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

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.

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.

Computer-aided mining of a psychrophilic cellobiose 2-epimerase from the Qinghai-Tibet Plateau gene catalogue

Cellobiose 2-epimerase (CE) catalyzes the conversion of the lactose into its high-value derivatives, epilactose and lactulose, which has great prospects in food applications. In this study, CE sequences from the Qinghai-Tibet Plateau gene catalogue, we screened these for structural flexibility through molecular dynamics simulation to identify potential psychrophilic CE candidates. One such psychrophilic CE we termed psyCE demonstrated exceptional epimerization activity, achieving an optimum activity of 122.2 ± 1.6 U/mg. Its kinetic parameters (Kcat and Km) for epimerization activity were 219.9 ± 5.6 s-1 and 261.9 ± 18.1 mM, respectively, representing the highest Kcat recorded among known cold-active CEs. Notably, this is the first report of a psychrophilic CE. The psyCE can effectively produce epilactose at 8 °C, converting 20.3 % of 200 mM lactose into epilactose within four hours. These findings suggest that psyCE is highly suitable for cryogenic food processing, and glaciers may serve as a valuable repository of psychrophilic enzymes.

Rational Design of Loop Dynamics for a Barrel-Shaped Enzyme by Introducing Disulfide Bonds

Loop dynamics redesign is an important strategy to manipulate protein function. Cellobiose 2-epimerase (CE) and other members of its superfamily are widely used for diverse industrial applications. The structural feature of the loops connecting barrel helices contributes greatly to the differences in their functional characteristics. Inspired by the in-silico mutation with molecular dynamics (MD) simulation analysis, we propose a strategy for identifying disulfide bond mutation candidates based on the prediction of protein flexibility and residue-residue interaction. The most beneficial mutant with the newly introduced disulfide bond would simultaneously improve both its thermostability and its reaction propensity to the targeting isomerization product. The ratio of the isomerization/epimerization catalytic rate was improved from 4:103 to 9:22. MD simulation and binding free energy calculations were applied to provide insights into molecular recognition upon mutations. The comparative analysis of enzyme/substrate binding modes indicates that the altered catalytic reaction pathway is due to less efficient binding of the native product. The key residue responsible for the observed phenotype was identified by energy decomposition and was further confirmed by the mutation experiment. The rational design of the key loop region might be a promising strategy to alter the catalytic behavior of all (α/α)6-barrel-like proteins.