Engineering of cyclodextrin glycosyltransferase reaction and product specificity

Facile preparation and characterization of biodegradable and biocompatible UV shielding transdermal patches based on natural rubber latex- dextrin blends

The physico-chemical and biological properties of natural rubber latex (NRL), entailing its biodegradability and biocompatibility, render it a promising material for various biomedical applications. This research explores the facile blending of NRL with dextrin in different compositions to investigate its potential as a prospective UV shielding transdermal patch for biomedical applications. The superior compatibility between the polymers after blending and the improved thermal stability have been established through FTIR, DSC, and TGA examinations, respectively. Optimization of blended polymers for compatibility, wettability, crystallinity, and static mechanical properties has been performed. Morphology characterization conducted via SEM and AFM techniques suggests a uniform morphology for the optimized blend system. The UV shielding ability of the blend has been confirmed by the evaluation of in-vitro UV shielding performance, UV protection factor (UPF), and the superior protection of the optimized system on living cells upon UV irradiation. The observed cell viability, swelling, erosion, porosity, hemocompatibility, and soil degradation properties suggest the NRL-DXT combination for the possible development of high-quality transdermal patches.

Enhancement of β-Cyclodextrin Production Using a Glycogen Debranching Enzyme from Saccharolobus solfataricus STB09

Efficient production of cyclodextrins (CDs) has always been challenging. CDs are primarily produced from starch via cyclodextrin glycosyltransferase (CGTase), which acts on α-1,4 glucosidic bonds; however, α-1,6 glucosidic bonds in starch suppress the enzymatic production of CDs. In this study, a glycogen debranching enzyme from Saccharolobus solfataricus STB09 (SsGDE) was utilized to promote the production of β-CD by hydrolyzing α-1,6 glucosidic bonds. The addition of SsGDE (750 U/g of starch) at the liquefaction stage remarkably improved the β-CD yield, with a 43.9% increase. Further mechanism exploration revealed that SsGDE addition could hydrolyze specific branches with less generation of byproducts, thereby promoting CD production. The chain segments of a degree of polymerization ≥13 produced by SsGDE debranching could also be utilized by β-CGTase to convert into CDs. Overall, these findings proposed a new approach of combining SsGDE with β-CGTase to enhance the CD yield.

A review on recent upgradation and strategies to enhance cyclodextrin glucanotransferase properties for its applications

Cyclodextrin glycosyltransferase (CGTase) is a significant extracellular enzyme with diverse functions. CGTase is widely used in production of cyclic α-(1,4)-linked oligosaccharides (cyclodextrins) from starch via transglycosylation reaction. Recent discoveries of novel CGTases from different microorganisms have expanded its applications but natural CGTase have lower yield, leading to heterologous expression for increased production to meet various needs. Moreover, significant advancements in directed evolution approach have been explored to alter the molecular structure of CGTase to enhance its performance. This review comprehensively summarizes the strategies employed in heterologous expression to boost CGTase production and secretion in various host. It also outlines molecular engineering approaches aimed to improving CGTase properties, including product and substrate specificity, catalytic efficiency, and thermal stability. Additionally, a considerable stability against changes in temperature and organic solvents can be obtained by immobilization.

Efficient production of α-monoglucosyl hesperidin by cyclodextrin glucanotransferase from Bacillus subtilis

α-Monoglucosyl hesperidin is a promising food additive with various activities. However, there are a few reports about the production of α-monoglucosyl hesperidin. Here, to develop a practical and safe process for α-monoglucosyl hesperidin synthesis, we used nonpathogenic Bacillus subtilis as a host to express cyclodextrin glucanotransferase (CGTase) from Bacillus sp. A2-5a. The promoters and signal peptides were screened to optimize the transcription and secretion of CGTase in B. subtilis. The results of optimization showed that the best signal peptide and promoter were YdjM and P_aprE, respectively. Finally, the enzyme activity increased to 46.5 U mL^-1, 8.7 times that of the enzyme expressed from the strain containing pP_HpaII-LipA, and the highest yield of α-monoglucosyl hesperidin was 2.70 g L^-1 by enzymatic synthesis using the supernatant of the recombinant B. subtilis WB800 harboring the plasmid pP_aprE-YdjM. This is the highest α-monoglucosyl hesperidin production level using recombinant CGTase to date. This work provides a generally applicable method for the scaled-up production of α-monoglucosyl hesperidin. KEY POINTS: • A three-step procedure was created for high throughput signal peptide screening. • YdjM and P_aprE were screened from 173 signal peptides and 13 promoters. • α-Monoglucosyl hesperidin was synthesized by CGTase with a yield of 2.70 g L^-1.

