Application of Escherichia coli maltodextrin-phosphorylase for the continuous production of glucose-1-phosphate

Biological strategies for oligo/polysaccharide synthesis: biocatalyst and microbial cell factory

Oligosaccharides and polysaccharides constitute the principal components of carbohydrates, which are important biomacromolecules that demonstrate considerable bioactivities. However, the variety and structural complexity of oligo/polysaccharides represent a major challenge for biological and structural explorations. To access structurally defined oligo/polysaccharides, biological strategies using glycoenzyme biocatalysts have shown remarkable synthetic potential attributed to their regioselectivity and stereoselectivity that allow mild, structurally controlled reaction without addition of protecting groups necessary in chemical strategies. This review summarizes recent biotechnological approaches of oligo/polysaccharide synthesis, which mainly includes in vitro enzymatic synthesis and cell factory synthesis. We have discussed the important factors involved in the production of nucleotide sugars. Furthermore, the strategies established in the cell factory and enzymatic syntheses are summarized, and we have highlighted concepts like metabolic flux rebuilding and regulation, enzyme engineering, and route design as important strategies. The research challenges and prospects are also outlined and discussed.

Phosphorylase-catalyzed bottom-up synthesis of short-chain soluble cello-oligosaccharides and property-tunable cellulosic materials

Cellulose-based materials are produced industrially in countless varieties via top-down processing of natural lignocellulose substrates. By contrast, cellulosic materials are only rarely prepared via bottom up synthesis and oligomerization-induced self-assembly of cellulose chains. Building up a cellulose chain via precision polymerization is promising, however, for it offers tunability and control of the final chemical structure. Synthetic cellulose derivatives with programmable material properties might thus be obtained. Cellodextrin phosphorylase (CdP; EC 2.4.1.49) catalyzes iterative β-1,4-glycosylation from α-d-glucose 1-phosphate, with the ability to elongate a diversity of acceptor substrates, including cellobiose, d-glucose and a range of synthetic glycosides having non-sugar aglycons. Depending on the reaction conditions leading to different degrees of polymerization (DP), short-chain soluble cello-oligosaccharides (COS) or insoluble cellulosic materials are formed. Here, we review the characteristics of CdP as bio-catalyst for synthetic applications and show advances in the enzymatic production of COS and reducing end-modified, tailored cellulose materials. Recent studies reveal COS as interesting dietary fibers that could provide a selective prebiotic effect. The bottom-up synthesized celluloses involve chains of DP ≥ 9, as precipitated in solution, and they form ~5 nm thick sheet-like crystalline structures of cellulose allomorph II. Solvent conditions and aglycon structures can direct the cellulose chain self-assembly towards a range of material architectures, including hierarchically organized networks of nanoribbons, or nanorods as well as distorted nanosheets. Composite materials are also formed. The resulting materials can be useful as property-tunable hydrogels and feature site-specific introduction of functional and chemically reactive groups. Therefore, COS and cellulose obtained via bottom-up synthesis can expand cellulose applications towards product classes that are difficult to access via top-down processing of natural materials.

Thermostable alpha-glucan phosphorylases: characteristics and industrial applications

α-Glucan phosphorylases (α-GPs) catalyze the reversible phosphorolysis of α-1,4-linked polysaccharides such as glycogen, starch, and maltodextrins, therefore playing a central role in the usage of storage polysaccharides. The discovery of these enzymes and their role in the course of catalytic conversion of glycogen was rewarded with the Nobel Prize in Physiology or Medicine in 1947. Nowadays, however, thermostable representatives attract special attention due to their vast potential in the enzymatic production of diverse carbohydrates and derivatives such as (functional) oligo- and (non-natural) polysaccharides, artificial starch, glycosides, and nucleotide sugars. One of the most recently explored utilizations of α-GPs is their role in the multi-enzymatic process of energy production stored in carbohydrate biobatteries. Regardless of their use, thermostable α-GPs offer significant advantages and facilitated bioprocess design due to their high operational temperatures. Here, we present an overview and comparison of up-to-date characterized thermostable α-GPs with a special focus on their reported biotechnological applications.

One-Pot Biosynthesis of High-Concentration α-Glucose 1-Phosphate from Starch by Sequential Addition of Three Hyperthermophilic Enzymes

α-Glucose 1-phosphate (G1P) is synthesized from 5% (w/v) corn starch and 1 M phosphate mediated by α-glucan phosphorylase (αGP) from the thermophilic bacterium Thermotoga maritima at pH 7.2 and 70 °C. To increase G1P yield from corn starch containing branched amylopectin, a hyper-thermostable isoamylase from Sulfolobus tokodaii was added for simultaneous starch gelatinization and starch-debranching hydrolysis at 85 °C and pH 5.5 before αGP use. The pretreatment of isoamylase increased G1P titer from 120 mM to 170 mM. To increase maltose and maltotriose utilization, the third thermostable enzyme, 4-glucanotransferase (4GT) from Thermococcus litoralis, was added during the late stage of G1P biotransformation, further increasing G1P titer to 200 mM. This titer is the highest G1P level obtained on starch or its derived products (maltodextrin and soluble starch). This study suggests that in vitro multienzyme biotransformation has an advantage of great engineering flexibility in terms of space and time compared with microbial fermentation.

