Enzymatic synthesis of glycosylated puerarin using maltogenic amylase from Bacillus stearothermophilus expressed in Bacillus subtilis

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.

Immobilization of recombinant Trametes versicolor aflatoxin B1-degrading enzyme (TV-AFB1D) with montmorillonite for absorption and in situ degradation of aflatoxin B1

Aflatoxin B1 is a highly carcinogenic and teratogenic substance mainly produced by toxin-producing strains such as Aspergillus flavus and Aspergillus parasitic. The efficient decomposition of aflatoxin is an important means to reduce its harm to humans and livestock. In this study, Trametes versicolor aflatoxin B1-degrading enzyme (TV-AFB1D) was recombinantly expressed in Bacillus subtilis (B. subtilis) 168. MMT-CTAB-AFB1D complex was prepared by the immobilization of TV-AFB1D and montmorillonite (MMT) by cross-linking glutaraldehyde. The results indicated that TV-AFB1D could recombinantly express in engineered B. subtilis 168 with a size of approximately 77 kDa. The immobilization efficiency of MMT-CTAB-AFB1D reached 98.63% when the concentration of glutaraldehyde was 5% (v/v). The relative activity of TV-AFB1D decreased to 72.36% after reusing for 10 times. The content of AFB1 in MMT-CTAB-AFB1D-AFB1 decreased to 1.1 µg/g from the initial 5.6 µg/g after incubation at 50 °C for 6 h. The amount of 80.4% AFB1 in the MMT-CTAB-AFB1D-AFB1 complex was degraded by in situ catalytic degradation. Thus, the strategy of combining adsorption and in situ degradation could effectively reduce the content of AFB1 residue in the MMT-CTAB-AFB1D complex.

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.

Improving Aqueous Solubility of Natural Antioxidant Mangiferin through Glycosylation by Maltogenic Amylase from Parageobacillus galactosidasius DSM 18751

Mangiferin is a natural antioxidant C-glucosidic xanthone originally isolated from the Mangifera indica (mango) plant. Mangiferin exhibits a wide range of pharmaceutical activities. However, mangiferin's poor solubility limits its applications. To resolve this limitation of mangiferin, enzymatic glycosylation of mangiferin to produce more soluble mangiferin glucosides was evaluated. Herein, the recombinant maltogenic amylase (MA; E.C. 3.2.1.133) from a thermophile Parageobacillus galactosidasius DSM 18751^T (PgMA) was cloned into Escherichia coli BL21 (DE3) via the expression plasmid pET-Duet-1. The recombinant PgMA was purified via Ni²⁺ affinity chromatography. To evaluate its transglycosylation activity, 17 molecules, including mangiferin (as sugar acceptors), belonging to triterpenoids, saponins, flavonoids, and polyphenol glycosides, were assayed with β-CD (as the sugar donor). The results showed that puerarin and mangiferin are suitable sugar acceptors in the transglycosylation reaction. The glycosylation products from mangiferin by PgMA were isolated using preparative high-performance liquid chromatography. Their chemical structures were glucosyl-α-(1→6)-mangiferin and maltosyl-α-(1→6)-mangiferin, determined by mass and nucleic magnetic resonance spectral analysis. The newly identified maltosyl-α-(1→6)-mangiferin showed 5500-fold higher aqueous solubility than that of mangiferin, and both mangiferin glucosides exhibited similar 1,1-diphenyl-2-picrylhydrazyl free radical scavenging activities compared to mangiferin. PgMA is the first MA with glycosylation activity toward mangiferin, meaning mangiferin glucosides have potential future applications.

Enzymatic modification of daidzin using heterologously expressed amylosucrase in Bacillus subtilis

Amylosucrases (ASase, EC 2.4.1.4) from Deinococcus geothermalis (DGAS) and Neisseria polysaccharea (NPAS) were heterologously expressed in Bacillus subtilis. While DGAS was successfully expressed, NPAS was not. Instead, NPAS was expressed in Escherichia coli. Recombinant DGAS and NPAS were purified using nickel-charged affinity chromatography and employed to modify daidzin to enhance its water solubility and bioavailability. Analyses by LC/MS revealed that the major products of transglycosylation using DGAS were daidzein diglucoside and daidzein triglucoside, whereas that obtained by NPAS was only daidzein diglucoside. The optimal bioconversion conditions for daidzein triglucoside, which was predicted to have the highest water-solubility among the daidzin derivatives, was determined to be 4% (w/v) sucrose and 250 mg/L daidzin in sodium phosphate pH 7.0, with a reaction time of 12 h. Taken together, we suggest that the yield and product specificity of isoflavone daidzin transglycosylation may be modulated by the source of ASase and reaction conditions.

