Versatile biotechnological applications of amylosucrase, a novel glucosyltransferase

Evaluation of amylose content: Structural and functional properties, analytical techniques, and future prospects

Amylose content (AC) is critical in evaluating starch properties, significantly influencing the food industry and human nutrition. Although amylose is not completely linear, its unique structure makes it a key research focus across various scientific fields. Understanding amylose's structural and functional properties is essential for its applications in medical, nutritional, and industrial sectors. Accurate determination of AC, from simple qualitative assessments to precise quantitative measurements, is vital for effectively processing and using starch-rich products. The choice of AC determination method depends on the specific application and the required accuracy and detail. This review summarizes amylose's structural and functional characteristics and recent advancements in qualitative and quantitative AC determination techniques. It also provides insights into future trends and prospects for these technologies, emphasizing the need for more rapid, convenient, accurate, and customizable methods. In conclusion, advancements in amylose determination should enhance accuracy, speed, and ease of use to improve quality control and applications across various sectors while expanding our understanding of amylose and its functionalities.

Construction and enzymatic characterization of a monomeric variant of dimeric amylosucrase from Deinococcus geothermalis

Amylosucrase (ASase; E.C. 2.4.1.4), a member of glycoside hydrolase family 13 (GH13), produces α-1,4-glucans and sucrose isomers using sucrose as its sole substrate. This study identifies and characterizes the dimeric structure of ASase from Deinococcus geothermalis (DgAS), highlighting essential amino acid residues for maintaining the dimeric state. The monomeric form, DgAS R30A, exhibited a higher affinity for sucrose compared to the wild-type (WT), especially during the formation of the ASase-glucose intermediate complex and subsequent hydrolysis. Notably, DgAS R30A produced a higher proportion of α-glucans with a degree of polymerization (DP) of ≤20 and fewer α-glucans with a DP of ≥31. This suggested that the reduced surface area of the oligosaccharide binding site in the monomeric form led to decreased binding of longer-chain maltooligosaccharides, favoring the formation of shorter DP α-glucans. Kinetic analysis revealed significantly lower Michaelis constants (Km) for DgAS R30A's total and hydrolysis activities, with the overall performance (kcat/Km) values for DgAS R30A exceeded those of the WT at all sucrose concentrations. Here, we report the first high-resolution homodimeric DgAS structure, revealing conserved active site residues and a unique dimerization interface. This study enhances our understanding of the molecular factors influencing the oligomeric state and enzyme activities.

Efficient Biosynthesis of Theanderose, a Potent Prebiotic, Using Amylosucrase from Deinococcus deserti

The study aimed to develop an efficient bioprocess for the discovery and synthesis of theanderose by using amylosucrase from Deinococcus deserti (DdAS). An unknown trisaccharide produced by DdAS was detected by high-performance anion-exchange chromatography-pulsed amperometric detection and high-performance liquid chromatography-evaporative light scattering detection, purified using medium-pressure liquid chromatography, and identified as theanderose (α-d-glucopyranosyl-(1→6)-α-d-glucopyranosyl-(1→2)-β-d-fructofuranoside) through nuclear magnetic resonance and mass spectrometry. DdAS synthesized theanderose with a 25.4% yield (174.1 g/L) using 2.0 M sucrose at 40 °C for 96 h. In an in vitro digestion model, theanderose showed a 6.5% hydrolysis rate over 16 h. Prebiotic efficacy tests confirmed that theanderose significantly enhanced the proliferation of selected Bifidobacterium strains in the culturing medium with theanderose as the main carbon source. Subsequently, fecal fermentation was performed by adding theanderose to the feces of 20 individuals of varying ages to assess its effect on the gut microbiota. Theanderose increased the relative abundance of Bifidobacteriaceae and Prevotellaceae while decreasing the population ratio of Lachnospiraceae and Ruminococcaceae. Conclusively, theanderose displayed excellent prebiotic potential when judged by low digestibility and selective growth of beneficial microbes over harmful microbes.

