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.

Use of ultrasound to increase the catalytic activity of α-L-rhamnosidase

α-L-rhamnosidase (Rha) is ubiquitous in nature and has high feasibility in the food and biotechnology industries. A green and environmentally friendly method was used to improve the activity of Rha. Here, we show that the effects of ultrasound treatment on the Rha. Ultrasonic treatment at 80 W for 10 min yielded the highest enzyme activity. Treatment increased enzyme activity by 26.3% and half-life by 124 min. Further, treatment increased the catalytic efficiency of Rha and increased the substrate conversion rate by 33.88%. These results demonstrate that ultrasound increases the catalytic activity and stability of Rha. Thus, ultrasonic treatment of Rha is cost-effective on the industrial scale.

Preparation of isoquercitrin and rhamnose from readily accessible rutin by a highly specific recombinant α-L-rhamnosidase (r-Rha1)

Isoquercitrin has superior in vivo bioactivities with respect to its primary glycoside rutin. Its conventional preparation was ineffective, with large chemical consumption and many by-products. Rhamnose, a high value-added monosaccharide, is usually separated from acid hydrolytes of rutin. This study aimed to establish a novel enzymatic hydrolysis-based approach for their preparation. α-L-rhamnosidase was expressed in Pichia pastoris GS115 and applied to enzymolysis of rutin. Then, one-factor-at-a-time optimisation of hydrolysis conditions was performed. Two compounds were produced in 0.02 M HAc-NaAc buffer (pH4.50) containing α-L-rhamnosidase/rutin (1:4, w/w) at 60 °C. Consequently, 20.0 g/L rutin was completely hydrolysed in 2 hrs, and isoquercitrin was obtained after purification by HPD-100 resin. Additionally, rhamnose was enriched by decolorisation and crystallisation. MD simulation analysis suggested that rutin was catalysed on the hydrophobic surface of r-Rha1 with van-der-Waals force being main driving force. This strategy is an efficient approach for preparation of isoquercitrin and rhamnose.

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.

Highly efficient bioconversion of icariin to icaritin by whole-cell catalysis

BACKGROUND

Icaritin is an aglycone of flavonoid glycosides from Herba Epimedii. It has good performance in the treatment of hepatocellular carcinoma in clinical trials. However, the natural icaritin content of Herba Epimedii is very low. At present, the icaritin is mainly prepared from flavonoid glycosides by α-L-rhamnosidases and β-glucosidases in two-step catalysis process. However, one-pot icaritin production required reported enzymes to be immobilized or bifunctional enzymes to hydrolyze substrate with long reaction time, which caused complicated operations and high costs. To improve the production efficiency and reduce costs, we explored α-L-rhamnosidase SPRHA2 and β-glucosidase PBGL to directly hydrolyze icariin to icaritin in one-pot, and developed the whole-cell catalytic method for efficient icaritin production.

RESULTS

The SPRHA2 and PBGL were expressed in Escherichia coli, respectively. One-pot production of icaritin was achieved by co-catalysis of SPRHA2 and PBGL. Moreover, whole-cell catalysis was developed for icariin hydrolysis. The mixture of SPRHA2 cells and PBGL cells transformed 200 g/L icariin into 103.69 g/L icaritin (yield 95.23%) in 4 h in whole-cell catalysis under the optimized reaction conditions. In order to further increase the production efficiency and simplify operations, we also constructed recombinant E. coli strains that co-expressed SPRHA2 and PBGL. Crude icariin extracts were also efficiently hydrolyzed by the whole-cell catalytic system.

CONCLUSIONS

Compared to previous reports on icaritin production, in this study, whole-cell catalysis showed higher production efficiency of icaritin. This study provides promising approach for industrial production of icaritin in the future.

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 K_m and V_max 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 K_m and V_max 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.

Homologous Expression and Characterization of α-L-rhamnosidase from Aspergillus niger for the Transformation of Flavonoids

Aspergillus niger has been used for homologous and heterologous expressions of many protein products. In this study, the α-L-rhamnosidase from A. niger (Rha-N1, GenBank XP_001389086.1) was homologously expressed in A. niger 3.350 by Agrobacterium tumefaciens-mediated transformation. The enzyme activity of Rha-N1 was 0.658 U/mL, which was obtained by cultivation of engineered A. niger in a 5-L bioreactor. Rha-N1 was purified by affinity chromatography and characterized. The optimum temperature and optimum pH for Rha-N1 were 60 °C and 4.5, respectively. Enzyme activity was promoted by Al³⁺, Li⁺, Mg²⁺, and Ba²⁺ and was inhibited by Mn²⁺, Fe³⁺, Ca²⁺, Cu²⁺, and organic solvents. The result indicated that rutin was the most suitable substrate for Rha-N1 by comparison with the other two flavonoid substrates hesperidin and naringin. The transformed products of isoquercitrin, hesperetin-7-O-glucoside, and prunin were identified by LC-MS and ¹H-NMR.

