Utilization of glycosyltransferases as a seamless tool for synthesis and modification of the oligosaccharides-A review

Glycosyltransferases (GTs) catalyze the transfer of active monosaccharide donors to carbohydrates to create a wide range of oligosaccharide structures. GTs display strong regioselectivity and stereoselectivity in producing glycosidic bonds, making them extremely valuable in the in vitro synthesis of oligosaccharides. The synthesis of oligosaccharides by GTs often gives high yields; however, the enzyme activity may experience product inhibition. Additionally, the higher cost of nucleotide sugars limits the usage of GTs for oligosaccharide synthesis. In this review, we comprehensively discussed the structure and mechanism of GTs based on recent literature and the CAZY website data. To provide innovative ideas for the functional studies of GTs, we summarized several remarkable characteristics of GTs, including folding, substrate specificity, regioselectivity, donor sugar nucleotides, catalytic reversibility, and differences between GTs and GHs. In particular, we highlighted the recent advancements in multi-enzyme cascade reactions and co-immobilization of GTs, focusing on overcoming problems with product inhibition and cost issues. Finally, we presented various types of GT that have been successfully used for oligosaccharide synthesis. We concluded that there is still an opportunity for improvement in enzymatically produced oligosaccharide yield, and future research should focus on improving the yield and reducing the production cost.

Recent Progress on Feasible Strategies for Arbutin Production

Arbutin is a hydroquinone glucoside and a natural product present in various plants. Arbutin potently inhibits melanin formation. This property has been exploited in whitening cosmetics and pharmaceuticals. Arbutin production relies mainly on chemical synthesis. The multi-step and complicated process can compromise product purity. With the increasing awareness of sustainable development, the current research direction prioritizes environment-friendly, biobased arbutin production. In this review, current strategies for arbutin production are critically reviewed, with a focus on plant extraction, chemical synthesis, biotransformation, and microbial fermentation. Furthermore, the bottlenecks and perspectives for future direction on arbutin biosynthesis are discussed.

Stability of Enzyme-Modified Flavonoid C- and O-Glycosides from Common Buckwheat Sprout Extracts during In Vitro Digestion and Colonic Fermentation

Common buckwheat sprout (CBS) contains more flavone C-glycosides (FCGs) and flavonol O-glycosides (FOGs) than does common buckwheat seed. Both flavonoids in CBS are well known for providing benefits to human health. However, they are relatively less bioaccessible and more directly degradable to aglycone during digestion than are multiglycosylated flavonoids. To overcome such limitations, the water solubility and digestion stability of FCGs and FOGs were enhanced by transglycosylation using cyclodextrin glycosyltransferase. Gastric conditions had little effect on the stability of FCGs and FOGs and their enzyme-modified compounds. In contrast, under intestinal conditions, transglycosylated FCGs lost a glucose moiety and reverted to their parent compounds before transglycosylation. Under colonic fermentation using human fecal samples, the different profiles and concentrations of short-chain fatty acids were suggested to be mainly due to the presence of transglycosylated FCGs and FOGs. These findings indicate that the process of transglycosylation changes the bioaccessibility of flavonoids in CBS.

Comprehensive study on transglycosylation of CGTase from various sources

Transglycosylation is the in-vivo or in-vitro process of transferring glycosyl groups from a donor to an acceptor, which is usually performed by enzymatic reactions because of their simplicity, low steric hindrance, high region-specificity, low production cost, and mild processing conditions. One of the enzymes commonly used in the transglycosylation reaction is cyclodextrin glucanotransferase (CGTase). The transglycosylated products, catalyzed by CGTase, are widely used in food additives, supplements, and personal care and cosmetic products. This is due to improvements in the solubility, stability, bioactivity and length of the synthesized products. This paper's focus is on the importance of enzymes used in the transglycosylation reaction, their characteristics and mechanism of action, sources and production yield, and donor and acceptor specificities. Moreover, the influence of intrinsic and extrinsic factors on the enzymatic reaction, catalysis of glycosidic linkages, and advantages of CGTase transglycosylation reactions are discussed in detail.

