Heterologous overproduction of β-fructofuranosidase from yeast Xanthophyllomyces dendrorhous, an enzyme producing prebiotic sugars

Characteristic of new Phaffia rhodozyma yeast strains isolated from birch slime fluxes in Poland

Three new strains of Phaffia rhodozyma yeast have recently been isolated in Poland. The aim of this study was to phenotypically characterize these strains and to compare them with the properties of the reference strain. The potential for carotenoid biosynthesis in these strains was also determined, depending on temperature, carbon, and nitrogen sources in the medium. Phaffia rhodozyma yeasts were also identified by MALDI-TOF MS. There were minor differences in cell morphology among the strains. All strains reproduced asexually by budding and formed spherical chlamydospores. No ability for sexual reproduction was observed. Physiological tests showed minor variations between the reference strain and the isolates, likely due to the geographical specificity of the habitat from which they were originally isolated. Analysis of protein spectra showed that the tested yeast isolates had seven common peaks of different intensities, with masses at 2200, 2369, 3213, 3628, 3776, 3921, and 4710 m/z. Moreover, additional strain-dependent spectra were found. The amount of synthesized carotenoids varied with the carbon and nitrogen sources used, as well as the temperature. The best producer of carotenoids was the P. rhodozyma CMIFS 102 isolate.

Mutant β-fructofuranosidase synthesizing blastose [β-d-Fruf-(2→6)-d-Glcp]

Fructooligosaccharides (FOS) are leading prebiotics that help keep the gut healthy and aid wellness by stimulating the growth and activity of beneficial intestinal bacteria. The best-studied FOS are inulin-type FOS, mainly oligosaccharides with β-Fruf-(2→1)-Fruf linkages, including 1-kestose [β-Fruf-(2→1)-β-Fruf-(2↔1)-α-Glcp] and nystose [β-Fruf-(2→1)-β-Fruf-(2→1)-β-Fruf-(2↔1)-α-Glcp]. However, the properties of other types of FOS-levan-type FOS with β-Fruf-(2→6)-Fruf linkages and neo-type FOS with β-Fruf-(2→6)-Glcp linkages-remain ambiguous because efficient methods have not been established for their synthesis. Here, using site-saturation mutation of residue His79 of β-fructofuranosidase from Zymomonas mobilis NBRC13756, we successfully obtained a mutant β-fructofuranosidase that specifically produces neo-type FOS. The H79G enzyme variant loses the native β-Fruf-(2→1)-Fru-transfer ability (which produces 1-kestose), and instead has β-Fruf-(2→6)-Glc-transfer ability and produces neokestose. Its hydrolytic activity specific to the β-Fruf-(2↔1)-α-Glcp bond of neokestose then yields blastose [β-Fruf-(2→6)-Glcp]. The enzyme produces 0.4 M blastose from 1.0 M sucrose (80 % of the theoretical yield). The production system for blastose established here will contribute to the elucidation of the physiological functions of this disaccharide.

Insights into the transglucosylation activity of α-glucosidase from Schwanniomyces occidentalis

The α-glucosidase from Schwanniomyces occidentalis (GAM1p) was expressed in Komagataella phaffii to about 70 mg/L, and its transferase activity studied in detail. Several isomaltooligosaccharides (IMOS) were formed using 200 g/L maltose. The major production of IMOS (81.3 g/L) was obtained when 98% maltose was hydrolysed, of which 34.8 g/L corresponded to isomaltose, 26.9 g/L to isomaltotriose, and 19.6 g/L to panose. The addition of glucose shifted the IMOS synthesis towards products containing exclusively α(1 → 6)-linkages, increasing the production of isomaltose and isomaltotriose about 2-4 fold, enabling the formation of isomaltotetraose, and inhibiting that of panose to about 12 times. In addition, the potential of this enzyme to glycosylate 12 possible hydroxylated acceptors, including eight sugars and four phenolic compounds, was evaluated. Among them, only sucrose, xylose, and piceid (a monoglucosylated derivative of resveratrol) were glucosylated, and the main synthesised products were purified and characterised by MS and NMR. Theanderose, α(1 → 4)-D-glucosyl-xylose, and a mixture of piceid mono- and diglucoside were obtained with sucrose, xylose, and piceid as acceptors, respectively. Maximum production of theanderose reached 81.7 g/L and that of the glucosyl-xylose 26.5 g/L, whereas 3.4 g/L and only 1 g/L were produced of the piceid mono- and diglucoside respectively. KEY POINTS: • Overexpression of a yeast α-glucosidase producing novel molecules. • Yeast enzyme producing the heterooligosaccharides theanderose and glucosyl-xylose. • Glycosylation of the polyphenol piceid by a yeast α-glucosidase.

