The thermoduric effects of site-directed mutagenesis of proline and lysine on dextransucrase from Leuconostoc mesenteroides 0326

Temperature-regulated cascade reaction for homogeneous oligo-dextran synthesis using a fusion enzyme

Based on the principle of cascade reaction, a fusion enzyme of dextransucrase and dextranase was designed without linker to catalyze the production of oligo-dextran with homogeneous molecular weight from sucrose in one catalytic step. Due to the different effects of temperature on the two components of the fusion enzyme, temperature served as the "toggle switch" for the catalytic efficiency of the two-level fusion enzyme, regulating the catalytic products of the fusion enzyme. Under optimal conditions, the fusion enzyme efficiently utilized 100 % of the sucrose, and the yield of oligo-dextran with a homogeneous molecular weight reached 70 %. The product has been purified and characterized. The probiotic potential of the product was evaluated by analyzing the growth of 10 probiotic species. Its cytotoxic and anti-inflammatory activities were also determined. The results showed that the long-chain oligo-dextran in this study had significantly better probiotic potential and anti-inflammatory activity compared to other oligosaccharides. This study provides a strategy for the application of oligo-dextran in the food and pharmaceutical industries.

The Discovery, Molecular Cloning, and Characterization of Dextransucrase LmDexA and Its Active Truncated Mutant from Leuconostoc mesenteroides NN710

Dextransucrases play a crucial role in the production of dextran from economical sucrose; therefore, there is a pressing demand to explore novel dextransucrases with better performance. This study characterized a dextransucrase enzyme, LmDexA, which was identified from the Leuconostoc mesenteroides NN710. This bacterium was isolated from the soil of growing dragon fruit in Guangxi province, China. We successfully constructed six different N-terminal truncated variants through sequential analysis. Additionally, a truncated variant, ΔN190LmDexA, was constructed by removing the 190 amino acids fragment from the N-terminal. This truncated variant was then successfully expressed heterologously in Escherichia coli and purified. The purified ΔN190LmDexA demonstrated optimal hydrolysis activity at a pH of 5.6 and a temperature of 30 °C. Its maximum specific activity was measured to be 126.13 U/mg, with a Km of 13.7 mM. Results demonstrated a significant improvement in the heterologous expression level and total enzyme activity of ΔN190LmDexA. ΔN190LmDexA exhibited both hydrolytic and transsaccharolytic enzymatic activities. When sucrose was used as the substrate, it primarily produced high-molecular-weight dextran (>400 kDa). However, upon the addition of maltose as a receptor, it resulted in the production of a significant amount of oligosaccharides. Our results can provide valuable information for enhancing the characteristics of recombinant dextransucrase and potentially converting sucrose into high-value-added dextran and oligosaccharides.

Mechanism analysis of a novel natural cationic modified dextran flocculant and its application in the treatment of blue algal blooms

Blue algae, a type of harmful microalgae, are responsible for causing harmful algal blooms that result in severe environmental issues. To address this problem, a biopolysaccharide-based flocculant was developed for treating blue algae blooms. This flocculant was created by modifying high molecular weight dextran using the natural cationic monomer betaine (Dex-Bet), making it environmentally friendly. Various techniques were used to characterize the prepared Dex-Bet flocculant, including infrared spectroscopy (FTIR), nuclear magnetic resonance hydrogen spectroscopy (1H NMR), X-ray diffraction spectroscopy (XRD), field emission scanning electron microscopy (FESEM), and thermogravimetric analysis (TGA). The effectiveness of the Dex-Bet flocculant was evaluated using kaolin-simulated wastewater. The results showed that the treated supernatant had a transmittance of up to 98.25 %. Zeta potential analysis revealed that the main mechanisms of flocculation were charge neutralization, charge patching, and adsorption bridging. The application of Dex-Bet in treating blue-green algae resulted in a maximum removal rate of 98.2 %. This study provides a potential flocculant for blue algae bloom treatment.