Identification of crucial amino acid residues involved in large ring cyclodextrin synthesis by amylomaltase from Corynebacterium glutamicum

Amylomaltase can be used to synthesize large ring cyclodextrins (LR-CDs), applied as drug solubilizer, gene delivery vehicle and protein aggregation suppressor. This study aims to determine the functional amino acid positions of Corynebacterium glutamicum amylomaltase (CgAM) involved in LR-CD synthesis by site-directed mutagenesis approach and molecular dynamic simulation. Mutants named Δ167, Y23A, P228Y, E231Y, A413F and G417F were constructed, purified, and characterized. The truncated CgAM, Δ167 exhibited no starch transglycosylation activity, indicating that the N-terminal domain of CgAM is necessary for enzyme activity. The P228Y, A413F and G417F produced larger LR-CDs from CD36-CD40 as compared to CD29 by WT. A413F and G417F mutants produced significantly low LR-CD yield compared to the WT. The A413F mutation affected all tested enzyme activities (starch tranglycosylation, disproportionation and cyclization), while the G417F mutation hindered the cyclization activity. P228Y mutation significantly lowered the k _cat of disproportionation activity, while E231Y mutant exhibited much higher k _cat and K _m values for starch transglycosylation, compared to that of the WT. In addition, Y23A mutation affected the kinetic parameters of starch transglycosylation and cyclization. Molecular dynamic simulation further confirmed these mutations' impacts on the CgAM and LR-CD interactions. Identified functional amino acids for LR-CD synthesis may serve as a model for future modification to improve the properties and yield of LR-CDs.

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.

Molecular mechanism of acceptor selection in cyclodextrin glycosyltransferases catalyzed ginsenoside transglycosylation

Understanding the mechanisms of enzyme specificity is increasingly important from a fundamental viewpoint and for practical applications. Transglycosylation has attracted many attentions due to its importance in improving the functional properties of acceptor substrates both in vivo and in vitro. Cyclodextrin glucanotransferase (CGTase) is one of the key enzymes in transglycosylation, it has a broad substrate spectrum and utilizes sugar as the donor. However, little is known about the acceptor selectivity of CGTase, which greatly hampers efforts toward the rational design of desirable transglycosylated derivatives. In this study, we found that the CGTase from Bacillus circulans, BcCGTase, was able to form glycosylated products with diverse ginsenosides. In particular, it not only carries out diverse mono-, di-, and even higher-order glycosylations via the transfer of glucose moieties to the COGlc positions, but also can glycosylate the C3-OH position of ginsenosides. In contrast, another CGTase from Bacillus licheniformis (BlCGTase) showed relatively specific acceptor preference with only several ginsenosides. Structural comparison between BcCGTase and BlCGTase revealed that the Arg74/K81 position within the acceptor-binding sites of BcCGTase/BlCGTase was responsible for the differences in catalytic specificity for ginsenoside F1. Further mutagenesis confirmed their roles in the acceptor selection. In conclusion, our study not only demonstrates the acceptor selectivity of CGTases, but also provides insight into the catalytic mechanism of CGTases, which will potentially increase the utility of CGTase for biosynthesis of new, rationally designed transglycosylated derivatives.

Mining for novel cyclomaltodextrin glucanotransferases unravels the carbohydrate metabolism pathway via cyclodextrins in Thermoanaerobacterales

Carbohydrate metabolism via cyclodextrins (CM-CD) is an uncommon starch-converting pathway that thoroughly depends on extracellular cyclomaltodextrin glucanotransferases (CGTases) to transform the surrounding starch substrate to α-(1,4)-linked oligosaccharides and cyclodextrins (CDs). The CM-CD pathway has emerged as a convenient microbial adaptation to thrive under extreme temperatures, as CDs are functional amphipathic toroids with higher heat-resistant values than linear dextrins. Nevertheless, although the CM-CD pathway has been described in a few mesophilic bacteria and archaea, it remains obscure in extremely thermophilic prokaryotes (Topt ≥ 70 °C). Here, a new monophyletic group of CGTases with an exceptional three-domain ABC architecture was detected by (meta)genome mining of extremely thermophilic Thermoanaerobacterales living in a wide variety of hot starch-poor environments on Earth. Functional studies of a representative member, CldA, showed a maximum activity in a thermoacidophilic range (pH 4.0 and 80 °C) with remarkable product diversification that yielded a mixture of α:β:γ-CDs (34:62:4) from soluble starch, as well as G3-G7 linear dextrins and fermentable sugars as the primary products. Together, comparative genomics and predictive functional analysis, combined with data of the functionally characterized key proteins of the gene clusters encoding CGTases, revealed the CM-CD pathway in Thermoanaerobacterales and showed that it is involved in the synthesis, transportation, degradation, and metabolic assimilation of CDs.

