Recombinant α-l-rhamnosidase from Aspergillus terreus in selective trimming of rutin

A comparative study of two α-L-rhamnosidases with high sequence identity

The GH78 α-L-rhamnosidase from Aspergillus tubingensis (AT-Rha) was proved to be a new clade of Aspergillus α-L-rhamnosidases in the previous study. A putative α-L-rhamnosidase from A. kawachii IFO 4308 (AK-Rha) has 92 % identity in amino acid sequence with AT-Rha. In this study, AK-Rha was expressed in P. pastoris and characterized. Similar to AT-rRha, the recombinant AK-Rha (AK-rRha) showed a narrow substrate specificity to naringin. Interestingly, the enzyme activity of AK-rRha was 0.816 U/mg toward naringin, significantly lower than 125.142 U/mg of AT-rRha. Their large differences in catalytic efficiency was mainly due to their differences in kcat values between AK-rRha (0.67 s-1) and AT-rRha (4.89 × 104 s-1). The molecular dynamics simulation exhibited that the overall conformation of AK-Rha was rigid and that of AT-Rha was flexible; the Loop Y-L located above the catalytic domain formed different steric hindrances to naringin, and interacted with the flavonoid matrices at different strengths. The polar solvation energy analysis implied that the glycosidic bond was more easily hydrolysed in AT-Rha. The comparative study verified that the main feature of AK-Rha and AT-Rha represented Aspergillus α-L-rhamnosidase was the narrow substrate specificity toward naringin, and provided an insight of the relationships between their catalytic abilities and structures.

Combinatorial metabolic engineering of Bacillus subtilis enables the efficient biosynthesis of isoquercitrin from quercetin

BACKGROUND

Isoquercitrin (quercetin-3-O-β-D-glucopyranoside) has exhibited promising therapeutic potentials as cardioprotective, anti-diabetic, anti-cancer, and anti-viral agents. However, its structural complexity and limited natural abundance make both bulk chemical synthesis and extraction from medical plants difficult. Microbial biotransformation through heterologous expression of glycosyltransferases offers a safe and sustainable route for its production. Despite several attempts reported in microbial hosts, the current production levels of isoquercitrin still lag behind industrial standards.

RESULTS

Herein, the heterologous expression of glycosyltransferase UGT78D2 gene in Bacillus subtilis 168 and reconstruction of UDP-glucose (UDP-Glc) synthesis pathway led to the synthesis of isoquercitrin from quercetin with titers of 0.37 g/L and 0.42 g/L, respectively. Subsequently, the quercetin catabolism blocked by disruption of a quercetin dioxygenase, three ring-cleavage dioxygenases, and seven oxidoreductases increased the isoquercitrin titer to 1.64 g/L. And the hydrolysis of isoquercitrin was eliminated by three β-glucosidase genes disruption, thereby affording 3.58 g/L isoquercitrin. Furthermore, UDP-Glc pool boosted by pgi (encoding glucose-6-phosphate isomerase) disruption increased the isoquercitrin titer to 10.6 g/L with the yield on quercetin of 72% and to 35.6 g/L with the yield on quercetin of 77.2% in a 1.3-L fermentor.

CONCLUSION

The engineered B. subtilis strain developed here holds great potential for initiating the sustainable and large-scale industrial production of isoquercitrin. The strategies proposed in this study provides a reference to improve the production of other flavonoid glycosides by engineered B. subtilis cell factories.

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.

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.

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.

Adding sorbitol improves the thermostability of α-l-rhamnosidase from Aspergillus niger and increases the conversion of hesperidin

