Synthesis of Malto-Oligosaccharides Via the Acceptor Reaction Catalyzed by Cyclodextrin Glycosyltransferases

Maltooligosaccharides: Properties, Production and Applications

Maltooligosaccharides (MOS) are homooligosaccharides that consist of 3-10 glucose molecules linked by α-1,4 glycosidic bonds. As they have physiological functions, they are commonly used as ingredients in nutritional products and functional foods. Many researchers have investigated the potential applications of MOS and their derivatives in the pharmaceutical industry. In this review, we summarized the properties and methods of fabricating MOS and their derivatives, including sulfated and non-sulfated alkylMOS. For preparing MOS, different enzymatic strategies have been proposed by various researchers, using α-amylases, maltooligosaccharide-forming amylases, or glycosyltransferases as effective biocatalysts. Many researchers have focused on using immobilized biocatalysts and downstream processes for MOS production. This review also provides an overview of the current challenges and future trends of MOS production.

Engineering of Cyclodextrin Glycosyltransferase through a Size/Polarity Guided Triple-Code Strategy with Enhanced α-Glycosyl Hesperidin Synthesis Ability

Hesperidin, a flavonoid enriched in citrus peel, can be enzymatically glycosylated using CGTase with significantly improved water solubility. However, the reaction catalyzed by wild-type CGTase is rather inefficient, reflected in the poor production rate and yield. By focusing on the aglycon attacking step, seven residues were selected for mutagenesis in order to improve the transglycosylation efficiency. Due to the lack of high-throughput screening technology regarding to the studied reaction, we developed a size/polarity guided triple-code strategy in order to reduce the library size. The selected residues were replaced by three rationally chosen amino acids with either changed size or polarity, leading to an extremely condensed library with only 32 mutants to be screened. Twenty-five percent of the constructed mutants were proved to be positive, suggesting the high quality of the constructed library. Specific transglycosylation activity of the best mutant Y217F was assayed to be 935.7 U/g, and its k_cat/K_mA is 6.43 times greater than that of the wild type. Homology modeling and docking computation suggest the source of notably enhanced catalytic efficiency is resulted from the combination of ligand transfer and binding effect. IMPORTANCE Size/polarity guided triple-code strategy, a novel semirational mutagenesis strategy, was developed in this study and employed to engineer the aglycon attacking site of CGTase. Screening pressure was set as improved hesperidin glucoside synthesis ability, and eight positive mutants were obtained by screening only 32 mutants. The high quality of the designed library confirms the effectiveness of the developed strategy is potentially valuable to future mutagenesis studies. Mechanisms of positive effect were explained. The best mutant exhibits 6.43 times enhanced k_cat/K_mA value and confirmed to be a superior whole-cell catalyst with potential application value in synthesizing hesperidin glucosides.

Production and Surfactant Properties of Tert-Butyl α-d-Glucopyranosides Catalyzed by Cyclodextrin Glucanotransferase

While testing the ability of cyclodextrin glucanotransferases (CGTases) to glucosylate a series of flavonoids in the presence of organic cosolvents, we found out that this enzyme was able to glycosylate a tertiary alcohol (tert-butyl alcohol). In particular, CGTases from Thermoanaerobacter sp. and Thermoanaerobacterium thermosulfurigenes EM1 gave rise to the appearance of at least two glycosylation products, which were characterized by mass spectrometry (MS) and nuclear magnetic resonance (NMR) as tert-butyl-α-D-glucoside (major product) and tert-butyl-α-D-maltoside (minor product). Using partially hydrolyzed starch as glucose donor, the yield of transglucosylation was approximately 44% (13 g/L of tert-butyl-α-D-glucoside and 4 g/L of tert-butyl-α-D-maltoside). The synthesized tert-butyl-α-D-glucoside exhibited the typical surfactant behavior (critical micellar concentration, 4.0–4.5 mM) and its properties compared well with those of the related octyl-α-D-glucoside. To the best of our knowledge, this is the first description of an enzymatic α-glucosylation of a tertiary alcohol.