Enhanced production of turanose using a mutant amylosucrase from Bifidobacterium thermophilum immobilized on silica carriers

Turanose (α-d-glucopyranosyl-(1→3)-α-d-fructose) is a rare disaccharide that is a potential low-calorigenic sweetener. This novel sucrose isomer has been efficiently synthesized by the amylosucrase from Bifidobacterium thermophilum (BtAS). In this study, we aimed to enhance turanose biosynthesis by designing a BtAS variant (BtAS-G374S) with improved thermal stability. The BtAS variant was immobilized on porosity-controlled silica carrier, and its enzymatic properties were thoroughly investigated. Using response surface methodology with central composite design, optimal immobilization conditions were determined to significantly boost the biosynthetic efficiency. The BtAS-G374S showed 1.6-fold higher specific activity (2.2 U/mg) than the wild-type enzyme (1.4 U/mg). Additionally, the turanose production yield of BtAS-G374S was significantly enhanced, reaching 65 %, compared to 25 % for the wild-type enzyme when reacting with 2 M sucrose. Immobilization of BtAS-G374S was optimized on controlled porosity carrier (CPC) silica carrier using Response Surface Methodology, achieving an enzyme activity of 7.89 U and an immobilization efficiency of 68.98 % under optimal conditions. Immobilization of BtAS-G374S on CPC silica carriers enhanced its pH and thermal stability. The immobilized enzyme showed a half-life of 50.23 h at 55 °C and retained 68 % of its initial biosynthetic yield after 10 reuses. These properties suggest its potential for efficient industrial turanose production.

Efficient biotransformation of naringenin to naringenin α-glucoside, a novel α-glucosidase inhibitor, by amylosucrase from Deinococcus wulumuquiensis

Amylosucrase (ASase) efficiently biosynthesizes α-glucoside using flavonoids as acceptor molecules and sucrose as a donor molecule. Here, ASase from Deinococcus wulumuqiensis (DwAS) biosynthesized more naringenin α-glucoside (NαG) with sucrose and naringenin as donor and acceptor molecules, respectively, than other ASases from Deinococcus sp. The biotransformation rate of DwAS to NαG was 21.3% compared to 7.1-16.2% for other ASases. Docking simulations showed that the active site of DwAS was more accessible to naringenin than those of others. The 217th valine in DwAS corresponded to the 221st isoleucine in Deinococcus geothermalis AS (DgAS), and the isoleucine possibly prevented naringenin from accessing the active site. The DwAS-V217I mutant had a significantly lower biosynthetic rate of NαG than DwAS. The kcat/Km value of DwAS with naringenin as the donor was significantly higher than that of DgAS and DwAS-V217I. In addition, NαG inhibited human intestinal α-glucosidase more efficiently than naringenin.

Efficient and novel biosynthesis of myricetin α-triglucoside with improved solubility using amylosucrase from Deinococcus deserti

Although myricetin (3,3',4',5,5',7-hexahydroxyflavone, MYR) has a high antioxidant capacity and health functions, its use as a functional food material is limited owing to its low stability and water solubility. Amylosucrase (ASase) is capable of biosynthesizing flavonol α-glycoside using flavonols as acceptor molecules and sucrose as a donor molecule. Here, ASase from Deinococcus deserti (DdAS) efficiently biosynthesizes a novel MYR α-triglucoside (MYRαG3) using MYR as the acceptor molecule. Comparative homology analysis and computational simulation revealed that DdAS has a different active pocket for the transglycosylation reaction. DdAS produced MYRαG3 with a conversion efficiency of 67.4 % using 10 mM MYR and 50 mM sucrose as acceptor and donor molecules, respectively. The structure of MYRαG3 was identified as MYR 4'-O-4″,6″-tri-O-α-D-glucopyranoside using NMR and LC-MS. In silico analysis confirmed that DdAS has a distinct active pocket compared to other ASases. In addition, molecular docking simulations predicted the synthetic sequence of MYRαG3. Furthermore, MYRαG3 showed a similar DPPH radical scavenging activity of 49 %, comparable to MYR, but with significantly higher water solubility, which increased from 0.03 μg/mL to 511.5 mg/mL. In conclusion, this study demonstrated the efficient biosynthesis of a novel MYRαG3 using DdAS and highlighted the potential of MYRαG3 as a functional material.

Bottom-Up Synthesized Glucan Materials: Opportunities from Applied Biocatalysis

Linear d-glucans are natural polysaccharides of simple chemical structure. They are comprised of d-glucosyl units linked by a single type of glycosidic bond. Noncovalent interactions within, and between, the d-glucan chains give rise to a broad variety of macromolecular nanostructures that can assemble into crystalline-organized materials of tunable morphology. Structure design and functionalization of d-glucans for diverse material applications largely relies on top-down processing and chemical derivatization of naturally derived starting materials. The top-down approach encounters critical limitations in efficiency, selectivity, and flexibility. Bottom-up approaches of d-glucan synthesis offer different, and often more precise, ways of polymer structure control and provide means of functional diversification widely inaccessible to top-down routes of polysaccharide material processing. Here the natural and engineered enzymes (glycosyltransferases, glycoside hydrolases and phosphorylases, glycosynthases) for d-glucan polymerization are described and the use of applied biocatalysis for the bottom-up assembly of specific d-glucan structures is shown. Advanced material applications of the resulting polymeric products are further shown and their important role in the development of sustainable macromolecular materials in a bio-based circular economy is discussed.

