Characterization of a α-l-rhamnosidase from Bacteroides thetaiotaomicron with high catalytic efficiency of epimedin C

Homologous expression of Aspergillus niger α-L-rhamnosidase and its application in enzymatic debittering of Ougan juice

The α-L-rhamnosidase (rha1) gene was homologously expressed in Aspergillus niger strains CCTCC 206047 and CCTCC 206047ΔpyrG, using hygromycin B and auxotrophic as selection markers. The engineered A. niger strains RHA001-1 and RHA003-1 were screened, yielding α-L-rhamnosidase activities of 20.81 ± 0.56 U/mL and 15.35 ± 0.87 U/mL, respectively. The copy numbers of the rha1 gene in strains RHA001-1 and RHA003-1 were found to be 18 and 14, respectively. Correlation analysis between copy number and enzyme activity in the A. niger strains revealed that α-L-rhamnosidase activity increased with the copy number of the rha1 gene. Recombinant α-L-rhamnosidase was utilized for the enzymatic debittering of Ougan juice, and its process conditions were optimized. Furthermore, the primary bitter substance neohesperidin (2.22 g/L) in Ougan juice was converted into hesperetin 7-O-glucoside (1.47 g/L) and hesperidin (0.143 g/L). This study presents a novel approach for the production of food-grade α-L-rhamnosidase and establishes a technical foundation for its application in the beverage industry.

Decoding polyphenol metabolism in patients with Crohn's disease: Insights from diet, gut microbiota, and metabolites

Crohn's disease (CD) is a chronic and progressive inflammatory disease that can involve any part of the gastrointestinal tract. The protective role of dietary polyphenols has been documented in preclinical models of CD. Gut microbiota mediates the metabolism of polyphenols and affects their bioactivity and physiological functions. However, it remains elusive the capacity of microbial polyphenol metabolism in CD patients and healthy controls (HCs) along with its correlation with polyphenols intake and polyphenol-derived metabolites. Thus, we aimed to decode polyphenol metabolism in CD patients through aspects of diet, gut microbiota, and metabolites. Dietary intake analysis revealed that CD patients exhibited decreased intake of polyphenols. Using metagenomic data from two independent clinical cohorts (FAH-SYSU and PRISM), we quantified abundance of polyphenol degradation associated bacteria and functional genes in CD and HCs and observed a lower capacity of flavonoids degradation in gut microbiota residing in CD patients. Furthermore, through analysis of serum metabolites and enterotypes in participants of FAH-SYSU cohort, we observed that CD patients exhibited reduced levels of serum hippuric acid (HA), one of polyphenol-derived metabolites. HA level was higher in healthier enterotypes (characterized by dominance of Ruminococcaceae and Prevotellaceae, dominant by HCs) and positively correlated with multiple polyphenols intake and abundance of bacteria engaged in flavonoids degradation as well as short-chain fatty acid production, which could serve as a biomarker for effective polyphenol metabolism by the gut microbiota and a healthier gut microbial community structure. Overall, our findings provide a foundation for future work exploring the polyphenol-based or microbiota-targeted therapeutic strategies in CD.

Gut microbiome-derived hydrolases-an underrated target of natural product metabolism

In recent years, there has been increasing interest in studying gut microbiome-derived hydrolases in relation to oral drug metabolism, particularly focusing on natural product drugs. Despite the significance of natural product drugs in the field of oral medications, there is a lack of research on the regulatory interplay between gut microbiome-derived hydrolases and these drugs. This review delves into the interaction between intestinal microbiome-derived hydrolases and natural product drugs metabolism from three key perspectives. Firstly, it examines the impact of glycoside hydrolases, amide hydrolases, carboxylesterase, bile salt hydrolases, and epoxide hydrolase on the structure of natural products. Secondly, it explores how natural product drugs influence microbiome-derived hydrolases. Lastly, it analyzes the impact of interactions between hydrolases and natural products on disease development and the challenges in developing microbial-derived enzymes. The overarching goal of this review is to lay a solid theoretical foundation for the advancement of research and development in new natural product drugs and personalized treatment.

