Biotransformation of methyl-β-D-glucopyranoside to higher chain alkyl glucosides by cell bound β-glucosidase of Pichia etchellsii

Whole-cell bioconversion using non-Leloir transglycosylation reactions: a review

Microbial biocatalysts are evolving technological tools for glycosylation research in food, feed and pharmaceuticals. Advances in bioengineered Leloir and non-Leloir carbohydrate-active enzymes allow for whole-cell biocatalysts to curtail production costs of purified enzymes while enhancing glucan synthesis through continued enzyme expression. Unlike sugar nucleotide-dependent Leloir glycosyltransferases, non-Leloir enzymes require inexpensive sugar donors and can be designed to match the high value, yield and selectivity of the former. This review addresses the current state of bacterial cell-based production of glucans and glycoconjugates via transglycosylation, and describes how alterations made to microbial hosts to surpass purified enzymes as the preferred mode of catalysis are steadily being acquired through genetic engineering, rational design and process optimization. A comprehensive exploration of relevant literature has been summarized to describe whole-cell biocatalysis in non-Leloir glycosylation reactions with various donors and acceptors, and the characterization, application and latest developments in the optimization of their use.

From Lactose to Alkyl Galactoside Fatty Acid Esters as Non-Ionic Biosurfactants: A Two-Step Enzymatic Approach to Cheese Whey Valorization

A library of alkyl galactosides was synthesized to provide the "polar head" of sugar fatty acid esters to be tested as non-ionic surfactants. The enzymatic transglycosylation of lactose resulted in alkyl β-D-galactopyranosides, whereas the Fischer glycosylation of galactose afforded isomeric mixtures of α- and β-galactopyranosides and α- and β-galactofuranosides. n-Butyl galactosides from either routes were enzymatically esterified with palmitic acid, used as the fatty acid "tail" of the surfactant, giving the corresponding n-butyl 6-O-palmitoyl-galactosides. Measurements of interfacial tension and emulsifying properties of n-butyl 6-O-palmitoyl-galactosides revealed that the esters of galactopyranosides are superior to those of galactofuranosides, and that the enantiopure n-butyl 6-O-palmitoyl-β-D-galactoside, prepared by the fully enzymatic route, leads to the most stable emulsion. These results pave the way to the use of lactose-rich cheese whey as raw material for the obtainment of bio-based surfactants.

Engineering CGTase to improve synthesis of alkyl glycosides

Alkyl glycoside surfactants with elongated carbohydrate chains are useful in different applications due to their improved biocompatibility. Cyclodextrin glucanotransferases can catalyze the elongation process through the coupling reaction. However, due to the presence of a hydrophobic tail, the interaction between an alkyl glycoside acceptor and the active site residues is weaker than the interaction with maltooligosaccharides at the corresponding site. Here we report the mutations of F197, G263 and E266 near the acceptor subsites in the CGTase CspCGT13 from Carboxydocella sp. The results showed that substitutions of both F197 and G263 were important for the binding of acceptor substrate dodecyl maltoside during coupling reaction. The double mutant F197Y/G263A showed enhanced coupling activity and displayed a 2-fold increase of the primary coupling product using γ-cyclodextrin as donor when compared to wildtype CspCGT13. Disproportionation activity was also reduced, which was also the case for another double mutant (F197Y/E266A) that however not showed the corresponding increase in coupling. A triple mutant F197Y/G263A/E266A maintained the increase in primary coupling product (1.8-fold increase) using dodecyl maltoside as acceptor, but disproportionation was approximately at the same level as in the double mutants. In addition, hydrolysis of starch was slightly increased by the F197Y and G263A substitutions, indicating that interactions at both positions influenced the selectivity between glycosyl and alkyl moieties.

