Immobilized sucrose phosphorylase fromLeuconostoc mesenteroides

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.

Production of glucosyl glycerol by immobilized sucrose phosphorylase: Options for enzyme fixation on a solid support and application in microscale flow format

2-O-(α-d-Glucopyranosyl)-sn-glycerol (αGG) is a natural osmolyte. αGG is produced industrially for application as an active cosmetic ingredient. The biocatalytic process involves a selective transglucosylation from sucrose to glycerol catalyzed by sucrose phosphorylase (SPase). Here we examined immobilization of SPase (from Leuconostoc mesenteroides) on solid support with the aim of enabling continuous production of αGG. By fusing SPase to the polycationic binding module Z_basic2 we demonstrated single-step noncovalent immobilization of the enzyme chimera to different porous supports offering an anionic surface. We showed that immobilization facilitated by Z_basic2 was similarly efficient as immobilization by multipoint covalent attachment on epoxy-activated supports in terms of production of αGG. Enzyme loadings of up to 90mg enzyme g^-1 support were obtained and the immobilized SPase was about half as effective as the enzyme in solution. The high regio- and chemo-selectivity of soluble SPase in αGG synthesis was retained in the immobilized enzyme and product yields of >85% were obtained at titers of ∼800mM. The Z_basic2-SPase immobilizates were fully recyclable: besides reuse of the enzyme activity, easy recovery of the solid support for fresh immobilizations was facilitated by the reversible nature of the enzyme attachment. Application of immobilized Z_basic2-SPase for continuous production of αGG in a microstructured flow reactor was demonstrated. Space-time yields of 500mmol αGG L^-1h^-1 were obtained at product titers of ∼200mM. The continuous microreactor was operated for 16days and an operational half-life of about 10days was determined.

Carbohydrate synthesis by disaccharide phosphorylases: reactions, catalytic mechanisms and application in the glycosciences

Disaccharide phosphorylases are glycosyltransferases (EC 2.4.1.α) of specialized carbohydrate metabolism in microorganisms. They catalyze glycosyl transfer to phosphate using a disaccharide as donor substrate. Phosphorylases for the conversion of naturally abundant disaccharides including sucrose, maltose, α,α-trehalose, cellobiose, chitobiose, and laminaribiose have been described. Structurally, these disaccharide phosphorylases are often closely related to glycoside hydrolases and transglycosidases. Mechanistically, they are categorized according the stereochemical course of the reaction catalyzed, whereby the anomeric configuration of the disaccharide donor substrate may be retained or inverted in the sugar 1-phosphate product. Glycosyl transfer with inversion is thought to occur through a single displacement-like catalytic mechanism, exemplified by the reaction coordinate of cellobiose/chitobiose phosphorylase. Reaction via configurational retention takes place through the double displacement-like mechanism employed by sucrose phosphorylase. Retaining α,α-trehalose phosphorylase (from fungi) utilizes a different catalytic strategy, perhaps best described by a direct displacement mechanism, to achieve stereochemical control in an overall retentive transformation. Disaccharide phosphorylases have recently attracted renewed interest as catalysts for synthesis of glycosides to be applied as food additives and cosmetic ingredients. Relevant examples are lacto-N-biose and glucosylglycerol whose enzymatic production was achieved on multikilogram scale. Protein engineering of phosphorylases is currently pursued in different laboratories with the aim of broadening the donor and acceptor substrate specificities of naturally existing enzyme forms, to eventually generate a toolbox of new catalysts for glycoside synthesis.

Recombinant sucrose phosphorylase from Leuconostoc mesenteroides: Characterization, kinetic studies of transglucosylation, and application of immobilised enzyme for production of α-d-glucose 1-phosphate

Sucrose phosphorylase catalyzes the reversible conversion of sucrose (alpha-D-glucopyranosyl-1,2-beta-D-fructofuranoside) and phosphate into D-fructose and alpha-D-glucose 1-phosphate. We report on the molecular cloning and expression of the structural gene encoding sucrose phosphorylase from Leuconostoc mesenteroides (LmSPase) in Escherichia coli DH10B. The recombinant enzyme, containing an 11 amino acid-long N-terminal metal affinity fusion peptide, was overproduced 60-fold in comparison with the natural enzyme. It was purified to apparent homogeneity using copper-loaded Chelating Sepharose and obtained in 20% yield with a specific activity of 190 Umg(-1). LmSPase was covalently attached onto Eupergit C with a binding efficiency of 50% and used for the continuous production of alpha-D-glucose 1-phosphate from sucrose and phosphate (600 mM each) in a packed-bed immobilised enzyme reactor (30 degrees C, pH 7.0). The reactor was operated at a stable conversion of 91% (550 mM product) and productivity of approximately 11 gl(-1)h(-1) for up to 600 h. A kinetic study of transglucosylation by soluble LmSPase was performed using alpha-d-glucose 1-phosphate as the donor substrate and various alcohols as acceptors. D- and L-arabitol were found to be good glucosyl acceptors.

In situ product removal as a tool for bioprocessing

In situ product removal (ISPR) is the fast removal of product from a producing cell thereby preventing its subsequent interference with cellular or medium components. Over the past 10 years ISPR techniques have developed substantially and its feasibility (with improvements in yield or productivity) for several processes demonstrated. Assessment of progress, however, compared to the potential benefits inherent in the ISPR approach to bioprocessing reveals that these are far from being exploited fully. Here we indicate future directions including application of the ISPR approach to a wider range of product groups and the development of novel, more specific ISPR methodologies, applicable under sterile conditions in the immediate vicinity of the producing cells. General guidelines for adaptation of an appropriate ISPR approach for a given product are also provided.