Optimization of Isomaltooligosaccharide Size Distribution by Acceptor Reaction of Weissella confusa Dextransucrase and Characterization of Novel α-(1→2)-Branched Isomaltooligosaccharides

Characterization of oligosaccharides produced by a truncated dextransucrase from Weissella confusa Wcp3a isolated from pozol, a traditional fermented corn beverage

Glucansucrase Dsr_Wcp3a from a Weissella confusa strain discovered in fermented maize (pozol) was produced in E. coli BL21 resulting in three truncated forms of the native enzyme. An important modification of specificity is observed, as the truncated enzymes synthesize low molecular weight dextran from sucrose, probably due to the absence of domains IV and V, compared to the native enzyme which produces high molecular weight dextran. Low molecular weight dextran is obtained from the non-processive addition of glucose molecules to sucrose (FIMOS) and glucose (IMOS), resulting in two gluco-isomalto-oligosaccharide series. The exclusive synthesis of IMOS occurs in reactions where glucose is included as acceptor in reactions with sucrose as glucosyl donor substrate, due to a higher affinity for glucose as acceptor. The truncated forms also synthesize OS with maltose as acceptor.

Gluco-oligosaccharides as potential prebiotics: Synthesis, purification, structural characterization, and evaluation of prebiotic effect

Prebiotics have long been used to modulate the gut microbiota and improve host health. Most established prebiotics are nondigestible carbohydrates, especially short-chain oligosaccharides. Recently, gluco-oligosaccharides (GlcOS) with 2-10 glucose residues and one or more O-glycosidic linkage(s) have been found to exert prebiotic potentials (not fully established prebiotics) because of their selective fermentation by beneficial gut bacteria. However, the prebiotic effects (non-digestibility, selective fermentability, and potential health effects) of GlcOS are highly variable due to their complex structure originating from different synthesis processes. The relationship between GlcOS structure and their potential prebiotic effects has not been fully understood. To date, a comprehensive summary of the knowledge of GlcOS is still missing. Therefore, this review provides an overview of GlcOS as potential prebiotics, covering their synthesis, purification, structural characterization, and prebiotic effect evaluation. First, GlcOS with different structures are introduced. Then, the enzymatic and chemical processes for GlcOS synthesis are critically reviewed, including reaction mechanisms, substrates, catalysts, the structures of resultant GlcOS, and the synthetic performance (yield and selectivity). Industrial separation techniques for GlcOS purification and structural characterization methods are discussed in detail. Finally, in vitro and in vivo studies to evaluate the non-digestibility, selective fermentability, and associated health effects of different GlcOS are extensively reviewed with a special focus on the GlcOS structure-function relationship.

Maltooligosaccharide forming amylases and their applications in food and pharma industry

Oligosaccharides are low molecular weight carbohydrates with a wide range of health benefits due to their excellent bio-preservative and prebiotic properties. The popularity of functional oligosaccharides among modern consumers has resulted in impressive market demand. Organoleptic and prebiotic properties of starch-derived oligosaccharides are advantageous to food quality and health. The extensive health benefits of oligosaccharides offered their applications in the food, pharmaceuticals, and cosmetic industry. Maltooligosaccharides and isomaltooligosaccharides comprise 2-10 glucose units linked by α-1-4 and α-1-6 glycoside bonds, respectively. Conventional biocatalyst-based oligosaccharides processes are often multi-steps, consisting of starch gelatinization, hydrolysis and transglycosylation. With higher production costs and processing times, the current demand cannot meet on a large-scale production. As a result, innovative and efficient production technology for oligosaccharides synthesis holds paramount importance. Malto-oligosaccharide forming amylase (EC 3.2.1.133) is one of the key enzymes with a dual catalytic function used to produce oligosaccharides. Interestingly, Malto-oligosaccharide forming amylase catalyzes glycosidic bond for its transglycosylation to its inheritance hydrolysis and alternative biocatalyst to the multistep technology. Genetic engineering and reaction optimization enhances the production of oligosaccharides. The development of innovative and cost-effective technologies at competitive prices becomes a national priority.