Screening and characterization of a GH78 α-l-rhamnosidase from Aspergillus terreus and its application in the bioconversion of icariin to icaritin with recombinant β-glucosidase

In this study, a GH78 α-L-rhamnosidase AtRha from Aspergillus terreus CCF3059 was screened and expressed in Pichia pastoris KM71H. The maximum enzyme activity of AtRha was 1000 U/mL after 12 days. AtRha was most active at 65 °C and pH 6.5, displaying excellent thermal stability and pH stability. The kinetic parameters Km, Vmax, kcat and kcat/Km values for pNPR were 0.481 mM, 659 μmol/min·mg, 1065 s-1 and 2214 s-1mM-1, respectively. AtRha could be inhibited by Fe2+, Hg2+ and Cu2+. Moreover, it displayed good tolerance to organic reagents with 52.6% activity in 15%(w/v) methanol. AtRha can hydrolyze icariin containing the α-1 rhamnoside linkage. Furthermore, AtRha and β-glucosidase TthBg3 showed excellent selectivity to cleave the rhamnose at the 3rd position and the glucosyl at the C-7 group of icariin, which established an effective and green method to produce the more pharmacological active icaritin. In addition, the optimal enzyme addition schemes and the reaction conditions were screened and optimized. After a two-stage transformation under optimized conditions, 0.5 g/L of icariin was transformed into 0.25 g/L of icaritin, with a corresponding molar conversion rate of 91.2%. Our findings provide a new, specific and cost-effective method for the production of icaritin in the industry.

[Enzymatic properties of α-L-rhamnosidase and the factors affecting its activity: a review]

α-L-rhamnosidase is a very important industrial enzyme that is widely distributed in a variety of organisms. α-L-rhamnosidase of different origins show functional diversity. For example, the optimal pH of α-L-rhamnosidase from bacteria is close to neutral or alkaline, while the optimal pH of α-L-rhamnosidase from fungi is in the acidic range. Furthermore, the enzymatic properties of α-L-rhamnosidases of different origins differ in terms of the optimal temperature, the thermal stability, and the substrate specificity, which determine the different applications of these enzymes. In this connection, it is crucial to elucidate the similarities and differences in the catalytic mechanism and substrate specificity of α-L-rhamnosidase of different origins through analyzing its enzymatic properties. Moreover, it is important to explore and understand the effects of aglycon and metal cations on enzyme activity and the competitive inhibition of L-rhamnose and glucose on enzymes. These knowledge can help discover α-L-rhamnosidase of industrial significance and promote its industrial application.

Microbial α-L-Rhamnosidases of Glycosyl Hydrolase Families GH78 and GH106 Have Broad Substrate Specificities toward α-L-Rhamnosyl- and α-L-Mannosyl-Linkages

α-L-Rhamnosidases (α-L-Rha-ases, EC 3.2.1.40) are glycosyl hydrolases (GHs) that hydrolyze a terminal α-linked L-rhamnose residue from a wide spectrum of substrates such as heteropolysaccharides, glycosylated proteins, and natural flavonoids. As a result, they are considered catalysts of interest for various biotechnological applications. α-L-rhamnose (6-deoxy-L-mannose) is structurally similar to the rare sugar α-L-mannose. Here we have examined whether microbial α-L-Rha-ases possess α-L-mannosidase activity by synthesizing the substrate 4-nitrophenyl α-L-mannopyranoside. Four α-L-Rha-ases from GH78 and GH106 families were expressed and purified from Escherichia coli cells. All four enzymes exhibited both α-L-rhamnosyl-hydrolyzing activity and weak α-L-mannosyl-hydrolyzing activity. SpRhaM, a GH106 family α-L-Rha-ase from Sphingomonas paucimobilis FP2001, was found to have relatively higher α-L-mannosidase activity as compared with three GH78 α-L-Rha-ases. The α-L-mannosidase activity of SpRhaM showed pH dependence, with highest activity observed at pH 7.0. In summary, we have shown that α-L-Rha-ases also have α-L-mannosidase activity. Our findings will be useful in the identification and structural determination of α-L-mannose-containing polysaccharides from natural sources for use in the pharmaceutical and food industries.

