Gene cloning and functional characterization by heterologous expression of the fructosyltransferase of Aspergillus sydowi IAM 2544

Inulin from halophilic archaeon Haloarcula: Production, chemical characterization, biological, and technological properties

Halophilic archaea are capable of producing fructans, which are fructose-based polysaccharides. However, their biochemical characterization and biological and technological properties have been scarcely studied. The aim of this study was to evaluate the production, chemical characterization, biological and technological properties of a fructan inulin-type biosynthesized by a halophilic archaeon. Fructan extraction was performed through ethanol precipitation and purification by diafiltration. The chemical structure was elucidated using Fourier Transform-Infrared Spectroscopy and Nuclear Magnetic Resonance (NMR). Haloarcula sp. M1 biosynthesizes inulin with an average molecular weight of 8.37 × 106 Da. The maximal production reached 3.9 g of inulin per liter of culture within seven days. The glass transition temperature of inulin was measured at 138.85 °C, and it exhibited an emulsifying index of 36.47 %, which is higher than that of inulin derived from chicory. Inulin from Haloarcula sp. M1 (InuH) demonstrates prebiotic capacity. This study represents the first report on the biological and technological properties of inulin derived from halophilic archaea.

Fructosyltransferase production by Aspergillus oryzae BM-DIA using solid-state fermentation and the properties of its nucleotide and protein sequences

Fructosyltransferase (FTase) catalyzes the transfer of a fructosyl group to a sucrose molecule or a fructooligosaccharide (FOS) when a FOS with a longer chain is formed. Production of FTase by two Aspergillus species and its mixture was exploited using solid-state fermentation (SSF) and employing agave sap as substrate. The maximum FTase activity (1.59 U/mL) by Aspergillus oryzae was obtained after 24 h, using a temperature of 30 °C, with an inoculum of 2 × 10⁷ spores/mL. The nucleotide sequence coding for the fructosyltransferase showed 1494 bp and encodes for a protein of 498 amino acids. The hypothetical molecular tertiary structure of Aspergillus oryzae BM-DIA FTase showed the presence of structural domains, such as a five-bladed beta-propeller domain characteristic of GH (glycoside hydrolase) and C terminal, which forms a beta-sandwich module. This study contributes to the knowledge of stability, compatibility, and genetic expression of Aspergillus oryzae BM-DIA under SSF bioprocess conditions for industrial production of fructosyltransferase.

Purification and biochemical characterization of an extracellular fructosyltransferase enzyme from Aspergillus niger sp. XOBP48: implication in fructooligosaccharide production

An extracellular fructosyltransferase (Ftase) enzyme with a molar mass of ≈70 kDa from a newly isolated indigenous coprophilous fungus Aspergillus niger sp. XOBP48 is purified to homogeneity and characterized in this study. The enzyme was purified to 4.66-fold with a total yield of 15.53% and specific activity of 1219.17 U mg^-1 of protein after a three-step procedure involving (NH₄)₂SO₄ fractionation, dialysis and anion exchange chromatography. Ftase showed optimum activity at pH 6.0 and temperature 50 °C. Ftase exhibited over 80% residual activity at pH range of 4.0-10.0 and ≈90% residual activity at temperature range of 40-60 °C for 6 h. Metal ion inhibitors Hg²⁺ and Ag⁺ significantly inhibited Ftase activity at 1 mmol concentration. Ftase showed K _m, v _max and k _cat values of 79.51 mmol, 45.04 µmol min^-1 and 31.5 min^-1, respectively, with a catalytic efficiency (k _cat/K _m) of 396 µmol^-1 min^-1 for the substrate sucrose. HPLC-RI experiments identified the end products of fructosyltransferase activity as monomeric glucose, 1-kestose (GF₂), and 1,1-kestotetraose (GF₃). This study evaluates the feasibility of using this purified extracellular Ftase for the enzymatic synthesis of biofunctional fructooligosaccharides.