Thermal Effect of Different Laying Modes on Cross-Linked Polyethylene (XLPE) Insulation and a New Estimation on Cable Ampacity

This paper verifies the fluctuation on thermal parameters and ampacity of the high-voltage cross-linked polyethylene (XLPE) cables with different insulation conditions and describes the results of a thermal aging experiment on the XLPE insulation with different operating years in different laying modes guided by Comsol Multiphysics modeling software. The thermal parameters of the cables applied on the models are detected by thermal parameter detection control platform and differential scanning calorimetry (DSC) measurement to assure the effectivity of the simulation. Several diagnostic measurements including Fourier infrared spectroscopy (FTIR), DSC, X-ray diffraction (XRD), and breakdown field strength were conducted on the treated and untreated specimens in order to reveal the changes of properties and the relationship between the thermal effect and the cable ampacity. Moreover, a new estimation on cable ampacity from the perspective on XLPE insulation itself has been proposed in this paper, which is also a possible way to judge the insulation condition of the cable with specific aging degree in specific laying mode for a period of time.

Production and Surfactant Properties of Tert-Butyl α-d-Glucopyranosides Catalyzed by Cyclodextrin Glucanotransferase

While testing the ability of cyclodextrin glucanotransferases (CGTases) to glucosylate a series of flavonoids in the presence of organic cosolvents, we found out that this enzyme was able to glycosylate a tertiary alcohol (tert-butyl alcohol). In particular, CGTases from Thermoanaerobacter sp. and Thermoanaerobacterium thermosulfurigenes EM1 gave rise to the appearance of at least two glycosylation products, which were characterized by mass spectrometry (MS) and nuclear magnetic resonance (NMR) as tert-butyl-α-D-glucoside (major product) and tert-butyl-α-D-maltoside (minor product). Using partially hydrolyzed starch as glucose donor, the yield of transglucosylation was approximately 44% (13 g/L of tert-butyl-α-D-glucoside and 4 g/L of tert-butyl-α-D-maltoside). The synthesized tert-butyl-α-D-glucoside exhibited the typical surfactant behavior (critical micellar concentration, 4.0–4.5 mM) and its properties compared well with those of the related octyl-α-D-glucoside. To the best of our knowledge, this is the first description of an enzymatic α-glucosylation of a tertiary alcohol.

Optimization of Regioselective α-Glucosylation of Hesperetin Catalyzed by Cyclodextrin Glucanotransferase

The regioselective α-glucosylation of hesperetin was achieved by a transglycosylation reaction catalyzed by cyclodextrin glucanotransferase (CGTase) from Thermoanaerobacter sp. using soluble starch as glucosyl donor. By combining mass spectrometry (ESI-TOF) and 2D-NMR analysis, the main monoglucosylated derivative was fully characterized (hesperetin 7-O-α-d-glucopyranoside). In order to increase the yield of monoglucoside, several reaction parameters were optimized: Nature and percentage of cosolvent, composition of the aqueous phase, glucosyl donor, temperature, and the concentrations of hesperetin and soluble starch. Under the optimal conditions, which included the presence of 30% of bis(2-methoxyethyl) ether as cosolvent, the maximum concentration of monoglucoside was approximately 2 mM, obtained after 24 h of reaction. To our knowledge, this is the first report of direct glucosylation of hesperetin employing free enzymes instead of whole cells.

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.

General N-and O-Linked Glycosylation of Lipoproteins in Mycoplasmas and Role of Exogenous Oligosaccharide

The lack of a cell wall, flagella, fimbria, and other extracellular appendages and the possession of only a single membrane render the mycoplasmas structurally simplistic and ideal model organisms for the study of glycoconjugates. Most species have genomes of about 800 kb and code for few proteins predicted to have a role in glycobiology. The murine pathogens Mycoplasma arthritidis and Mycoplasma pulmonis have only a single gene annotated as coding for a glycosyltransferase but synthesize glycolipid, polysaccharide and glycoproteins. Previously, it was shown that M. arthritidis glycosylated surface lipoproteins through O-linkage. In the current study, O-linked glycoproteins were similarly found in M. pulmonis and both species of mycoplasma were found to also possess N-linked glycans at residues of asparagine and glutamine. Protein glycosylation occurred at numerous sites on surface-exposed lipoproteins with no apparent amino acid sequence specificity. The lipoproteins of Mycoplasma pneumoniae also are glycosylated. Glycosylation was dependent on the glycosidic linkages from host oligosaccharides. As far as we are aware, N-linked glycoproteins have not been previously described in Gram-positive bacteria, the organisms to which the mycoplasmas are phylogenetically related. The findings indicate that the mycoplasma cell surface is heavily glycosylated with implications for the modulation of mycoplasma-host interactions.