Heterologous Expression of Thermotolerant α-Glucosidase in Bacillus subtilis 168 and Improving Its Thermal Stability by Constructing Cyclized Proteins

α-glucosidase is an essential enzyme for the production of isomaltooligosaccharides (IMOs). Allowing α-glucosidase to operate at higher temperatures (above 60 °C) has many advantages, including reducing the viscosity of the reaction solution, enhancing the catalytic reaction rate, and achieving continuous production of IMOs. In the present study, the thermal stability of α-glucosidase was significantly improved by constructing cyclized proteins. We screened a thermotolerant α-glucosidase (AGL) with high transglycosylation activity from Thermoanaerobacter ethanolicus JW200 and heterologously expressed it in Bacillus subtilis 168. After forming the cyclized α-glucosidase by different isopeptide bonds (SpyTag/SpyCatcher, SnoopTag/SnoopCatcher, SdyTag/SdyCatcher, RIAD/RIDD), we determined the enzymatic properties of cyclized AGL. The optimal temperature of all cyclized AGL was increased by 5 °C, and their thermal stability was generally improved, with SpyTag-AGL-SpyCatcher having a 1.74-fold increase compared to the wild-type. The results of molecular dynamics simulations showed that the RMSF values of cyclized AGL decreased, indicating that the rigidity of the cyclized protein increased. This study provides an efficient method for improving the thermal stability of α-glucosidase.

Comprehensive utilization of sucrose resources via chemical and biotechnological processes: A review

Sucrose, one of the most widespread disaccharides in nature, has been available in daily human life for many centuries. As an abundant and cheap sweetener, sucrose plays an essential role in our diet and the food industry. However, it has been determined that many diseases, such as obesity, diabetes, hyperlipidemia, etc., directly relate to the overconsumption of sucrose. It arouses many explorations for the conversion of sucrose to high-value chemicals. Production of valuable substances from sucrose by chemical methods has been studied since a half-century ago. Compared to chemical processes, biotechnological conversion approaches of sucrose are more environmentally friendly. Many enzymes can use sucrose as the substrate to generate functional sugars, especially those from GH68, GH70, GH13, and GH32 families. In this review, enzymatic catalysis and whole-cell fermentation of sucrose for the production of valuable chemicals were reviewed. The multienzyme cascade catalysis and metabolic engineering strategies were addressed.

Synthesis of improved long-chain isomaltooligosaccharide, using a novel glucosyltransferase derived from Thermoanaerobacter thermocopriae, with maltodextrin

Isomaltooligosaccharide (IMO), considered to be a prebiotic, reportedly has health effects, particularly in terms of digestion; however, the prebiotic effects of IMOs depend largely on the degree of polymerization. Currently, IMOs are commercially produced using transglucosidase (TG) derived from Aspergillus niger. Here, we report a novel Thermoanaerobacter thermocopriae-derived TG (TtTG) that can produce long-chain IMOs (L-IMOs) using maltodextrin as the main substrate. A putative carbohydrate-binding gene comprising carbohydrate-binding module 35 and glycoside hydrolase family 15 domain was cloned and successfully overexpressed in Escherichia coli BL21 (DE3) cells. The resulting purified recombinant enzyme (TtTG) had a molecular mass of 94 kDa. TtTG displayed an optimal pH of 4.0 (higher than that of commercial TG) and an optimal temperature of 60 °C (same as that of commercial TG). TtTG also enabled the synthesis of oligosaccharides using various saccharides, such as palatinose, kojibiose, sophorose, maltose, cellobiose, isomaltose, gentiobiose, and trehalose, which acted as specific acceptors. TtTG could also produce a medium-sized L-IMO, different from that by dextran-dextrinase and TG, from maltodextrin, as the sole substrate. Thus, the novel combination of maltodextrin and TtTG shows potential as an effective method for commercially producing L-IMOs with improved prebiotic effects.

Heterologous Expression of a Thermostable α-Glucosidase from Geobacillus sp. Strain HTA-462 by Escherichia coli and Its Potential Application for Isomaltose⁻Oligosaccharide Synthesis