Characterization of a mycelial fructosyltransferase from Aspergillus tamarii NKRC 1229 for efficient synthesis of fructooligosaccharides

An efficient system for biotransformation of sucrose to fructooligosaccharides (FOS) was obtained using Aspergillus tamarii NKRC 1229 mycelial fructosyltransferase (m-FTase). Zymographic analysis confirmed mycelial localization of the FTase (36 U/g) and lyophilized fungal pellets were used for bioconversion. m-FTase had molecular weight ∼75 kDa with optimum activity at pH 7.0 and 20 °C. FOS production after parametric optimization (sucrose - 50% w/v, m-FTase dose - 4.5% w/v, inoculum age - 48 h and incubation time - 24 h) reached 325 g/L (55% yield) with 14% residual sucrose, 25% glucose and 6% fructose. FTase activity was enhanced after pre-treatment with organic solvents and SDS. FOS was purified in a single step using gel filtration matrix, Bio-Gel P2. FOS was characterized using Diffusion ordered spectroscopy-Nuclear Magnetic Resonance (¹H DOSY-NMR) and Fourier-transform infrared spectroscopy (FTIR). Continuous generation of FOS was achieved using recyclable mycelia upto 10 consecutive cycles.

High level production of a recombinant acid stable exoinulinase from Aspergillus kawachii

Exoinulinases-enzymes extensively studied in recent decades because of their industrial applications-need to be produced in suitable quantities in order to meet production demands. We describe here the production of an acid-stable recombinant inulinase from Aspergillus kawachii in the Pichia pastoris system and the recombinant enzyme's biochemical characteristics and potential application to industrial processes. After an appropriate cloning strategy, this genetically engineered inulinase was successfully overproduced in fed-batch fermentations, reaching up to 840 U/ml after a 72-h cultivation. The protein, purified to homogeneity by chromatographic techniques, was obtained at a 42% yield. The following biochemical characteristics were determined: the enzyme had an optimal pH of 3, was stable for at least 3 h at 55 °C, and was inhibited in catalytic activity almost completely by Hg⁺². The respective K_m and V_max for the recombinant inulinase with inulin as substrate were 1.35 mM and 2673 μmol/min/mg. The recombinant enzyme is an exoinulinase but also possesses synthetic activity (i. e., fructosyl transferase). The high level of production of this recombinant plus its relevant biochemical properties would argue that the process presented here is a possible recourse for industrial applications in carbohydrate processing.

Heterologous expression of Aspergillus terreus fructosyltransferase in Kluyveromyces lactis

Fructo-oligosaccharides are prebiotic and hypocaloric sweeteners that are usually extracted from chicory. They can also be produced from sucrose using fructosyltransferases, but the only commercial enzyme suitable for this purpose is Pectinex Ultra, which is produced with Aspergillus aculeatus. Here we used the yeast Kluyveromyces lactis to express a secreted recombinant fructosyltransferase from the inulin-producing fungus Aspergillus terreus. A synthetic codon-optimised version of the putative β-fructofuranosidase ATEG 04996 (XP 001214174.1) from A. terreus NIH2624 was secreted as a functional protein into the extracellular medium. At 60°C, the purified A. terreus enzyme generated the same pattern of oligosaccharides as Pectinex Ultra, but at lower temperatures it also produced oligomers with up to seven units. We achieved activities of up to 986.4U/mL in high-level expression experiments, which is better than previous reports of optimised Aspergillus spp. fermentations.

Enzymatic trends of fructooligosaccharides production by microorganisms

Fructooligosaccharides are influential prebiotics that affect various physiological functions in such a way that they promote positive impact to health. They occur naturally in many fruits and vegetables in trace amounts. However, they are mainly produced commercially by the reaction of microbial enzymes with di- or polysaccharides, such as sucrose or inulin as a substrate. For maximum production of fructooligosaccharides on an industrial level, development of more enzymes with high activity and stability is required. This has attracted the attention of biotechnologists and microbiologists worldwide. This study aims to discuss the new trends in the production of fructooligosaccharide and its effect on numerous health qualities through which it creates great demand in the sugar market.