Research Progress on Synthesis and Application of Cyclodextrin Polymers

Cyclodextrins (CDs) are a series of cyclic oligosaccharides formed by amylose under the action of CD glucosyltransferase that is produced by Bacillus. After being modified by polymerization, substitution and grafting, high molecular weight cyclodextrin polymers (pCDs) containing multiple CD units can be obtained. pCDs retain the internal hydrophobic-external hydrophilic cavity structure characteristic of CDs, while also possessing the stability of polymer. They are a class of functional polymer materials with strong development potential and have been applied in many fields. This review introduces the research progress of pCDs, including the synthesis of pCDs and their applications in analytical separation science, materials science, and biomedicine.

CGTase, a novel antimicrobial protein from Bacillus cereus YUPP-10, suppresses Verticillium dahliae and mediates plant defence responses

Verticillium wilt is a plant vascular disease caused by the soilborne fungus Verticillium dahliae that severely limits cotton production. In a previous study, we screened Bacillus cereus YUPP-10, an efficient antagonistic bacterium, to uncover mechanisms for controlling verticillium wilt. Here, we report a novel antimicrobial cyclodextrin glycosyltransferase (CGTase) from YUPP-10. Compared to other CGTases, six different conserved domains were identified, and six mutants were constructed by gene splicing with overlap extension PCR. Functional analysis showed that domain D was important for hydrolysis activity and domains A1 and C were important for inducing disease resistance. Direct effects of recombinant CGTase on V. dahliae included reduced mycelial growth, spore germination, spore production, and microsclerotia germination. In addition, CGTase also elicited cotton's innate defence reactions. Transgenic Arabidopsis thaliana lines that overexpress CGTase showed higher resistance to verticillium wilt. Transgenic CGTase A. thaliana plants grew faster and resisted disease better. CGTase overexpression enabled a burst of reactive oxygen species production and activated pathogenesis-related gene expression, indicating that the transgenic cotton was better prepared to protect itself from infection. Our work revealed that CGTase could inhibit the growth of V. dahliae, activate innate immunity, and play a major role in the biocontrol of fungal pathogens.

High-level production of γ-cyclodextrin glycosyltransferase in recombinant Escherichia coli BL21 (DE3): culture medium optimization, enzymatic properties characterization, and product specificity analysis

Purpose

γ-Cyclodextrin glycosyltransferase (γ-CGTase) catalyzes the biotransformation of low-cost starch into valuable γ-cyclodextrin (γ-CD), which is widely applied in biotechnology, food, and pharmaceutical industries. However, the low specificity and activity of soluble γ-CGTase increase the production cost of γ-CD, thereby limiting its applications. Therefore, the present study aimed at optimizing an economical medium for high production of γ-CGTase by the recombinant Escherichia coli (E. coli) BL21 (DE3) and evaluating its enzymatic properties and product specificity.

Methods

The γ-CGTase production was optimized using the combination of Plackett-Burman experimental design (PBD) and Box-Behnken design-response surface methodology (BBD-RSM). The hydrolysis and cyclization properties of γ-CGTase were detected under the standard assay conditions with buffers of various pHs and different reaction temperatures. The product specificity of γ-CGTase was investigated by high-performance liquid chromatography (HPLC) analysis of three CDs (α-, β-, γ-CD) in the biotransformation product of cassava starch.

Results

The γ-CGTase activity achieved 53992.10 U mL−1 under the optimum conditions with the significant factors (yeast extract 38.51 g L−1, MgSO4 4.19 mmol L−1, NiSO4 0.90 mmol L−1) optimized by the combination of PBD and BBD-RSM. The recombinant γ-CGTase exhibited favorable stability in a wide pH and temperature range and maintained both the hydrolysis and cyclization activity under the pH 9.0 and 50 °C. Further analysis of the products from cassava starch catalyzed by the γ-CGTase reported that the majority (90.44%) of product CDs was the γ form, which was nearly 11% higher than the wild enzyme. Cyclododecanone added to the transformation system could enhance the γ-CD purity to 98.72%, which is the highest purity value during the transformation process reported so far.