In this study, we found the addition of sorbitol could improve the thermostability of α-l-rhamnosidase from Aspergillus niger. When α-l-rhamnosidase with sorbitol was heat-treated at 60°C, 65°C, and 70°C, the half-life t_1/2 increased by 28-, 18-, and 9-fold, respectively. Inactivation thermodynamic analysis showed that both E_a and ΔG^≠ of α-l-rhamnosidase increased. Through the response surface methodology (RSM) analysis, the higher hesperidin conversion (63.26%) by α-l-rhamnosidase was attained with 0.7 M sorbitol at 60°C and pH 4.5 for 10 min. Furthermore, hesperidin could be completely hydrolyzed after 10 hr of reaction. Overall, the results indicated that the addition of sorbitol improved the thermostability of α-l-rhamnosidase and increased the enzymatic conversion of hesperidin to hesperetin-7-O-glucoside (HMG). It also provided a simple and efficient way to increase enzymatic conversion of other valuable flavonoid monomers due to the broad substrate specificities of α-l-rhamnosidase from A. niger. PRACTICAL APPLICATIONS: Hesperetin-7-O-glucoside (HMG), a derhamnosylation product of hesperidin, is considered as a synthetic precursor for novel and efficient sweeteners and is important in food, functional food, and nutraceutical industries. Compared to chemical hydrolysis methods, the enzymatic conversion of hesperidin is milder and has the advantages of high specificity. Adding sorbitol can improve the thermostability of α-l-rhamnosidase and increase the enzyme efficacy against hesperidin. This study gave more evidence that adding sorbitol could improve the thermostability of enzymes and provide a better choice for improving biotransformation potency of enzymes.

Antioxidative effect of dietary flavonoid isoquercitrin on human ovarian granulosa cells HGL5 in vitro

This study aimed to examine the effect of dietary flavonoid isoquercitrin on ovarian granulosa cells using the immortalized human cell line HGL5. Cell viability, survival, apoptosis, release of steroid hormones 17beta-estradiol and progesterone, and human transforming growth factor-beta2 (TGF-beta2) and TGF-beta2 receptor as well as intracellular reactive oxygen species (ROS) generation were investigated after isoquercitrin treatment at the concentration range of 5-100 microg.ml-1. It did not cause any significant change (p>0.05) in cell viability as studied by AlamarBlue assay in comparison to control. No significant change was observed (p>0.05) in the proportion of live, dead and apoptotic cells as revealed by apoptotic assay using flow cytometry. Similarly, the release of 17beta-estradiol, progesterone, TGF-beta2 and its receptor were not affected significantly (p>0.05) by isoquercitrin as detected by ELISA, in comparison to control. Except for the highest concentration of 100 microg.ml-1, which led to oxidative stress, isoquercitrin exhibited antioxidative activity at lower concentration used in the study (5, 10, 25, and 50 microg.ml-1) by hampering the production of intracellular ROS, in comparison to control, as detected by chemiluminescence assay (p<0.05). Findings of the present study indicate an existence of the antioxidative pathway that involves inhibition of intracellular ROS generation by isoquercitrin in human ovarian granulosa cells.

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.

Improved Production of Recombinant Myrosinase in Pichia pastoris

The effect of the deletion of a 57 bp native signal sequence, which transports the nascent protein through the endoplasmic reticulum membrane in plants, on improved AtTGG1 plant myrosinase production in Pichia pastoris was studied. Myrosinase was extracellularly produced in a 3-liter laboratory fermenter using α-mating factor as the secretion signal. After the deletion of the native signal sequence, both the specific productivity (164.8 U/L/h) and volumetric activity (27 U/mL) increased more than 40-fold compared to the expression of myrosinase containing its native signal sequence in combination with α-mating factor. The deletion of the native signal sequence resulted in slight changes in myrosinase properties: the optimum pH shifted from 6.5 to 7.0 and the maximal activating concentration of ascorbic acid increased from 1 mM to 1.5 mM. Kinetic parameters toward sinigrin were determined: 0.249 mM (K_m) and 435.7 U/mg (V_max). These results could be applied to the expression of other plant enzymes.

Dual Substrate Specificity of the Rutinosidase from Aspergillus niger and the Role of Its Substrate Tunnel