Gene cloning and enzyme structure modeling of the Aspergillus oryzae N74 fructosyltransferase

The fructooligosaccharides (FOS) represent an important source of prebiotic compounds that are widely used as an ingredient in functional foods. Recently, the strain Aspergillus oryzae N74 was reported as a potential microorganism for the industrial production of FOS, due to its high yields of FOS production. In this work, we used a PCR-cloning strategy to clone the A. oryzae N74 ftase gene as a previous step for recombinant enzyme production. Ftase showed a 1630 bp size with a 99% similarity with other A. oryzae strains and between 1 to 68% identities with other Aspergillus strains. This gene encodes for a 525 amino acids protein with 99% similarity with other A. oryzae strains and between 11 to 69% similarities with other Aspergillus strains. Finally, an A. oryzae N74 FTase tertiary structure model was predicted base on its similarity with other glycoside hydrolase 32 family members. The active site was located inside the β-propeller domain and was formed for non-charged polar and charged amino acids. In summary, these results shows the high level of sequence conservation between A. oryzae strains and represent a first step towards the development of a FOS production industrial process using recombinant microorganism carrying the ftase gene from A. oryzae N74.

Crystal structures of Aspergillus japonicus fructosyltransferase complex with donor/acceptor substrates reveal complete subsites in the active site for catalysis

Fructosyltransferases catalyze the transfer of a fructose unit from one sucrose/fructan to another and are engaged in the production of fructooligosaccharide/fructan. The enzymes belong to the glycoside hydrolase family 32 (GH32) with a retaining catalytic mechanism. Here we describe the crystal structures of recombinant fructosyltransferase (AjFT) from Aspergillus japonicus CB05 and its mutant D191A complexes with various donor/acceptor substrates, including sucrose, 1-kestose, nystose, and raffinose. This is the first structure of fructosyltransferase of the GH32 with a high transfructosylation activity. The structure of AjFT comprises two domains with an N-terminal catalytic domain containing a five-blade beta-propeller fold linked to a C-terminal beta-sandwich domain. Structures of various mutant AjFT-substrate complexes reveal complete four substrate-binding subsites (-1 to +3) in the catalytic pocket with shapes and characters distinct from those of clan GH-J enzymes. Residues Asp-60, Asp-191, and Glu-292 that are proposed for nucleophile, transition-state stabilizer, and general acid/base catalyst, respectively, govern the binding of the terminal fructose at the -1 subsite and the catalytic reaction. Mutants D60A, D191A, and E292A completely lost their activities. Residues Ile-143, Arg-190, Glu-292, Glu-318, and His-332 combine the hydrophobic Phe-118 and Tyr-369 to define the +1 subsite for its preference of fructosyl and glucosyl moieties. Ile-143 and Gln-327 define the +2 subsite for raffinose, whereas Tyr-404 and Glu-405 define the +2 and +3 subsites for inulin-type substrates with higher structural flexibilities. Structural geometries of 1-kestose, nystose and raffinose are different from previous data. All results shed light on the catalytic mechanism and substrate recognition of AjFT and other clan GH-J fructosyltransferases.

Fructan and its relationship to abiotic stress tolerance in plants

Numerous studies have been published that attempted to correlate fructan concentrations with freezing and drought tolerance. Studies investigating the effect of fructan on liposomes indicated that a direct interaction between membranes and fructan was possible. This new area of research began to move fructan and its association with stress beyond mere correlation by confirming that fructan has the capacity to stabilize membranes during drying by inserting at least part of the polysaccharide into the lipid headgroup region of the membrane. This helps prevent leakage when water is removed from the system either during freezing or drought. When plants were transformed with the ability to synthesize fructan, a concomitant increase in drought and/or freezing tolerance was confirmed. These experiments indicate that besides an indirect effect of supplying tissues with hexose sugars, fructan has a direct protective effect that can be demonstrated by both model systems and genetic transformation.

Molecular and biochemical characterization of a beta-fructofuranosidase from Xanthophyllomyces dendrorhous