Efficient biosynthesis of prunin in methanol cosolvent system by an organic solvent-tolerant α-L-rhamnosidase from Spirochaeta thermophila

Prunin of desirable bioactivity and bioavailability can be transformed from plant-derived naringin by the key enzyme α-L-rhamnosidase. However, the production was limited by unsatisfactory properties of α-L-rhamnosidase such as thermostability and organic solvent tolerance. In this study, biochemical characteristics, and hydrolysis capacity of a novel α-L-rhamnosidase from Spirochaeta thermophila (St-Rha) were investigated, which was the first characterized α-L-rhamnosidase for Spirochaeta genus. St-Rha showed a higher substrate specificity towards naringin and exhibited excellent thermostability and methanol tolerance. The Km of St-Rha in the methanol cosolvent system was decreased 7.2-fold comparing that in the aqueous phase system, while kcat/Km value of St-Rha was enhanced 9.3-fold. Meanwhile, a preliminary conformational study was implemented through comparative molecular dynamics simulation analysis to explore the mechanism underlying the methanol tolerance of St-Rha for the first time. Furthermore, the catalytic ability of St-Rha for prunin preparation in the 20% methanol cosolvent system was explored, and 200 g/L naringin was transformed into 125.5 g/L prunin for 24 h reaction with a corresponding space-time yield of 5.2 g/L/h. These results indicated that St-Rha was a novel α-L-rhamnosidase suitable for hydrolyzing naringin in the methanol cosolvent system and provided a better alternative for improving the efficient production yield of prunin.

Aspergillus oryzae α-l-rhamnosidase: Crystal structure and insight into the substrate specificity

The subsequent biochemical and structural investigations of the purified recombinant α-l-rhamnosidase from Aspergillus oryzae expressed in Pichia pastoris, designated as rAoRhaA, were performed. The specific activity of the rAoRhaA wild-type was higher toward hesperidin and narirutin, where the l-rhamnose residue was α-1,6-linked to β-d-glucoside, than toward neohesperidin and naringin with an α-1,2-linkage to β-d-glucoside. However, no activity was detected toward quercitrin, myricitrin, and epimedin C. rAoRhaA kinetic analysis indicated that Km values for neohesperidin, naringin, and rutin were lower compared to those for hesperidin and narirutin. kcat values for hesperidin and narirutin were higher than those for neohesperidin, naringin, and rutin. High catalytic efficiency (kcat /Km ) toward hesperidin and narirutin was a result of a considerably high kcat value, while Km values for hesperidin and narirutin were higher than those for naringin, neohesperidin, and rutin. The crystal structure of rAoRhaA revealed that the catalytic domain was represented by an (α/α)6 -barrel with the active site located in a deep cleft and two β-sheet domains were also present in the N- and C-terminal sites of the catalytic domain. Additionally, five asparagine-attached N-acetylglucosamine molecules were observed. The catalytic residues of AoRhaA were suggested to be Asp254 and Glu524, and their catalytic roles were confirmed by mutational studies of D254N and E524Q variants, which lost their activity completely. Notably, three aspartic acids (Asp117, Asp249, and Asp261) located at the catalytic pocket were replaced with asparagine. D117N variant showed reduced activity. D249N and D261N variants activities drastically decreased.