Synthesis and characterization of isomaltulose-derived oligosaccharides produced by transglucosylation reaction of Leuconostoc mesenteroides dextransucrase

This paper reports the efficient enzymatic synthesis of a homologous series of isomaltulose-derived oligosaccharides with degrees of polymerization ranging from 3 to 9 through the transglucosylation reaction using a dextransucrase from Leuconostoc mesenteroides B-512F. The total oligosaccharide yield obtained under optimal conditions was 41-42% (in weight with respect to the initial amount of isomaltulose) after 24-48 h of reaction. Nuclear magnetic resonance (NMR) structural characterization indicated that dextransucrase specifically transferred glucose moieties of sucrose to the C-6 of the nonreducing glucose residue of isomaltulose. Likewise, monitoring the progression of the content of each individual oligosaccharide indicated that oligosaccharide acceptor products of low molecular weight acted in turn as acceptors for further transglucosylation to yield oligosaccharides of a higher degree of polymerization. The produced isomaltulose-derived oligosaccharides can be considered as isomalto-oligosaccharides (IMOs) because they are linked by only α-(1→6) bonds. In addition, having isomaltulose as the core structure, these IMO-like structures could possess appealing bioactive properties that could find potential applications as functional food ingredients.

Synthesis of novel bioactive lactose-derived oligosaccharides by microbial glycoside hydrolases

Prebiotic oligosaccharides are increasingly demanded within the Food Science domain because of the interesting healthy properties that these compounds may induce to the organism, thanks to their beneficial intestinal microbiota growth promotion ability. In this regard, the development of new efficient, convenient and affordable methods to obtain this class of compounds might expand even further their use as functional ingredients. This review presents an overview on the most recent interesting approaches to synthesize lactose-derived oligosaccharides with potential prebiotic activity paying special focus on the microbial glycoside hydrolases that can be effectively employed to obtain these prebiotic compounds. The most notable advantages of using lactose-derived carbohydrates such as lactosucrose, galactooligosaccharides from lactulose, lactulosucrose and 2-α-glucosyl-lactose are also described and commented.

Biocatalytic synthesis of maltodextrin-based acrylates from starch and α-cyclodextrin

Novel 2-(β-maltooligooxy)-ethyl (meth)acrylate monomers are successfully synthesized by CGTase from Bacillus macerans catalyzed coupling of 2-(β-glucosyloxy)-ethyl acrylate and methacrylate with α-cyclodextrin or starch. HPLC-UV analysis shows that the CGTase catalyzed reaction yields 2-(β-maltooligooxy)-ethyl acrylates with 1 to 15 glucopyranosyl units. (1) H NMR spectroscopy reveals that the β-linkage in the acceptor molecule is preserved during the CGTase catalyzed coupling reaction, whereas the newly introduced glucose units are attached by α-(1,4)-glycosidic linkages. The synthesized 2-(β-maltooligooxy)-ethyl acrylate monomers are successfully polymerized by aqueous free radical polymerization to yield the comb-shaped glycopolymer poly(2-(β-maltooligooxy)-ethyl acrylate).

Enzymatic conversions of starch

This article surveys methods for the enzymatic conversion of starch, involving hydrolases and nonhydrolyzing enzymes, as well as the role of microorganisms producing such enzymes. The sources of the most common enzymes are listed. These starch conversions are also presented in relation to their applications in the food, pharmaceutical, pulp, textile, and other branches of industry. Some sections are devoted to the fermentation of starch to ethanol and other products, and to the production of cyclodextrins, along with the properties of these products. Light is also shed on the enzymes involved in the digestion of starch in human and animal organisms. Enzymatic processes acting on starch are useful in structural studies of the substrates and in understanding the characteristics of digesting enzymes. One section presents the application of enzymes to these problems. The information that is included covers the period from the early 19th century up to 2009.