An extracellular beta-fructofuranosidase from the yeast Xanthophyllomyces dendrorhous was characterized biochemically, molecularly, and phylogenetically. This enzyme is a glycoprotein with an estimated molecular mass of 160 kDa, of which the N-linked carbohydrate accounts for 60% of the total mass. It displays optimum activity at pH 5.0 to 6.5, and its thermophilicity (with maximum activity at 65 to 70 degrees C) and thermostability (with a T(50) in the range 66 to 71 degrees C) is higher than that exhibited by most yeast invertases. The enzyme was able to hydrolyze fructosyl-beta-(2-->1)-linked carbohydrates such as sucrose, 1-kestose, or nystose, although its catalytic efficiency, defined by the k(cat)/K(m) ratio, indicates that it hydrolyzes sucrose approximately 4.2 times more efficiently than 1-kestose. Unlike other microbial beta-fructofuranosidases, the enzyme from X. dendrorhous produces neokestose as the main transglycosylation product, a potentially novel bifidogenic trisaccharide. Using a 41% (wt/vol) sucrose solution, the maximum fructooligosaccharide concentration reached was 65.9 g liter(-1). In addition, we isolated and sequenced the X. dendrorhous beta-fructofuranosidase gene (Xd-INV), showing that it encodes a putative mature polypeptide of 595 amino acids and that it shares significant identity with other fungal, yeast, and plant beta-fructofuranosidases, all members of family 32 of the glycosyl-hydrolases. We demonstrate that the Xd-INV could functionally complement the suc2 mutation of Saccharomyces cerevisiae and, finally, a structural model of the new enzyme based on the homologous invertase from Arabidopsis thaliana has also been obtained.

Microbial production of fructosyltransferases for synthesis of pre-biotics

Fructooligosaccharides (FOS) are prebiotic substances found in several vegetable or natural foods. The main commercial production of FOS comes from enzymatic transformation of sucrose by the microbial enzyme fructosyltransferase. The development of more efficient enzymes, with high activity and stability, is required and this has attracted the interest of biotechnologists and microbiologists with production by several microorganisms being studied. This article reviews and discusses FOS chemical structure, enzyme characteristics, the nomenclature, producer microorganisms and enzyme production both in solid state fermentation and submerged cultivation.

Two types of beta-fructofuranosidases from Aspergillus oryzae KB

Aspergillus oryzae KB produces two types of beta-fructofuranosidases, F1 and F2. F1 produces 1-kestose, nystose, and fructosyl nystose from sucrose through its transfructosylation action. F2 hydrolyzes sucrose to glucose and fructose. N-Terminal amino acid sequences of the purified enzymes were DYNAAPPNLST for F1 and YSGDLRPQ for F2. Each enzyme encoding gene was identified in the genome of Aspergillus oryzae. Although the KB strain showed a higher production of F2 than F1 in a low sucrose liquid medium, F2 production gradually decreased, whereas F1 production increased with increasing sucrose concentration in the medium. Synthesis of F1 and F2 mRNAs analyzed on reverse-transcription polymerase chain reaction corresponded to individual enzymatic production. During liquid culture of the KB strain, F1 synthesizes fructooligosaccharides from sucrose through transfructosylation, and F2 gradually hydrolyzes it. In a highly concentrated sucrose medium, intake of sucrose into the KB strain was depressed by F1 through synthesis of transfer products, fructooligosaccharides.

Database mining and transcriptional analysis of genes encoding inulin-modifying enzymes of Aspergillus niger

As a soil fungus, Aspergillus niger can metabolize a wide variety of carbon sources, employing sets of enzymes able to degrade plant-derived polysaccharides. In this study the genome sequence of A. niger strain CBS 513.88 was surveyed, to analyse the gene/enzyme network involved in utilization of the plant storage polymer inulin, and of sucrose, the substrate for inulin synthesis in plants. In addition to three known activities, encoded by the genes suc1 (invertase activity; designated sucA), inuE (exo-inulinase activity) and inuA/inuB (endo-inulinase activity), two new putative invertase-like proteins were identified. These two putative proteins lack N-terminal signal sequences and therefore are expected to be intracellular enzymes. One of these two genes, designated sucB, is expressed at a low level, and its expression is up-regulated when A. niger is grown on sucrose- or inulin-containing media. Transcriptional analysis of the genes encoding the sucrose- (sucA) and inulin-hydrolysing enzymes (inuA and inuE) indicated that they are similarly regulated and all strongly induced on sucrose and inulin. Analysis of a DeltacreA mutant strain of A. niger revealed that expression of the extracellular inulinolytic enzymes is under control of the catabolite repressor CreA. Expression of the inulinolytic enzymes was not induced by fructose, not even in the DeltacreA background, indicating that fructose did not act as an inducer. Evidence is provided that sucrose, or a sucrose-derived intermediate, but not fructose, acts as an inducer for the expression of inulinolytic genes in A. niger.

