Small-molecule glucosylation by sucrose phosphorylase: structure–activity relationships for acceptor substrates revisited

Regioselective glucosylation of (+)-catechin using a new variant of sucrose phosphorylase from Bifidobacterium adolescentis

Mutation Q345F in sucrose phosphorylase from Bifidobacterium adolescentis (BaSP) has shown to allow efficient (+)-catechin glucosylation yielding a regioisomeric mixture: (+)-catechin-3'-O-α-D-glucopyranoside, (+)-catechin-5-O-α-D-glucopyranoside and (+)-catechin-3',5-O-α-D-diglucopyranoside with a ratio of 51 : 25 : 24. Here, we efficiently increased the control of (+)-catechin glucosylation regioselectivity with a new variant Q345F/P134D. The same products were obtained with a ratio of 82 : 9 : 9. Thanks to bioinformatics models, we successfully explained the glucosylation favoured at the OH-3' position due to the mutation P134D.

Whole cell-based catalyst for enzymatic production of the osmolyte 2-O-α-glucosylglycerol

Background

Glucosylglycerol (2-O-α-d-glucosyl-sn-glycerol; GG) is a natural osmolyte from bacteria and plants. It has promising applications as cosmetic and food-and-feed ingredient. Due to its natural scarcity, GG must be prepared through dedicated synthesis, and an industrial bioprocess for GG production has been implemented. This process uses sucrose phosphorylase (SucP)-catalyzed glycosylation of glycerol from sucrose, applying the isolated enzyme in immobilized form. A whole cell-based enzyme formulation might constitute an advanced catalyst for GG production. Here, recombinant production in Escherichia coli BL21(DE3) was compared systematically for the SucPs from Leuconostoc mesenteroides (LmSucP) and Bifidobacterium adolescentis (BaSucP) with the purpose of whole cell catalyst development.

Results

Expression from pQE30 and pET21 plasmids in E. coli BL21(DE3) gave recombinant protein at 40–50% share of total intracellular protein, with the monomeric LmSucP mostly soluble (≥ 80%) and the homodimeric BaSucP more prominently insoluble (~ 40%). The cell lysate specific activity of LmSucP was 2.8-fold (pET21; 70 ± 24 U/mg; N = 5) and 1.4-fold (pQE30; 54 ± 9 U/mg, N = 5) higher than that of BaSucP. Synthesis reactions revealed LmSucP was more regio-selective for glycerol glycosylation (~ 88%; position O2 compared to O1) than BaSucP (~ 66%), thus identifying LmSucP as the enzyme of choice for GG production. Fed-batch bioreactor cultivations at controlled low specific growth rate (µ = 0.05 h⁻¹; 28 °C) for LmSucP production (pET21) yielded ~ 40 g cell dry mass (CDM)/L with an activity of 2.0 × 10⁴ U/g CDM, corresponding to 39 U/mg protein. The same production from the pQE30 plasmid gave a lower yield of 6.5 × 10³ U/g CDM, equivalent to 13 U/mg. A single freeze–thaw cycle exposed ~ 70% of the intracellular enzyme activity for GG production (~ 65 g/L, ~ 90% yield from sucrose), without releasing it from the cells during the reaction.

Conclusions

Compared to BaSucP, LmSucP is preferred for regio-selective GG production. Expression from pET21 and pQE30 plasmids enables high-yield bioreactor production of the enzyme as a whole cell catalyst. The freeze–thaw treated cells represent a highly active, solid formulation of the LmSucP for practical synthesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01569-4.