Rutinosidases (α-l-rhamnopyranosyl-(1-6)-β-d-glucopyranosidases, EC 3.2.1.168, CAZy GH5) are diglycosidases that cleave the glycosidic bond between the disaccharide rutinose and the respective aglycone. Similar to many retaining glycosidases, rutinosidases can also transfer the rutinosyl moiety onto acceptors with a free -OH group (so-called transglycosylation). The recombinant rutinosidase from Aspergillus niger (AnRut) is selectively produced in Pichia pastoris. It can catalyze transglycosylation reactions as an unpurified preparation directly from cultivation. This enzyme exhibits catalytic activity towards two substrates; in addition to rutinosidase activity, it also exhibits β-d-glucopyranosidase activity. As a result, new compounds are formed by β-glucosylation or rutinosylation of acceptors such as alcohols or strong inorganic nucleophiles (NaN₃). Transglycosylation products with aliphatic aglycones are resistant towards cleavage by rutinosidase, therefore, their side hydrolysis does not occur, allowing higher transglycosylation yields. Fourteen compounds were synthesized by glucosylation or rutinosylation of selected acceptors. The products were isolated and structurally characterized. Interactions between the transglycosylation products and the recombinant AnRut were analyzed by molecular modeling. We revealed the role of a substrate tunnel in the structure of AnRut, which explained the unusual catalytic properties of this glycosidase and its specific transglycosylation potential. AnRut is attractive for biosynthetic applications, especially for the use of inexpensive substrates (rutin and isoquercitrin).

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.

Isolated Silymarin Flavonoids Increase Systemic and Hepatic Bilirubin Concentrations and Lower Lipoperoxidation in Mice

Bilirubin is considered to be one of the most potent endogenous antioxidants in humans. Its serum concentrations are predominantly affected by the activity of hepatic bilirubin UDP-glucuronosyl transferase (UGT1A1). Our objective was to analyze the potential bilirubin-modulating effects of natural polyphenols from milk thistle (Silybum marianum), a hepatoprotective herb. Human hepatoblastoma HepG2 cells were exposed to major polyphenolic compounds isolated from milk thistle. Based on in vitro studies, 2,3-dehydrosilybins A and B were selected as the most efficient compounds and applied either intraperitoneally or orally for seven days to C57BL/6 mice. After, UGT1A1 mRNA expression, serum, intrahepatic bilirubin concentrations, and lipoperoxidation in the liver tissue were analyzed. All natural polyphenols used increased intracellular concentration of bilirubin in HepG2 cells to a similar extent as atazanavir, a known bilirubinemia-enhancing agent. Intraperitoneal application of 2,3-dehydrosilybins A and B (the most efficient flavonoids from in vitro studies) to mice (50 mg/kg) led to a significant downregulation of UGT1A1 mRNA expression (46 ± 3% of controls, p < 0.005) in the liver and also to a significant increase of the intracellular bilirubin concentration (0.98 ± 0.03vs.1.21 ± 0.02 nmol/mg, p < 0.05). Simultaneously, a significant decrease of lipoperoxidation (61 ± 2% of controls, p < 0.005) was detected in the liver tissue of treated animals, and similar results were also observed after oral treatment. Importantly, both application routes also led to a significant elevation of serum bilirubin concentrations (125 ± 3% and 160 ± 22% of the controls after intraperitoneal and oral administration, respectively, p < 0.005 in both cases). In conclusion, polyphenolic compounds contained in silymarin, in particular 2,3-dehydrosilybins A and B, affect hepatic and serum bilirubin concentrations, as well as lipoperoxidation in the liver. This phenomenon might contribute to the hepatoprotective effects of silymarin.

An alkali tolerant α-l-rhamnosidase from Fusarium moniliforme MTCC-2088 used in de-rhamnosylation of natural glycosides

Analkali tolerant α-l-rhamnosidase has been purified to homogeneity from the culture filtrate of a new fungal strain, Fusarium moniliforme MTCC-2088, using concentration by ultrafiltration and cation exchange chromatography on CM cellulose column. The molecular mass of the purified enzyme has been found to be 36.0 kDa using SDS-PAGE analysis. The K_m value using p-nitrophenyl-α-l-rhamnopyranoside as the variable substrate in 0.2 M sodium phosphate buffer pH10.5 at50 °C was 0.50 mM. The catalytic rate constant was15.6 s^-1giving the values of k_cat/K_m is 3.12 × 10⁴M^-1 s^-1. The pH and temperature optima of the enzyme were 10.5 and 50 °C, respectively. The purified enzyme had better stability at 10 °C in basic pH medium. The enzyme derhamnosylated natural glycosides like naringin to prunin, rutin to isoquercitrin and hesperidin to hesperetin glucoside. The purified α-l-rhamnosidase has potential for enhancement of wine aroma.