Conclusion

The yield of γ-CGTase activity obtained from the optimized medium was 2.83-fold greater than the unoptimized medium, and the recombinant γ-CGTase exhibited a favorable thermal and pH stability, and higher γ-cyclization specificity. These results will provide a fundamental basis for the high productivity and purity of γ-CD in the industrial scale.

Cyclodextrin glycosyltransferase-treated germinated brown rice flour improves the cytotoxic capacity of HepG2 cell and has a positive effect on type-2 diabetic mice

Germinated brown rice (GBR) consists of bioactive compounds (BCs) that are very useful for diabetes treatment. Modified GBR-based flour (MGBRF) was produced by modifying the starch in GBR with 0, 299.19, 598.38, and 897.57 U/ml of cyclodextrin glycosyltransferase (CGTase) for 1 hr and then spray-dried to examine its antidiabetic and cytotoxic effects. The results showed that the slowly digestible starch and resistant starch by modifying the starch in GBR with 598.38 U/ml of CGTase were 55.8% and 5.92% corresponding to the increase of γ-amino butyric acid (GABA) and ferulic acid (FA) with 4.31 ± 0.68 mg/ml and 3.10 ± 0.02 mg/ml, respectively. The extract from MGBRF showed strong cytotoxic capacity against HepG2. Furthermore, the in vivo study revealed the stability of the glycemic index (GI) by consuming MGBRF with significant impacts on diabetes. These results suggest that MGBRF through the action of CGTase plays a major role in antidiabetes and HepG2 cell product value addition. PRACTICAL APPLICATIONS: GBR consists of BCs that are useful for diabetes and cancer treatment. However, when using this or GBR-based products, it is difficult to evaluate the effect of functional properties, especially for diabetes and/or cancer diseases due to high starch content. Therefore, the modification of starch to limit digestible starch, increase SDS and RS as well as to enhance the effect of BCs on diabetes and cytotoxic activity on cancer cell should be studied before producing various based products from GBR. The results in this study indicated that CGTase increased BCs without any glycosides BCs in the extract. The MGBRF changed to higher RS and SDS while increasing the BCs. The extract of MGBRF showed strong cytotoxic activity against HepG2 cell and a positive effect on type 2-diabetic mice. Hence, this study produces new information for effective use of GBR-based food as a functional food.

Combined Optimization of Codon Usage and Glycine Supplementation Enhances the Extracellular Production of a β-Cyclodextrin Glycosyltransferase from Bacillus sp. NR5 UPM in Escherichia coli

Two optimization strategies, codon usage modification and glycine supplementation, were adopted to improve the extracellular production of Bacillus sp. NR5 UPM β-cyclodextrin glycosyltransferase (CGT-BS) in recombinant Escherichia coli. Several rare codons were eliminated and replaced with the ones favored by E. coli cells, resulting in an increased codon adaptation index (CAI) from 0.67 to 0.78. The cultivation of the codon modified recombinant E. coli following optimization of glycine supplementation enhanced the secretion of β-CGTase activity up to 2.2-fold at 12 h of cultivation as compared to the control. β-CGTase secreted into the culture medium by the transformant reached 65.524 U/mL at post-induction temperature of 37 °C with addition of 1.2 mM glycine and induced at 2 h of cultivation. A 20.1-fold purity of the recombinant β-CGTase was obtained when purified through a combination of diafiltration and nickel-nitrilotriacetic acid (Ni-NTA) affinity chromatography. This combined strategy doubled the extracellular β-CGTase production when compared to the single approach, hence offering the potential of enhancing the expression of extracellular enzymes, particularly β-CGTase by the recombinant E. coli.

High-level extracellular secretion and characterization of the thermophilic β-cyclodextrin glucanotranferase from Paenibacillus campinasensis in Escherichia coli