Active-Site His85 of Pasteurella dagmatis Sialyltransferase Facilitates Productive Sialyl Transfer and So Prevents Futile Hydrolysis of CMP-Neu5Ac

Sialyltransferases of the GT-80 glycosyltransferase family are considered multifunctional because of the array of activities detected. They exhibit glycosyl transfer, trans-sialylation, and hydrolysis activities. How these enzymes utilize their active-site residues in balancing the different enzymatic activities is not well understood. In this study of Pasteurella dagmatis α2,3sialyltransferase, we show that the conserved His85 controls efficiency and selectivity of the sialyl transfer. A His85→Asn variant was 200 times less efficient than wild-type for sialylation of lactose, and exhibited relaxed site selectivity to form not only the α2,3- but also the α2,6-sialylated product (21 %). The H85N variant was virtually inactive in trans-sialylation but showed almost the same CMP-Neu5Ac hydrolase activity as wild-type. The competition between sialyl transfer and hydrolysis in the conversion of CMP-Neu5Ac was dependent on the lactose concentration; this was characterized by a kinetic partition ratio of 85 m^-1 for the H85N variant, compared to 17 000 m^-1 for the wild-type enzyme. His85 promotes the productive sialyl transfer to lactose and so prevents hydrolysis of CMP-Neu5Ac in the reaction.

Walking a Fine Line with Sucrose Phosphorylase: Efficient Single-Step Biocatalytic Production of l-Ascorbic Acid 2-Glucoside from Sucrose

The 2-O-α-d-glucoside of l-ascorbic acid (AA-2G) is a highly stabilized form of vitamin C, with important industrial applications in cosmetics, food, and pharmaceuticals. AA-2G is currently produced through biocatalytic glucosylation of l-ascorbic acid from starch-derived oligosaccharides. Sucrose would be an ideal substrate for AA-2G synthesis, but it lacks a suitable transglycosidase. We show here that in a narrow pH window (pH 4.8-6.0, with sharp optimum at pH 5.2), sucrose phosphorylases catalyzed the 2-O-α-glucosylation of l-ascorbic acid from sucrose with high efficiency and perfect site-selectivity. Optimized synthesis with the enzyme from Bifidobacterium longum at 40 °C gave a concentrated product (155 g L^-1 ; 460 mm), from which pure AA-2G was readily recovered in ∼50 % overall yield, thus providing the basis for advanced production. The peculiar pH dependence is suggested to arise from a "reverse-protonation" mechanism in which the catalytic base Glu232 on the glucosyl-enzyme intermediate must be protonated for attack on the anomeric carbon from the 2-hydroxyl of the ionized l-ascorbate substrate.

Synthesis of the rare disaccharide nigerose by structure-based design of a phosphorylase mutant with altered regioselectivity

In the absence of the natural acceptor inorganic phosphate wild-type sucrose phosphorylase from Bifidobacterium adolescentis (BaSP) produces maltose (4-O-α-d-glucopyranosyl-d-glucose) and kojibiose (2-O-α-d-glucopyranosyl-d-glucose) as sole transfer products. A Q345F exchange switches the enzyme's regioselectivity from 2 to 3 exclusively, yielding the rare sugar nigerose (3-O-α-d-glucopyranosyl-d-glucose, sakebiose).

Diversity of phosphorylases in glycoside hydrolase families

Phosphorylases are useful catalysts for the practical preparation of various sugars. The number of known specificities was 13 in 2002 and is now 30. The drastic increase in available genome sequences has facilitated the discovery of novel activities. Most of these novel phosphorylase activities have been identified through the investigations of glycoside hydrolase families containing known phosphorylases. Here, the diversity of phosphorylases in each family is described in detail.

Biotechnological advances in UDP-sugar based glycosylation of small molecules

Glycosylation of small molecules like specialized (secondary) metabolites has a profound impact on their solubility, stability or bioactivity, making glycosides attractive compounds as food additives, therapeutics or nutraceuticals. The subsequently growing market demand has fuelled the development of various biotechnological processes, which can be divided in the in vitro (using enzymes) or in vivo (using whole cells) production of glycosides. In this context, uridine glycosyltransferases (UGTs) have emerged as promising catalysts for the regio- and stereoselective glycosylation of various small molecules, hereby using uridine diphosphate (UDP) sugars as activated glycosyldonors. This review gives an extensive overview of the recently developed in vivo production processes using UGTs and discusses the major routes towards UDP-sugar formation. Furthermore, the use of interconverting enzymes and glycorandomization is highlighted for the production of unusual or new-to-nature glycosides. Finally, the technological challenges and future trends in UDP-sugar based glycosylation are critically evaluated and summarized.