Xylan derived carbon dots composite with PCL/PLA for construction biomass nanofiber membrane used as fluorescence sensor for detection Cu2+ in real samples

Water and soil pollution caused by Cu2+ is not conducive to sustainable development of environment and could cause damage to environment and even human body. Currently, fluorescent sensor solutions analysis method has been used for Cu2+ detection, but they also suffer from drawbacks including easy leakage, difficult storage, and inaccurate. Herein, a green solid-state biomass fluorescence platform (NBU-CDs) consisting of xylan-derived carbon dots (U-CDs) and polylactic acid/polycaprolactone (PLA/PCL) was designed by using in situ electrospinning technology. The prepared NBU-CDs fluorescence platform showed good fluorescence effect and can be served as fluorescence sensor for detecting Cu2+ with high sensitively, selectively and low detection limit (LOD = 0.83 μM). The practical applications of NBU-CDs exhibited high specificity for Cu2+ detection in zebrafish, water samples (school lake, Xuanwu Lake and Yangtze River) with high recovery rates of 97 %-104 % and soil (pond soil, grassland soil and bamboo soil) samples, respectively. The developed fluorescence platform was utilized to predict water and soil safety by monitoring Cu2+ concentration and provides a new strategy for Cu2+ detection.

Heterologous Expression and Characterization of a Thermostable α-L-Rhamnosidase from Thermoclostridium stercorarium subsp. thermolacticum DSM 2910 and Its Application in the Biotransformation of Rutin

An α-L-rhamnosidase gene from Thermoclostridium. stercorarium subsp. thermolacticum DSM 2910 (TstRhaA) was cloned and expressed. The maximum TstRhaA activity of the protein reached 25.2 U/ml, and the molecular mass was approximately 106.6 kDa. The protein was purified 8.0-fold by Ni-TED affinity with an overall recovery of 16.6% and a specific activity of 187.9 U/mg. TstRhaA activity was the highest at 65°C and pH 6.5. In addition, it exhibited excellent thermal stability, better pH stability, good tolerance to low concentrations of organic reagents, and high catalytic activity for p-nitrophenyl-α-L-rhamnopyranoside (pNPR). Substrate specificity studies showed that TstRhaA exhibited a high specific activity for rutin. At 60°C, pH 6.5, and 0.3 U/ml enzyme dosage, 60 g/l rutin was converted to 45.55 g/l isoquercitrin within 150 min. The molar conversion rate of rutin and the yield of isoquercitrin were 99.8% and 12.22 g/l/h, respectively. The results suggested that TstRhaA could be used for mass production of isoquercitrin.

Advancements in the Biotransformation and Biosynthesis of the Primary Active Flavonoids Derived from Epimedium

Epimedium is a classical Chinese herbal medicine, which has been used extensively to treat various diseases, such as sexual dysfunction, osteoporosis, cancer, rheumatoid arthritis, and brain diseases. Flavonoids, such as icariin, baohuoside I, icaritin, and epimedin C, are the main active ingredients with diverse pharmacological activities. Currently, most Epimedium flavonoids are extracted from Epimedium plants, but this method cannot meet the increasing market demand. Biotransformation strategies promised huge potential for increasing the contents of high-value Epimedium flavonoids, which would promote the full use of the Epimedium herb. Complete biosynthesis of major Epimedium flavonoids by microbial cell factories would enable industrial-scale production of Epimedium flavonoids. This review summarizes the structures, pharmacological activities, and biosynthesis pathways in the Epimedium plant, as well as the extraction methods of major Epimedium flavonoids, and advancements in the biotransformation and complete microbial synthesis of Epimedium flavonoids, which would provide valuable insights for future studies on Epimedium herb usage and the production of Epimedium flavonoids.