A strain CGT-1 producing β-cyclodextrin glucanotranferase (β-CGTase) was identified as Paenibacillus campinasensis by morphological analysis and 16s rDNA analysis. The gene coding for β-CGTase was cloned, sequenced, and expressed in Escherichia coli BL21(DE3). Recombinant β-CGTase was purified and its purity evaluated by SDS-PAGE, showing it encodes a mature protein with a molecular mass of 74 kDa. The β-CGTase was most active at pH 7.0 and 65 °C, respectively. More than 80% activity was retained after incubation at 55 °C for 5 h. The stability of the enzyme was in a pH range from 5.5 to 10.0. The K _m and V _max for the enzyme activity on CGTase were 3.75 mg/mL and 290.75 μmol/min, respectively. The recombinant plasmid pET28a-DacD-cgt-his, pET28a-OmpA-cgt-his, pET28a-OmpT-cgt-his, and pET28a-CGTase-cgt-his were constructed by cloning the signal peptide genes DacD, OmpA, OmpT, and signal peptide derived from cgtase gene into pET28a-cgt-his, respectively. The production of the recombinant β-CGTase with pET28a-DacD-cgt-his reached 60.89 U/mL after 72 h of culture, which produced an approximately 1.98, 2.93, 4.15 to 9.74-fold higher activity than those containing OmpA, CGTase, OmpT, and the control without signal peptide, respectively. The culture conditions for extracellular production of the recombinant β-CGTase in E. coli BL21(DE3) were optimized. The CGTase activity reached the highest level (37.67 U/mL) under the induction of 0.03 mM IPTG at OD₆₀₀ of 0.8 at 30 °C after 48 h of culture. Optimization of the extracellular secretion of the β-CGTase from Paenibacillus campinasensis in recombinant E. coli laid the foundation for further industrial production and application of β-CGTase.

A single mutation in cyclodextrin glycosyltransferase from Paenibacillus barengoltzii changes cyclodextrin and maltooligosaccharides production

Cyclodextrin glycosyltransferases (CGTases) are bacterial enzymes that catalyze starch conversion into cyclodextrins, which have several biotechnological applications including solubilization of hydrophobic compounds, masking of unpleasant odors and flavors in pharmaceutical preparations, and removal of cholesterol from food. Additionally, CGTases produce maltooligosaccharides, which are linear molecules with potential benefits for human health. Current research efforts are concentrated in the development of engineered enzymes with improved yield and/or particular product specificity. In this work, we analyzed the role of four residues of the CGTase from Paenibacillus barengoltzii as determinants of product specificity. Single mutations were introduced in the CGTase-encoding gene to obtain mutants A137V, A144V, L280A and M329I and the activity of recombinant proteins was evaluated. The residue at position 137 proved to be relevant for CGTase activity. Molecular dynamics studies demonstrated additionally that mutation A137V produces a perturbation in the catalytic site of the CGTase, which correlates with a 10-fold reduction in its catalytic efficiency. Moreover, this mutant showed increased production of maltooligosaccharides with a high degree of polymerization, mostly maltopentaose to maltoheptaose. Our results highlight the role of residue 137 as a determinant of product specificity in this CGTase and may be applied to the rational design of saccharide-producing enzymes.

Starch-Modifying Enzymes

Starch is a carbohydrate polymer found abundantly on earth. It is synthesized in plants as a short-term storage compound for respiration in the leaves and for long-term storage in the tubers, seeds and roots of plants. A wide variety of enzymes modify or convert starch into various products. The classes of enzymes that act on starch include endoamylases, exoamylases, debranching enzymes and transferases. Starch-modifying enzymes of microbial origin are utilized in a wide variety of industrial applications. Alkaline-active amylases are diverse in terms of optimum reaction conditions, substrate and product specificity. Amylases that are active at lower temperatures and alkaline conditions are most suited for detergent formulation. Other notable starch-modifying enzymes from alkaliphiles include maltooligosaccharide-forming amylases and cyclodextrin glycosyltransferases (CGTases), which produce a variety of maltooligosaccharides and cyclodextrins, respectively. Such compounds are used in the food, fine chemical, pharmaceutical and cosmetic industries, among others. Alkaline-active amylases are also applicable in the paper, textile and leather industries and also in bioremediation and alkaline waste water treatment. Their application in these fields is further enhanced through stabilization and improving their specificity and catalytic action by employing nanotechnology and genetic engineering. Graphical Abstract *Alkaline alpha-amylase AmyK from Bacillus sp. KSM-1378. Shirai T, Igarashi K, Ozawa T, Hagihara H, Kobayashi T, Ozaki K, Ito S (2007) Proteins 66:600-610. Source: Protein Data Bank in Europe (PDBe).