Efficient synthesis and characterization of lactulosucrose by Leuconostoc mesenteroides B-512F dextransucrase

This work describes an efficient enzymatic synthesis and NMR structural characterization of the trisaccharide β-D-galactopyranosyl-(1→4)-β-D-fructofuranosyl-(2→1)-α-D-glucopyranoside, also termed as lactulosucrose. This oligosaccharide was formed by the Leuconostoc mesenteroides B-512F dextransucrase-catalyzed transfer of the glucosyl residue from sucrose to the 2-hydroxyl group of the reducing unit of lactulose. The enzymatic reaction was carried out under optimal conditions, i.e., at 30 °C in 20 mM sodium acetate buffer with 0.34 mM CaCl(2) at pH 5.2, and the effect of factors such as reaction time (0-48 h), enzyme charge (0.8, 1.6, and 2.4 U mL(-1)), and sucrose:lactulose concentration ratios (20:40, 30:30, and 40:20, expressed in g/100 mL) on the formation of transfer products were studied. The highest formation in lactulosucrose was attained at 8 and 24-32 h by using 20%:40% and 30%:30% sucrose:lactulose mixtures, respectively, with 1.6 or 2.4 U mL(-1) dextransucrase, leading to lactulosucrose yields of 27-35% in weight respect to the initial amount of lactulose. Furthermore, minor tetra- and pentasaccharide, both probably derived from lactulose, were also detected and quantified. Likewise, the capacity of lactulosucrose to act as D-glucosyl donor once the sucrose was consumed, could explain its decrease from 16 to 24 h when the highest charge of dextransucrase was used. Considering the chemical structure of the synthesized oligosaccharides, lactulosucrose and its derivatives could potentially be excellent candidates for an emerging prebiotic ingredient.

Synthesis and characterization of a potential prebiotic trisaccharide from cheese whey permeate and sucrose by Leuconostoc mesenteroides dextransucrase

The production of new bioactive oligosaccharides is currently garnering much attention for their potential use as functional ingredients. This work addresses the enzymatic synthesis and NMR structural characterization of 2-α-D-glucopyranosyl-lactose derived from sucrose:lactose and sucrose:cheese whey permeate mixtures by using a Leuconostoc mesenteroides B-512F dextransucrase. The effect of synthesis conditions, including concentration of substrates, molar ratio of donor/acceptor, enzyme concentration, reaction time, and temperature, on the formation of transfer products is evaluated. Results indicated that cheese whey permeate is a suitable material for the synthesis of 2-α-D-glucopyranosyl-lactose, giving rise to yields around 50% (in weight respect to the initial amount of lactose) under the optimum reaction conditions. According to its structure, this trisaccharide is an excellent candidate for a new prebiotic ingredient, due to the reported high resistance of α-(1→2) linkages to the digestive enzymes in humans and animals, as well as to its potential selective stimulation of beneficial bacteria in the large intestine mainly attributed to the two linked glucose units located at the reducing end that reflects the disaccharide kojibiose (2-α-D-glucopyranosyl-D-glucose). These findings could contribute to broadening the use of important agricultural raw materials, such as sucrose or cheese whey permeates, as renewable substrates for enzymatic synthesis of oligosaccharides of nutritional interest.

Production of Galacto-oligosaccharides by the β-Galactosidase from Kluyveromyces lactis : comparative analysis of permeabilized cells versus soluble enzyme

The transgalactosylation activity of Kluyveromyces lactis cells was studied in detail. Cells were permeabilized with ethanol and further lyophilized to facilitate the transit of substrates and products. The resulting biocatalyst was assayed for the synthesis of galacto-oligosaccharides (GOS) and compared with two soluble β-galactosidases from K. lactis (Lactozym 3000 L HP G and Maxilact LGX 5000). Using 400 g/L lactose, the maximum GOS yield, measured by HPAEC-PAD analysis, was 177 g/L (44% w/w of total carbohydrates). The major products synthesized were the disaccharides 6-galactobiose [Gal-β(1→6)-Gal] and allolactose [Gal-β(1→6)-Glc], as well as the trisaccharide 6-galactosyl-lactose [Gal-β(1→6)-Gal-β(1→4)-Glc], which was characterized by MS and 2D NMR. Structural characterization of another synthesized disaccharide, Gal-β(1→3)-Glc, was carried out. GOS yield obtained with soluble β-galactosidases was slightly lower (160 g/L for Lactozym 3000 L HP G and 154 g/L for Maxilact LGX 5000); however, the typical profile with a maximum GOS concentration followed by partial hydrolysis of the newly formed oligosaccharides was not observed with the soluble enzymes. Results were correlated with the higher stability of β-galactosidase when permeabilized whole cells were used.