α-L-rhamnosidase: production, properties, and applications

α-L-rhamnosidase [EC 3.2.1.40] belongs to glycoside hydrolase (GH) families (GH13, GH78, and GH106 families) in the carbohydrate-active enzymes (CAZy) database, which specifically hydrolyzes the non-reducing end of α-L-rhamnose. Αccording to the sites of catalytic hydrolysis, α-L-rhamnosidase can be divided into α-1, 2-rhamnosidase, α-1, 3-rhamnosidase, α-1, 4-rhamnosidase and α-1, 6-rhamnosidase. α-L-rhamnosidase is an important enzyme for various biotechnological applications, especially in food, beverage, and pharmaceutical industries. α-L-rhamnosidase has a wide range of sources and is commonly found in animals, plants, and microorganisms, and its microbial source includes a variety of bacteria, molds and yeasts (such as Lactobacillus sp., Aspergillus sp., Pichia angusta and Saccharomyces cerevisiae). In recent years, a series of advances have been achieved in various aspects of α-validates the above-described-rhamnosidase research. A number of α-L-rhamnosidases have been successfully recombinant expressed in prokaryotic systems as well as eukaryotic systems which involve Pichia pastoris, Saccharomyces cerevisiae and Aspergillus niger, and the catalytic properties of the recombinant enzymes have been improved by enzyme modification techniques. In this review, the sources and production methods, general and catalytic properties and biotechnological applications of α-L-rhamnosidase in different fields are summarized and discussed, concluding with the directions for further in-depth research on α-L-rhamnosidase.

Screening and characterization of a β-xylosidase from Bifidobacterium breve K-110 and its application in the biotransformation of the total flavonoids of epimedium to icariin with α-l-rhamnosidase

Among the flavonoids of epimedium, epimedin B, epimedin C, and icariin are considered to be representative components and their structures are quite similar. Besides sharing the same backbone, the main difference is the sugar groups attached at the positions of C-3 and C-7. Despite their structural similarities, their potencies differ significantly, and only icariin is currently included in the Chinese Pharmacopoeia as a quality marker (Q-marker) for epimedium flavonoids. Furthermore, icariin has the functions of anti-aging, anti-inflammation, antioxidation, anti-osteoporosis, and ameliorating fibrosis. We used bioinformatics to look for the GH43 family β-xylosidase genes BbXyl from Bifidobacterium breve K-110, which has a length of 1347 bp and codes for 448 amino acids. This will allow us to convert epimedin B and epimedin C into icariin in a specific way. The expression level of recombinant BbXyl in TB medium containing 1 % inulin as carbon source, with an inducer concentration of 0.05 mmol/L and a temperature of 28 °C, was 86.4 U/mL. Previous studies found that the α-l-rhamnosidase BtRha could convert epoetin C to produce icariin, so we combined BbXyl and BtRha to catalyze the conversion of epimedium total flavonoids in vitro and in vivo to obtain the product icariin. Under optimal conditions, in vitro hydrolysis of 5 g/L of total flavonoids of epimedium eventually yielded a concentration of icariin of 678.1 μmol/L. To explore the conversion of total flavonoids of epimedium in vivo. Under the optimal conditions, the yield of icariin reached 97.27 μmol/L when the total flavonoid concentration of epimedium was 1 g/L. This study is the first to screen xylosidases for the targeted conversion of epimedin B to produce icariin, and the first to report that epimedin B and epimedin C in the raw epimedium flavonoids can convert efficiently to icariin by a collaborative of β-xylosidase and α-l-rhamnosidase.

Insights into glycosidic bond specificity of an engineered selective α-L-rhamnosidase N12-Rha via activity assays and molecular modelling

αL-rhamnosidase (EC 3.2.1.40) has been widely used in food processing and pharmaceutical preparation. The recombinant α-L-rhamnosidase N12-Rha from Aspergillus niger JMU-TS528 had significantly higher catalytic activity on α-1,6 glycosidic bond than α-1,2 glycosidic bond, and had no activity on α-1,3 glycosidic bond. The activities of hydrolyzed hesperidin and naringin were 7240 U/mL and 945 U/mL, respectively, which are 10.63 times that of native α-L-rhamnosidase. The activity could maintain more than 80% at pH 3–6 and 40–60℃. Quantum chemistry calculations showed that charge difference of the C-O atoms of the α-1,2, α-1,3 and α-1,6 bonds indicated that α-1,6 bond is most easily broken and α-1,3 bond is the most stable. Molecular dynamics simulations revealed that the key residue Trp359 that may affect substrate specificity and the main catalytic sites of N12-Rha are located in the (α/α)6-barrel domain.