Chitinous material bioconversion by three new chitinases from the yeast Mestchnikowia pulcherrima

BACKGROUND

Chitinases are widely distributed enzymes that perform the biotransformation of chitin, one of the most abundant polysaccharides on the biosphere, into useful value-added chitooligosaccharides (COS) with a wide variety of biotechnological applications in food, health, and agricultural fields. One of the most important group of enzymes involved in the degradation of chitin comprises the glycoside hydrolase family 18 (GH18), which harbours endo- and exo-enzymes that act synergistically to depolymerize chitin. The secretion of a chitinase activity from the ubiquitous yeast Mestchnikowia pulcherrima and their involvement in the post-harvest biological control of fungal pathogens was previously reported.

RESULTS

Three new chitinases from M. pulcherrima, MpChit35, MpChit38 and MpChit41, were molecularly characterized and extracellularly expressed in Pichia pastoris to about 91, 90 and 71 mU ml- 1, respectively. The three enzymes hydrolysed colloidal chitin with optimal activity at 45 ºC and pH 4.0-4.5, increased 2-times their activities using 1 mM of Mn2+ and hydrolysed different types of commercial chitosan. The partial separation and characterization of the complex COS mixtures produced from the hydrolysis of chitin and chitosan were achieved by a new anionic chromatography HPAEC-PAD method and mass spectrometry assays. An overview of the predicted structures of these proteins and their catalytic modes of action were also presented. Depicted their high sequence and structural homology, MpChit35 acted as an exo-chitinase producing di-acetyl-chitobiose from chitin while MpChit38 and MpChit41 both acted as endo-chitinases producing tri-acetyl-chitotriose as main final product.

CONCLUSIONS

Three new chitinases from the yeast M. pulcherrima were molecularly characterized and their enzymatic and structural characteristics analysed. These enzymes transformed chitinous materials to fully and partially acetylated COS through different modes of splitting, which make them interesting biocatalysts for deeper structural-function studies on the challenging enzymatic conversion of chitin.

Simultaneous microwave-assisted extraction of bioactive compounds from aged garlic

In this work, the simultaneous extraction of bioactives (organosulfur compounds, such as S-allyl-L-cysteine (SAC), carbohydrates, such as neokestose and neonystose, and total phenolic compounds) from aged garlic has been optimized for the first time to obtain multifunctional extracts for further application as food ingredients. Analytical methods using liquid chromatography coupled to mass spectrometry (HPLC-MS) and by hydrophilic interaction liquid chromatography with evaporative light scattering detection (HILIC-ELSD) were also previously optimized. High sensitivity (limits of detection between 0.013 and 0.77 µg mL^-1) and appropriate repeatability (< 12%) and accuracy (> 92%) for the analysis of bioactives were achieved. After selecting water as the extraction solvent and microwave-assisted extraction (MAE) as the most efficient technique, operation conditions were optimized using a Box-Behnken experimental design (60 min; 120 °C; 0.05 g mL^-1; 1 cycle) to maximize the content of bioactives from different aged garlic samples. Regarding organosulfur compounds, only SAC (traces-2.32 mg g^-1 dry sample) and cycloalliin (1.23-3.01 mg g^-1 dry sample) were detected in all samples, while amino acids such as arginine (0.24-3.45 mg g^-1 dry sample) and proline (0.43-3.91 mg g^-1 dry sample) were, in general, the most abundant. Bioactive carbohydrates (from trisaccharides to nonasaccharides) were only detected in fresh garlic and aged garlic processed under mild conditions, whereas all garlic extracts showed antioxidant activity. The developed MAE methodology is shown as a successful alternative to other procedures for the simultaneous extraction of aged garlic bioactives intended by the food and nutraceutical industries, among others.