Increased yield of enzymatic synthesis by chromatographic selection of different N-glycoforms of yeast invertase

Invertases are glycosidases applied for synthesis of alkyl glycosides that are important and effective surfactants. Stability of invertases in the environment with increased content of organic solvent is crucial for increase of productivity of glycosidases. Their stability is significantly influenced by N-glycosylation. However, yeast N-glycosylation pathways may synthesize plethora of N-glycan structures. A total natural crude mixture of invertase glycoforms (EINV) extracted from Saccharomyces cerevisiae was subfractionated by anion-exchange chromatography on industrial monolithic supports to obtain different glycoforms (EINV1-EINV3). Separated glycoforms exhibited different stabilities in water-alcohol solutions that are in direct correlation with the amount of phosphate bound to N-glycans. Observed differences in stability of different invertase glycoforms were used to improve productivity of methyl β-d-fructofuranoside (MF) synthesis. The efficiency and yield of MF synthesis were improved more than 50% when the most stabile glycoform bearing the lowest amount of phosphorylated N-glycans is selected and utilized. These data underline the importance of analysis of glycan structures attached to glycoproteins, demonstrate different impact of N-glycans on the surface charge and enzyme stability in regard to particular reaction environment, and provide a platform for improvement of yield of industrial enzymatic synthesis by chromatographic selection of glycoforms on monolithic supports.

Subcritical Methanolysis of Starch and Transglycosidation to Produce Dodecyl Polyglucosides

Biosurfactants based on carbohydrates are of special interest because of their production from renewable resources, nontoxicity, biocompatibility, and environmental friendliness. Dodecyl polyglucosides, a type of nonionic surfactant synthesized with methyl polyglucosides obtained from the eco-friendly subcritical methanolysis of renewable resource of starch, is no doubt good for ecosystem. With the subcritical methanolysis of starch, the methyl polyglucosides were obtained without any catalyst. Under the reaction condition of the weight ratio of methanol to starch of 7.5, temperature of 220 °C, and reaction time of 2 h, the yield of methyl polyglucosides was 85%. Dodecyl polyglucosides were synthesized by transglycosidation with methyl polyglucosides, and the green nonionic surfactant has excellent surface activity. The critical micelle concentration and hydrophilic lipophilic balance are 0.022 wt % and 12, respectively.

Biotransformation of 4-methylcoumarins by cambial meristematic cells of Camptotheca acuminata

Cambial meristematic cell (CMC) suspension cultures were investigated as a new biotransformation system for the first time. Four 4-methylcoumarins substrates were transformed by CMCs of Camptotheca acuminata into four corresponding products, including 4,8-dimethylcoumarin-7-O-β-d-glucopyranoside (I-1), 4,7-dimethylcoumarin-6-O-β-d-glucopyranoside (II-1), 6-hydroxy-7-methoxyl-4- methylcoumarin (III-1), and 4,7-dimethylcoumarin-5-O-β-d-glucopyranoside (IV-1), of which I-1, II-1, and IV-1 were new compounds. In addition, the biotransformation time and the amount of substrate were investigated to compare the biotransformation rate and optimize the biotransformation conditions of the four substrates in C. acuminata CMCs suspension cultures. The results suggested C. acuminata CMCs were able to select glycosylate phenolic hydroxyl groups of 4-methylcoumarins I, II, and IV, with high regio- and stereoselectivity, but no corresponding glycoside of any phenolic hydroxyl group of compound III was detected. Simultaneously, the result also showed that the C. acuminata CMCs were able to transform the 7-hydroxy groups of substrate III to its corresponding methylated products. Furthermore, the monoamine oxidase (MAO) inhibition activities of biotransformed products were evaluated, and the data showed that all the products possessed good MAO inhibition activities in vitro. In conclusion, C. acuminata CMCs could be applied to glycosylation biotransformation as a novel plant-based system due to the successful application of bioconversion of exogenous coumarins.

Cambial meristematic cell (CMC) suspension cultures were investigated as a new biotransformation system for the first time.