Potential roles of gut microbes in biotransformation of natural products: An overview

Natural products have been extensively applied in clinical practice, characterized by multi-component and multi-target, many pharmacodynamic substances, complex action mechanisms, and various physiological activities. For the oral administration of natural products, the gut microbiota and clinical efficacy are closely related, but this relationship remains unclear. Gut microbes play an important role in the transformation and utilization of natural products caused by the diversity of enzyme systems. Effective components such as flavonoids, alkaloids, lignans, and phenols cannot be metabolized directly through human digestive enzymes but can be transformed by enzymes produced by gut microorganisms and then utilized. Therefore, the focus is paid to the metabolism of natural products through the gut microbiota. In the present study, we systematically reviewed the studies about gut microbiota and their effect on the biotransformation of various components of natural products and highlighted the involved common bacteria, reaction types, pharmacological actions, and research methods. This study aims to provide theoretical support for the clinical application in the prevention and treatment of diseases and provide new ideas for studying natural products based on gut biotransformation.

Icariside I - A novel inhibitor of the kynurenine-AhR pathway with potential for cancer therapy by blocking tumor immune escape

BACKGROUND

Although therapeutic antibodies against immune checkpoints such as PD-1/PD-L1 have achieved unprecedented success in clinical tumor patients, there are still many patients who are ineffective or have limited responses to immune checkpoint blockade (ICB). Discovery of novel strategies for cancer immunotherapy including natural small molecules is needed.

METHODS

Owing to its extremely low content in Epimedium genus, we firstly constructed a microbial cell factory to enzymatically biosynthesize icariside I, a natural flavonoid monosaccharide from Herbal Epimedium. Using a combination of targeted MS-based metabolomics, flow cytometric analysis, and biological assays, the therapeutic potentials of icariside I were subsequently investigated in vivo and in vitro.

RESULTS

We find that icariside I markedly downregulates a series of intermediate metabolites such as kynurenine, kynurenic acid and xanthurenic acid and corresponding key enzymes involved in kynurenine-AhR pathway in both tumor cells and tumor-bearing mice. In vivo, oral administration of icariside I downregulates SLC7A8 and PAT4 transporters and AhR, thus inhibiting nuclear PD-1 in CTLs. Moreover, icariside I significantly upregulates CD8 + T cells in both peripheral blood and tumor tissues of tumor-bearing mice. Consequently, interferon-γ (IFN-γ) secreted by CD8 + T cells suppresses tumor growth through activation of JAK1-STAT1 signaling, thus inducing tumor cell apoptosis.

CONCLUSIONS

These results suggest that icariside I could be an effective small molecule drug for tumor immunotherapy by blocking kynurenine-AhR pathway and tumor immune escape.

Computer-Aided Design of α-L-Rhamnosidase to Increase the Synthesis Efficiency of Icariside I

Icariside I, the glycosylation product of icaritin, is a novel effective anti-cancer agent with immunological anti-tumor activity. However, very limited natural icariside I content hinders its direct extraction from plants. Therefore, we employed a computer-aided protein design strategy to improve the catalytic efficiency and substrate specificity of the α-L-rhamnosidase from Thermotoga petrophila DSM 13995, to provide a highly-efficient preparation method. Several beneficial mutants were obtained by expanding the active cavity. The catalytic efficiencies of all mutants were improved 16-200-fold compared with the wild-type TpeRha. The double-point mutant DH was the best mutant and showed the highest catalytic efficiency (k cat /K M : 193.52 s-1 M-1) against icariin, which was a 209.76-fold increase compared with the wild-type TpeRha. Besides, the single-point mutant H570A showed higher substrate specificity than that of the wild-type TpeRha in hydrolysis of different substrates. This study provides enzyme design strategies and principles for the hydrolysis of rhamnosyl natural products.