Insights into the Structure of the Highly Glycosylated Ffase from Rhodotorula dairenensis Enhance Its Biotechnological Potential

Rhodotorula dairenensis β-fructofuranosidase is a highly glycosylated enzyme with broad substrate specificity that catalyzes the synthesis of 6-kestose and a mixture of the three series of fructooligosaccharides (FOS), fructosylating a variety of carbohydrates and other molecules as alditols. We report here its three-dimensional structure, showing the expected bimodular arrangement and also a unique long elongation at its N-terminus containing extensive O-glycosylation sites that form a peculiar arrangement with a protruding loop within the dimer. This region is not required for activity but could provide a molecular tool to target the dimeric protein to its receptor cellular compartment in the yeast. A truncated inactivated form was used to obtain complexes with fructose, sucrose and raffinose, and a Bis-Tris molecule was trapped, mimicking a putative acceptor substrate. The crystal structure of the complexes reveals the major traits of the active site, with Asn387 controlling the substrate binding mode. Relevant residues were selected for mutagenesis, the variants being biochemically characterized through their hydrolytic and transfructosylating activity. All changes decrease the hydrolytic efficiency against sucrose, proving their key role in the activity. Moreover, some of the generated variants exhibit redesigned transfructosylating specificity, which may be used for biotechnological purposes to produce novel fructosyl-derivatives.

The β-Fructofuranosidase from Rhodotorula dairenensis: Molecular Cloning, Heterologous Expression, and Evaluation of Its Transferase Activity

The β-fructofuranosidase from the yeast Rhodotorula dairenensis (RdINV) produces a mixture of potential prebiotic fructooligosaccharides (FOS) of the levan-, inulin- and neo-FOS series by transfructosylation of sucrose. In this work, the gene responsible for this activity was characterized and its functionality proved in Pichia pastoris. The amino acid sequence of the new protein contained most of the characteristic elements of β-fructofuranosidases included in the family 32 of the glycosyl hydrolases (GH32). The heterologous yeast produced a protein of about 170 kDa, where N-linked and O-linked carbohydrates constituted about 15% and 38% of the total protein mass, respectively. Biochemical and kinetic properties of the heterologous protein were similar to the native enzyme, including its ability to produce prebiotic sugars. The maximum concentration of FOS obtained was 82.2 g/L, of which 6-kestose represented about 59% (w/w) of the total products synthesized. The potential of RdINV to fructosylate 19 hydroxylated compounds was also explored, of which eight sugars and four alditols were modified. The flexibility to recognize diverse fructosyl acceptors makes this protein valuable to produce novel glycosyl-compounds with potential applications in food and pharmaceutical industries.

Levansucrase from Bacillus amyloliquefaciens KK9 and Its Y237S Variant Producing the High Bioactive Levan-Type Fructooligosaccharides

Levan-typed fructooligosaccharide (LFOS), a β-2,6 linked oligofructose, displays the potential application as a prebiotic and therapeutic dietary supplement. In the present study, LFOS was synthesized using levansucrase from Bacillus amyloliquefaciens KK9 (LsKK9). The wild-type LsKK9 was cloned and expressed in E. coli, and purified by cation exchanger chromatography. Additionally, Y237S variant of LsKK9 was constructed based on sequence alignment and structural analysis to enhance the LFOS production. High-performance anion-exchange chromatography coupled with pulsed amperometric detection (HPAEC-PAD) analysis indicated that Y237S variant efficiently produced a higher amount of short-chain LFOS than wild type. Also, the concentration of enzyme and sucrose in the reactions was optimized. Finally, prebiotic activity assay demonstrated that LFOS produced by Y237S variant had higher prebiotic activity than that of the wild-type enzyme, making the variant enzyme attractive for food biotechnology.

Deciphering the molecular specificity of phenolic compounds as inhibitors or glycosyl acceptors of β-fructofuranosidase from Xanthophyllomyces dendrorhous

Enzymatic glycosylation of polyphenols is a tool to improve their physicochemical properties and bioavailability. On the other hand, glycosidic enzymes can be inhibited by phenolic compounds. In this work, we studied the specificity of various phenolics (hydroquinone, hydroxytyrosol, epigallocatechin gallate, catechol and p-nitrophenol) as fructosyl acceptors or inhibitors of the β-fructofuranosidase from Xanthophyllomyces dendrorhous (pXd-INV). Only hydroquinone and hydroxytyrosol gave rise to the formation of glycosylated products. For the rest, an inhibitory effect on both the hydrolytic (H) and transglycosylation (T) activity of pXd-INV, as well as an increase in the H/T ratio, was observed. To disclose the binding mode of each compound and elucidate the molecular features determining its acceptor or inhibitor behaviour, ternary complexes of the inactive mutant pXd-INV-D80A with fructose and the different polyphenols were analyzed by X-ray crystallography. All the compounds bind by stacking against Trp105 and locate one of their phenolic hydroxyls making a polar linkage to the fructose O2 at 3.6–3.8 Å from the C2, which could enable the ulterior nucleophilic attack leading to transfructosylation. Binding of hydroquinone was further investigated by soaking in absence of fructose, showing a flexible site that likely allows productive motion of the intermediates. Therefore, the acceptor capacity of the different polyphenols seems mediated by their ability to make flexible polar links with the protein, this flexibility being essential for the transfructosylation reaction to proceed. Finally, the binding affinity of the phenolic compounds was explained based on the two sites previously reported for pXd-INV.