Isomaltose-oligosaccharides (IMOs), as food ingredients with prebiotic functionality, can be prepared via enzymatic synthesis using α-glucosidase. In the present study, the α-glucosidase (GSJ) from Geobacillus sp. strain HTA-462 was cloned and expressed in Escherichia coli BL21 (DE3). Recombinant GSJ was purified and biochemically characterized. The optimum temperature condition of the recombinant enzyme was 65 °C, and the half-life was 84 h at 60 °C, whereas the enzyme was active over the range of pH 6.0-10.0 with maximal activity at pH 7.0. The α-glucosidase activity in shake flasks reached 107.9 U/mL and using 4-Nitrophenyl β-D-glucopyranoside (pNPG) as substrate, the K_m and Vmax values were 2.321 mM and 306.3 U/mg, respectively. The divalent ions Mn²⁺ and Ca²⁺ could improve GSJ activity by 32.1% and 13.8%. Moreover, the hydrolysis ability of recombinant α-glucosidase was almost the same as that of the commercial α-glucosidase (Bacillus stearothermophilus). In terms of the transglycosylation reaction, with 30% maltose syrup under the condition of 60 °C and pH 7.0, IMOs were synthesized with a conversion rate of 37%. These studies lay the basis for the industrial application of recombinant α-glucosidase.

Synthesis of Isomaltooligosaccharides by Saccharomyces cerevisiae Cells Expressing Aspergillus niger α-Glucosidase

The α-glucosidase encoded by the aglA gene of Aspergillus niger is a secreted enzyme belonging to family 31 of glycoside hydrolases. This enzyme has a retaining mechanism of action and displays transglycosylating activity that makes it amenable to be used for the synthesis of isomaltooligosaccharides (IMOs). We have expressed the aglA gene in Saccharomyces cerevisiae under control of a galactose-inducible promoter. Recombinant yeast cells expressing the aglA gene produced extracellular α-glucosidase activity about half of which appeared cell bound whereas the other half was released into the culture medium. With maltose as the substrate, panose is the main transglycosylation product after 8 h of incubation, whereas isomaltose is predominant after 24 h. Isomaltose also becomes predominant at shorter times if a mixture of maltose and glucose is used instead of maltose. To facilitate IMO production, we have designed a procedure by which yeast cells can be used directly as the catalytic agent. For this purpose, we expressed in S. cerevisiae gene constructs in which the aglA gene is fused to glycosylphosphatidylinositol anchor sequences, from the yeast SED1 gene, that determine the covalent binding of the hybrid protein to the cell membrane. The resulting hybrid enzymes were stably attached to the cell surface. The cells from cultures of recombinant yeast strains expressing aglA-SED1 constructions can be used to produce IMOs in successive batches.

A novel approach of integrated bioprocessing of cane molasses for production of prebiotic and functional bioproducts

In this work, the sugar industry by-product cane molasses was investigated as feedstock for acceptor reactions by dextransucrase from Leuconostoc mesenteroides MTCC 10508, leading to the biosynthesis of oligosaccharides. The starch industry corn fiber residue was used as a source for acceptor molecules, maltose, in the reaction. Production of approximately 124g oligosaccharides (DP3-DP6) per kg of fresh molasses was achieved. Further, cane molasses based medium was demonstrated as a sole carbon source for L. mesenteroides growth and dextransucrase production. d-Fructose released by dextransucrase activity as processing by-product was transformed into the functional monosaccharide with zero caloric value, d-psicose, by inducing its epimerization. Quantitative analysis approximated 37g d-psicose per kg of fresh molasses. Thus, the study established a novel approach of integrated bioprocessing of cane molasses into prebiotic and functional food additives.

Site Directed Mutagenesis of Dextransucrase DsrM from Weissella cibaria: Transformation to a Reuteransucrase

Glucansucrases produce α-glucans and gluco-oligosaccharides; the linkage type and molecular weight of glucans impacts their functionality. This study compared the catalytic specificities of dextransucrase DsrM from Weissella cibaria 10M and derivatives of this enzymes with GtfA from Lactobacillus reuteri TMW1.656. The N-variable region, which is dispensable for GtfA activity, was essential for DsrM activity. Parallel amino acid substitutions in DsrM-ΔS and GtfA-ΔN indicated that the acceptor binding site residues determining the linkage type differ in these enzymes. DsrM-V583P:V586I had comparable enzyme activity as the respective GtfA derivative but did not increase the proportion of α-(1→4) linkages. DsrM-S622N had low enzyme activity and an unaltered proportion of α-(1→4) linkages while the analogous GtfA-S1062N maintained enzyme activity but increased the proportion of α-(1→4) linkages. This study of dextransucrase from Weissella spp. thus elucidated differences between glucansucrases and will facilitate study of the structure-function relationships of dextran and isomalto-oligosaccharides.