Amylosucrase from Deinococcus geothermalis can be modulated under different reaction conditions to produce novel quercetin 4'-O-α-d-isomaltoside

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.

Glycosylation of flavonoids by sucrose- and starch-utilizing glycoside hydrolases: A practical approach to enhance glycodiversification

Flavonoids are ubiquitous and diverse in plants and inseparable from the human diet. However, in terms of human health, their further research and application in functional food and pharmaceutical industries are hindered by their low water solubility. Therefore, flavonoid glycosylation has recently attracted research attention because it can modulate the physicochemical and biochemical properties of flavonoids. This review represents a comprehensive overview of the O-glycosylation of flavonoids catalyzed by sucrose- and starch-utilizing glycoside hydrolases (GHs). The characteristics of this feasible biosynthesis approach are systematically summarized, including catalytic mechanism, specificity, reaction conditions, and yields of the enzymatic reaction, as well as the physicochemical properties and bioactivities of the product flavonoid glycosides. The cheap glycosyl donor substrates and high yields undoubtedly make it a practical flavonoid modification approach to enhance glycodiversification.

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.

Flavonoid Synthesis by Deinococcus sp. 43 Isolated from the Ginkgo Rhizosphere

Flavonoids are crucial in physiological and pharmaceutical processes, especially the treatment of cancer and the prevention of cardiovascular and cerebrovascular diseases. Flavonoid-producing plants and fungi have been extensively reported, but bacteria have been much less investigated as a source of flavonoid production. Deinococcus sp. 43, a spherical flavonoid-producing bacteria from the Ginkgo rhizosphere, was reported in this study. First, the whole genome of Deinococcus sp. 43 was sequenced and a series of flavonoid anabolic genes were annotated. Simultaneously, High Performance Liquid Chromatography (HPLC) results showed that Deinococcus sp. 43 was capable of producing flavonoids, with a maximum quercetin output of 2.9 mg/L. Moreover, the relative expression of key genes involved in flavonoid synthesis was determined to test the completeness of the flavonoid anabolic pathway. The results of LC-MS analysis demonstrated that the flavonoids produced by Deinococcus sp. 43 were significantly different between intracellular and extracellular environments. The concentration of multiple glycosylated flavonoids was substantially higher in extracellular than intracellular environments, while the majority of flavonoids obtained in intracellular environments were hydroxylated multiple times. Lastly, the flavonoid biosynthetic pathway of Deinococcus sp. 43 was constructed based on the genomic analysis and the detected flavonoids. In conclusion, this study represents the first comprehensive characterization of the flavonoid-producing pathway of Deinococcus. The findings demonstrate that the strain has excellent potential as a genetically engineered strain for the industrial production of flavonoids.

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.

Fisetin glycosides synthesized by cyclodextrin glycosyltransferase from Paenibacillus sp. RB01: characterization, molecular docking, and antioxidant activity

Fisetin is a flavonoid that exhibits high antioxidant activity and is widely employed in the pharmacological industries. However, the application of fisetin is limited due to its low water solubility. In this study, glycoside derivatives of fisetin were synthesized by an enzymatic reaction using cyclodextrin glycosyltransferase (CGTase) from Paenibacillus sp. RB01 in order to improve the water solubility of fisetin. Under optimal conditions, CGTase was able to convert more than 400 mg/L of fisetin to its glycoside derivatives, which is significantly higher than the previous biosynthesis using engineered E. coli. Product characterization by HPLC and LC-MS/MS revealed that the transglycosylated products consisted of at least five fisetin glycoside derivatives, including fisetin mono-, di- and triglucosides, as well as their isomers. Enzymatic analysis by glucoamylase and α-glucosidase showed that these fisetin glycosides were formed by α-1,4-glycosidic linkages. Molecular docking demonstrated that there are two possible binding modes of fisetin in the enzyme active site containing CGTase-glysosyl intermediate, in which O7 and O4' atoms of fisetin positioned close to the C1 of glycoside donor, corresponding to the isomers of the obtained fisetin monoglucosides. In addition, the water solubility and the antioxidant activity of the fisetin monoglucosides were tested. It was found that their water solubility was increased at least 800 times when compared to that of their parent molecule while still maintaining the antioxidant activity. This study revealed the potential application of CGTase to improve the solubility of flavonoids.

Endophytic Bacterial Communities of Ginkgo biloba Leaves During Leaf Developmental Period

Plant-specialized secondary metabolites have ecological functions in mediating interactions between plants and their entophytes. In this study, high-throughput gene sequencing was used to analyze the composition and abundance of bacteria from Ginkgo leaves at five different sampling times. The results indicated that the bacterial community structure varied during leaf developmental stage. Bacterial diversity was observed to be the highest at T2 stage and the lowest at T1 stage. Proteobacteria, Firmicutes, Actinobacteria, Chloroflexi, Cyanobacteria, and Bacteroidetes were found as the dominant phyla. The major genera also showed consistency across sampling times, but there was a significant variation in their abundance, such as Bacillus, Lysinibacillus, and Staphylococcus. Significant correlations were observed between endophytic bacteria and flavonoids. Especially, Staphylococcus showed a significant positive correlation with quercetin, and changes in the abundance of Staphylococcus also showed a strong correlation with flavonoid content. In order to determine the effect of flavonoids on endophytic bacteria of Ginkgo leaves, an extracorporeal culture of related strains (a strain of Staphylococcus and a strain of Deinococcus) was performed, and it was found that the effect of flavonoids on them remained consistent. The predicted result of Tax4Fun2 revealed that flavonoids might lead to a lower abundance of endophytic microorganisms, which further proved the correlation between bacterial communities and flavonoids. This study provided the first insight into the bacterial community composition during the development of Ginkgo leaves and the correlation between the endophytic bacteria and flavonoids.

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.

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.