Direct conversion of cellulose into ethanol and ethyl-β-d-glucoside via engineered Saccharomyces cerevisiae

Simultaneous saccharification and fermentation (SSF) of cellulose via engineered Saccharomyces cerevisiae is a sustainable solution to valorize cellulose into fuels and chemicals. In this study, we demonstrate the feasibility of direct conversion of cellulose into ethanol and a biodegradable surfactant, ethyl-β-d-glucoside, via an engineered yeast strain (i.e., strain EJ2) expressing heterologous cellodextrin transporter (CDT-1) and intracellular β-glucosidase (GH1-1) originating from Neurospora crassa. We identified the formation of ethyl-β-d-glucoside in SSF of cellulose by the EJ2 strain owing to transglycosylation activity of GH1-1. The EJ2 strain coproduced 0.34 ± 0.03 g ethanol/g cellulose and 0.06 ± 0.00 g ethyl-β-d-glucoside/g cellulose at a rate of 0.30 ± 0.02 g·L^-1 ·h^-1 and 0.09 ± 01 g·L^-1 ·h^-1 , respectively, during the SSF of Avicel PH-101 cellulose, supplemented only with Celluclast 1.5 L. Herein, we report a possible coproduction of a value-added chemical (alkyl-glucosides) during SSF of cellulose exploiting the transglycosylation activity of GH1-1 in engineered S. cerevisiae. This coproduction could have a substantial effect on the overall technoeconomic feasibility of theSSF of cellulose.

Synthesis of octyl-β-D-glucopyranoside catalyzed by Thai rosewood β-glucosidase-displaying Pichia pastoris in an aqueous/organic two-phase system

We explored the ability of a Thai rosewood β-glucosidase-displaying P. pastoris whole-cell biocatalyst (Pp-DCBGL) system to synthesize alkyl β-D-glucosides. The primary investigation centered on the synthesis of octyl-β-D-glucopyranoside (octyl-glu, OG). OG could be synthesized through reverse hydrolysis reaction with very low efficiency. Then, OG was synthesized between BG and octanol by a transglycosylation reaction. In a 2-ml reaction system, OG was synthesized with a conversion rate of 51.1% in 3h when 5 mg/ml BG was utilized as the glucosyl donor under optimized conditions. And, even after being reused four times, the Pp-DCBGL was relatively stable. Additionally, a 500-ml-scale reaction system was conducted in a 2-L stirred reactor with a conversion rate of 47.5% in 1.5 h. Moreover, the conversion rate did not decrease after the whole-cell catalyst was reused two times. In conclusion, Pp-DCBGL has high reaction efficiency and operational stability, which is a powerful biocatalyst available for industrial synthesis.

Pilot studies on scale-up biocatalysis of 7-β-xylosyl-10-deacetyltaxol and its analogues by an engineered yeast

Paclitaxel content in yew tree is extremely low, causing a worldwide shortage of this important anticancer drug. Yew tree can also produce abundant 7-β-xylosyl-10-deacetyltaxol that can be bio-converted into 10-deacetyltaxol for semi-synthesis of paclitaxel. However, the bio-conversion by the screened natural microorganisms was inefficient. We have constructed the recombinant yeast with a glycoside hydrolase gene from Lentinula edodes and explored the bioconversion. Based on previously established reaction conditions, the bioconversion of 7-β-xylosyl-10-deacetyltaxol or its extract was further optimized and scaled up with the engineered yeast harvested from 200-L scale high-cell-density fermentation. The optimization included the freeze-dried cell amount, dimethyl sulfoxide concentration, addition of 0.5% antifoam supplement, and substrate concentration. A 93-95% bioconversion and 83% bioconversion of 10 and 15 g/L 7-β-xylosyltaxanes in 10 L reaction volume were achieved, respectively. The yield of 10-deacetyltaxol reached 10.58 g/L in 1 L volume with 15 g/L 7-β-xylosyl-10-deacetyltaxol. The conversion efficiencies were not only much higher than those of other reports and our previous work, but also realized in 10 L reaction volume. A pilot-scale product purification was also established. Our study bridges the gap between the basic research and commercial utilization of 7-β-xylosyl-10-deacetyltaxol for the industrial production of semi-synthetic paclitaxel.