Cloning and characterization of a novel invertase from the obligate biotroph Uromyces fabae and analysis of expression patterns of host and pathogen invertases in the course of infection

Invertases are key enzymes in carbon partitioning in higher plants. They gain additional importance in the distribution of carbohydrates in the event of wounding or pathogen attack. Although many researchers have found an increase in invertase activity upon infection, only a few studies were able to determine whether the source of this activity was host or parasite. This article analyzes the role of invertases involved in the biotrophic interaction of the rust fungus Uromyces fabae and its host plant, Vicia faba. We have identified a fungal gene, Uf-INV1, with homology to invertases and assessed its contribution to pathogenesis. Expression analysis indicated that transcription began upon penetration of the fungus into the leaf, with high expression levels in haustoria. Heterologous expression of Uf-INV1 in Saccharomyces cerevisiae and Pichia pastoris allowed a biochemical characterization of the enzymatic activity associated with the secreted gene product INV1p. Expression analysis of the known vacuolar and cell-wall-bound invertase isoforms of V. faba indicated a decrease in the expression of a vacuolar invertase, whereas one cell-wall-associated invertase exhibited increased expression. These changes were not confined to the infected tissue, and effects also were observed in remote plant organs, such as roots. These findings hint at systemic effects of pathogen infection. Our results support the hypothesis that pathogen infection establishes new sinks which compete with physiological sink organs.

Structure-function relationships of glucansucrase and fructansucrase enzymes from lactic acid bacteria

Lactic acid bacteria (LAB) employ sucrase-type enzymes to convert sucrose into homopolysaccharides consisting of either glucosyl units (glucans) or fructosyl units (fructans). The enzymes involved are labeled glucansucrases (GS) and fructansucrases (FS), respectively. The available molecular, biochemical, and structural information on sucrase genes and enzymes from various LAB and their fructan and alpha-glucan products is reviewed. The GS and FS enzymes are both glycoside hydrolase enzymes that act on the same substrate (sucrose) and catalyze (retaining) transglycosylation reactions that result in polysaccharide formation, but they possess completely different protein structures. GS enzymes (family GH70) are large multidomain proteins that occur exclusively in LAB. Their catalytic domain displays clear secondary-structure similarity with alpha-amylase enzymes (family GH13), with a predicted permuted (beta/alpha)(8) barrel structure for which detailed structural and mechanistic information is available. Emphasis now is on identification of residues and regions important for GS enzyme activity and product specificity (synthesis of alpha-glucans differing in glycosidic linkage type, degree and type of branching, glucan molecular mass, and solubility). FS enzymes (family GH68) occur in both gram-negative and gram-positive bacteria and synthesize beta-fructan polymers with either beta-(2-->6) (inulin) or beta-(2-->1) (levan) glycosidic bonds. Recently, the first high-resolution three-dimensional structures have become available for FS (levansucrase) proteins, revealing a rare five-bladed beta-propeller structure with a deep, negatively charged central pocket. Although these structures have provided detailed mechanistic insights, the structural features in FS enzymes dictating the synthesis of either beta-(2-->6) or beta-(2-->1) linkages, degree and type of branching, and fructan molecular mass remain to be identified.

Engineering fructan metabolism in plants

Fructans, or polyfructosylsucroses, are storage carbohydrates present in many higher plants. They are also considered healthy food ingredients. Engineering crops into high level production of specific fructan molecules is one of the mayor strategic research goals. Understanding the properties of fructosyltransferases is important, in order to direct the synthesis of fructans. In plants at least two fructosyltransferases are needed to synthesise fructans. One enzyme synthesises the fructan trisaccharide 1-kestose, the next enzyme uses 1-kestose for elongation and/or modification, producing longer fructans. The specificity of fructosyltransferases determines the type of glycosidic bond formed and the donor and acceptor substrates used. This enables the synthesis of many structurally diverse fructans. The production of these molecules in crops such as sugar beet and potato makes the commercial use of fructans feasible.