Fusion enzyme design based on the "channelization" cascade theory and homogenous dextran product improvement

Homogeneous low molecular weight dextran can be used to improve microcirculation and expand blood volume. However, the synthesis and separation of low molecular weight dextran are chemically difficult and environmentally unfriendly. Here, a one-step strategy for the synthesis of homogeneous low molecular weight dextran was developed. Dextransucrase and dextranase were fused by the addition of different length linker peptides. An artificial bifunctional enzyme was created to directly convert sucrose into low molecular weight dextran (13,050 Da), and the related substrate channel mechanism was found. The substrate channel adaptability was studied by changing the length of the linker and its corresponding product behavior. Compared with the mixture of two free enzymes, the residence lag time demonstrates the degree of substrate channelization of a series of fusion enzymes. And found that the highest channelization degree is not equal to produce homogenous dextran. Whereas a fusion enzyme with the appropriate linker (the one with the best substrate channel adaptation) will produce dextran with a homogeneous molecular weight. By studying the temperature dynamics of the fusion enzyme to adjust the two-stage catalytic efficiency of the fusion enzyme, we have increased the yield of low molecular weight homogeneous dextran (Yield of 62 %).

The stability improvement of dextransucrase by artificial extension modification of the V domain of the enzyme

Improving enzyme stability is very important for enzyme applications. Structural modification is a reliable and effective method to improve the characteristics of protein. By artificially extending the C-terminus, 6 domain modification variants of different sizes were constructed, and a new enzyme species with high stability was obtained. Experimental results affirmed that high stability can be achieved by decreasing the degree of domain freedom. The optimum temperatures of domain modification variants were improved by 10 °C compared with the original enzyme. Specifically, compared with the original enzyme, the half-life of the variant dexYG-fdx (D-F) was increased to 280% under 35 °C and 200% under 45 °C, and the pH tolerance range was wider. Further structural simulations and molecular docking studies provided a reasonable explanation (The increased domain reduced the degree of freedom of the enzyme terminal to some extent) for this variant to increase stability and produce dextran. This study can provide valuable information for increasing the characteristics of recombinant dextransucrase.

Bacterial α-Glucan and Branching Sucrases from GH70 Family: Discovery, Structure-Function Relationship Studies and Engineering

Glucansucrases and branching sucrases are classified in the family 70 of glycoside hydrolases. They are produced by lactic acid bacteria occupying very diverse ecological niches (soil, buccal cavity, sourdough, intestine, dairy products, etc.). Usually secreted by their producer organisms, they are involved in the synthesis of α-glucans from sucrose substrate. They contribute to cell protection while promoting adhesion and colonization of different biotopes. Dextran, an α-1,6 linked linear α-glucan, was the first microbial polysaccharide commercialized for medical applications. Advances in the discovery and characterization of these enzymes have remarkably enriched the available diversity with new catalysts. Research into their molecular mechanisms has highlighted important features governing their peculiarities thus opening up many opportunities for engineering these catalysts to provide new routes for the transformation of sucrose into value-added molecules. This article reviews these different aspects with the ambition to show how they constitute the basis for promising future developments.

Improving the catalytic efficiency and substrate affinity of a novel esterase from marine Klebsiella aerogenes by random and site-directed mutation

A novel esterase (EstKa) from marine Klebsiella aerogenes was characterized with hydrolytic activity against p-nitrophenyl caprylate (pNPC, C₈) under optimum conditions (50 °C and pH 8.5). After two rounds of mutagenesis, two highly potential mutants (I6E9 and L7B11) were obtained with prominent activity, substrate affinity and thermostability. I6E9 (L90Q/P96T) and L7B11 (A37S/Q100L/S133G/R138C/Q156R) were 1.56- and 1.65-fold higher than EstKa in relative catalytic efficiency. The influence of each amino acid on enzyme activity was explored by site-directed mutation. The mutants Pro96Thr and Gln156Arg showed 1.29- and 1.48-fold increase in catalytic efficiency (Kcat/Km) and 54.4 and 36.2% decrease in substrate affinity (Km), respectively. The compound mutant Pro96Thr/Gln156Arg exhibited 68.9% decrease in Km and 1.41-fold increase in Kcat/Km relative to EstKa. Homology model structure analysis revealed that the replacement of Gln by hydrophilic Arg on the esterase surface improved the microenvironment stability and the activity. The replacement of Pro by Thr enabled the esterase enzyme to retain 90% relative activity after 3 h incubation at 45 °C. Structural analysis confirmed that the formation of a hydrogen bond leads to a notable increase of catalytic efficiency under high temperature conditions.

