Efficient production of skimmin and 6′-succinylskimmin from umbelliferone by organic solvent-tolerant Bacillus licheniformis ZSP01 using nitrogen sources regulation strategy

A thermostable glycosyltransferase from Paenibacillus polymyxa NJPI29: recombinant expression, characterization, and application in synthesis of glycosides

Glycosylation is a prominent biological mechanism, affecting the structural and functional diversity of many natural products. In this study, a novel thermostable uridine diphosphate-dependent glycosyltransferase gene PpGT1 was cloned from Paenibacillus polymyxa NJPI29 and recombinantly expressed in B. subtilis WB600. The purified PpGT1 had a molecular weight of 45 kDa, as estimated using SDS-PAGE. The PpGT1 could catalyze the glycosylation of vanillic acid, methyl vanillate, caffeic acid, cinnamic alcohol, and ferulic acid. Moreover, PpGT1 possessed good thermostability and retained 80% of its original activity even after 12 h of incubation at 45 °C. In addition, PpGT1 remained stable within a neutral to alkaline pH range as well as in the presence of metal ions. The synthesis of methyl vanillate 4-O-β-D-glucoside by purified PpGT1 reached a yield 3.58 mM in a system with pH 8.0, 45 °C, 12 mM UDP-Glc, and 4 mM methyl vanillate. 3D-structure-based amino acid sequence alignments revealed that the catalytic residues and C-terminated PSPG motif were conserved. These unusual properties indicated that PpGT1 is a candidate UGT for valuable natural product industrial applications.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02855-z.

A Glycolipid Glycosyltransferase with Broad Substrate Specificity from the Marine Bacterium "Candidatus Pelagibacter sp." Strain HTCC7211

In the marine environment, phosphorus availability significantly affects the lipid composition in many cosmopolitan marine heterotrophic bacteria, including members of the SAR11 clade and the Roseobacter clade. Under phosphorus stress conditions, nonphosphorus sugar-containing glycoglycerolipids are substitutes for phospholipids in these bacteria. Although these glycoglycerolipids play an important role as surrogates for phospholipids under phosphate deprivation, glycoglycerolipid synthases in marine microbes are poorly studied. In the present study, we biochemically characterized a glycolipid glycosyltransferase (GT_cp) from the marine bacterium “Candidatus Pelagibacter sp.” strain HTCC7211, a member of the SAR11 clade. Our results showed that GT_cp is able to act as a multifunctional enzyme by synthesizing different glycoglycerolipids with UDP-glucose, UDP-galactose, or UDP-glucuronic acid as sugar donors and diacylglycerol (DAG) as the acceptor. Analyses of enzyme kinetic parameters demonstrated that Mg²⁺ notably changes the enzyme’s affinity for UDP-glucose, which improves its catalytic efficiency. Homology modeling and mutational analyses revealed binding sites for the sugar donor and the diacylglycerol lipid acceptor, which provided insights into the retaining mechanism of GT_cp with its GT-B fold. A phylogenetic analysis showed that GT_cp and its homologs form a group in the GT4 glycosyltransferase family. These results not only provide new insights into the glycoglycerolipid synthesis mechanism in lipid remodeling but also describe an efficient enzymatic tool for the future synthesis of bioactive molecules.

IMPORTANCE The bilayer formed by membrane lipids serves as the containment unit for living microbial cells. In the marine environment, it has been firmly established that phytoplankton and heterotrophic bacteria can replace phospholipids with nonphosphorus sugar-containing glycoglycerolipids in response to phosphorus limitation. However, little is known about how these glycoglycerolipids are synthesized. Here, we determined the biochemical characteristics of a glycolipid glycosyltransferase (GT_cp) from the marine bacterium “Candidatus Pelagibacter sp.” strain HTCC7211. GT_cp and its homologs form a group in the GT4 glycosyltransferase family and can synthesize neutral glycolipids (monoglucosyl-1,2-diacyl-sn-glycerol [MGlc-DAG] and monogalactosyl [MGal]-DAG) and monoglucuronic acid diacylglycerol (MGlcA-DAG). We also uncovered the key residues for DAG binding through molecular docking, site-direct mutagenesis, and subsequent enzyme activity assays. Our data provide new insights into the glycoglycerolipid synthesis mechanism in lipid remodeling.

Biochemical characterization of an organic solvent-tolerant glycosyltransferase from Bacillus licheniformis PI15 with potential application for raspberry ketone glycoside production

Raspberry ketone is a primary aroma component of the red raspberry. The glycosylation of this compound is a potential approach used to improve its pharmaceutical properties. In this work, raspberry ketone glycosides are produced in bacteria for the first time. Bacillus licheniformis PI15, an organic solvent-tolerant glycosyltransferase-producing strain, was isolated from chemically polluted soil. The cloning and heterologous expression of a glycosyltransferase, which was designated PI-GT1, in Escherichia coli BL21 resulted in the expression of an active and soluble protein that accounted for 15% of the total cell protein content. Purified PI-GT1 was highly active and stable over a broad pH range (6.0-10.0) and showed excellent pH stability. PI-GT1 maintained almost 60% of its maximal activity after 3 H of incubation at 20-40 °C and demonstrated optimal activity at 30 °C. Additionally, PI-GT1 displayed high stability and activity in the presence of hydrophilic solvents with log P ≤ -0.2 and retained more than 80% of its activity after 3 H of treatment. Supplementation with 10% DMSO markedly improved the glycosylation of raspberry ketone, resulting in a value 26 times higher than that in aqueous solution. The organic solvent-tolerant PI-GT1 may have potential uses in industrial chemical and pharmaceutical synthesis applications.

