Characterization of an epilactose-producing cellobiose 2-epimerase from Thermoanaerobacterium saccharolyticum

Characterization of an epilactose-producing cellobiose 2-epimerase from Clostridium sp. TW13 and reutilization of waste milk

A novel cellobiose 2-epimerase gene (CsCEase1) from Clostridium sp. TW13 was successfully overexpressed. CsCEase1, with a molecular weight of 45.0 kDa, exhibited a specific activity of 254.75 U/mg and showed optimal activity at 40 °C and pH 7.5. Using CsCEase1, 44.30 % of lactose was converted into epilactose, yielding a production level of 26.58 g/L. An efficient purification method was developed, incorporating crystallization and β-galactosidase treatment to remove the unconverted lactose, while Saccharomyces cerevisiae was used to consume the produced glucose. Final purification with activated carbon resulted in epilactose with 98 % purity and a recovery rate of 66.47 %. Furthermore, CsCEase1 was incubated with whey power and expired milk, achieving epilactose conversion rates of 29.65 % and 32.69 %, respectively. These findings highlight the potential of CsCEase1 for the cost-effective and environmentally sustainable production of epilactose from dairy waste.

Advances and prospects on production of lactulose and epilactose by cellobiose 2-epimerases: A review

Lactulose and epilactose are nondigestible disaccharides with a wide range of applications in clinical medicine, nutrition, and the food industry due to their health-benefiting properties. Their chemical synthesis typically involves stringent catalytic conditions and intricate reaction procedures, resulting in elevated production costs and challenges in product separation. Cellobiose 2-epimerases (CEs) facilitate the isomerization and epimerization of lactose to produce lactulose and epilactose directly, without the need for co-substrates. This enzymatic process offers advantages such as mild reaction conditions, straightforward operation, high conversion efficiency, and reduced by-product formation. Recently, numerous CE genes have been identified and characterized, with their enzymatic properties undergoing extensive analysis. This review consolidates information on the properties of CEs from various sources and examines their catalytic mechanisms based on crystal structure data. Additionally, the current research progress in the enzymatic synthesis of lactulose and epilactose is comprehensively reviewed. The future direction of CE research is discussed, highlighting the potential for large-scale production of lactulose and epilactose through environmentally sustainable enzymatic methods.

Novel Cellobiose 2-Epimerase from Thermal Aquatic Metagenome for the Production of Epilactose

Epilactose is a prebiotic molecule that exerts a bifidogenic effect and increases calcium and iron absorption in the small intestine. This study identifies a novel cellobiose 2-epimerase gene (ceM) by investigating metagenomic data generated from a thermal aquatic habitat. The computation of secondary and tertiary structure analysis, molecular docking, and MD simulation analysis indicated the protein CEM to be a novel cellobiose 2-epimerase. The gene was expressed in Escherichia coli, followed by biochemical characterization of the purified protein. CEM is capable of transforming lactose into the high-value rare sugar, epilactose, in a wide range of temperatures (4-70 °C) and pH (6.0-10.0). The enzyme was exposed to 50 °C, and hardly a 10% loss in activity was recorded after 32 h of heat treatment, suggesting that CEM is a thermostable protein. CEM is a kinetically highly efficient enzyme, with a turnover number of 9832 ± 490 s-1 for lactose to epilactose epimerization. The maximum conversion yield of 26% epilactose was obtained in 15 min of catalytic reaction. Further, the enzyme was successfully tested to transform lactose in milk and whey samples.

Identification of a novel cellobiose 2-epimerase from Acidobacteriota bacterium and its application for in-situ milk catalysis

Introduction

Cellobiose 2-epimerase (CE) catalyzes the interconversion of glucosyl and mannosyl groups at the reducing end of β-1,4-linked disaccharides. This enzyme is pivotal for converting lactose into prebiotics like epilactose, offering a potential solution for lactose-intolerant-friendly dairy products. However, current CEs are hindered by pH and thermal instability in milk processing, as their neutral-to-alkaline pH optima clash with milk's mildly acidic conditions (pH 6.5-6.7), and their poor thermolability requires costly post-processing enzyme removal.

Methods

We identified a novel CE from the acidophilic Acidobacteriota bacterium (Acba-CE) and characterized its properties. Its enzymatic activity was assessed under varying pH and temperature conditions, including milk-processing environments.