Purification and Characterization of a Novel α-L-Rhamnosidase from Papiliotrema laurentii ZJU-L07 and Its Application in Production of Icariin from Epimedin C

Icariin is the most effective bioactive compound in Herba Epimedii. To enhance the content of icariin in the epimedium water extract, a novel strain, Papiliotrema laurentii ZJU-L07, producing an intracellular α-L-rhamnosidase was isolated from the soil and mutagenized. The specific activity of α-L-rhamnosidase was 29.89 U·mg-1 through purification, and the molecular mass of the enzyme was 100 kDa, as assayed by SDS-PAGE. The characterization of the purified enzyme was determined. The optimal temperature and pH were 55 °C and 7.0, respectively. The enzyme was stable in the pH range 5.5-9.0 for 2 h over 80% and the temperature range 30-40 °C for 2 h more than 70%. The enzyme activity was inhibited by Ca2+, Fe2+, Cu2+, and Mg2+, especially Fe2+. The kinetic parameters of Km and Vmax were 1.38 mM and 24.64 μmol·mg-1·min-1 using pNPR as the substrate, respectively. When epimedin C was used as a nature substrate to determine the kinetic parameters of α-L-rhamnosidase, the values of Km and Vmax were 3.28 mM and 0.01 μmol·mg-1·min-1, respectively. The conditions of enzymatic hydrolysis were optimized through single factor experiments and response surface methodology. The icariin yield increased from 61% to over 83% after optimization. The enzymatic hydrolysis method could be used for the industrialized production of icariin. At the same time, this enzyme could also cleave the α-1,2 glycosidic linkage between glucoside and rhamnoside in naringin and neohesperidin, which could be applicable in other biotechnological processes.

α-L-rhamnosidase from Penicillium tardum and Its Application for Biotransformation of Citrus Rhamnosides

Enzymatic deramnosylation of flavonoids is a convenient tool for improving the quality of citrus juices. α-L-rhamnosidase with a specific activity of 33.1 units/mg was isolated and characterized from the culture liquid of Penicillium tardum. The molecular weight of the enzyme was 95 kDa according to the data of gel filtration on Sepharose 6B and gel electrophoresis in SDS-PAGE. The pH optimum of the enzyme activity was 5.0, and the thermo optimum was 60 °C. Enzyme showed high stability in the temperature range of 45-50 and at 60-70 °C. It retained 80 to 50% of the initial activity for 90 min. The half-life of α-L-rhamnosidase at 70 °C increased twofold in the presence of 20-40% glycerol and 2.3-fold in the presence of 4 M sorbitol. The enzyme was completely inhibited in the presence of 10^-3 M Ag⁺ and Cd²⁺ and approximately by 90% in the presence of Fe²⁺, Fe³⁺, and Al³⁺ ions. More than 60%, the enzyme activity was inhibited by Hg²⁺, Co²⁺, and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide methiodide. Activating effect of Ca²⁺ ions was also noted. K_m and V_max for the hydrolysis of p-nitrophenyl-α-L-rhamnopyranoside and naringin were 0.7 mM and 38.3 µM/min/mg and 1.34 mM and 43.7 µM/min/mg, respectively. Penicillium tardum α-L-rhamnosidase hydrolyzed naringin, neohesperidin, hesperidin, rutin, and narirutin at high rate, which allowed us to consider it as an effective tool for transformation of bioflavonoids in food industry.

