidase purified from Armillaria mellea mycelia

Background

The biological activities of ginseng saponins (ginsenosides) are associated with type, number, and position of sugar moieties linked to aglycone skeletons. Deglycosylated minor ginsenosides are known to be more biologically active than major ginsenosides. Accordingly, the deglycosylation of major ginsenosides can provide the multibioactive effects of ginsenosides. The purpose of this study was to transform ginsenoside Rb2, one of the protopanaxadiol-type major ginsenosides, into minor ginsenosides using β-glycosidase (BG-1) purified from Armillaria mellea mycelium.

Methods

Ginsenoside Rb2 was hydrolyzed by using BG-1; the hydrolytic properties of Rb2 by BG-1 were also characterized. In addition, the influence of reaction conditions such as reaction time, pH, and temperature, and transformation pathways of Rb2, Rd, F2, compound O (C-O), and C-Y by treatment with BG-1 were investigated.

Results

BG-1 first hydrolyzes 3-O-outer β-d-glucoside of Rb2, then 3-O-β-d-glucoside of C-O into C-Y. C-Y was gradually converted into C-K with a prolonged reaction time, but the pathway of Rb2 → Rd → F2 → C-K was not observed. The optimum reaction conditions for C-Y and C-K formation from Rb2 by BG-1 were pH 4.0-4.5, temperature 45-60°C, and reaction time 72-96 h.

Conclusion

β-Glycosidase purified from A. mellea mycelium can be efficiently used to transform Rb2 into C-Y and C-K. To our best knowledge, this is the first result of transformation from Rb2 into C-Y and C-K by basidiomycete mushroom enzyme.