Results

Acba-CE exhibits an acidic pH optimum (6.0), retaining 95% activity at milk pH (6.5). Notably, it undergoes rapid thermal inactivation at pasteurization temperatures, enabling complete enzyme deactivation during standard pasteurization without additional steps. In milk systems, Acba-CE achieves 28.5% lactose-to-epilactose conversion at refrigeration temperatures (10°C), demonstrating strong cold adaptability.

Discussion

To our knowledge, this is the first reported CE from the Acidobacteriota phylum, combining acidophilic activity with low-temperature adaptability. Acba-CE represents a breakthrough for in situ dairy modification, eliminating key bottlenecks in milk processing and enabling next-generation functional milk production.

Improvement of cellobiose 2-epimerase expression in Bacillus subtilis for efficient bioconversion of lactose to epilactose

Epilactose, a lactose derivative known for its prebiotic properties and potential health benefits, has garnered significant interest. Cellulose 2-epimerase (CEase) is responsible for catalyzing the conversion of lactose to epilactose. In this study, the enhancement of food-grade CEase expression in Bacillus subtilis WB600 was systematically investigated. Among seven selected epilactose-producing CEases, Rhodothermus marinus CEase (RmCE) exhibited the highest epimerization activity when expressed in B. subtilis. Translational and transcriptional regulations were employed to enhance CEase expression by screening effective N-terminal coding sequences (NCSs) and promoters. The final strain demonstrated efficient production of CEase, with epimerization activity reaching 273.6 ± 6.5 U/mL and 1255 ± 26.4 U/mL in shake-flask and fed-batch cultivation, respectively. Utilizing only 0.25 % (V/V) of the fed-batch cultivation broth for lactose biotransformation, epilactose was efficiently produced from 300 g/L of lactose within 4 h, achieving a yield of 29.5 %. These findings provide significant support for the potential industrialization of enzymatic epilactose production.

A novel cellobiose 2-epimerase from anaerobic halophilic Iocasia fonsfrigidae and its ability to convert lactose in fresh goat milk into epilactose

BACKGROUND

Cellobiose 2-epimerase (CE) has received great attention due to its potential applications in the food and pharmaceutical industries. In this study, a novel CE from mesophilic anaerobic halophilic bacterium Iocasia fonsfrigidae strain SP3-1 (IfCE) was successfully expressed in Escherichia coli and characterized.

RESULTS

Unlike other CEs, the purified IfCE shows only epimerization activity toward β-1,4-glycosidic linkages of disaccharides, including mannobiose, cellobiose and lactose, but not for monosaccharides, β-1,4-glycosidic linkages of trisaccharides and α-1,4-glycosidic linkages of disaccharides. Only one epimerization product was obtained from the action of IfCE against mannobiose, cellobiose and lactose. Under optimum conditions, 31.0% of epilactose, a rare and low-calorie prebiotic sweetener with medicinal and pharmacological properties, was obtained from 10 mg mL-1 lactose. IfCE was highly active against lactose under NaCl concentrations up to 500 mmol L-1, possibly due to the excessive basic (arginine and lysine) and acidic (aspartic and glutamic acids) amino acid residues, which are localized on the surface of the halophilic enzyme structure. These residues may protect the enzyme from Cl- and Na+ ions from the environment, respectively. Under normal conditions, IfCE was able to convert lactose present in fresh goat milk to epilactose with a conversion yield of 31% in 10 min. In addition, IfCE has been investigated as a safe enzyme for human allergen.

CONCLUSION

The results suggested that IfCE is a promising candidate to increase the quality and value of milk and dairy products by converting lactose that causes digestive problems in people with lactose intolerance into epilactose. © 2024 Society of Chemical Industry.

Engineering Bacillus subtilis for highly efficient production of functional disaccharide lactulose from lactose

Bioconversion of lactose to functional lactose derivatives attracts increasing attention. Lactulose is an important high-value lactose derivative, which has been widely used in pharmaceutical, nutraceutical, and food industries. Lactulose can be enzymatically produced from lactose by cellobiose 2-epimerase (CEase). Several studies have already focused on the food-grade expression of CEase, but they are all aimed at the biosynthesis of epilactose. Herein, we reported for the first time the biosynthesis of lactulose using the recombinant food-grade Bacillus subtilis. Lactulose biosynthesis was optimized by varying lactulose-producing CEases and expression vectors. Caldicellulosiruptor saccharolyticus CEase and pP43NMK were determined to be the optimal CEase and expression vector. Fine-tuning of CEase expression was investigated by screening a beneficial N-terminal coding sequence. After fed-batch cultivation, the highest fermentation isomerization activity reached 11.6 U/mL. Lactulose was successfully produced by the broth of the engineered B. subtilis with a yield of 52.1 %.