Will isomalto-oligosaccharides, a well-established functional food in Asia, break through the European and American market? The status of knowledge on these prebiotics

This critical review article presents the current state of knowledge on isomalto-oligosaccharides, some well known functional oligosaccharides in Asia, to evaluate their potential as emergent prebiotics in the American and European functional food market. It includes first a unique inventory of the different families of compounds which have been considered as IMOs and their specific structure. A description has been given of the different production methods including the involved enzymes and their specific activities, the substrates, and the types of IMOs produced. Considering the structural complexity of IMO products, specific characterization methods are described, as well as purification methods which enable the body to get rid of digestible oligosaccharides. Finally, an extensive review of their techno-functional and nutritional properties enables placing IMOs inside the growing prebiotic market. This review is of particular interest considering that IMO commercialization in America and Europe is a topical subject due to the recent submission by Bioneutra Inc. (Canada) of a novel food file to the UK Food Standards Agency, as well as several patents for IMO production.

Effect of dextransucrase cellobiose acceptor products on the growth of human gut bacteria

The selective fermentation by human gut bacteria of gluco-oligosaccharides obtained from the reaction between the glucosyl group of sucrose and cellobiose, catalyzed by dextransucrases (DSR) from Leuconostoc mesenteroides , has been evaluated. Oligosaccharides were fractionated according to their molecular weight, and their effect on the growth of different bacterial groups was studied. To determine the structure (position and configuration of glycosidic linkages)-function relationship, their properties were compared to those of DSR maltose acceptor products (DSRMal) and of recognized prebiotic carbohydrates (fructo-oligosaccharides, FOS). Cellobiose acceptor products (DSRCel) showed bifidogenic properties similar to those of FOS. However, no significant differences related to molecular weight or isomeric configurations were found for DSRCel and DSRMal products.

Cellulose nanocrystal/gold nanoparticle composite as a matrix for enzyme immobilization

A novel nanocomposite consisting of cellulose nanocrystals (CNCs) functionalized with gold nanoparticles (AuNPs) serving as an excellent support for enzyme immobilization with phenomenally high loading is presented in this work. As testing models, cyclodextrin glycosyl transferase (CGTase) and alcohol oxidase were conjugated on an activated CNC/AuNP matrix. This catalytic platform exhibits significant biocatalytic activity with excellent enzyme stability and without apparent loss of the original activity. The recovered specific activities were approximately 70% and 95% for CGTase and alcohol oxidase, respectively. This novel and inexpensive material is anticipated to extend to other enzymes, enhancing the enzyme loading and activity as well as the stability in both operation and storage.

Structure-function relationship in cyclodextrin glycosyltransferase from Bacillus circulans DF 9R

Cyclodextrin glycosyltransferases (CGTases E.C.2.4.1.19) catalyze cyclomaltooligosaccharides (cyclodextrins) production, an important industrial process. We herein report structural features of Bacillus circulans DF 9R cyclodextrin glycosyltransferase including its sequence and several aspects of enzyme structure-function relationship. Protein ethoxyformylation, under our experimental conditions, indicated that only one out of the 13 enzyme histidines was modified leading to a drastic drop in cyclizing and hydrolytic activity. Besides, tryptic digestion of the (14)C ethoxyformylated protein and studies of the peptide mixture showed that histidine 233 is the most reactive histidine residue. This is the first cyclodextrin glycosyltransferase with a known primary structure and a glutamine instead of glycine residue at position 179 in the highly conserved -6 subsite, shown to be involved in substrate binding. The presence of glycine at that position was considered as a requirement for such binding following the induced-fit mechanism already proposed. Moreover, the enzyme has all the features previously described for an alpha- or alpha/beta-cyclodextrin producer.

Glycosyltransferase-catalyzed synthesis of bioactive oligosaccharides

Mammalian cell surfaces are all covered with bioactive oligosaccharides which play an important role in molecular recognition events such as immune recognition, cell-cell communication and initiation of microbial pathogenesis. Consequently, bioactive oligosaccharides have been recognized as a medicinally relevant class of biomolecules for which the interest is growing. For the preparation of complex and highly pure oligosaccharides, methods based on the application of glycosyltransferases are currently recognized as being the most effective. The present paper reviews the potential of glycosyltransferases as synthetic tools in oligosaccharide synthesis. Reaction mechanisms and selected characteristics of these enzymes are described in relation to the stereochemistry of the transfer reaction and the requirements of sugar nucleotide donors. For the application of glycosyltransferases, accepted substrate profiles are summarized and the whole-cell approach versus isolated enzyme methodology is compared. Sialyltransferase-catalyzed syntheses of gangliosides and other sialylated oligosaccharides are described in more detail in view of the prominent role of these compounds in biological recognition.