Crystal structure of native α-L-rhamnosidase from Aspergillus terreus

α-L-Rhamnosidases cleave terminal nonreducing α-L-rhamnosyl residues from many natural rhamnoglycosides. This makes them catalysts of interest for various biotechnological applications. The X-ray structure of the GH78 family α-L-rhamnosidase from Aspergillus terreus has been determined at 1.38 Å resolution using the sulfur single-wavelength anomalous dispersion phasing method. The protein was isolated from its natural source in the native glycosylated form, and the active site contained a glucose molecule, probably from the growth medium. In addition to its catalytic domain, the α-L-rhamnosidase from A. terreus contains four accessory domains of unknown function. The structural data suggest that two of these accessory domains, E and F, might play a role in stabilizing the aglycon portion of the bound substrate.

"Sweet Flavonoids": Glycosidase-Catalyzed Modifications

Natural flavonoids, especially in their glycosylated forms, are the most abundant phenolic compounds found in plants, fruit, and vegetables. They exhibit a large variety of beneficial physiological effects, which makes them generally interesting in a broad spectrum of scientific areas. In this review, we focus on recent advances in the modifications of the glycosidic parts of various flavonoids employing glycosidases, covering both selective trimming of the sugar moieties and glycosylation of flavonoid aglycones by natural and mutant glycosidases. Glycosylation of flavonoids strongly enhances their water solubility and thus increases their bioavailability. Antioxidant and most biological activities are usually less pronounced in glycosides, but some specific bioactivities are enhanced. The presence of l-rhamnose (6-deoxy-α-l-mannopyranose) in rhamnosides, rutinosides (rutin, hesperidin) and neohesperidosides (naringin) plays an important role in properties of flavonoid glycosides, which can be considered as "pro-drugs". The natural hydrolytic activity of glycosidases is widely employed in biotechnological deglycosylation processes producing respective aglycones or partially deglycosylated flavonoids. Moreover, deglycosylation is quite commonly used in the food industry aiming at the improvement of sensoric properties of beverages such as debittering of citrus juices or enhancement of wine aromas. Therefore, natural and mutant glycosidases are excellent tools for modifications of flavonoid glycosides.

The Stoichiometry of Isoquercitrin Complex with Iron or Copper Is Highly Dependent on Experimental Conditions

Interaction of flavonoids with transition metals can be partially responsible for their impact on humans. Stoichiometry of the iron/copper complex with a flavonoid glycoside isoquercitrin, a frequent component of food supplements, was assessed using competitive and non-competitive methods in four (patho)physiologically-relevant pH values (4.5. 5.5, 6.8, and 7.5). Isoquercitrin chelated all tested ions (Fe²⁺, Fe³⁺, Cu²⁺, and Cu⁺) but its affinity for Cu⁺ ions proved to be very low. In general, the chelation potency dropped with pH lowering. Metal complexes of 1:1 stoichiometry were mostly formed, however, they were not stable and the stoichiometry changed depending on conditions. Isoquercitrin was able to reduce both Cu²⁺ and Fe³⁺ ions at low ratios, but its reducing potential was diminished at higher ratios (isoquercitrin to metal) due to the metal chelation. In conclusion, this study emphasizes the need of using multiple different methods for the assessment of chelation potential in moderately-active metal chelators, like flavonoids.

Synthesis and Antiradical Activity of Isoquercitrin Esters with Aromatic Acids and Their Homologues