Lactulose production from lactose isomerization by chemo-catalysts and enzymes: Current status and future perspectives

Lactulose, a semisynthetic nondigestive disaccharide with versatile applications in the food and pharmaceutical industries, has received increasing interest due to its significant health-promoting effects. Currently, industrial lactulose production is exclusively carried out by chemical isomerization of lactose via the Lobry de Bruyn-Alberda van Ekenstein (LA) rearrangement, and much work has been directed toward improving the conversion efficiency in terms of lactulose yield and purity by using new chemo-catalysts and integrated catalytic-purification systems. Lactulose can also be produced by an enzymatic route offering a potentially greener alternative to chemo-catalysis with fewer side products. Compared to the controlled trans-galactosylation by β-galactosidase, directed isomerization of lactose with high isomerization efficiency catalyzed by the most efficient lactulose-producing enzyme, cellobiose 2-epimerase (CE), has gained much attention in recent decades. To further facilitate the industrial translation of CE-based lactulose biotransformation, numerous studies have been reported on improving biocatalytic performance through enzyme mediated molecular modification. This review summarizes recent developments in the chemical and enzymatic production of lactulose. Related catalytic mechanisms are also highlighted and described in detail. Emerging techniques that aimed at advancing lactulose production, such as the boronate affinity-based technique and molecular biological techniques, are reviewed. Finally, perspectives on challenges and opportunities in lactulose production and purification are also discussed.

Identification of a thermostable cellobiose 2-epimerase from Caldicellulosiruptor sp. Rt8.B8 and production of epilactose using Bacillus subtilis

BACKGROUND

Epilactose, a potential prebiotics, was derived from lactose through enzymatic catalysis. However, production and purification of epilactose are currently difficult due to powerless enzymes and inefficient downstream processing steps.

RESULTS

The encoding gene of cellobiose 2-epimerase (CE) from Caldicellulosiruptor sp. Rt8.B8 was cloned and expressed in Escherichia coli BL21(DE3). The enzyme was purified and it was suitable for industrial production of epilactose from lactose without by-products, because of high k_cat (197.6 s^-1 ) and preferable thermostability. The Rt8-CE gene was further expressed in the Bacillus subtilis strain. We successfully produced epilactose from 700 g L^-1 lactose in 30.4% yield by using the recombinant Bacillus subtilis whole cells. By screening of a β-galactosidase from Bacillus stearothermophilus (BsGal), a process for separating epilactose and lactose was established, which showed a purity of over 95% in a total yield of 69.2%. In addition, a mixed rare sugar syrup composed of epilactose and d-tagatose was successfully produced from lactose through the co-expression of l-arabinose isomerase and β-galactosidase.

CONCLUSION

Our study shed light on the efficient production of epilactose using a food-grade host expressing a novel CE enzyme. Moreover, an efficient and low-cost process was attempted to obtain high purity epilactose. In order to improve the utilization of raw materials, the production process of mixed syrup containing epilactose and d-tagatose with prebiotic properties produced from lactose was also established for the first time. © 2021 Society of Chemical Industry.

Molecular Characterization of a Mesophilic Cellobiose 2-Epimerase That Maintains a High Catalytic Efficiency at Low Temperatures

Cellobiose 2-epimerase (CE) can catalyze bioconversion of lactose to its prebiotic derivative epilactose. The catalytic property of a novel CE from Treponema brennaborense (Trbr-CE) was investigated. Trbr-CE showed the highest catalytic efficiency of epimerization toward lactose among all of the previously reported CEs. This enzyme's specific activity could reach as high as 208.5 ± 5.3 U/mg at its optimum temperature, which is 45 °C. More importantly, this enzyme demonstrated a considerably high activity at low temperatures, suggesting Trbr-CE as a promising enzyme for industrial low-temperature production of epilactose. This structurally flexible enzyme exhibited a comparatively high binding affinity toward substrates, which was confirmed by both experimental verification and computational analysis. Molecular dynamics (MD) simulations and binding free energy calculations were applied to provide insights into molecular recognition upon temperature changes. Compared with thermophilic CEs, Trbr-CE presents a more negative enthalpy change and a higher entropy change when the temperature drops.