Microarray analysis of iron deficiency chlorosis in near-isogenic soybean lines

BACKGROUND

Iron is one of fourteen mineral elements required for proper plant growth and development of soybean (Glycine max L. Merr.). Soybeans grown on calcareous soils, which are prevalent in the upper Midwest of the United States, often exhibit symptoms indicative of iron deficiency chlorosis (IDC). Yield loss has a positive linear correlation with increasing severity of chlorotic symptoms. As soybean is an important agronomic crop, it is essential to understand the genetics and physiology of traits affecting plant yield. Soybean cultivars vary greatly in their ability to respond successfully to iron deficiency stress. Microarray analyses permit the identification of genes and physiological processes involved in soybean's response to iron stress.

RESULTS

RNA isolated from the roots of two near isogenic lines, which differ in iron efficiency, PI 548533 (Clark; iron efficient) and PI 547430 (IsoClark; iron inefficient), were compared on a spotted microarray slide containing 9,728 cDNAs from root specific EST libraries. A comparison of RNA transcripts isolated from plants grown under iron limiting hydroponic conditions for two weeks revealed 43 genes as differentially expressed. A single linkage clustering analysis of these 43 genes showed 57% of them possessed high sequence similarity to known stress induced genes. A control experiment comparing plants grown under adequate iron hydroponic conditions showed no differences in gene expression between the two near isogenic lines. Expression levels of a subset of the differentially expressed genes were also compared by real time reverse transcriptase PCR (RT-PCR). The RT-PCR experiments confirmed differential expression between the iron efficient and iron inefficient plants for 9 of 10 randomly chosen genes examined. To gain further insight into the iron physiological status of the plants, the root iron reductase activity was measured in both iron efficient and inefficient genotypes for plants grown under iron sufficient and iron limited conditions. Iron inefficient plants failed to respond to decreased iron availability with increased activity of Fe reductase.

CONCLUSION

These experiments have identified genes involved in the soybean iron deficiency chlorosis response under iron deficient conditions. Single linkage cluster analysis suggests iron limited soybeans mount a general stress response as well as a specialized iron deficiency stress response. Root membrane bound reductase capacity is often correlated with iron efficiency. Under iron-limited conditions, the iron efficient plant had high root bound membrane reductase capacity while the iron inefficient plants reductase levels remained low, further limiting iron uptake through the root. Many of the genes up-regulated in the iron inefficient NIL are involved in known stress induced pathways. The most striking response of the iron inefficient genotype to iron deficiency stress was the induction of a profusion of signaling and regulatory genes, presumably in an attempt to establish and maintain cellular homeostasis. Genes were up-regulated that point toward an increased transport of molecules through membranes. Genes associated with reactive oxidative species and an ROS-defensive enzyme were also induced. The up-regulation of genes involved in DNA repair and RNA stability reflect the inhospitable cellular environment resulting from iron deficiency stress. Other genes were induced that are involved in protein and lipid catabolism; perhaps as an effort to maintain carbon flow and scavenge energy. The under-expression of a key glycolitic gene may result in the iron-inefficient genotype being energetically challenged to maintain a stable cellular environment. These experiments have identified candidate genes and processes for further experimentation to increase our understanding of soybeans' response to iron deficiency stress.

Synthesis of methyl α-d-glucooligosaccharides by entrapped dextransucrase from Leuconostoc mesenteroides B-1299

The synthesis of methyl alpha-D-glucooligosaccharides, using sucrose as glucosyl donor and methyl alpha-D-glucopyranoside as acceptor, was studied with dextransucrase from Leuconostoc mesenteroides NRRL B-1299. The enzyme was immobilized by entrapment in alginate. By NMR and mass spectrometry we identified three homologous series (S1-S3) of methyl alpha-D-glucooligosaccharides. Series S2 and S3 were characterized by the presence of alpha(1-->2) linkages, in combination with alpha(1-->6) bonds. Two parameters, sucrose to acceptor concentration ratio (S/A) and the total sugar concentration (TSC) determined the yield of methyl alpha-D-glucooligosaccharides. The maximum concentration achieved of the first acceptor product, methyl alpha-D-isomaltoside, was 65 mM using a S/A 1:4 and a TSC of 336 g l(-1). When increasing temperature, a shift of selectivity towards compounds containing alpha(1-->2) bonds was observed. The formation of leucrose as a side process was very significant (reaching values of 32 g l(-1)) at high sucrose concentrations.