Transformation of multi-component ginkgolide into ginkgolide B by Coprinus comatus

BACKGROUND

As the strongest antagonist of the platelet activating factor, ginkgolide B (GB) possesses anti-ischemic, anti-oxidant and anti-convulsant properties, and it is used for the treatment of thrombosis in clinical practice. Till now, GB is usually obtained from extraction of Ginkgo biloba leaves through column chromatography with an extremely low yield and high cost, which can not meet clinical requirement. Therefore, it is urgent to find a new method to prepare GB.

RESULTS

In the current study, we studied the ability and mechanism to transform multi-component ginkgolide into GB by Coprinus comatus in order to enhance the GB yield. Except for ginkgolide A (GA) and GB, all the other ginkgolides in the extract were transformed by the strain. In the case of culture medium containing 20 g/L glucose, the transformation product was identified as 12% GA and 88% GB by high performance liquid chromatography-Mass spectrometry (HPLC-MS), two stage mass spectrometry (MS/MS) and nuclear magnetic resonance (NMR). Partial GA was also transformed into GB according to the yield (76%) and the content of GA in the raw ginkgolide (28.5%). Glucose was the key factor to transform ginkgolides. When glucose concentration in medium was higher than 40 g/L, all ginkgolides were transformed into the GB. Proteomic analysis showed that C. comatus transformed ginkgolide into GB by producing 5 aldo/keto reductases and catalases, and enhancing the metabolism of glucose, including Embden-Meyerhof pathway (EMP), hexose monophophate pathway (HMP) and tricarboxylic acid (TCA).

CONCLUSIONS

C. comatus could transform ginkgolides into GB when the medium contained 40 g/L glucose. When the strain transformed ginkgolides, the glucose metabolism was enhanced and the strain synthesized more aldo/keto reductases and catalases. Our current study laid the groundwork for industrial production of GB.

Biotransformation of 11-keto-β-boswellic acid by Cunninghamella blakesleana

11-Keto-β-boswellic acid (KBA), as one of the active constituents in the gum resin of Boswellia serrata, possesses significant biological activities including anti-inflammatory activity. However, its extensive metabolism and low polarity has limited the systemic availability of KBA. The present research was aimed to obtain and explore the various possible derivatives of KBA through biotransformation by Cunninghamella blakesleana AS 3.970. A total of ten transformed compounds were isolated and purified, and their chemical structures were characterized as 7β-hydroxy-11-keto-β-boswellic acid; 7β, 15α-dihydroxy-11-keto-β-boswellic acid ; 7β, 16β-dihydroxy-11-keto-β-boswellic acid; 7β, 16α-dihydroxy-11-keto-β-boswellic acid; 7β, 22β-dihydroxy-11-keto-β-boswellic acid; 7β, 21β-dihydroxy-11-keto-β-boswellic acid; 7β, 20β-dihydroxy-11-keto-β-boswellic acid; 7β, 30-dihydroxy-11-keto-β-boswellic acid; 3α, 7β-dihydroxy-11-oxours-12-ene-24, 30-dioic acid and 3α, 7β-dihydroxy-30-(2-hydroxypropanoyloxy)-11-oxours-12-en-24-oic acid by various spectroscopic methods. The biotransformation processes include hydroxylation, oxidation and esterification. Primary structure-activity relationships (SAR) of inhibitory effects on NO production in RAW 264.7 macrophage cells are discussed.