Insight into the potential factors influencing the catalytic direction in cellobiose 2-epimerase by crystallization and mutagenesis

Cellobiose 2-epimerase (CE) is commonly recognized as an epimerase as most CEs mainly exhibit an epimerization activity towards disaccharides. In recent years, several CEs have been found to possess bifunctional epimerization and isomerization activities. They can convert lactose into lactulose, a high-value disaccharide that is widely used in the food and pharmaceutical industries. However, the factors that determine the catalytic direction in CEs are still not clear. In this study, the crystal structures of three newly discovered CEs, CsCE (a bifunctional CE from Caldicellulosiruptor saccharolyticus), StCE (a bifunctional CE from Spirochaeta thermophila DSM 6578) and BtCE (a monofunctional CE from Bacillus thermoamylovorans B4166), were determined at 1.54, 2.05 and 1.80 Å resolution, respectively, in order to search for structural clues to their monofunctional/bifunctional properties. A comparative analysis of the hydrogen-bond networks in the active pockets of diverse CEs, YihS and mannose isomerase suggested that the histidine corresponding to His188 in CsCE is uniquely required to catalyse isomerization. By alignment of the apo and ligand-bound structures of diverse CEs, it was found that bifunctional CEs tend to have more flexible loops and a larger entrance around the active site, and that the flexible loop 148-181 in CsCE displays obvious conformational changes during ligand binding. It was speculated that the reconstructed molecular interactions of the flexible loop during ligand binding helped to motivate the ligands to stretch in a manner beneficial for isomerization. Further site-directed mutagenesis analysis of the flexible loop in CsCE indicated that the residue composition of the flexible loop did not greatly impact epimerization but affects isomerization. In particular, V177D and I178D mutants showed a 50% and 80% increase in isomerization activity over the wild type. This study provides new information about the structural characteristics involved in the catalytic properties of CEs, which can be used to guide future molecular modifications.

Computer-aided search for a cold-active cellobiose 2-epimerase

Cellobiose 2-epimerase (CE) is a promising industrial enzyme that can catalyze bioconversion of lactose to its high-value derivatives, namely epilactose and lactulose. A need exists in the dairy industry to catalyze lactose bioconversions at low temperatures to avoid microbial growth. We focused on the discovery of cold-active CE in this study. A genome mining method based on computational prediction was used to screen the potential genes encoding cold-active enzymes. The CE-encoding gene from Roseburia intestinalis, with a predicted high structural flexibility, was expressed heterologously in Escherichia coli. The catalytic property of the recombinant enzyme was extensively studied. The optimum temperature and pH of the enzyme were 45°C and 7.0, respectively. The specific activity of this enzyme to catalyze conversion of lactose to epilactose was measured to be 77.3 ± 1.6 U/mg. The kinetic parameters, including turnover number (k_cat), Michaelis constant (K_m), and catalytic efficiency (k_cat/K_m) using lactose as a substrate were 117.0 ± 7.7 s^-1, 429.9 ± 57.3 mM, and 0.27 mM^-1s^-1, respectively. In situ production of epilactose was carried out at 8°C: 20.9% of 68.4 g/L lactose was converted into epilactose in 4 h using 0.02 mg/mL (1.5 U/mL, measured at 45°C) of recombinant enzyme. The enzyme discovered by this in silico method is suitable for low-temperature applications.

Simulation-guided enzyme discovery: A new microbial source of cellobiose 2-epimerase

Cellobiose 2-epimerase (CE) is a promising industrial enzyme that can be utilized in the dairy industry. More thermostable CEs from different microorganisms are still needed for a higher lactulose productivity. This study demonstrated the feasibility to use molecular dynamics (MD) simulation as the preliminary computational filter for thermostable enzymes screening. Sequence information of eleven uncharacterized CEs were chosen to be analyzed by MD simulations. The CE from Dictyoglomus thermophilum (Dith-CE) was determined experimentally to be one of the most thermostable CEs with the highest epimerization (160 ± 6.5 U mg^-1) and isomerization activities (3.52 ± 0.23 U mg^-1) among all the reported CEs. This enzyme shows the highest isomerization activity at 85 °C and pH 7.0. The kinetic parameters (k_cat and K_m) of isomerization activity of this CE are 3.98 ± 0.3 s^-1 and 235.2 ± 11.2 mM, respectively. These results suggest that the CE from Dith-CE is a promising lactulose-producing enzyme.