Characterization of a unique pH-dependent amylosucrase from Deinococcus cellulosilyticus

The amylosucrase (ASase, EC 2.4.1.4) utilizes sucrose as the sole substrate to catalyze multifunctional reactions. It can naturally synthesize α-1,4-linked glucans such as amylose as well as sucrose isomers with more favorable properties than sucrose with a lower intestinal digestibility and non-cariogenic properties. The amino acid sequence of the asase gene from Deinococcus cellulosilyticus (DceAS) exhibits low homology with those of other ASases from other Deinococcus species. In this study, we cloned and expressed DceAS and demonstrated its high activity at pH 6 and pH 8 and maintained stability. It showed higher polymerization activity at pH 6 than at pH 8, but similar isomerization activity and produced more turanose and trehalulose at pH 6 than at pH 8 and produced more isomaltulose at pH 8. Furthermore, the molecular weight of DceAS was 226.6 kDa at pH 6 and 145.5 kDa at pH 8, indicating that it existed as a trimer and dimer, respectively under those conditions. Additionally, circular dichroism spectra showed that the DceAS secondary structure was different at pH 6 and pH 8. These differences in reaction products at different pHs can be harnessed to naturally produce sucrose alternatives that are more beneficial to human health.

Enzymatic Synthesis of α-Glucan Microparticles Using Amylosucrases from Bifidobacterium Species and Its Physicochemical Properties

α-Glucan microparticles (GMPs) have significant potential as high-value biomaterials in various industries. This study proposes a bottom-up approach for producing GMPs using four amylosucrases from Bifidobacterium sp. (BASs). The physicochemical characteristics of these GMPs were analyzed, and the results showed that the properties of the GMPs varied depending on the type of enzymes used in their synthesis. As common properties, all GMPs exhibited typical B-type crystal patterns and poor colloidal dispersion stability. Interestingly, differences in the physicochemical properties of GMPs were generated depending on the synthesis rate of linear α-glucan by the enzymes and the degree of polymerization (DP) distribution. Consequently, we found differences in the properties of GMPs depending on the DP distribution of linear glucans prepared with four BASs. Furthermore, we suggest that precise control of the type and characteristics of the enzymes provides the possibility of producing GMPs with tailored physicochemical properties for various industrial applications.

Secretory expression of amylosucrase in Bacillus licheniformis through twin-arginine translocation pathway

Amylosucrase (EC 2.4.1.4) is a versatile enzyme with significant potential in biotechnology and food production. To facilitate its efficient preparation, a novel expression strategy was implemented in Bacillus licheniformis for the secretory expression of Neisseria polysaccharea amylosucrase (NpAS). The host strain B. licheniformis CBBD302 underwent genetic modification through the deletion of sacB, a gene responsible for encoding levansucrase that synthesizes extracellular levan from sucrose, resulting in a levan-deficient strain, B. licheniformis CBBD302B. Neisseria polysaccharea amylosucrase was successfully expressed in B. licheniformis CBBD302B using the highly efficient Sec-type signal peptide SamyL, but its extracellular translocation was unsuccessful. Consequently, the expression of NpAS via the twin-arginine translocation (TAT) pathway was investigated using the signal peptide SglmU. The study revealed that NpAS could be effectively translocated extracellularly through the TAT pathway, with the signal peptide SglmU facilitating the process. Remarkably, 62.81% of the total expressed activity was detected in the medium. This study marks the first successful secretory expression of NpAS in Bacillus species host cells, establishing a foundation for its future efficient production.

ONE-SENTENCE SUMMARY

Amylosucrase was secreted in Bacillus licheniformis via the twin-arginine translocation pathway.

Biotransformation-guided purification of a novel glycoside derived from the extracts of Chinese herb Baizhi

Our pursuit of new compounds with enhanced bioavailability and bioactivity prompted us to employ the biotransformation-guided purification (BGP) approach which leverages proficient in vitro biotransformation techniques. Angelica dahurica roots, also called Baizhi in Chinese traditional medicine, are famous for their anti-inflammatory and analgesic properties. Herein, we applied the BGP methodology to Baizhi extracts, employing Deinococcus geothermalis amylosucrase (DgAS), an enzyme demonstrating catalytic competence across diverse substrates, for biotransformation. Initiating with a 70 % methanol extraction, we obtained the crude extract of commercial Baizhi powder, followed by an additional extraction using ethyl acetate. Notably, reactions performed on this extract yielded limited quantities of novel compounds. Subsequently, the extract underwent partitioning into four fractions based on HPLC profiling, leading to the successful isolation of a compound with significant yield from fraction 2 mixtures upon reaction with DgAS. Structural elucidation confirmed the compound as byakangelicin-7″-O-α-glucopyranoside (BG-G), a new alpha glycoside derivative of byakangelicin. Furthermore, validation experiments verified the capacity of DgAS to glycosylate pure byakangelicin, yielding BG-G. Remarkably, the aqueous solubility of BG-G exceeded that of byakangelicin by over 29,000-fold. In conclusion, BGP emerges as a potent strategy combining traditional medicinal insights with robust enzymatic tools for generating new compounds.