Ca2+ assisted glycosylation of phenolic compounds by phenolic-UDP-glycosyltransferase from Bacillus subtilis PI18

A phenolic-UDP-glycosyltransferase Bs-PUGT from Bacillus subtilis PI18 was cloned and expressed in Escherichia coli BL21 (DE3). The purified Bs-PUGT could catalyze the glycosylation of tyrosol, 4-hydroxybenzyl alcohol, 2-hydroxybenzyl alcohol, caffeic acid, cinnamic alcohol, ferulic acid, and so on. This enzyme showed a high activity and stability over a broad pH range and was sensitive to temperature. Studies on the kinetic parameters indicated that the affinity of Bs-PUGT to UDP-G (Km) and its catalytic efficiency (Kcat) increased by 1.5-fold and 1.7-fold, respectively, with the addition of 10 mM Ca²⁺. The most effective glycosylation of caffeic acid catalyzed by whole-cell E. coli/Bs-PUGT was achieved with a molar yield of 78.3% in a system with pH 8.0, 30 °C, 25 g/L sucrose, 10 mM Ca²⁺, and 0.5 g/L substrate concentration. The addition of Ca²⁺ increased the molar yield of caffeic acid glucosides and shortened the reaction. This work proposes a strategy for the efficient glycosylation of phenolic compounds by microbe-derived glycosyltransferase assisted by metal ions.

Efficient biosynthesis, analysis, solubility and anti-bacterial activities of succinylglycosylated naringenin

A novel water-soluble flavonoid with good anti-bacterial activities, naringenin-6″-succl-7-O-glucoside (7-SGN), was synthesised. It was biotransformed from naringenin by Bacillus amyloliquefaciens FJ18 in aqueous miscible organic media, and characterised by LC-MS and NMR analysis. The solubility of 7-SGN in water was approximately 102 times higher than that of naringenin. These results demonstrated that both the water solubility and the anti-bacterial activity of 7-SGN were significantly improved.

Switching glycosyltransferase UGTBL1 regioselectivity toward polydatin synthesis using a semi-rational design

Conduct structure-guided modification on the “hotspot” of glycosyltransferase UGT_BL1 to significantly adjust its regioselectivity toward polydatin production.

Mining of efficient microbial UDP-glycosyltransferases by motif evolution cross plant kingdom for application in biosynthesis of salidroside

The plant kingdom provides a large resource of natural products and various related enzymes are analyzed. The high catalytic activity and easy genetically modification of microbial enzymes would be beneficial for synthesis of natural products. But the identification of functional genes of target enzymes is time consuming and hampered by many contingencies. The potential to mine microbe-derived glycosyltransferases (GTs) cross the plant kingdom was assessed based on alignment and evolution of the full sequences and key motifs of target enzymes, such as Rhodiola-derived UDP-glycosyltransferase (UGT73B6) using in salidroside synthesis. The GTs from Bacillus licheniformis ZSP01 with high PSPG motif similarity were speculated to catalyze the synthesis of salidroside. The UGT_BL1, which had similarity (61.4%) PSPG motif to UGT73B6, displayed efficient activity and similar regioselectivity. Highly efficient glycosylation of tyrosol (1 g/L) was obtained by using engineered E. coli harboring UGT_BL1 gene, which generated 1.04 g/L salidroside and 0.99 g/L icariside D2. All glycosides were secreted into the culture medium and beneficial for downstream purification. It was the first report on the genome mining of UGTs from microorganisms cross the plant kingdom. The mining approach may have broader applications in the selection of efficient candidate for making high-value natural products.

Precisely regulated galactosylation of nucleoside analogues in aqueous hydrophilic solvents catalyzed by solvent-stable β-galactosidase

Precisely regulated galactosylation of nucleoside analogues by the addition of aqueous hydrophilic solvents.

High production of succinyl isoflavone glycosides by Bacillus licheniformis ZSP01 resting cells in aqueous miscible organic medium

To achieve efficient production of succinyldaidzin and succinylgenistin, resting cells of a solvent-stable strain Bacillus licheniformis ZSP01 were used to react with pure isoflavones or soybean flour extract in a reaction medium with 10% dimethyl sulfoxide. Strikingly, 0.8 mM daidzein, 0.8 mM genistein, 2.0 mM daidzin, and 2.0 mM genistin were transformed to succinyl isoflavone glycosides in 27 H (yield >90%). The soybean flour extract (6.1%, w/v) contained 0.32 mM daidzein, 0.84 mM daidzin, 0.38 mM genistein, and 1.04 mM genistin. Over 95% of total isoflavones (daidzein, daidzin, genistein, and genistin) in the soybean flour extract were converted to succinyl isoflavone glycosides after 27 H. Strain ZSP01 shows both high glycosylation and succinylation activities. These results suggest that B. licheniformis ZSP01 could be useful for the efficient production of succinyl soybean isoflavone glycosides.