Domain shuffling of cyclodextrin glucanotransferases for tailored product specificity and thermal stability

Cyclodextrin glucanotransferases (CGTases) convert α-1,4-glucans to cyclic oligosaccharides (cyclodextrins, CD), which have found applications in the food and the pharmaceutical industries. In this study, we used two CGTases with different cyclization activities, product specificities, and pH and temperature optima to construct chimeric variants for the synthesis of large-ring CD. We used (a) a synthetic thermostable CGTase mainly forming α- and β-CD (CD6 and CD7) derived from Geobacillus stearothermophilus ET1/NO2 (GeoT), and (b) a CGTase with lower cyclization activity from the alkaliphilic Bacillus sp. G825-6, which mainly synthesizes γ-CD (CD8). The A1, B, A2, and CDE domains of the G825-6 CGTase were replaced with corresponding GeoT CGTase domains by utilizing a megaprimer cloning approach. A comparison of the optimum temperature and pH, thermal stability, and CD products synthesized by the variants revealed that the B domain had a major impact on the cyclization activity, thermal stability, and product specificity of the constructed chimera. Complete suppression of the synthesis of CD6 was observed with the variants GeoT-A1/B and GeoT-A1/A2/CDE. The variant GeoT-A1/A2/CDE showed the desired enzyme properties for large-ring CD synthesis. Its melting temperature was 9 °C higher compared to the G825-6 CGTase and it synthesized up to 3.3 g·L-1 CD9 to CD12, corresponding to a 1.8- and 2.3-fold increase compared to GeoT and G825-6 CGTase, respectively. In conclusion, GeoT-A1/A2/CDE may be a candidate for the further development of CGTases specifically forming larger CD.

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.

Cyclodextrin enhanced the soluble expression of Bacillus clarkii γ-CGTase in Escherichia coli

BACKGROUND

Cyclodextrin glycosyltransferases (CGTases) catalyze the synthesis of cyclodextrins, which are circular α-(1,4)-linked glucans used in many applications in the industries related to food, pharmaceuticals, cosmetics, chemicals, and agriculture, among others. Economic use of these CGTases, particularly γ-CGTase, requires their efficient production. In this study, the effects of chemical chaperones, temperature and inducers on cell growth and the production of soluble γ-CGTase by Escherichia coli were investigated.

RESULTS

The yield of soluble γ-CGTase in shake-flask culture approximately doubled when β-cyclodextrin was added to the culture medium as a chemical chaperone. When a modified two-stage feeding strategy incorporating 7.5 mM β-cyclodextrin was used in a 3-L fermenter, a dry cell weight of 70.3 g·L^- 1 was achieved. Using this cultivation approach, the total yield of γ-CGTase activity (50.29 U·mL^- 1) was 1.71-fold greater than that observed in the absence of β-cyclodextrin (29.33 U·mL^- 1).

CONCLUSIONS

Since β-cyclodextrin is inexpensive and nontoxic to microbes, these results suggest its universal application during recombinant protein production. The higher expression of soluble γ-CGTase in a semi-synthetic medium showed the potential of the proposed process for the economical production of many enzymes on an industrial scale.

High-level secretion and characterization of cyclodextrin glycosyltransferase in recombinant Komagataella phaffii

Cyclodextrin glycosyltransferase (CGTase) catalyzes the conversion of starch into cyclodextrin (CD), which is widely applied in food, pharmaceutical, cosmetic, and agricultural industries. For efficient production of CD, high yield of CGTase with good characteristics is necessary. In this study, the cgt gene from Bacillus pseudalcaliphilus was expressed in Komagataella phaffii after codon optimization and expression vector selection. The β-CGTase activity in the transformant reached 3885.1UmL^-1, which is the highest value reported so far, at 28°C, 6% inoculum ratio, and 1.5% methanol addition following 24h of incubation. The recombinant CGTase showed high specific activity at 80°C without any γ-CGTase activity, and had good stability in a wide pH and temperature range. These results demonstrate that the recombinant CGTase could have potential industrial applications.

Upscale production of a recombinant cyclodextrin glycosyltransferase from Paenibacillus macerans in Escherichia coli

Cyclodextrin glucanotransferase (CGTase) is an important enzyme with multiple functions in starch utilization. In the present study, a fermentation process for the production of CGTase from Escherichia coli harboring the recombinant plasmid pET28b(+)-CGTase was investigated and optimized. The optimal fermentation and expression conditions were 10.0 g/L glycerol, 20.0 g/L tryptone, and 10.0 g/L yeast extract with an initial pH of 7.0, an IPTG concentration of 0.1 mM and an induction temperature of 28 °C for 10 h. The resulting CGTase activity reached up to 36.4 U/L and was 2.1-fold higher than before optimization. Under these optimal fermentation conditions, the up-scaled fermentation was carried out in a 500-L fermentor, and a CGTase activity of 45.2 U/L was achieved. This study provides a foundation for the industrial production of CGTase.