Response surface methodology based optimization of β-glucosidase production from Pichia pastoris

The thermotolerant yeast Pichia etchellsii produces multiple cell bound β-glucosidases that can be used for synthesis of important alkyl- and aryl-glucosides. Present work focuses on enhancement of β-glucosidase I (BGLI) production in Pichia pastoris. In the first step, one-factor-at-a-time experimentation was used to investigate the effect of aeration, antifoam addition, casamino acid addition, medium pH, methanol concentration, and mixed feed components on BGLI production. Among these, initial medium pH, methanol concentration, and mixed feed in the induction phase were found to affect BGLI production. A 3.3-fold improvement in β-glucosidase expression was obtained at pH 7.5 as compared to pH 6.0 on induction with 1 % methanol. Addition of sorbitol, a non-repressing substrate, led to further enhancement in β-glucosidase production by 1.4-fold at pH 7.5. These factors were optimized with response surface methodology using Box-Behnken design. Empirical model obtained was used to define the optimum "operating space" for fermentation which was a pH of 7.5, methanol concentration of 1.29 %, and sorbitol concentration of 1.28 %. Interaction of pH and sorbitol had maximum effect leading to the production of 4,400 IU/L. The conditions were validated in a 3-L bioreactor with accumulation of 88 g/L biomass and 2,560 IU/L β-glucosidase activity.

Recent biotechnological progress in enzymatic synthesis of glycosides

Glycosylation is one of the most important post-modification processes of small molecules and enables the parent molecule to have increased solubility, stability, and bioactivity. Enzyme-based glycosylation has achieved significant progress due to advances in protein engineering, DNA recombinant techniques, exploitation of biosynthetic gene clusters of natural products, and computer-based modeling programs. Our report summarizes glycosylation data that have been published within the past five years to provide an overall review of current progress. We also present the future trends and perspectives for glycosylation.

Synthesis of hexyl α-glucoside and α-polyglucosides by a novel Microbacterium isolate

Alkyl-glucosides and alkyl-polyglucosides are the new-generation biodegradable surfactants with good emulsifying and wetting properties. The α-forms of these glucosides occur in antibiotics and also stimulate nasal absorption of many drugs. In this paper, we report the synthesis of hexyl α-glucoside and α-polyglucosides using cell-bound α-glucosidase activity of a novel strain of Microbacterium paraoxydans. A number of cell-bound glycosyl hydrolase activities were detected in the isolate with the maximum hydrolytic activity of 180 IU g(-1) dry wt cells on p-nitrophenyl-α-D-glucopyranoside. In a micro-aqueous system, at a water activity of 0.69, 1.8 g l(-1) of hexyl α-glucoside (corresponding to about 25 % yield) was synthesized by whole cells with maltose and hexanol as substrates. The concentration was enhanced to 11 g l(-1) (~60 % yield) in a biphasic system at a water content of 60 %. (1)H and (13)C NMR spectra of the purified compound confirmed the synthesized product to be hexyl-α-D-glucopyranoside, while the presence of hexyl di- and tri-glucosides was confirmed by electrospray ionization mass spectrometry. The cell-driven synthesis makes this an extremely attractive alternative for synthesis of such compounds.

An efficient novel glycosylation of flavonoid by β-fructosidase resistant to hydrophilic organic solvents

An effective approach was successfully developed to isolate glycosidase with resistance of hydrophilic organic solvent, simultaneously with acceptor specificity of the target substrate. By this approach, an efficient solvent tolerant glycosidase producing bacterium Arthrobacter nicotianae XM6 was obtained. The β-fructosidase from strain XM6 shows high activity and stability in 10-25% DMSO and 10-20% methanol with 90-99% yields of puerarin glycosides. The addition of hydrophilic solvents not only greatly promoted the solubility of puerarin, but also regulated main products from multifructosyl puerarin to monofructosyl puerarin with increasing solvent concentration. Extraordinary highly efficient synthesis of puerarin glycosides (111.3 g/L of monofructosyl puerarin and 35.6 g/L of difructosyl puerarin) was attained in 25% DMSO solvent system from 110.4 g/L puerarin, which resulted a great facility for purification in large-scale process. The most novelty was that the β-fructosidase did not hydrolyze almost the newly formed glycosides using simply sucrose as donor.