Dual promoter strategy enhances co-expression of α-L-rhamnosidase and enhanced fluorescent protein for whole-cell catalysis and bioresource valorization

Developing circular economy is the only way to improve the efficiency of resource utilization. Whole-cell catalysis is an effective method to recycle enzymes, improve catalytic efficiency, and reduce production costs. The enzyme, α-L-rhamnosidase has considerable application prospects in the field of biocatalysis as it can hydrolyze a variety of α-L rhamnoses. In the present study, the genes for α-L-rhamnosidase (rhaB1) and enhanced fluorescent protein (EGFP) were co-expressed using a bi-promoter expression vector pRSFDuet1 and their enzymatic properties were evaluated. To our knowledge, this study has established an effective rhamnosidase-fluorescent indicator and whole-cell catalytic system for the first time. Moreover, we analyzed the change in the activity of the crude rhaB1-EGFP as well as its whole-cell during the biocatalysis process using fluorescence intensity. Recombinant rhaB1-EGFP as a product which contains rhaB1 and EGFP showed higher thermal stability, pH stability, and conversion efficiency than rhaB1, and its optimum temperature for rutin catalysis was ideal for industrial applications. Moreover, under the optimal conditions of a rutin concentration of 0.05 g/L, pH of 6.0, temperature of 40 °C, a yield of 92.5% was obtained. Furthermore, we demonstrated the relationship between the fluorescence intensity and enzyme activity. This study established a highly efficient whole-cell catalytic system whose activity can be evaluated by fluorescence intensity, providing a reference for enzyme recycling.

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.

Heterologous Expression and Characterization of a New Clade of Aspergillus α-L-Rhamnosidase Suitable for Citrus Juice Processing

α-L-Rhamnosidase is a glycoside hydrolase capable of removing naringin from citrus juice. However, α-L-rhamnosidases always have broad substrate spectra, causing negative effects on citrus juice. In this study, a α-L-rhamnosidase-expressing fungal strain, JMU-TS529, was identified, and its α-L-rhamnosidase was characterized. As a result, JMU-TS529 was identified as Aspergillus tubingensis via morphological and molecular characteristics. The predicted protein sequence shared an amino acid identity of less than 30% with previously characterized α-L-rhamnosidases. The optimal pH and temperature were 4.0 and 50-60 °C, respectively. Most importantly, the α-L-rhamnosidase showed a strong ability to hydrolyze naringin but scarcely acted on other substrates. Furthermore, the enzyme could efficiently remove naringin from pomelo juice without changing its attractive aroma. These results indicate that the present enzyme represents a new clade of Aspergillus α-L-rhamnosidase that is desirable for debittering citrus juice, providing a better alternative for improving the quality of citrus juice.

Upscale of recombinant α-L-rhamnosidase production by Pichia pastoris Mut(S) strain

Pichia pastoris is currently one of the most preferred microorganisms for recombinant enzyme production due to its efficient expression system. The advantages include the production of high amounts of recombinant proteins containing the appropriate posttranslational modifications and easy cultivation conditions. α-L-Rhamnosidase is a biotechnologically important enzyme in food and pharmaceutical industry, used for example in debittering of citrus fruit juices, rhamnose pruning from naringin, or enhancement of wine aromas, creating a demand for the production of an active and stable enzyme. The production of recombinant α-L-rhamnosidase cloned in the Mut(S) strain of P. pastoris KM71H was optimized. The encoding gene is located under the control of the AOX promoter, which is induced by methanol whose concentration is instrumental for these strain types. Fermentation was upscaled in bioreactors employing various media and several methanol-feeding strategies. It was found that fed batch with BSM media was more effective compared to BMMH (Buffered Methanol-complex Medium) media due to lower cost and improved biomass formation. In BSM (Basal Salt Medium) medium, the dry cell weight reached approximately 60 g/L, while in BMMH it was only 8.3 g/L, without additional glycerol, which positively influenced the amount of enzyme produced. New methanol feeding strategy, based on the level of dissolved oxygen was developed in this study. This protocol that is entirely independent on methanol monitoring was up scaled to a 19.5-L fermenter with 10-L working volume with the productivity of 13.34 mgprot/L/h and specific activity of α-L-rhamnosidase of 82 U/mg. The simplified fermentation protocol was developed for easy and effective fermentation of P. pastoris Mut(S) based on dissolved oxygen monitoring in the induction phase of an enzyme production.