An extremely thermostable maltogenic amylase from Staphylothermus marinus: Bacillus expression of the gene and its application in genistin glycosylation

The most extremely thermostable maltogenic amylase (SMMA) from archaeon Staphylothermus marinus has many potential applications in food processing. To ensure safety of microbial origin, a recombinant plasmid containing the enzymic gene and a constitutive promoter AmyR2 was constructed, and then transformed into a GRAS microorganism Bacillus subtilis. The purified SMMA from the liquid cultures of Bacillus has a specific activity of 66.96U/mg, two times more than that from Escherichia coli. SMMA was further employed to catalyze the genistion glycosylation using γ-CD as both glucosyl donors and solubilizer. Glycosylated genistins with one to four additional α-glucosyls and a molar percentage of 69.87% in genistin reaction mixture were identified and quantified by HPLC-UV-MS. The glycosylated genistins at 0.2-1.2mM showed an enhanced DPPH free radical scavenging capacity. To our knowledge, this is the first report on the Bacillus expression of archaeal maltogenic amylase.

Heterologous expression and enzymatic characterization of γ-glutamyltranspeptidase from Bacillus amyloliquefaciens

γ-Glutamyltranspeptidase (GGT) catalyzes the cleavage of γ-glutamyl compounds and the transfer of γ-glutamyl moiety to water or to amino acid/peptide acceptors. GGT can be utilized for the generation of γ-glutamyl peptides or glutamic acid, which are used as food taste enhancers. In the present study, Bacillus amyloliquefaciens SMB469 with high GGT activity was isolated from Doenjang, a traditional fermented soy food of Korea. The gene encoding GGT from B. amyloliquefaciens SMB469 (BaGGT469) was cloned from the isolate, and heterologously expressed in E. coli and B. subtilis. For comparison, three additional GGT genes were cloned from B. subtilis 168, B. licheniformis DSM 13, and B. amyloliquefaciens FZB42. The BaGGT469 protein was composed of 591 amino acids. The final protein comprises two separate polypeptide chains of 45.7 and 19.7 kDa, generated via autocatalytic cleavage. The specific activity of BaGGT469 was determined to be 17.8 U/mg with γ-L-glutamyl-p-nitroanilide as the substrate and diglycine as the acceptor. GGTs from B. amyloliquefaciens showed 1.4- and 1.7-fold higher transpeptidase activities than those from B. subtilis and B. licheniformis, respectively. Especially, recombinant B. subtilis expressing BaGGT469 demonstrated 11- and 23-fold higher GGT activity than recombinant E. coli and the native B. amyloliquefaciens, respectively, did. These results suggest that BaGGT469 can be utilized for the enzymatic production of various γ-glutamyl compounds.

Over-expression, secretion, biochemical characterisation, and structure analysis of Bacillus subtilis aminopeptidase

BACKGROUND

Aminopeptidases have great application in the food industry. Current research on the expression of aminopeptidases mainly focuses on the Escherichia coli expression system. However, the application of recombinant E. coli in the food industry is restricted due to its pathogenicity and low secretory efficiency, which should be concerned in the industrial production of aminopeptidases.

RESULTS

The gene of aminopeptidase from Bacillus subtilis Zj016 (BSAP) was identified. Over-expression and secretion of BSAP were achieved in a B. subtilis expression system with the signal peptide of itself. The yield researched 52 ± 1.9 U mL(-1) , which was 18 times that of the wild-type microbe. The purified enzyme was stable at pH 7.5-9.0 and below 60°C, and was inhibited by several metal ions except appropriate Co(2+) . BSAP was most active toward p-nitroaniline derivatives of Leu, Arg and Lys. Homology modelling and structure analysis showed that there was a flexible protease-associated domain in the predicted structure of BSAP.

CONCLUSIONS

The study presented a simple procedure for over-expression and purification of BSAP. The substrate specificity and structure information were indicated based on the characterisation and homology modelling. This will be useful for further research of aminopeptidases not only from an academic standpoint but also from an applied point of view.

Overproduction of a thermostable 4-α-glucanotransferase by codon optimization at N-terminus region

BACKGROUND

4-α-Glucanotransferases are useful enzymes to modify starch owing to their transglycosylation activity. In this study, codon optimizations were conducted to overproduce a thermostable 4-α-glucanotransferase from Thermus thermophilus (TTαGT).

RESULTS

Two variants, termed TTαGT-P4CCG and TTαGT-mut6, were constructed, which have the optimized codon at the first rare codon and optimized codons at all six chosen rare codons at the N-terminus of TTαGT, respectively. In the Escherichia coli system, the expression of both optimized genes was enhanced by about 100-fold relative to that of the original gene, whereas all six mutated codons contributed to the overall enhancement of TTαGT production in Bacillus subtilis. On the basis of the αGTase activity of the crude cell extracts, relative activities of 1:2.9:5.8 were determined for TTαGT, TTαGT-P4CCG and TTαGT-mut6, respectively, in B. subtilis. In addition, the activity of TTαGT-mut6 from B. subtilis grown without antibiotics was as much as that with the antibiotics. Finally, after heat treatment, the specific activity of TTαGT-mut6 from B. subtilis was 1.5-fold greater than that from E. coli.

CONCLUSION

The codon-optimized TTαGT that was produced in a GRAS microorganism, B. subtilis, without the selection antibiotics is potentially useful in the food industry as a food-grade enzyme.