Flavonoid-Modifying Capabilities of the Human Gut Microbiome-An In Silico Study

Flavonoids are a major group of dietary plant polyphenols and have a positive health impact, but their modification and degradation in the human gut is still widely unknown. Due to the rise of metagenome data of the human gut microbiome and the assembly of hundreds of thousands of bacterial metagenome-assembled genomes (MAGs), large-scale screening for potential flavonoid-modifying enzymes of human gut bacteria is now feasible. With sequences of characterized flavonoid-transforming enzymes as queries, the Unified Human Gastrointestinal Protein catalog was analyzed and genes encoding putative flavonoid-modifying enzymes were quantified. The results revealed that flavonoid-modifying enzymes are often encoded in gut bacteria hitherto not considered to modify flavonoids. The enzymes for the physiologically important daidzein-to-equol conversion, well studied in Slackiaisoflavoniconvertens, were encoded only to a minor extent in Slackia MAGs, but were more abundant in Adlercreutzia equolifaciens and an uncharacterized Eggerthellaceae species. In addition, enzymes with a sequence identity of about 35% were encoded in highly abundant MAGs of uncultivated Collinsella species, which suggests a hitherto uncharacterized daidzein-to-equol potential in these bacteria. Of all potential flavonoid modification steps, O-deglycosylation (including derhamnosylation) was by far the most abundant in this analysis. In contrast, enzymes putatively involved in C-deglycosylation were detected less often in human gut bacteria and mainly found in Agathobacter faecis (formerly Roseburia faecis). Homologs to phloretin hydrolase, flavanonol/flavanone-cleaving reductase and flavone reductase were of intermediate abundance (several hundred MAGs) and mainly prevalent in Flavonifractor plautii. This first comprehensive insight into the black box of flavonoid modification in the human gut highlights many hitherto overlooked and uncultured bacterial genera and species as potential key organisms in flavonoid modification. This could lead to a significant contribution to future biochemical-microbiological investigations on gut bacterial flavonoid transformation. In addition, our results are important for individual nutritional recommendations and for biotechnological applications that rely on novel enzymes catalyzing potentially useful flavonoid modification reactions.

Effects of Xian-Ling-Gu-Bao capsule on the gut microbiota in ovariectomized rats: Metabolism and modulation

Xian-Ling-Gu-Bao capsule (XLGB) has been proven to prevent and treat osteoporosis. However, as a long-term oral formula, XLGB's effects on the metabolic capacity, structure and function of gut microbiota have yet to be elucidated in ovariectomized (OVX) rats. Our objectives were to evaluate the capacity of gut microbiota for metabolizing XLGB ingredients and to assess the effect of this prescription on gut microbiota. Herein, an integrated analysis that combined ultrahigh-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) and ultrahigh-performance liquid chromatography tandem triple quadrupole mass spectrometry (UPLC-TQD-MS) was conducted to determine the metabolic capacity of gut microbiota. The effects of XLGB on gut microbiota were explored by metagenomic sequencing in OVX rats. Fecal samples from each group were collected after intragastric administration for three months. In total, 64 biotransformation products were fully characterized with rat gut microbiota from the OVX group and the XLGB group. The deglycosylation reaction was the main biotransformation pathway in core structures in the group that was incubated with XLGB. Compared with the OVX group, different biotransformation products and pathways of the XLGB group after incubation for 2 h and 8 h were described. After three months of feeding with XLGB, the domesticated gut microbiota was conducive to the production of active absorbed components via deglycosylation, such as icaritin, psoralen and isopsoralen. Comparisons of the gut microbiota of the OVX and XLGB groups showed differences in the relative abundances of the two dominant bacterial divisions, namely, Firmicutes and Bacteroidetes. The proportion of Firmicutes was significantly lower and that of Bacteroidetes was significantly higher in the XLGB group. This result demonstrated that XLGB could provide a basis for the treatment of osteoporosis by regulating lipid and bile acid metabolism. In addition, the increase in Lactobacillus, Bacteroides and Prevotella could be an important factor that led to easier production of active absorbed aglycones in the XLGB group. Our observation provided further evidence of the importance of gut microbiota in the metabolism and potential activity of XLGB.