High production of genistein diglucoside derivative using cyclodextrin glycosyltransferase from Paenibacillus macerans

Genistein has been regarded as one important soy isoflavone with multiple health benefits, whereas its applications are limited by the low hydrophilicity. To improve the water solubility, codon optimized cyclodextrin glycosyltransferase from Paenibacillus macerans was employed for genistein transglycosylation in this study. At least four transglycosylation products were produced and identified by HPLC and LC-MS: genistein monoglucoside, diglucoside, triglucoside, and tetraglucoside derivatives. Obviously, the yields of genistein monoglucoside and genistein diglucoside exhibited great superiority compared with other two products. To maximize the yield of genistein diglucoside, various reaction conditions such as genistein dissolvents, glycosyl donors, substrates concentrations and ratios, enzyme concentrations, reaction pH, temperature, and time were optimized. Finally, the yield of genistein diglucoside was enhanced by 1.5-fold under the optimum reaction system. Our study demonstrates that the production of genistein diglucoside could be specifically enhanced, which is one important genistein derivative with better water solubility and stability.

Effects of immobilization, pH and reaction time in the modulation of α-, β- or γ-cyclodextrins production by cyclodextrin glycosyltransferase: Batch and continuous process

This study reports the immobilization of a β-CGTase on glutaraldehyde pre-activated silica and its use to production of cyclodextrins in batch and continuous reactions. We were able to modulate the cyclodextrin production (α-, β- and γ-CD) by immobilization and changing the reaction conditions. In batch reactions, the immobilized enzyme reached to maximum productions of 4.9mgmL^-1 of α-CD, 3.6mgmL^-1 of β-CD and 3.5mgmL^-1 of γ-CD at different conditions of temperature, pH and reaction time. In continuous reactor, varying the residence time and pH it was possible to produce at pH 4.0 and 141min of residence time preferentially γ-CD (0.75 and 3.36mgmL^-1 of α- and γ-CD, respectively), or at pH 8.0 and 4.81min α- and β-CDs (3.44 and 3.51mgmL^-1).

Development and Application of Cyclodextrin Hydrolyzing Mutant Enzyme Which Hydrolyzes β- and γ-CD Selectively

Cyclodextrins (CDs) are produced from starch by cyclodextrin glucanotransferase (CGTase), which has cyclization activity. Specifically, α-CD is an important biomolecule, as it is a molecular carrier and soluble dietary fiber used in the food industry. Upon inspection of the conserved regions of the glycoside hydrolase (GH) 13 family amylases, the amino acids K232 and H233 of CGTase were identified as playing an important role in enzyme reaction specificity. A novel CD hydrolyzing enzyme, cyclodextrin glycosyl transferase (CGTase)-alpha, was developed using site-directed mutagenesis at these positions. Action pattern analysis using various substrates revealed that CGTase-alpha was able to hydrolyze β- and γ-CD, but not α-CD. This selective CD hydrolyzing property was employed to purify α-CD from a CD mixture solution. The α-CD that remained after treatment with CGTase-alpha and exotype glucoamylase was purified using hydrophobic interaction chromatography with 99% purity.

Rational design to change product specificities and thermostability of cyclodextrin glycosyltransferase from Paenibacillus sp

Functional modification of cyclodextrin glycosyltransferase (CGTases) for better product specificity and thermostability is of great importance for industrial applications.

Glycemic Response to Corn Starch Modified with Cyclodextrin Glycosyltransferase and its Relationship to Physical Properties

Corn starch was modified with cyclodextrin glycosyltransferase (CGTase) below the gelatinization temperature. The porous granules with or without CGTase hydrolysis products may be used as an alternative to modified corn starches in foods applications. The amount and type of hydrolysis products were determined, containing mainly β-cyclodextrin (CD), which will influence pasting behavior and glycemic response in mice. Irregular surface and small holes were observed by microscopic analysis and differences in pasting properties were observed in the presence of hydrolysis products. Postprandial blood glucose in mice fed gelatinized enzymatically modified starch peaked earlier than their ungelatinized counterparts. However, in ungelatinized enzymatically modified starches, the presence of β- CD may inhibit the orientation of amylases slowing hydrolysis, which may help to maintain lower blood glucose levels. Significant correlations were found between glycemic curves and viscosity pattern of starches.