Starch-based materials for drug delivery in the gastrointestinal tract-A review

Starch is a natural copolymer with unique physicochemical characteristics. Historically, it has been physically, chemically, or enzymatically modified to obtain ad-hoc functional properties for its use in different applications. In this context, the use of starch-based materials in drug delivery systems (DDSs) has gained great attention mainly because it is cheap, biodegradable, biocompatible, and renewable. This paper reviews the state of the art in starch-based materials design for their use in drug-controlled release with internal stimulus responsiveness; i.e., pH, temperature, colonic microbiota, or enzymes; specifically, those orally administered for its release in the gastrointestinal tract (GIT). Physical-chemical principles in the design of these materials taking into account their response to a particular stimulus are discussed. The relationship between the type of DDSs structure, starch modification routes, and the corresponding drug release profiles are systematically analyzed. Furthermore, the challenges and prospects of starch-based materials for their use in stimulus-responsive DDSs are also debated.

Customizing Starch Properties: A Review of Starch Modifications and Their Applications

Starch has been a convenient, economically important polymer with substantial applications in the food and processing industry. However, native starches present restricted applications, which hinder their industrial usage. Therefore, modification of starch is carried out to augment the positive characteristics and eliminate the limitations of the native starches. Modifications of starch can result in generating novel polymers with numerous functional and value-added properties that suit the needs of the industry. Here, we summarize the possible starch modifications in planta and outside the plant system (physical, chemical, and enzymatic) and their corresponding applications. In addition, this review will highlight the implications of each starch property adjustment.

Whole-cell bioconversion using non-Leloir transglycosylation reactions: a review

Microbial biocatalysts are evolving technological tools for glycosylation research in food, feed and pharmaceuticals. Advances in bioengineered Leloir and non-Leloir carbohydrate-active enzymes allow for whole-cell biocatalysts to curtail production costs of purified enzymes while enhancing glucan synthesis through continued enzyme expression. Unlike sugar nucleotide-dependent Leloir glycosyltransferases, non-Leloir enzymes require inexpensive sugar donors and can be designed to match the high value, yield and selectivity of the former. This review addresses the current state of bacterial cell-based production of glucans and glycoconjugates via transglycosylation, and describes how alterations made to microbial hosts to surpass purified enzymes as the preferred mode of catalysis are steadily being acquired through genetic engineering, rational design and process optimization. A comprehensive exploration of relevant literature has been summarized to describe whole-cell biocatalysis in non-Leloir glycosylation reactions with various donors and acceptors, and the characterization, application and latest developments in the optimization of their use.

Recent trends in the modification of polyphenolic compounds using hydroxylation and glycosylation

Polyphenols are bioactive molecules that are used in therapeutics. Polyphenol hydroxylation and glycosylation have been shown to increase their bioavailability, solubility, bioactivity, and stability for use in various applications. Ortho-hydroxylation of polyphenols using tyrosinase allows high selectivity and yield without requiring a cofactor, while meta- and para-hydroxylation of polyphenols are mediated by site-specific hydroxylases and cytochrome P450s, although these processes are somewhat rare. O-glycosylation of polyphenols proceeds further after hydroxylation. The O-glycosylation reaction typically requires nucleotide diphosphate (NDP) sugar. However, amylosucrase (AS) has emerged as a promising enzyme for polyphenol glycosylation in large-scale production without requiring NDP-sugar. Overall, this review describes recent findings on the enzymatic mechanisms, enzyme engineering, and applications of enzymatic reactions.