Efficient production of isomelezitose by a glucosyltransferase activity in Metschnikowia reukaufii cell extracts

Metschnikowia reukaufii is a widespread yeast able to grow in the plants' floral nectaries, an environment of extreme conditions with sucrose concentrations exceeding 400 g l-1 , which led us into the search for enzymatic activities involved in this sugar use/transformation. New oligosaccharides were produced by transglucosylation processes employing M. reukaufii cell extracts in overload-sucrose reactions. These products were purified and structurally characterized by MS-ESI and NMR techniques. The reaction mixture included new sugars showing a great variety of glycosidic bonds including α-(1→1), α-(1→3) and α-(1→6) linkages. The main product synthesized was the trisaccharide isomelezitose, whose maximum concentration reached 81 g l-1 , the highest amount reported for any unmodified enzyme or microbial extract. In addition, 51 g l-1 of the disaccharide trehalulose was also produced. Both sugars show potential nutraceutical and prebiotic properties. Interestingly, the sugar mixture obtained in the biosynthetic reactions also contained oligosaccharides such as esculose, a rare trisaccharide with no previous NMR structure elucidation, as well as erlose, melezitose and theanderose. All the sugars produced are naturally found in honey. These compounds are of biotechnological interest due to their potential food, cosmeceutical and pharmaceutical applications.

Two-Step Production of Neofructo-Oligosaccharides Using Immobilized Heterologous Aspergillus terreus 1F-Fructosyltransferase Expressed in Kluyveromyces lactis and Native Xanthophyllomyces dendrorhous G6-Fructosyltransferase

Fructo-oligosaccharides (FOS) are prebiotic low-calorie sweeteners that are synthesized by the transfer of fructose units from sucrose by enzymes known as fructosyltransferases. If these enzymes generate β-(2,6) glycosidic bonds, the resulting oligosaccharides belong to the neoseries (neoFOS). Here, we characterized the properties of three different fructosyltransferases using a design of experiments approach based on response surface methodology with a D-optimal design. The reaction time, pH, temperature, and substrate concentration were used as parameters to predict three responses: The total enzyme activity, the concentration of neoFOS and the neoFOS yield relative to the initial concentration of sucrose. We also conducted immobilization studies to establish a cascade reaction for neoFOS production with two different fructosyltransferases, achieving a total FOS yield of 47.02 ± 3.02%. The resulting FOS mixture included 53.07 ± 1.66 mM neonystose (neo-GF3) and 20.8 ± 1.91 mM neo-GF4.

First crystal structure of an endo-levanase - the BT1760 from a human gut commensal Bacteroides thetaiotaomicron

The endo-levanase BT1760 of a human gut commensal Bacteroides thetaiotaomicron randomly cuts a β-2,6-linked fructan, levan, into fructo-oligosaccharides providing a prebiotic substrate for gut microbiota. Here we introduce the crystal structure of BT1760 at resolution of 1.65 Å. The fold of the enzyme is typical for GH32 family proteins: a catalytic N-terminal five-bladed β-propeller connected with a C-terminal β-sandwich domain. The levantetraose-bound structure of catalytically inactive mutant E221A at 1.90-Å resolution reveals differences in substrate binding between the endo-acting fructanases. A shallow substrate-binding pocket of the endo-inulinase INU2 of Aspergillus ficuum binds at least three fructose residues at its flat bottom. In the levantetraose-soaked crystal of the endo-levanase E221A mutant the ligand was bent into the pond-like substrate pocket with its fructose residues making contacts at −3, −2, −1 and + 1 subsites residing at several pocket depths. Binding of levantetraose to the β-sandwich domain was not detected. The N- and C-terminal modules of BT1760 did not bind levan if expressed separately, the catalytic domain lost its activity and both modules tended to precipitate. We gather that endo-levanase BT1760 requires both domains for correct folding, solubility and stability of the protein.