Efficient bioconversion of epimedin C to icariin by a glycosidase from Aspergillus nidulans

Herba Epimedii is a traditional Chinese herbal medicine that contains a mixture of bioactive flavonoid glycosides. Among them, icariin has the most outstanding bioactive functions, while epimedin C exhibits substantial toxicity. A recombinant α-L-rhamnosidase (^synAnRhaE) from Aspergillus nidulans was expressed in Escherichia coli to promote the efficient bioconversion of epimedin C to icariin. A hydrolase activity of 574.5 U L^-1 was acquired via optimized fed-batch fermentation in a 5-L bioreactor. The enzyme proved to be stable in an acidulous pH range below 55 °C with an optimal pH of 4.5 and optimal temperature of 55 °C. Epimedin C (1 g L^-1) was 100% converted to icariin within 90 min using recombinant cells. The resting cells proved to be selective for epimedin C and 2″-O-rhamnosylicariside II in crude extracts of the epimedium plant. This work provides an original and efficient biocatalyst system that can be applied in industrialized production of icariin.

Preparation of isoquercitrin by biotransformation of rutin using α-L-rhamnosidase from Aspergillus niger JMU-TS528 and HSCCC purification

Isoquercitrin is a flavonoid with important applications in the pharmaceutical and nutraceutical industries. However, a low yield and high production cost hinders the industrial preparation of isoquercitrin. In the present study, isoquercitrin was prepared by biotransformation of rutin using α-L-rhamnosidase from Aspergillus niger JMU-TS528 combined with high-speed countercurrent chromatography (HSCCC) purification. As a result, the optimum transformation pH, temperature, and time were pH 4.0, 60 °C, and 60 min, respectively. The K_m and V_max were 0.36 mM and 0.460 mmol/min, respectively. For isoquercitrin production, the optimal rutin concentration and transformation time were approximately 1000 mg/L and 60 min. The rutin transformation rate reached 96.44%. The isoquercitrin was purified to a purity of 97.83% using one-step purification with HSCCC. The isoquercitrin was identified using UPLC-Q-TOF-MS. The comprehensive results indicated that the biotransformation procedure using the α-L-rhamnosidase from A. niger JMU-TS528 combined with HSCCC was a simple and effective process to prepare isoquercitrin, which might facilitate the production of isoquercitrin for industrial use.

Effects of β-glucosidase and α-rhamnosidase on the Contents of Flavonoids, Ginkgolides, and Aroma Components in Ginkgo Tea Drink

Ginkgo tea is a kind of health food produced from Ginkgo biloba leaves. The market of Ginkgo tea encountered many difficulties because of its bad palatability and vague function statement. In this study, two kinds of glycosidase were used to improve the flavor of Ginkgo tea, and three kinds of bioactivities were selected to investigate the health care function of the tea infusion. The aroma components extracted by headspace absorb (HSA) method during the making of Ginkgo tea were analyzed by GC-MS. The flavonoids and ginkgolides released into the tea infusion were studied by HPLC. A combination of β-glucosidase (β-G) and α-rhamnosidase (α-R) was applied during the making of the tea. The contents of characteristic aroma components and the release of total flavonoids and ginkgolides were increased significantly by adding β-G and α-R. The composition of flavone glycosides was changed greatly. The free radical scavenging, inhibition of inflammatory cell activation, and tumor cytotoxicity activities of the tea were demonstrably improved. According to the release of active components, Ginkgo tea can be brewed repeatedly for at least three times. The enzymes used here show potential application prospects in the making of Ginkgo tea or tea drink to get higher contents of flavonoids, ginkgolides, and aroma components.

Biochemical Characterization of the α-l-Rhamnosidase DtRha from Dictyoglomus thermophilum: Application to the Selective Derhamnosylation of Natural Flavonoids

α-l-Rhamnosidases are catalysts of industrial tremendous interest, but their uses are still somewhat limited by their poor thermal stabilities and selectivities. The thermophilic DtRha from Dictyoglomus thermophilum was cloned, and the recombinant protein was easily purified to homogeneity to afford 4.5 mg/L culture of biocatalyst. Michaelis-Menten parameters demonstrated it to be fully specific for α-l-rhamnose. Most significantly, DtRha demonstrated to have a stronger preference for α(1 → 2) linkage rather than α(1 → 6) linkage when removing rhamnosyl moiety from natural flavonoids. This selectivity was fully explained by the difference of binding of the corresponding substrates in the active site of the protein.