Identification and characterization of a novel high-activity amylosucrase from Salinispirillum sp. LH10-3-1

In this study, a novel high-activity amylosucrase from Salinispirillum sp. LH10-3-1 (SaAS) was identified and characterized. The recombinant enzyme was determined as a monomer with a molecular mass of 75 kDa. SaAS protein exhibited the maximum total and polymerization activities at pH 9.0 and maximum hydrolysis activity at pH 8.0. The optimum temperature for total, polymerization, and hydrolysis activities were 40, 40, and 45 °C, respectively. Under the optimal pH and temperature, SaAS had a specific activity of 108.2 U/mg. SaAS also showed excellent salt tolerance and could retain 77.4% of its original total activity at 4.0 M NaCl. The addition of Mg²⁺, Ba²⁺, and Ca²⁺ enhanced the total activity of SaAS. When the conversion of 0.1 M and 1.0 M sucrose was catalyzed at pH 9.0 and 40 °C for 24 h, the ratios of hydrolysis, polymerization, and isomerization reactions were 11.9:77.4:10.7 and 15.3:53.5:31.2, respectively. The α-arbutin yield of 60.3% was achieved from 20 mM sucrose and 5 mM hydroquinone catalyzed by SaAS. KEY POINTS: • A novel amylosucrase from Salinispirillum sp. LH10-3-1 (SaAS) was characterized. • SaAS has the highest specific enzyme activity among all known amylosucrase. • SaAS has hydrolysis, polymerization, isomerization, and glucosyltransferase activities.

Identification and analysis of antioxidant peptides from sorghum (Sorghum bicolor L. Moench) on the basis of in vitro simulated gastrointestinal digestion

Sorghum (Sorghum bicolor L. Moench) antioxidant peptides in vitro simulated through continuous gastrointestinal (GI) digestion in comparison with rice (Oryza sativa L.) were identified and functionally analysed. It was demonstrated that the protein digestibility of sorghum and rice increased by 11.27% and 14.10% after GI digestion, respectively. The concentrations of the rice peptides GG14, GG12, SF11, and LQ9 and the sorghum peptide KP9 in the gastrointestinal tract were 0.018, 0.712, 0.548, 0.188, and 0.265 μg mL^-1, respectively. An assay of the scavenging ability showed that the sorghum peptide KP9 had the strongest ABTS-scavenging ability, with an IC₅₀ value of 44.44 mg mL^-1. The rice peptide LQ9 had the strongest DPPH and OH radical scavenging activity, with IC₅₀ values of 10.41 and 25.78 mg mL^-1, respectively. These five selectively synthesized peptides were predicted to be nontoxic and to have good ADMET absorption properties. The results indicated that the sorghum and rice peptides obtained by in vitro digestion were separated and purified with certain antioxidant activities and could be consumed as functional foods to modulate certain chronic diseases.

Enzymatic Synthesis of Novel and Highly Soluble Puerarin Glucoside by Deinococcus geothermalis Amylosucrase

Puerarin (daidzein-8-C-glucoside) is an isoflavone isolated from several leguminous plants of the genus Pueraria. Puerarin possesses several pharmacological properties; however, the poor solubility of puerarin limits its applications. To resolve this poor solubility, Deinococcus geothermalis amylosucrase (DgAS) was used to modify puerarin into more soluble derivatives. The results showed that DgAS could biotransform puerarin into a novel compound: puerarin-4′-O-α-glucoside. The biotransformation reaction was manipulated at different temperatures, pH values, sucrose concentrations, reaction times, and enzyme concentrations. The results showed that the optimal reaction condition was biotransformed by 200 μg/mL DgAS with 20% (w/v) sucrose at pH 6 and incubated at 40 °C for 48 h, and the optimal production yield was 35.1%. Puerarin-4′-O-α-glucoside showed 129-fold higher solubility than that of puerarin and, thus, could be further applied for pharmacological use in the future.

Novel Glycosylation by Amylosucrase to Produce Glycoside Anomers

Simple Summary

All livings are composed of cells, which contain lipid, proteins, nuclei acids, and saccharides. Saccharides include polysaccharides, oligo saccharides, disaccharides, which are linked by monosaccharides. Monosaccharides such as glucose exist in two forms, named α and β anomer, in solution. In addition, monosaccharides could be linked with lipid, proteins, nuclei acids or other saccharide to form glycosides through glycosylation. In nature, glycosylation is catalyzed by enzymes. Until now, all enzymes catalyzed glycosylation to form glycosides with either α or β form but not both. This study found an enzyme, amylosucrase from Deinococcus geothermalis (DgAS), could catalyze glycosylation of a kind of lipid named ganoderic acids triterpenoids from a medicinal fungus Ganoderma lucidum to form both α and β anomer of glycosides. This is the first report that enzymes could catalyze such glycosylation and a possible reaction mechanism was proposed.