Enzymatic Synthesis of a Novel Pterostilbene α-Glucoside by the Combination of Cyclodextrin Glucanotransferase and Amyloglucosidase

The synthesis of a novel α-glucosylated derivative of pterostilbene was performed by a transglycosylation reaction using starch as glucosyl donor, catalyzed by cyclodextrin glucanotransferase (CGTase) from Thermoanaerobacter sp. The reaction was carried out in a buffer containing 20% (v/v) DMSO to enhance the solubility of pterostilbene. Due to the formation of several polyglucosylated products with CGTase, the yield of monoglucoside was increased by the treatment with a recombinant amyloglucosidase (STA1) from Saccharomyces cerevisiae (var. diastaticus). This enzyme was not able to hydrolyze the linkage between the glucose and pterostilbene. The monoglucoside was isolated and characterized by combining ESI-MS and 2D-NMR methods. Pterostilbene α-d-glucopyranoside is a novel compound. The α-glucosylation of pterostilbene enhanced its solubility in water to approximately 0.1 g/L. The α-glucosylation caused a slight loss of antioxidant activity towards ABTS˙⁺ radicals. Pterostilbene α-d-glucopyranoside was less toxic than pterostilbene for human SH-S5Y5 neurons, MRC5 fibroblasts and HT-29 colon cancer cells, and similar for RAW 264.7 macrophages.

Use of chitin and chitosan to produce new chitooligosaccharides by chitinase Chit42: enzymatic activity and structural basis of protein specificity

Background

Chitinases are ubiquitous enzymes that have gained a recent biotechnological attention due to their ability to transform biological waste from chitin into valued chito-oligomers with wide agricultural, industrial or medical applications. The biological activity of these molecules is related to their size and acetylation degree. Chitinase Chit42 from Trichoderma harzianum hydrolyses chitin oligomers with a minimal of three N-acetyl-d-glucosamine (GlcNAc) units. Gene chit42 was previously characterized, and according to its sequence, the encoded protein included in the structural Glycoside Hydrolase family GH18.

Results

Chit42 was expressed in Pichia pastoris using fed-batch fermentation to about 3 g/L. Protein heterologously expressed showed similar biochemical properties to those expressed by the natural producer (42 kDa, optima pH 5.5–6.5 and 30–40 °C). In addition to hydrolyse colloidal chitin, this enzyme released reducing sugars from commercial chitosan of different sizes and acetylation degrees. Chit42 hydrolysed colloidal chitin at least 10-times more efficiently (defined by the k_cat/K_m ratio) than any of the assayed chitosan. Production of partially acetylated chitooligosaccharides was confirmed in reaction mixtures using HPAEC-PAD chromatography and mass spectrometry. Masses corresponding to (d-glucosamine)_1–8-GlcNAc were identified from the hydrolysis of different substrates. Crystals from Chit42 were grown and the 3D structure determined at 1.8 Å resolution, showing the expected folding described for other GH18 chitinases, and a characteristic groove shaped substrate-binding site, able to accommodate at least six sugar units. Detailed structural analysis allows depicting the features of the Chit42 specificity, and explains the chemical nature of the partially acetylated molecules obtained from analysed substrates.

Conclusions

Chitinase Chit42 was expressed in a heterologous system to levels never before achieved. The enzyme produced small partially acetylated chitooligosaccharides, which have enormous biotechnological potential in medicine and food. Chit42 3D structure was characterized and analysed. Production and understanding of how the enzymes generating bioactive chito-oligomers work is essential for their biotechnological application, and paves the way for future work to take advantage of chitinolytic activities.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0895-x) contains supplementary material, which is available to authorized users.

Production, Purification, and Gene Cloning of a β-Fructofuranosidase with a High Inulin-hydrolyzing Activity Produced by a Novel Yeast Aureobasidium sp. P6 Isolated from a Mangrove Ecosystem

After screening of over 300 yeast strains isolated from the mangrove ecosystems, it was found that Aureobasidium sp. P6 strain had the highest inulin-hydrolyzing activity. Under the optimal conditions, this yeast strain produced an inulin-hydrolyzing activity of 30.98 ± 0.8 U/ml after 108 h of a 10-l fermentation. After the purification, a molecular weight of the enzyme which had the inulin-hydrolyzing activity was estimated to be 47.6 kDa, and the purified enzyme could actively hydrolyze both sucrose and inulin and exhibit a transfructosylating activity at 30.0 % sucrose, converting sucrose into fructooligosaccharides (FOS), indicating that the purified enzyme was a β-D-fructofuranosidase. After the full length of a β-D-fructofuranosidase gene (accession number KU308553) was cloned from Aureobasidium sp. P6 strain, a protein deduced from the cloned gene contained the conserved sequences MNDPNGL, RDP, ECP, FS, and Q of a glycosidehydrolase GH32 family, respectively, but did not contain a conserved sequence SVEVF, and the amino acid sequence of the protein from Aureobasidium sp. P6 strain had a high similarity to that of the β-fructofuranosidase from any other fungal strains. After deletion of the β-D-fructofuranosidase gene, the disruptant still had low inulin hydrolyzing and invertase activities and a trace amount of the transfructosylating activity, indicating that the gene encoding an inulinase may exist in the Aureobasidium sp. P6 strain.