Current studies on the enzymatic preparation 2-O-α-d-glucopyranosyl-l-ascorbic acid with cyclodextrin glycosyltransferase

2-O-α-d-glucopyranosyl-l-ascorbic acid (AA-2G) is one of the most important l-ascorbic acid derivatives because of its resistance to reduction and oxidation and its easy degradation by α-glucosidase to release l-ascorbic acid and glucose. Thus, AA-2G has commercial uses in food, medicines and cosmetics. This article presents a review of recent studies on the enzymatic production of AA-2G using cyclodextrin glycosyltransferase. Reaction mechanisms with different donor substrates are discussed. Protein engineering, physical and biological studies of cyclodextrin glycosyltransferase are introduced from the viewpoint of effective AA-2G production. Future prospects for the production of AA-2G using cyclodextrin glycosyltransferase are reviewed.

Optimization of Regioselective α-Glucosylation of Hesperetin Catalyzed by Cyclodextrin Glucanotransferase

The regioselective α-glucosylation of hesperetin was achieved by a transglycosylation reaction catalyzed by cyclodextrin glucanotransferase (CGTase) from Thermoanaerobacter sp. using soluble starch as glucosyl donor. By combining mass spectrometry (ESI-TOF) and 2D-NMR analysis, the main monoglucosylated derivative was fully characterized (hesperetin 7-O-α-d-glucopyranoside). In order to increase the yield of monoglucoside, several reaction parameters were optimized: Nature and percentage of cosolvent, composition of the aqueous phase, glucosyl donor, temperature, and the concentrations of hesperetin and soluble starch. Under the optimal conditions, which included the presence of 30% of bis(2-methoxyethyl) ether as cosolvent, the maximum concentration of monoglucoside was approximately 2 mM, obtained after 24 h of reaction. To our knowledge, this is the first report of direct glucosylation of hesperetin employing free enzymes instead of whole cells.

Optimization of pectinase immobilization on grafted alginate-agar gel beads by 24 full factorial CCD and thermodynamic profiling for evaluating of operational covalent immobilization

Pectinase produced by a honey derived from the fungus Aspergillus awamori KX943614 was covalently immobilized onto gel beads made of alginate and agar. Polyethyleneimine, glutaraldehyde, loading time and enzyme's units were optimized by 2⁴ full factorial central composite design (CCD). The immobilization process increased the optimal working pH for the free pectinase from 5 to a broader range of pH4.5-5.5 and the optimum operational temperature from 55°C to a higher temperature, of 60°C, which is favored to reduce the enzyme's microbial contamination. The thermodynamics studies showed a thermal stability enhancement against high temperature for the immobilized formula. Moreover, an increase in half-lives and D-values was achieved. The thermodynamic studies proved that immobilization of pectinase made a remarkable increase in enthalpy and free energy because of enzyme stability enhancement. The reusability test revealed that 60% of pectinase's original activity was retained after 8 successive cycles. This gel formula may be convenient for immobilization of other industrial enzymes.

Immobilization of His-tagged recombinant xylanase from Penicillium occitanis on nickel-chelate Eupergit C for increasing digestibility of poultry feed

Recombinant xylanase 2 from Penicillium occitanis expressed with an His-tag in Pichia pastoris, termed PoXyn2, was immobilized on nickel-chelate Eupergit C by covalent coupling reaction with a high immobilization yield up to 93.49%. Characterization of the immobilized PoXyn2 was further evaluated. The optimum pH was not affected by immobilization, but the immobilized PoXyn2 exhibited more acidic and large optimum pH range (pH 2.0-4.0) than that of the free PoXyn2 (pH 3.0). The free PoXyn2 had an optimum temperature of 50 °C, whereas that of the immobilized enzyme was shifted to 65 °C. Immobilization increased both pH stability and thermostability when compared with the free enzyme. Thermodynamically, increase in enthalpy and free energy change after covalent immobilization could be credited to the enhanced stability. Immobilized xylanase could be reused for 10 consecutive cycles retaining 60% of its initial activity. It was found to be effective in releasing reducing sugar from poultry feed. Immobilization on Eupergit C is important due to its mechanical resistance at high pH and temperature. Hence, considerable stability and reusability of bound enzyme may be advantageous for its industrial application.

Biocatalytic synthesis of maltodextrin-based acrylates from starch and α-cyclodextrin

Novel 2-(β-maltooligooxy)-ethyl (meth)acrylate monomers are successfully synthesized by CGTase from Bacillus macerans catalyzed coupling of 2-(β-glucosyloxy)-ethyl acrylate and methacrylate with α-cyclodextrin or starch. HPLC-UV analysis shows that the CGTase catalyzed reaction yields 2-(β-maltooligooxy)-ethyl acrylates with 1 to 15 glucopyranosyl units. (1) H NMR spectroscopy reveals that the β-linkage in the acceptor molecule is preserved during the CGTase catalyzed coupling reaction, whereas the newly introduced glucose units are attached by α-(1,4)-glycosidic linkages. The synthesized 2-(β-maltooligooxy)-ethyl acrylate monomers are successfully polymerized by aqueous free radical polymerization to yield the comb-shaped glycopolymer poly(2-(β-maltooligooxy)-ethyl acrylate).