A novel alpha-glucosidase from the acidophilic archaeon Ferroplasma acidiphilum strain Y with high transglycosylation activity and an unusual catalytic nucleophile

Ferroplasma acidiphilum strain Y (DSM 12658), a ferrous iron-oxidizing, acidophilic and mesophilic archaeon, was found to produce a membrane-bound alpha-glucosidase (alphaGluFa) showing no significant similarity to any of the known glycoside hydrolases classified in different families and having an unusual catalytic site consisting of a threonine and a histidine residue. The highest alpha-glucosidase activity was found at low pH, 2.4-3.5, and the substrate preference order was: sucrose>maltose>maltotriose >>maltotetraose>>malto-oligosaccharides from maltopentaose to maltoheptaose>>>soluble starch (kcat/K(m) was 293.0, 197.0, 18.8, 0.3 and 0.02 s(-1) x mM(-1) respectively). The enzyme was able to transfer glucosyl groups from maltose as donor, to produce exclusively maltotriose (up to 300 g/l). Chemical modification and electrospray ionization MS analysis of 5-fluoro-alpha-D-glucopyranosyl-enzyme derivatives, coupled with site-directed mutagenesis, strongly suggested that the putative catalytic nucleophile in this enzyme is Thr212. Iron was found to be essential for enzyme activity and integrity, and His390 was shown to be essential for iron binding. These results suggest that the metalloenzyme alphaGluFa is a new member of the glycosyl hydrolase family that uses a novel mechanism for sugar glycosylation and/or transglycosylation.

Dietary fiber as a versatile food component: An industrial perspective

The continued emphasis on the importance of dietary fibers to the Western diet and the need for products with a lower calorific content is pressuring food companies to allocate more resources to the development of fiber-enriched products. The challenge to the industry is to accomplish this goal without sacrificing the organoleptic appeal of some of their core offerings. As future research details specific nutritional benefits of individual components of dietary fiber, food companies will need flexible alternatives in order to validate new 'functional' food claims and to respond rapidly to emerging trends in fiber-enriched products. These objectives will be achieved by understanding the physicochemical basis for the biotechnical functionality of fibers and by developing, and making available fibers which provide a broad spectrum of bioactive and texture modulating properties.

Synthesis and modifications of carbohydrates, using biotransformations

Enzymes continue to be used as important catalysts, for the generation of rare and 'unnatural' monosaccharides and for the selective formation of glycosidic linkages. Multi-enzyme systems have been employed in one-pot strategies for multistep reaction sequences and for co-factor regeneration. The efficiency of glycosidases for glycosylation reactions has been dramatically increased by active-site mutagenesis to generate glycosynthases. First reports have detailed the expansion and optimization of glycosynthase substrate specificity by directed evolution. Novel glycosyltransferases are being identified from genomic databases and have been shown to glycosylate complex metabolites, such as glycopeptide antibiotics, with exquisite selectivity and in good yields. An emerging field is the application of glycosynthases and glycosyltransferases to reactions on solid support, generating potential applications in microarrays.

Safety evaluation of an α-cyclodextrin glycosyltranferase preparation

Alpha-cyclodextrin glucosyltransferase (alpha-CGTase, EC 2.4.1.19) is an amylolytic enzyme used for the production of alpha-cyclodextrin (alpha-CD), a novel, soluble dietary fiber, from food-grade starch. The safety of an alpha-CGTase preparation obtained by batch fermentation from a recombinant strain of Escherichia coli K12 harboring the alpha-CGTase gene from Klebsiella oxytoca strain M5a1 was examined. In a 13-week subchronic toxicity study in rats, the administration by gavage of the alpha-CGTase preparation at levels of up to 20 ml/kg bw/day, corresponding to a total organic solids dosage of 260 mg/kg bw/day, did not cause any systemic toxic effect. Some signs of irritation were observed in the respiratory tract which occurred, however, in one sex only and/or were not dose-related. Accordingly, these changes were considered to be an unspecific consequence of the reflux and aspiration of the dosing solution. There was no evidence of a genotoxic activity in Ames tests and a chromosome aberration test in cultured human lymphocytes. It is concluded that the examined alpha-CGTase preparation is safe when used for the production of alpha-CD.