Exploring the transferase activity of Ffase from Schwanniomyces occidentalis, a β-fructofuranosidase showing high fructosyl-acceptor promiscuity

The β-fructofuranosidase from the yeast Schwanniomyces occidentalis (Ffase) produces the prebiotic sugars 6-kestose and 1-kestose by transfructosylation of sucrose, which makes it of biotechnological interest. In this study, the hydrolase and transferase activity of this enzyme was kinetically characterized and its potential to synthesize new fructosylated products explored. A total of 40 hydroxylated compounds were used as potential fructosyl-acceptor alternatives to sucrose. Only 17 of them, including some monosaccharides, disaccharides, and oligosaccharides as well as alditols and glycosides were fructosylated. The best alternative acceptors were the alditols. The major transfer product of the reaction including mannitol was purified and characterized as 1-O-β-D-fructofuranosyl-D-mannitol, whose maximum concentration reached 44 g/L, representing about 7.3 % of total compounds in the mixture and 89 % of all products generated by transfructosylation. The reactions including erythritol produced 35 g/L of an isomer mixture comprising 1- and 4-O-β-D-fructofuranosyl-D-erythritol. In addition, Ffase produced 24 g/L of the disaccharide blastose by direct fructosylation of glucose, which makes it the first enzyme characterized from yeast showing this ability. Thus, novel fructosylated compounds with potential applications in food and pharmaceutical industries can be obtained due to the Ffase fructosyl-acceptor promiscuity.

Structural Analysis of β-Fructofuranosidase from Xanthophyllomyces dendrorhous Reveals Unique Features and the Crucial Role of N-Glycosylation in Oligomerization and Activity

Xanthophyllomyces dendrorhousβ-fructofuranosidase (XdINV)is a highly glycosylated dimeric enzyme that hydrolyzes sucrose and releases fructose from various fructooligosaccharides (FOS) and fructans. It also catalyzes the synthesis of FOS, prebiotics that stimulate the growth of beneficial bacteria in human gut. In contrast to most fructosylating enzymes, XdINV produces neo-FOS, which makes it an interesting biotechnology target. We present here its three-dimensional structure, which shows the expected bimodular arrangement and also a long extension of its C terminus that together with anN-linked glycan mediate the formation of an unusual dimer. The two active sites of the dimer are connected by a long crevice, which might indicate its potential ability to accommodate branched fructans. This arrangement could be representative of a group of GH32 yeast enzymes having the traits observed in XdINV. The inactive D80A mutant was used to obtain complexes with relevant substrates and products, with their crystals structures showing at least four binding subsites at each active site. Moreover, two different positions are observed from subsite +2 depending on the substrate, and thus, a flexible loop (Glu-334-His-343) is essential in binding sucrose and β(2-1)-linked oligosaccharides. Conversely, β(2-6) and neo-type substrates are accommodated mainly by stacking to Trp-105, explaining the production of neokestose and the efficient fructosylating activity of XdINV on α-glucosides. The role of relevant residues has been investigated by mutagenesis and kinetics measurements, and a model for the transfructosylating reaction has been proposed. The plasticity of its active site makes XdINV a valuable and flexible biocatalyst to produce novel bioconjugates.

An efficient continuous flow process for the synthesis of a non-conventional mixture of fructooligosaccharides

A sustainable and scalable process for the production of a new mixture of fructooligosaccharides (FOS) was developed using a continuous-flow approach based on an immobilized whole cells-packed bed reactor. The technological transfer from a classical batch system to an innovative flow environment allowed a significant improvement of the productivity. Moreover, the stability of this production system was ascertained by up to 7 days of continuous working. These results suggest the suitability of the proposed method for a large-scale production of the desired FOS mixture, in view of a foreseeable use as a novel prebiotic preparation.