Isoquercitrin, (IQ, quercetin-3-O-β-d-glucopyranoside) is known for strong chemoprotectant activities. Acylation of flavonoid glucosides with carboxylic acids containing an aromatic ring brings entirely new properties to these compounds. Here, we describe the chemical and enzymatic synthesis of a series of IQ derivatives at the C-6″. IQ benzoate, phenylacetate, phenylpropanoate and cinnamate were prepared from respective vinyl esters using Novozym 435 (Lipase B from Candida antarctica immobilized on acrylic resin). The enzymatic procedure gave no products with “hydroxyaromatic” acids, their vinyl esters nor with their benzyl-protected forms. A chemical protection/deprotection method using Steglich reaction yielded IQ 4-hydroxybenzoate, vanillate and gallate. In case of p-coumaric, caffeic, and ferulic acid, the deprotection lead to the saturation of the double bonds at the phenylpropanoic moiety and yielded 4-hydroxy-, 3,4-dihydroxy- and 3-methoxy-4-hydroxy-phenylpropanoates. Reducing capacity of the cinnamate, gallate and 4-hydroxyphenylpropanoate towards Folin-Ciocalteau reagent was significantly lower than that of IQ, while other derivatives displayed slightly better or comparable capacity. Compared to isoquercitrin, most derivatives were less active in 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, but they showed significantly better 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid, ABTS) scavenging activity and were substantially more active in the inhibition of tert-butylhydroperoxide induced lipid peroxidation of rat liver microsomes. The most active compounds were the hydroxyphenylpropanoates.

A Sustainable One-Pot, Two-Enzyme Synthesis of Naturally Occurring Arylalkyl Glucosides

A sustainable, convenient, scalable, one-pot, two-enzyme method for the glucosylation of arylalkyl alcohols was developed. The reaction scheme is based on a transrutinosylation catalyzed by a rutinosidase from A. niger using the cheap commercially available natural flavonoid rutin as glycosyl donor, followed by selective "trimming" of the rutinoside unit catalyzed by a rhamnosidase from A. terreus. The process was validated with the syntheses of several natural bioactive glucosides, which could be isolated in up to 75 % yield without silica-gel chromatography.

Enhancing the thermostability of α-L-rhamnosidase from Aspergillus terreus and the enzymatic conversion of rutin to isoquercitrin by adding sorbitol

Background

Thermally stable α-L-rhamnosidase with cleaving terminal α-L-rhamnose activity has great potential in industrial application. Therefore, it is necessary to find a proper method to improve the thermal stability of α-L-rhamnosidase.

Results

In this study, addition of sorbitol has been found to increase the thermostability of α-L-rhamnosidase from Aspergillus terreus at temperatures ranging from 65 °C to 80 °C. Half-life and activation free energy with addition of 2.0 M sorbitol at 70 °C were increased by 17.2-fold, 8.2 kJ/mol, respectively. The analyses of the results of fluorescence spectroscopy and CD have indicated that sorbitol helped to protect the tertiary and secondary structure of α-L-rhamnosidase. Moreover, the isoquercitrin yield increased from 60.01 to 96.43% with the addition of 1.5 M of sorbitol at 70 °C.

Conclusion

Our findings provide an effective approach for enhancing the thermostability of α-L-rhamnosidase from Aspergillus terreus, which makes it a good candidate for industrial processes of isoquercitrin preparation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-017-0342-9) contains supplementary material, which is available to authorized users.

Quercetin and its analogues: optical and acido–basic properties

This study is focused on eight structurally analogous natural flavonoids that exhibit a wide range of biological activities, which are of interest in pharmacy, cosmetics and the food industry.

Isoquercitrin Esters with Mono- or Dicarboxylic Acids: Enzymatic Preparation and Properties

A series of isoquercitrin (quercetin-3-O-β-d-glucopyranoside) esters with mono- or dicarboxylic acids was designed to modulate hydro- and lipophilicity and biological properties. Esterification of isoquercitrin was accomplished by direct chemoenzymatic reaction using Novozym 435 (lipase from Candida antarctica), which accepted C₅- to C12-dicarboxylic acids; the shorter ones, such as oxalic (C₂), malonic (C₃), succinic (C₄) and maleic (C₄) acids were not substrates of the lipase. Lipophilicity of monocarboxylic acid derivatives, measured as log P, increased with the chain length. Esters with glutaric and adipic acids exhibited hydrophilicity, and the dodecanedioic acid hemiester was more lipophilic. All derivatives were less able to reduce Folin-Ciocalteau reagent (FCR) and scavenge DPPH (1,1-diphenyl-2-picrylhydrazyl) than isoquercitrin; ABTS (2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)) radical-scavenging activity was comparable. Dodecanoate and palmitate were the least active in FCR and ABTS scavenging; dodecanoate and hemiglutarate were the strongest DPPH scavengers. In contrast, most derivatives were much better inhibitors of microsomal lipoperoxidation than isoquercitrin; butyrate and hexanoate were the most efficient. Anti-lipoperoxidant activity of monocarboxylic derivatives, except acetates, decreased with increasing aliphatic chain. The opposite trend was noted for dicarboxylic acid hemiesters, isoquercitrin hemidodecanedioate being the most active. Overall, IQ butyrate, hexanoate and hemidodecanedioate are the most promising candidates for further studies.