Chiral resolution through stereoselective transglycosylation by sucrose phosphorylase: application to the synthesis of a new biomimetic compatible solute, (R)-2-O-α-D-glucopyranosyl glyceric acid amide

Sucrose phosphorylase catalysed glycosylation of glyceric acid amide with complete regio- and diastereo-selectivity is studied. (R)-2-O-α-D-Glucopyranosyl glyceric acid amide was obtained in high yield from single-step transformation of racemic glyceric acid amide and sucrose. Non-productive binding of (S)-glyceric acid amide appeared to underlie strict enantiodiscrimination by the enzyme, thus supporting chiral resolutions based on stereoselective transglycosylation.

Structural basis for reversible phosphorolysis and hydrolysis reactions of 2-O-α-glucosylglycerol phosphorylase

2-O-α-Glucosylglycerol phosphorylase (GGP) from Bacillus selenitireducens catalyzes both the reversible phosphorolysis of 2-O-α-glucosylglycerol (GG) and the hydrolysis of β-d-glucose 1-phosphate (βGlc1P). GGP belongs to the glycoside hydrolase (GH) family 65 and can efficiently and specifically produce GG. However, its structural basis has remained unclear. In this study, the crystal structures of GGP complexed with glucose and the glucose analog isofagomine and glycerol were determined. Subsite -1 of GGP is similar to those of other GH65 enzymes, maltose phosphorylase and kojibiose phosphorylase, whereas subsite +1 is largely different and is well designed for GG recognition. An automated docking analysis was performed to complement these crystal structures, βGlc1P being docked at an appropriate position. To investigate the importance of residues at subsite +1 in the bifunctionality of GGP, we constructed mutants at these residues. Y327F and K587A did not show detectable activities for either reverse phosphorolysis or βGlc1P hydrolysis. Y572F also showed significantly reduced activities for both of these reactions. In contrast, W381F showed significantly reduced reverse phosphorolytic activity but retained βGlc1P hydrolysis. The mode of substrate recognition and the reaction mechanisms of GGP were proposed based on these analyses. Specifically, an extensive hydrogen bond network formed by Tyr-327, Tyr-572, Lys-587, and water molecules contributes to fixing the acceptor molecule in both reverse phosphorolysis (glycerol) and βGlc1P hydrolysis (water) for a glycosyl transfer reaction. This study will contribute to the development of a large scale production system of GG by facilitating the rational engineering of GGP.

2-O-α-D-glucosylglycerol phosphorylase from Bacillus selenitireducens MLS10 possessing hydrolytic activity on β-D-glucose 1-phosphate

The glycoside hydrolase family (GH) 65 is a family of inverting phosphorylases that act on α-glucosides. A GH65 protein (Bsel_2816) from Bacillus selenitireducens MLS10 exhibited inorganic phosphate (Pi)-dependent hydrolysis of kojibiose at the rate of 0.43 s⁻¹. No carbohydrate acted as acceptor for the reverse phosphorolysis using β-d-glucose 1-phosphate (βGlc1P) as donor. During the search for a suitable acceptor, we found that Bsel_2816 possessed hydrolytic activity on βGlc1P with a k_cat of 2.8 s⁻¹; moreover, such significant hydrolytic activity on sugar 1-phosphate had not been reported for any inverting phosphorylase. The H₂¹⁸O incorporation experiment and the anomeric analysis during the hydrolysis of βGlc1P revealed that the hydrolysis was due to the glucosyl-transferring reaction to a water molecule and not a phosphatase-type reaction. Glycerol was found to be the best acceptor to generate 2-O-α-d-glucosylglycerol (GG) at the rate of 180 s⁻¹. Bsel_2816 phosphorolyzed GG through sequential Bi-Bi mechanism with a k_cat of 95 s⁻¹. We propose 2-O-α-d-glucopyranosylglycerol: phosphate β-d-glucosyltransferase as the systematic name and 2-O-α-d-glucosylglycerol phosphorylase as the short name for Bsel_2816. This is the first report describing a phosphorylase that utilizes polyols, and not carbohydrates, as suitable acceptor substrates.