Enzymatic glycosylation of small molecules: challenging substrates require tailored catalysts

Glycosylation can significantly improve the physicochemical and biological properties of small molecules like vitamins, antibiotics, flavors, and fragrances. The chemical synthesis of glycosides is, however, far from trivial and involves multistep routes that generate lots of waste. In this review, biocatalytic alternatives are presented that offer both stricter specificities and higher yields. The advantages and disadvantages of different enzyme classes are discussed and illustrated with a number of recent examples. Progress in the field of enzyme engineering and screening are expected to result in new applications of biocatalytic glycosylation reactions in various industrial sectors.

Enzymatic production of β-D-glucose-1-phosphate from trehalose

β-D-Glucose-1-phosphate (βGlc1P) is an efficient glucosyl donor for both enzymatic and chemical glycosylation reactions but is currently very costly and not available in large amounts. This article provides an efficient production method of βGlc1P from trehalose and phosphate using the thermostable trehalose phosphorylase from Thermoanaerobacter brockii. At the process temperature of 60 °C, Escherichia coli expression host cells are lysed and cell treatment prior to the reaction is, therefore, not required. In this way, the theoretical maximum yield of 26% could be easily achieved. Two different purification strategies have been compared, anion exchange chromatography or carbohydrate removal by treatment with trehalase and yeast, followed by chemical phosphate precipitation. In a next step, βGlc1P was precipitated with ethanol but this did not induce crystallization, in contrast to what is observed with other glycosylphosphates. After conversion of the product to its cyclohexylammonium salt, however, crystals could be readily obtained. Although both purification methods were quantitative (>99% recovery), a large amount of product (50%) was lost during crystallization. Nevertheless, a production process for crystalline βGlc1P is now available from the cheap substrates trehalose and inorganic phosphate.

Physiological aggregation of maltodextrin phosphorylase from Pyrococcus furiosus and its application in a process of batch starch degradation to alpha-D-glucose-1-phosphate

Maltodextrin phosphorylase from Pyrococcus furiosus (PF1535) was fused with the cellulose-binding domain of Clostridium cellulovorans serving as an aggregation module. After molecular cloning of the corresponding gene fusion construct and controlled expression in Escherichia coli BL21, 83% of total maltodextrin phosphorylase activity (0.24 U/mg of dry cell weight) was displayed in active inclusion bodies. These active inclusion bodies were easily isolated by nonionic detergent treatment and directly used for maltodextrin conversion to alpha-D-glucose-1-phosphate in a repetitive batch mode. Only 10% of enzyme activity was lost after ten conversion cycles at optimum conditions.

High expression of a synthetic gene encoding potato alpha-glucan phosphorylase in Aspergillus niger

We describe the successful heterologous expression of the Solanum tuberosum alpha-glucan phosphorylase (GP) gene in Aspergillus niger. Special attention was paid to the influence of different codon usage and A+T content in the coding region on GP protein expression. Use of A. niger-preferred codon usage and lower A+T content in a synthetic gene (GP-syn) resulted in a significant improvement in the level of the GP mRNA and a dramatic increase in the quantity of GP protein produced such that it accounted for approximately 10% of the total soluble protein. We suggest that redesigning the primary DNA sequence encoding a desired protein product can be an extremely effective method for improving heterologous protein production in filamentous fungi.

Efficient downstream processing of maltodextrin phosphorylase from Escherichia coli and stabilization of the enzyme by immobilization onto hydroxyapatite

Downstream processing by biospecific chromatography of maltodextrin phosphorylase from Escherichia coli, overexpressed in E. coli, was substantially improved by a novel approach using ceramic hydroxyapatite. Wild-type and a less active mutant enzyme were purified from crude bacterial cell extracts in one efficient separation step that yielded phosphorylase in purity > 95% in at least 90% recoveries. At pH 6.9 and 25 degrees C, wild-type and mutant phosphorylases eluted from the hydroxyapatite column at a phosphate concentration of 0.4 M whereas calcium ions failed to displace the enzymes. The dynamic capacity for phosphorylase binding in the presence of bulk proteins was approximately 3 mg enzyme ml-1 matrix. The interaction of E. coli phosphorylase with hydroxyapatite seems to be mediated by surface amino groups, so that the bound enzyme retained almost full catalytic activity. Compared to the soluble enzyme, immobilization onto hydroxyapatite resulted in a more than 30-fold stabilization of wild-type phosphorylase against thermal and proteolytic inactivation and thus could improve the operational stability of phosphorylase during conversion of polysaccharide to glucose 1-phosphate.