Amylosucrase as a transglucosylation tool: From molecular features to bioengineering applications

Amylosucrase (EC 2.4.1.4, ASase), an outstanding sucrose-utilizing transglucosylase in the glycoside hydrolase family 13, can produce glucans with only α-1,4 linkages. Generally, on account of a double-displacement mechanism, ASase can catalyze polymerization, isomerization, and hydrolysis reactions with sucrose as the sole substrate, and has transglycosylation capacity to attach glucose molecules from sucrose to extra glycosyl acceptors. Based on extensive enzymology research, this review presents the characteristics of various ASases, including their microbial metabolism, preparation, and enzymatic properties, and exhibits structure-based strategies in the improvement of activity, specificity, and thermostability. As a vital transglucosylation tool of producing sugars, carbohydrate-based bioactive compounds, and materials, the bioengineering applications of ASases are also systematically summarized.

What regulates the catalytic activities in AGE catalysis? An answer from quantum mechanics/molecular mechanics simulations

The AGE superfamily (AGEs) is made up of kinds of isomerase which are very important both physiologically and industrially. One of the most intriguing aspects of AGEs has to do with the mechanism that regulates their activities in single conserved active pocket. In order to clarify the relationship among single conserved active pocket and two activities in AGEs, results for the epimerization activity catalyzed by RaCE and the isomerization activity catalyzed by SeYihS were obtained by using QM/MM umbrella sampling simulations and 2D-FES calculations. Our results show that both of them have similar enzyme-substrate combination mode for inner pyranose ring in single conserved active pocket even though they have different substrate specificity. This means that the pathways of ring opening catalyzed by them are similar. However, one non-conserved residue (Leu183 in RaCE, Met175 in SeYihS) in the active site, which has different steric hindrance, causes a small but effective change in the direction of ring opening in stage 1. And then this change will induce a fundamentally different catalytic activity for RaCE and SeYihS in stage 2. Our results give a novel viewpoint about the regulatory mechanism between CE and YihS in AGEs, and may be helpful for further experiments of rational enzyme design based on the (α/α)₆-barrel basic scaffold.

Characterisation of a novel cellobiose 2-epimerase from thermophilic Caldicellulosiruptor obsidiansis for lactulose production

BACKGROUND

Lactulose, a bioactive lactose derivative, has been widely used in food and pharmaceutical industries. Isomerisation of lactose to lactulose by cellobiose 2-epimerase (CE) has recently attracted increasing attention, since CE produces lactulose with high yield from lactose as a single substrate. In this study, a new lactulose-producing CE from Caldicellulosiruptor obsidiansis was extensively characterised.

RESULTS

The recombinant enzyme exhibited maximal activity at pH 7.5 and 70 °C. It displayed high thermostability with T_m of 86.7 °C. The half-life was calculated to be 8.1, 2.8 and 0.6 h at 75, 80, and 85 °C, respectively. When lactose was used as substrate, epilactose was rapidly produced in a short period, and afterwards both epilactose and lactose were steadily isomerised to lactulose, with a final ratio of 35:11:54 for lactose:epilactose:lactulose. When the reverse reaction was investigated using lactulose as substrate, both lactose and epilactose appeared to be steadily produced from the start.

CONCLUSION

The recombinant CE showed both epimerisation and isomerisation activities against lactose, making it an alternative promising biocatalyst candidate for lactulose production. © 2016 Society of Chemical Industry.

Hidden Reaction: Mesophilic Cellobiose 2-Epimerases Produce Lactulose

Lactulose (4-O-β-d-galactopyranosyl-d-fructofuranose) is a prebiotic sugar derived from the milk sugar lactose (4-O-β-d-galactopyranosyl-d-glucopyranose). In our study we observed for the first time that known cellobiose 2-epimerases (CEs; EC 5.1.3.11) from mesophilic microorganisms were generally able to catalyze the isomerization reaction of lactose into lactulose. Commonly, CEs catalyze the C2-epimerization of d-glucose and d-mannose moieties at the reducing end of β-1,4-glycosidic-linked oligosaccharides. Thus, epilactose (4-O-β-d-galactopyranosyl-d-mannopyranose) is formed with lactose as substrate. So far, only four CEs, exclusively from thermophilic microorganisms, have been reported to additionally catalyze the isomerization reaction of lactose into lactulose. The specific isomerization activity of the seven CEs in this study ranged between 8.7 ± 0.1 and 1300 ± 37 pkat/mg. The results indicate that very likely all CEs are able to catalyze both the epimerization as well as the isomerization reaction, whereby the latter is performed at a comparatively much lower reaction rate.