Analysis of the Effect of N555 Mutations on the Product Specificity of Dextransucrase Using Caffeic Acid Phenethyl Ester as an Acceptor Substrate

Bioglycosylation is an efficient strategy to improve biological activities and physicochemical properties of natural compounds to develop structural modifications of drugs. In this study, an N555 residue was identified as a candidate for site-directed mutagenesis through sequence alignment with GTF180ΔN. Caffeic acid phenethyl ester (CAPE) was used as an acceptor substrate. Two generated mutants, N555Q and N555E, demonstrated significant specificity of distribution of products. Under identical conditions, the conversion rates of diglycoside products (CAPE-2G) generated by the N555E (80.8%) and N555Q (84.5%) mutants were 3.30- and 3.46-fold higher than those generated by the original enzyme (24.4%). The structural simulation results demonstrated that a new hydrogen bond was formed between the N555 residue and CAPE, and the N555 residue was closely related to substrate elongation. These results provide a reference for subsequent studies. Suitable mutants for transfer of diglycosides have important application potential in the food and pharmaceutical industries.

Different strategies to co-immobilize dextransucrase and dextranase onto agarose based supports: Operational stability study

Co-immobilization is a groundbreaking technique for enzymatic catalysis, sometimes strategic, as for dextransucrase and dextranase. In this approach, dextranase hydrolytic action removes the dextran layer that covers dextransucrase reactive groups, improving the immobilization. Another advantage is the synergic effect of the two enzymes towards prebiotic oligosaccharides production. Thus, both enzymes were co-immobilized onto the heterobifunctional support Amino-Epoxy-Glyoxyl-Agarose (AMEG) and the ion exchanger support monoaminoethyl-N-ethyl-agarose (Manae) at pH 5.2 and 10, followed or not by glutaraldehyde treatment. This work is the first attempt to immobilize dextransucrase under alkaline conditions. The immobilized dextransucrase on AMEG support at pH 10 (12.78 ± 0.70 U/g) presents a similar activity of the biocatalyst produced at pH 5.2 (14.95 ± 0.82 U/g). The activity of dextranase immobilized onto Manae was 5-fold higher than the obtained onto AMEG support. However, the operational stability test showed that the biocatalyst produced on AMEG at pH 5.2 kept >60% of both enzyme activities for five batches. The glutaraldehyde treatment was not worthwhile to improve the operational stability of this biocatalyst.

Engineering Leuconostoc mesenteroides dextransucrase by inserting disulfide bridges for enhanced thermotolerance

The disulfide bridge is a very important part of the peptide chain and plays an important role in stabilizing the protein structure and maintaining its active function. One hundred and fourteen potential disulfide bridges were determined by Disulfide by Design™, and 4 disulfide bridges were constructed for the purpose of obtaining new enzyme species with high thermotolerance. High thermotolerance is achieved by increasing the number of hydrogen bonds between amino acids. The optimum temperatures of mutant L838C-V887C and A948C-A1013C were improved by 10 °C compared to that of the original enzyme, which was beneficial to reduce the viscosity of the reaction system. Some of the mutations resulted in the alteration of catalytic specificity, and the products D739C-F932C and A948C-A1013C catalyzed synthesis of dextran containing a new α(1-4) glycosidic linkage and α(1-2) glycosidic linkage. This study may provide information valuable for increasing the reaction temperature of recombinant dextransucrase. The molecular docking study presents a plausible explanation for reaction specificity alteration and optimum temperature improvement for the mutants.

Transglycosylation Improved Caffeic Acid Phenethyl Ester Anti-Inflammatory Activity and Water Solubility by Leuconostoc mesenteroides Dextransucrase

Bioglycosylation is an efficient strategy to improve the biological activity and physicochemical properties of natural compounds for therapeutic drug development. In this study, two caffeic acid phenethyl ester (CAPE) glucosides (G-CAPE and 2G-CAPE) were synthesized by transglycosylation with dextransucrase from Leuconostoc mesenteroides 0326 with CAPE as an acceptor and sucrose as a donor. The products were purified and the structures were characterized. The physicochemical properties, anti-inflammatory activity, and cytotoxicity of the two CAPE glucosides were measured. The water solubility of G-CAPE and 2G-CAPE is 35 and 90 times higher, respectively, than that of CAPE. Compared to CAPE, the monoglycoside product showed superior anti-inflammatory effects, and its inhibition rate of NO, IF-6, and TNF-α is 93.4%, 76.81%, and 56.58% in RAW 264.7 macrophages, respectively, at 20 μM. Also, the cytotoxicity of both products was significantly improved. These glycosylation-modified CAPEs circumvent some of the flaws in CAPE application in anti-inflammatory drugs.