Abstract

Glycosylation occurring at either lipids, proteins, or sugars plays important roles in many biological systems. In nature, enzymatic glycosylation is the formation of a glycosidic bond between the anomeric carbon of the donor sugar and the functional group of the sugar acceptor. This study found novel glycoside anomers without an anomeric carbon linkage of the sugar donor. A glycoside hydrolase (GH) enzyme, amylosucrase from Deinococcus geothermalis (DgAS), was evaluated to glycosylate ganoderic acid F (GAF), a lanostane triterpenoid from medicinal fungus Ganoderma lucidum, at different pH levels. The results showed that GAF was glycosylated by DgAS at acidic conditions pH 5 and pH 6, whereas the activity dramatically decreased to be undetectable at pH 7 or pH 8. The biotransformation product was purified by preparative high-performance liquid chromatography and identified as unusual α-glucosyl-(2→26)-GAF and β-glucosyl-(2→26)-GAF anomers by mass and nucleic magnetic resonance (NMR) spectroscopy. We further used DgAS to catalyze another six triterpenoids. Under the acidic conditions, two of six compounds, ganoderic acid A (GAA) and ganoderic acid G (GAG), could be converted to α–glucosyl-(2→26)-GAA and β–glucosyl-(2→26)-GAA anomers and α-glucosyl-(2→26)-GAG and β-glucosyl-(2→26)-GAG anomers, respectively. The glycosylation of triterpenoid aglycones was first confirmed to be converted via a GH enzyme, DgAS. The novel enzymatic glycosylation-formed glycoside anomers opens a new bioreaction in the pharmaceutical industry and in the biotechnology sector.

Production of New Isoflavone Diglucosides from Glycosylation of 8-Hydroxydaidzein by Deinococcus geothermalis Amylosucrase

8-Hydroxydaidzein (8-OHDe) is a non-natural isoflavone polyphenol isolated from fermented soybean foods. 8-OHDe exhibits a wide range of pharmaceutical activities. However, both the poor solubility and instability of 8-OHDe limit its applications. To resolve the limitations of 8-OHDe, Deinococcus geothermalis amylosucrase (DgAS) has previously been used to glycosylate 8-OHDe to produce soluble and stable 8-OHDe-7-O-α-glucopyranoside (8-OHDe-7-G) in a 0.5 h reaction time. In this study, we aimed to use DgAS and an extended reaction time to produce 8-OHDe diglucosides. At least three 8-OHDe derivatives were produced after a 24 h reaction time, and two major products were successfully purified and identified as new compounds: 8-OHDe-7-O-[α-glucopyranosyl-(1→6)-α-glucopyranoside] (8-OHDe-7-G2) and 8-OHDe-7,4′-O-α-diglucopyranoside (8-OHDe-7-G-4′-G). 8-OHDe-7-G-4′-G showed a 4619-fold greater aqueous solubility than 8-OHDe. In addition, over 92% of the 8-OHDe diglucosides were stable after 96 h, while only 10% of the 8-OHDe could be detected after being subjected to the same conditions. The two stable 8-OHDe diglucoside derivatives have the potential for pharmacological usage in the future.

Optimized enzymatic synthesis of digestive resistant anomalous isoquercitrin glucosides using amylosucrase and response surface methodology

Diverse flavonoid glycosides are present in the plant kingdom. Advanced technologies have been utilized to synthesize glycosyl flavonoids which exhibit good physicochemical characteristics. Previously, novel isoquercitrin (IQ) mono-, di-, and tri-glucosides (IQ-G1', IQ-G2', and IQ-G3'; atypical IQ-Gs (IQ-G_ap)) were synthesized through the reaction of amylosucrase. Here, the regio-selective transglycosylation yields were predicted using response surface methodology for three variables (glucose donor (sucrose; 100-1500 mM), glucose acceptor (IQ; 100-400 µM), and pH (5.0-8.8)) using 1 unit/mL of enzyme at 45 °C; then, the optima were verified according to the experimental responses. Acidity (pH 5.0) was a major contributor for IQ-G1' production (> 50%), and high sucrose concentration (1500 mM) limited IQ-G3' production (< 15%). Low sucrose concentration (100 mM) at pH 7.0 promoted higher glycosyl IQ production (> 30%). Time-course production of IQ-G_ap showed an exponential growth with different rates. IQ-G_ap was stable under the simulated intestinal conditions compared with typical IQ-Gs. Digestive stable IQ-G_ap can be effectively synthesized by modulating reaction conditions; thereby, atypical glycosyl products may contribute to the elucidation of nutraceutical potential of flavonoid glycosides. KEY POINTS: •Predictions of RSM were validated for the regio-selective IQ-G_ap production. • Time course changes of IQ-G_ap indicate non-processive glycosylation of DGAS. • IQ-G_ap exceed typical IQ-G in digestive stability at simulated intestinal condition.