Stevia Glycosides: Chemical and Enzymatic Modifications of Their Carbohydrate Moieties to Improve the Sweet-Tasting Quality

Stevia glycosides, extracted from the leaves of the plant Stevia rebaudiana Bertoni, display an amazing high degree of sweetness. As processed plant products, they are considered as excellent bio-alternatives for sucrose and artificial sweeteners. Being noncaloric and having beneficial properties for human health, they are the subject of an increasing number of studies for applications in food and pharmacy. However, one of the main obstacles for the successful commercialization of Stevia sweeteners, especially in food, is their slight bitter aftertaste and astringency. These undesirable properties may be reduced or eliminated by modifying the carbohydrate moieties of the steviol glycosides. A promising procedure is to subject steviol glycosides to enzymatic glycosylation, thereby introducing additional monosaccharide residues into the molecules. Depending on the number and positions of the monosaccharide units, the taste quality and sweetness potency of the compounds will vary. Many studies have been performed already, and this review summarizes the structures of native steviol glycosides and the recent data of modifications of the carbohydrate moieties that have been published to provide an overview of the current progress.

Immobilization of Glycoside Hydrolase Families GH1, GH13, and GH70: State of the Art and Perspectives

Glycoside hydrolases (GH) are enzymes capable to hydrolyze the glycosidic bond between two carbohydrates or even between a carbohydrate and a non-carbohydrate moiety. Because of the increasing interest for industrial applications of these enzymes, the immobilization of GH has become an important development in order to improve its activity, stability, as well as the possibility of its reuse in batch reactions and in continuous processes. In this review, we focus on the broad aspects of immobilization of enzymes from the specific GH families. A brief introduction on methods of enzyme immobilization is presented, discussing some advantages and drawbacks of this technology. We then review the state of the art of enzyme immobilization of families GH1, GH13, and GH70, with special attention on the enzymes β-glucosidase, α-amylase, cyclodextrin glycosyltransferase, and dextransucrase. In each case, the immobilization protocols are evaluated considering their positive and negative aspects. Finally, the perspectives on new immobilization methods are briefly presented.

Advances in Enzymatic Glycoside Synthesis

A robust platform for facile defined glycan synthesis does not exist. Yet the need for such technology has never been greater as researchers seek to understand the full scope of carbohydrate function, stretching beyond the classical roles of structure and energy storage to encompass highly nuanced cell signaling events. To comprehensively explore and exploit the full diversity of carbohydrate functions, we must first be able to synthesize them in a controlled manner. Toward this goal, traditional chemical syntheses are inefficient while nature's own synthetic enzymes, the glycosyl transferases, can be challenging to express and expensive to employ on scale. Glycoside hydrolases represent a pool of glycan processing enzymes that can be either used in a transglycosylation mode or, better, engineered to function as "glycosynthases," mutant enzymes capable of assembling glycosides. Glycosynthases grant access to valuable glycans that act as functional and structural probes or indeed as inhibitors and therapeutics in their own right. The remodelling of glycosylation patterns in therapeutic proteins via glycoside hydrolases and their mutants is an exciting frontier in both basic research and industrial scale processes.

Enhancing the α-Cyclodextrin Specificity of Cyclodextrin Glycosyltransferase from Paenibacillus macerans by Mutagenesis Masking Subsite -7

Cyclodextrin glycosyltransferases (CGTases) (EC 2.4.1.19) catalyze the conversion of starch or starch derivates into mixtures of α-, β-, and γ-cyclodextrins. Because time-consuming and expensive purification procedures hinder the widespread application of single-ingredient cyclodextrins, enzymes with enhanced specificity are needed. In this study, we tested the hypothesis that the α-cyclodextrin selectivity of Paenibacillus macerans α-CGTase could be augmented by masking subsite -7 of the active site, blocking the formation of larger cyclodextrins, particularly β-cyclodextrin. Five single mutants and three double mutants designed to remove hydrogen-bonding interactions between the enzyme and substrate at subsite -7 were constructed and characterized in detail. Although the rates of α-cyclodextrin formation varied only modestly, the rate of β-cyclodextrin formation decreased dramatically in these mutants. The increase in α-cyclodextrin selectivity was directly proportional to the increase in the ratio of their kcat values for α- and β-cyclodextrin formation. The R146A/D147P and R146P/D147A double mutants exhibited ratios of α-cyclodextrin to total cyclodextrin production of 75.1% and 76.1%, approximately one-fifth greater than that of the wild-type enzyme (63.2%), without loss of thermostability. Thus, these double mutants may be more suitable for the industrial production of α-cyclodextrin than the wild-type enzyme. The production of β-cyclodextrin by these mutants was almost identical to their production of γ-cyclodextrin, which was unaffected by the mutations in subsite -7, suggesting that subsite -7 was effectively blocked by these mutations. Further increases in α-cyclodextrin selectivity will require identification of the mechanism or mechanisms by which these small quantities of larger cyclodextrins are formed.