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.

Uncommon Glycosidases for the Enzymatic Preparation of Glycosides

Most of the reports in literature dedicated to the use of glycosyl hydrolases for the preparation of glycosides are about gluco- (α- and β-form) and galacto-sidase (β-form), reflecting the high-availability of both anomers of glucosides and of β-galactosides and their wide-ranging applications. Hence, the idea of this review was to analyze the literature focusing on hardly-mentioned natural and engineered glycosyl hydrolases. Their performances in the synthetic mode and natural hydrolytic potential are examined. Both the choice of articles and their discussion are from a biomolecular and a biotechnological perspective of the biocatalytic process, shedding light on new applicative ideas and on the assortment of biomolecular diversity. The hope is to elicit new interest for the development of biocatalysis and to gather attention of biocatalyst practitioners for glycosynthesis.

Crystal structure of a novel two domain GH78 family α-rhamnosidase from Klebsiella oxytoca with rhamnose bound

The crystal structure of the GH78 family α-rhamnosidase from Klebsiella oxytoca (KoRha) has been determined at 2.7 Å resolution with rhamnose bound in the active site of the catalytic domain. Curiously, the putative catalytic acid, Asp 222, is preceded by an unusual non-proline cis-peptide bond which helps to project the carboxyl group into the active centre. This KoRha homodimeric structure is significantly smaller than those of the other previously determined GH78 structures. Nevertheless, the enzyme displays α-rhamnosidase activity when assayed in vitro, suggesting that the additional structural domains found in the related enzymes are dispensible for function. Proteins 2015; 83:1742–1749. © 2015 The Authors. Proteins: Structure, Function, and Bioinformatics Published by Wiley Periodicals, Inc.

Chemoenzymatic synthesis of α-L-rhamnosides using recombinant α-L-rhamnosidase from Aspergillus terreus

This study describes an efficient, large scale fermentation of a recombinant α-L-rhamnosidase originating from Aspergillus terreus. High-cell-density Pichia pastoris fermentation resulted in yields up to 627 U/L/h. The recombinant enzyme was used for the reverse rhamnosylation of various small organic compounds. A full factorial experimental design setup was applied to identify the importance of temperature, substrate concentrations, solvent type and concentration as well as the acidity of the reaction mixture. Careful optimization of these parameters allowed the synthesis of a range of α-L-rhamnosides among which cyclohexyl α-L-rhamnopyranoside, anisyl α-L-rhamnopyranoside and 2-phenylethyl α-L-rhamnopyranoside. In addition, α-L-rhamnosylation of phenolic hydroxyls in phenols such as hydroquinone, resorcinol, catechol and phenol was observed, which is a rather unique reaction catalyzed by glycosidases.

Enhancement of the selective enzymatic biotransformation of rutin to isoquercitrin using an ionic liquid as a co-solvent

An ionic liquid (IL)-containing buffer system was first applied in the conversion of rutin to isoquercitrin. High substrate solubility was achieved to enhance the selectivity and efficiency of hesperidinase-catalyzed reaction. Ten ILs were selected as co-solvents to assist catalytic reactions in this biotransformation process. The transformed products of rutin were identified by LC-MS. The [Bmim][BF(4)]-glycine-sodium hydroxide buffer (pH 9) (10:90, v/v) was found to be the best medium for the biotransformation of isoquercitrin from rutin with higher selectivity and efficiency. The reaction time was reduced by 0.33-fold while the conversion of rutin and the yield of isoquercitrin were increased by 1.67-fold and 2.33-fold. The results suggest that IL co-solvents have great potential to enhance the selectively enzymatic hydrolysis of rutin for isoquercitrin production.