A novel strategy for D-psicose and lipase co-production using a co-culture system of engineered Bacillus subtilis and Escherichia coli and bioprocess analysis using metabolomics

To develop an economically feasible fermentation process, this study designed a novel bioprocess based on the co-culture of engineered Bacillus subtilis and Escherichia coli for the co-production of extracellular D-psicose and intracellular lipase. After optimizing the co-culture bioprocess, 11.70 g/L of D-psicose along with 16.03 U/mg of lipase was obtained; the glucose and fructose were completely utilized. Hence, the conversion rate of D-psicose reached 69.54%. Compared with mono-culture, lipase activity increased by 58.24%, and D-psicose production increased by 7.08%. In addition, the co-culture bioprocess was explored through metabolomics analysis, which included 168 carboxylic acids and derivatives, 70 organooxygen compounds, 34 diazines, 32 pyridines and derivatives, 30 benzene and substituted derivatives, and other compounds. It also could be found that the relative abundance of differential metabolites in the co-culture system was significantly higher than that in the mono-culture system. Pathway analysis revealed that, tryptophan metabolism and β-alanine metabolism had the highest correlation and played an important role in the co-culture system; among them, tryptophan metabolism regulates protein synthesis and β-alanine metabolism, which is related to the formation of metabolic by-products. These results confirm that the co-cultivation of B. subtilis and E. coli can provide a novel idea for D-psicose and lipase biorefinery, and are beneficial for the discovery of valuable secondary metabolites such as turanose and morusin.

Physicochemical properties of turanose and its potential applications as a sucrose substitute

Among the structural isomers of sucrose, turanose has been considered as one of good candidates as novel sweetener due to its mild taste, low calorie, and anti-cariogenicity. Here, various physicochemical properties of turanose, such as solubility, temperature and pH stabilities, viscosity, non-enzymatic browning reaction, and dynamic vapor sorption, were investigated by comparing them to those of other commercial sugars. Turanose did not significantly hydrolyze through the simulated digestion tract overall but in the artificial small intestinal environment specifically, turanose degraded by only 18% when sucrose was hydrolyzed by 36% after 4 h. In addition, physicochemical properties of turanose confirmed that it had a potential to replace sucrose due to similar or better product qualities as a food ingredient than other types of sugars with similar chemical structure. Thus, our study suggests that turanose can be applied as a functional sweetener or bulking agent in food processing.

Biosynthesis of glyceride glycoside (nonionic surfactant) by amylosucrase, a powerful glycosyltransferase

Amylosucrase (ASase, E.C. 2.4.1.4) is a powerful transglycosylation enzyme that can transfer glucose from sucrose to the hydroxyl (-OH) group of various compounds. In this study, recombinant ASases from Deinococcus geothermalis (DgAS) and Bifidobacterium thermophilum (BtAS) were used to synthesize biosurfactants based on the computational analysis of predicted docking simulations. Successful predictions of the binding affinities, conformations, and three-dimensional structures of three surfactants were computed from receptor-ligand binding modes. DgAS and BtAS were effective in the synthesis of biosurfactants from glyceryl caprylate, glyceryl caprate, and polyglyceryl-2 caprate. The results of the transglycosylation reaction were consistent for both ASases, with glyceryl caprylate acceptor showing the highest concentration, as confirmed by thin layer chromatography. Furthermore, the transglycosylation reactions of DgAS were more effective than those of BtAS. Among the three substrates, glyceryl caprylate glycoside and glyceryl caprate glycoside were successfully purified by liquid chromatography-mass spectrometry (LC-MS) with the corresponding molecular weights.

Natural compounds against cytotoxic drug-induced cardiotoxicity: A review on the involvement of PI3K/Akt signaling pathway

Cardiotoxicity is a critical concern in the use of several cytotoxic drugs. Induction of apoptosis, inflammation, and autophagy following dysregulation of the PI3K/Akt signaling pathway contributes to the cardiac damage induced by these drugs. Several natural compounds (NCs), including ferulic acid, gingerol, salvianolic acid B, paeonol, apigenin, calycosin, rutin, neferine, higenamine, vincristine, micheliolide, astragaloside IV, and astragalus polysaccharide, have been reported to suppress cytotoxic drug-induced cardiac injury. This article reviews these NCs that have been reported to have a protective effect against cytotoxic drug-induced cardiotoxicity through regulation of the PI3K/Akt signaling pathway.

