An overview of purification methods of glycoside hydrolase family 70 dextransucrase

Rational design of a self-assembly promoting fusion domain enhances high molecular weight levan synthesis by levansucrase SacB

The catalytic product of levansucrase from Bacillus subtilis (SacB) is mainly composed of 10 % high molecular weight levan (HMW, ~2000 kDa) and 90 % low molecular weight levan (LMW, ~7000 Da). In order to achieve efficient production of food hydrocolloid, high molecular weight levan (HMW), with the help of molecular dynamics simulation software, a protein self-assembly element, Dex-GBD, was found and fused with the C-terminus of SacB to construct a novel fusion enzyme, SacB-GBD. The product distribution of SacB-GBD was reversed compared with SacB, and the proportion of HMW in the total polysaccharide was significantly increased to >95 %. We then confirmed that the self-assembly was responsible for the reversal of the SacB-GBD product distribution by the simultaneous modulation of SacB-GBD particle size and product distribution by SDS. The hydrophobic effect may be the main driver of self-assembly as analyzed by molecular simulations and hydrophobicity determination. Our study provides an enzyme source for the industrial production of HMW and provides a new theoretical basis for guiding the molecular modification of levansucrase towards the size of the catalytic product.

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.

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.

Synthesis of glucooligosaccharides with prebiotic potential by glucansucrase URE 13-300 acceptor reactions with maltose, raffinose and lactose

In the present work, we report an efficient synthesis of glucooligosaccharides (GOSs) with prebiotic potential by novel glucansucrase URE 13-300 from Leuconostoc mesenteroides URE 13 strain. The highest total yield of GOSs with degree of polymerization (DP) from 3 to 6 was obtained with maltose as an acceptor and maltose/sucrose (M/S) ratio 1-136 g/L. An efficient modulation of GOSs composition is achieved by varying the M/S ratio. At M/S = 1, 2, 4 and 7 the content of DP3 products gradually increase from 54.50 to 91.70%. When the M/S ratio was decreased the synthesis of DP>3 GOSs is predominant and reaches 75.60% (M/S = 0.25). In addition, the maltose derived GOSs with DP>3, as well as raffinose and lactose glucosylation products have a branched structure which is prerequisite for increased prebiotic potential. The synthesized GOSs were efficiently metabolized by probiotic strains of Lb. plantarum S26, Lb. brevis S27 and Lb. sakei S16, and the calculated values of specific growth rate (μ) were nearly identical to this on glucose media, when maltose derived GOSs were used as a carbohydrate source. Strain specific features were observed in the utilization of the synthesized GOSs, as well as in the production of lactic acid and acetic acid.

Sugar Beet Pulp as Leuconostoc mesenteroides T3 Support for Enhanced Dextransucrase Production on Molasses

Sugar beet pulp (SBP) and molasses, as an agro industrial waste material, are produced in large amounts annually. Thus, a major challenge nowadays is to develop procedures that could increase the value of the generated waste. In this study, SBP as a support for cell immobilization and molasses as a source of nutrients were used for a dextransucrase (DS) production by Leuconostoc mesenteroides T3. The influence of SBP in native form (SBP-N) and after treatment with NaOH (SBP-NaOH) on DS production was investigated. The optimal medium composition for the maximum DS production was determined by varying the concentration of molasses, SBP, and sucrose. The maximum DS yield of 2.02 U/ml was obtained in the medium with 2.5 % of molasses, 2.5 % SBP-NaOH, and 4 % of sucrose concentration. Scanning electron microscopy (SEM) showed immobilization of Lc. mesenteroides T3 cells onto SBP-NaOH. According to the obtained results, the production of DS on molasses could be improved by using NaOH-treated SBP as a carrier for whole-cell immobilization. Our study reveals the basis for the development of process for DS production with additional reduction of expenses by using waste materials for obtaining the valuable biotechnological product.

Purification, optimization of assay, and stability studies of dextransucrase isolated from Weissella cibaria JAG8

Dextransucrase-producing (Gen Bank accession no. KC110687) Weissella cibaria JAG8 was isolated from apple. The cell-free extract containing dextransucrase with specific activity of 1.0 U/mg was purified by polyethylene glycol (PEG). A concentration of 33% (v/v) PEG-400 fractionation gave a specific activity of 20.0 U/mg, whereas 15% (w/v) PEG-1500 resulted in a specific activity of 10.6 U/mg. The PEG-400-purified enzyme was further purified by chromatography using a Sephacryl S-300HR column, which resulted in 37-fold purification with 37 U/mg. The non-denaturing sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of column-purified enzyme showed a single homogenous band of 177 kDa by silver staining. The production of dextran was confirmed by in situ detection of the activity band using periodic acid-Schiff's base staining. The optimum assay conditions for dextransucrase were 35°C, pH 5.4, and 5.0% (w/v) sucrose concentration. The enzyme followed Michaelis-Menten kinetics with Km of 13 mM and Vmax 27.5 U/mg. The enzyme was stable in 10-500 mM sodium acetate buffer, pH 5.4. A 22% increase in enzyme activity was observed with 2 mM magnesium chloride; 64% loss in enzyme activity was observed with 10 mM ethylenediamine tetraacetic acid (EDTA), whereas a complete loss in activity was observed with 5 M urea. The dextransucrase was stable up to 35°C and pH of 5.4 for 1 hr.

Artificial intelligence based optimization of exocellular glucansucrase production from Leuconostoc dextranicum NRRL B-1146

Two different artificial intelligence techniques namely artificial neural network (ANN) and genetic algorithm (GA) were integrated for optimizing fermentation medium for the production of glucansucrase. The experimental data reported in a previous study were used to build the neural network. The ANN was trained using the back propagation algorithm. The ANN predicted values showed good agreement with the experimentally reported ones from a response surface based experiment. The concentrations of three medium components: viz Tween 80, sucrose and K2HPO4 served as inputs to the neural network model and the enzyme activity as the output of the model. A model was generated with a coefficient of correlation (R2) of 1.0 for the training set and 0.90 for the test data. A genetic algorithm was used to optimize the input space of the neural network model to find the optimum settings for maximum enzyme activity. This artificial neural network supported genetic algorithm predicted a maximum glucansucrase activity of 6.92U/ml at medium composition of 0.54% (v/v) Tween 80, 5.98% (w/v) sucrose and 1.01% (w/v) K2HPO4. ANN-GA predicted model gave a 6.0% increase of enzyme activity over the regression based prediction for optimized enzyme activity. The maximum enzyme activity experimentally obtained using the ANN-GA designed medium was 6.75+/-0.09U/ml which was in good agreement with the predicted value.