Engineering of cyclodextrin glucanotransferases and the impact for biotechnological applications

Cyclodextrin glucanotransferases (CGTases) are industrially important enzymes that produce cyclic alpha-(1,4)-linked oligosaccharides (cyclodextrins) from starch. Cyclodextrin glucanotransferases are also applied as catalysts in the synthesis of glycosylated molecules and can act as antistaling agents in the baking industry. To improve the performance of CGTases in these various applications, protein engineers are screening for CGTase variants with higher product yields, improved CD size specificity, etc. In this review, we focus on the strategies employed in obtaining CGTases with new or enhanced enzymatic capabilities by searching for new enzymes and improving existing enzymatic activities via protein engineering.

Optimized synthesis of specific sizes of maltodextrin glycosides by the coupling reactions of Bacillus macerans cyclomaltodextrin glucanyltransferase

Bacillus macerans cyclomaltodextrin glucanyltransferase (CGTase, EC 2.4.1.19), in reaction with cyclomaltohexaose and methyl alpha-D-glucopyranoside, methyl beta-D-glucopyranoside, phenyl alpha-D-glucopyranoside, and phenyl beta-D-glucopyranoside gave four kinds of maltodextrin glycosides. The reactions were optimized by using different ratios of the individual d-glucopyranosides to cyclomaltohexaose, from 0.5 to 5.0, to obtain the maximum molar percent yields of products, which were from 68.3% to 78.6%, depending on the particular D-glucopyranoside, and also to obtain different maltodextrin chain lengths. The lower ratios of 0.5-1.0 gave a wide range of sizes from d.p. 2-17 and higher. As the molar ratio was increased from 1.0 to 3.0, the larger sizes, d.p. 9-17, decreased, and the small and intermediate sizes, d.p. 2-8, increased; as the molar ratios were increased further from 3.0 to 5.0, the large sizes completely disappeared, the intermediate sizes, d.p. 4-8, decreased, and the small sizes, d.p. 2 and 3 became predominant. A comparison is made with the synthesis of maltodextrins by the reaction of CGTase with different molar ratios of d-glucose to cyclomaltohexaose.

Glucosyltransferases acting on starch or sucrose for the synthesis of oligosaccharides

In this work we review the extraordinary biotechnological potential of two glycosyltransferases, cyclodextrin glucanotransferase and dextransucrase, especially their utility in the synthesis of oligosaccharides. Both enzymes are non-Leloir transferases that require neither co-factors nor activated substrates, as they directly employ the free energy of cleavage of starch and sucrose, respectively. Cyclodextrin glucanotransferase is able to produce cyclodextrins from starch. In the presence of appropriate acceptors (e.g., carbohydrates), this enzyme furnishes oligosaccharides containing α(1[Formula: see text]4) bonds. Thus, we have found that glucose, maltose, and sucrose readily serve as acceptors to form the corresponding [Glc-α(1[Formula: see text]4)]n- oligosaccharides, with the degree of polymerization being controlled by the starch:acceptor ratio. The ability of other sugars and related compounds to act as acceptors is also reviewed. Dextransucrase is a glycansucrase that synthesizes dextran using sucrose as glucosyl donor. The formation of dextrans can be quantitatively replaced with the formation of novel oligosaccharides by adding alternative carbohydrate acceptors to the reaction medium. With the dextransucrase from Leuconostoc mesenteroides B-1299, we have investigated the synthesis of gluco- oligosaccharides containing α(1[Formula: see text]2) bonds using methyl 1-O-α-D-glucopyranoside as the acceptor. These products constitute a class of nondigestible nutraceutical oligosaccharides with prebiotic properties relating to the stabilization and enhancement of gastrointestinal tract flora, and are being increasingly used by the food industry.Key words: glycansucrases, cyclodextrin glucanotransferase, cyclodextrin glucosyltransferase, dextransucrase, acceptor products, gluco-oligosaccharides, malto-oligosaccharides, coupling sugar, nutraceuticals, functional foods, prebiotics.