Using Amylosucrase for the Controlled Synthesis of Novel Isoquercitrin Glycosides with Different Glycosidic Linkages

Many attempts have been made to obtain natural products with certain glycosidic linkages for improvement of their chemo-physical characteristics. Amylosucrase from Deinococcus geothermalis (DGAS; EC.4.2.1.4) is able to transglycosylate natural products. A model compound, isoquercitrin (IQ; quercetin-3-O-glucoside), was employed for producing new IQ glucosides (IQ-Gs). Treatment of IQ with DGAS produced monoglucoside (IQ-G1'), diglucosides (IQ-G2' and IQ-G2″), and triglucoside (IQ-G3). Structural analysis by mass and nuclear magnetic resonance spectrometry revealed that three of the four IQ-Gs were unreported new compounds possessing α-1,2-, α-1,4-, and/or α-1,6-glucosidic linkages at the 3-O-glucosyl moiety of IQ. IQ-G2' and IQ-G3 were dominantly produced at pH 5.0 and 7.2 and 1500 and 100 mM sucrose, respectively (yields of total IQ-Gs: 50-97%). Kinetic studies indicated that the production rate was dependent on buffer/pH and sucrose concentration. The diverse transglycosylations were verified with a molecular docking simulation. This study sheds light on methods for simple glycodiversification of natural products using DGAS, which can synthesize diversely branched glycosides by modulating reaction conditions.

Molecular Docking and Kinetic Studies of the A226N Mutant of Deinococcus geothermalis Amylosucrase with Enhanced Transglucosylation Activity

Amylosucrase (ASase, E.C. 2.4.1.4) is capable of efficient glucose transfer from sucrose, acting as the sole donor molecule, to various functional acceptor compounds, such as polyphenols and flavonoids. An ASase variant from Deinococcus geothermalis, in which the 226^th alanine is replaced with asparagine (DgAS-A226N), shows increased polymerization activity due to changes in the flexibility of the loop near the active site. In this study, we further investigated how the mutation modulates the enzymatic activity of DgAS using molecular dynamics and docking simulations to evaluate interactions between the enzyme and phenolic compounds. The computational analysis revealed that the A226N mutation could induce and stabilize structural changes near the substratebinding site to increase glucose transfer efficiency to phenolic compounds. Kinetic parameters of DgAS-A226N and WT DgAS were determined with sucrose and 4-methylumbelliferone (MU) as donor and acceptor molecules, respectively. The k_cat/K_m value of DgAS-A226N with MU (6.352 mM^-1min^-1) was significantly higher than that of DgAS (5.296 mM^-1min^-1). The enzymatic activity was tested with a small phenolic compound, hydroquinone, and there was a 1.4-fold increase in α-arbutin production. From the results of the study, it was concluded that DgAS-A226N has improved acceptor specificity toward small phenolic compounds by way of stabilizing the active conformation of these compounds.

Comparative study on four amylosucrases from Bifidobacterium species

Amylosucrase (ASase) is α-glucan-producing enzyme. Four putative ASase genes (bdas, blas, bpas, and btas) were cloned from Bifidobacterium sp. and expressed in Escherichia coli. All ASases from Bifidobacterium sp. (BAS) displayed typical ASase properties with slightly different characteristics. Among the BASs studied, BdAS and BpAS showed maximal enzyme activities at 35 and 30 °C, respectively, whereas BlAS and BtAS were maximally active at higher temperatures, i.e., 45 and 50 °C, respectively. BpAS exhibited optimum pH under slightly basic conditions (pH 8.0), while BdAS, BlAS, and BtAS preferred weakly acidic conditions (pH 5.0-6.0). All BASs showed higher isomerization activities. Particularly, BlAS produced more trehalulose than turanose. Although polymerization was the highest for BtAS, BtAS synthesized α-1, 4-glucans with a lower degree of polymerization than that of the other BASs. The versatile properties of the BASs described could contribute to the efficient production of highly valuable biomaterials for the agriculture, food, and pharmaceutical industries.

Application of Transglutaminase in Developing Cassava-based Wet Noodle for Quality and Shelf Life Improvement: A Review

Characteristic of cassava flour is relatively similar to wheat flour. Cassava flour has the potential to substitute 70-80% of wheat flour as the main ingredient for wet noodle production. Unfortunately, cassava flour has no gluten and lower protein content than wheat flour, which is important for the characteristic of a wet noodle. Therefore, transglutaminase (MTGase) is often applied in non-gluten products to improve its texture. This enzyme catalyzes the reaction between lysine and glutamine to form isopeptide cross-links. Moreover, the addition of MTGase to cassava-based wet noodle improves its texture and color. In addition, this effect gives better palatability for wet noodle. This enzyme can increase the shelf life of wet noodles and safe for our health. The present study demonstrates with patent and literature data the potential of MTGase in noodles based on cassava flour.