Biochemistry of Plant Galactomannans. Advances in Carbohydrate Chemistry and Biochemistry Volume 35. Elsevier; 1978. pp. 341-76. [DOI: 10.1016/s0065-2318(08)60221-8]

Guar (Cyamopsis tetragonoloba L.) plant gum: From biological applications to advanced nanomedicine

Natural polymers are an efficient class of eco-friendly and biodegradable polymers, because they are readily available, come from natural sources, inexpensive and can be chemically modified with the correct reagents. Guar gum (GG) is a natural polymer with great potential to be used in pharmaceutical formulations due to its unique composition and lack of toxicity. GG can be designed to suit the needs of the biological and medical engineering sectors. In the development of innovative drug delivery systems, GG is commonly utilized as a rate-controlling excipient. In this review, different properties of GG including chemical composition, extraction methods and its usefulness in diabetes, cholesterol lowering, weight control, tablet formulations as well as its food application were discussed. The other purpose of this study is to evaluate potential use of GG and its derivatives for advanced nanomedicine such as drug delivery, tissue engineering and nanosensing. It should be noted that some applicable patents in medical area have also been included in the rest of this survey to extend knowledge about guar gum and its polymeric nature.

Functional diversity of three tandem C-terminal carbohydrate-binding modules of a β-mannanase

Carbohydrate active enzymes, such as those involved in plant cell wall and storage polysaccharide biosynthesis and deconstruction, often contain repeating noncatalytic carbohydrate-binding modules (CBMs) to compensate for low-affinity binding typical of protein–carbohydrate interactions. The bacterium Saccharophagus degradans produces an endo-β-mannanase of glycoside hydrolase family 5 subfamily 8 with three phylogenetically distinct family 10 CBMs located C-terminally from the catalytic domain (SdGH5_8-CBM10x3). However, the functional roles and cooperativity of these CBM domains in polysaccharide binding are not clear. To learn more, we studied the full-length enzyme, three stepwise CBM family 10 (CBM10) truncations, and GFP fusions of the individual CBM10s and all three domains together by pull-down assays, affinity gel electrophoresis, and activity assays. Only the C-terminal CBM10-3 was found to bind strongly to microcrystalline cellulose (dissociation constant, K_d = 1.48 μM). CBM10-3 and CBM10-2 bound galactomannan with similar affinity (K_d = 0.2–0.4 mg/ml), but CBM10-1 had 20-fold lower affinity for this substrate. CBM10 truncations barely affected specific activity on carob galactomannan and konjac glucomannan. Full-length SdGH5_8-CBM10x3 was twofold more active on the highly galactose-decorated viscous guar gum galactomannan and crystalline ivory nut mannan at high enzyme concentrations, but the specific activity was fourfold to ninefold reduced at low enzyme and substrate concentrations compared with the enzyme lacking CBM10-2 and CBM10-3. Comparison of activity and binding data for the different enzyme forms indicates unproductive and productive polysaccharide binding to occur. We conclude that the C-terminal-most CBM10-3 secures firm binding, with contribution from CBM10-2, which with CBM10-1 also provides spatial flexibility.

Microbial β-mannosidases and their industrial applications

Heteropolymers of mannan are polysaccharide components of the plant cell wall of gymnosperms and some angiosperms, including palm trees (Arecales and Monocot). Degradation of the complex structure of these polysaccharides requires the synergistic action of enzymes that disrupt the internal carbon skeleton of mannan and accessory enzymes that remove side chain substituents. However, complete degradation of these polysaccharides is carried out by an exo-hydrolase termed β-mannosidase. Microbial β-mannosidases belong to families 1, 2, and 5 of glycosyl hydrolases, and catalyze the hydrolysis of non-reducing ends of mannose oligomers. Besides, these enzymes are also involved in transglycosylation reactions. Because of their activity at different temperatures and pH values, these enzymes are used in a variety of industrial applications and the pharmaceutical, food, and biofuel industries.

Mannanase hydrolysis of spruce galactoglucomannan focusing on the influence of acetylation on enzymatic mannan degradation

BACKGROUND

Galactoglucomannan (GGM) is the most abundant hemicellulose in softwood, and consists of a backbone of mannose and glucose units, decorated with galactose and acetyl moieties. GGM can be hydrolyzed into fermentable sugars, or used as a polymer in films, gels, and food additives. Endo-β-mannanases, which can be found in the glycoside hydrolase families 5 and 26, specifically cleave the mannan backbone of GGM into shorter oligosaccharides. Information on the activity and specificity of different mannanases on complex and acetylated substrates is still lacking. The aim of this work was to evaluate and compare the modes of action of two mannanases from Cellvibrio japonicus (CjMan5A and CjMan26A) on a variety of mannan substrates, naturally and chemically acetylated to varying degrees, including naturally acetylated spruce GGM. Both enzymes were evaluated in terms of cleavage patterns and their ability to accommodate acetyl substitutions.

RESULTS

CjMan5A and CjMan26A demonstrated different substrate preferences on mannan substrates with distinct backbone and decoration structures. CjMan5A action resulted in higher amounts of mannotriose and mannotetraose than that of CjMan26A, which mainly generated mannose and mannobiose as end products. Mass spectrometric analysis of products from the enzymatic hydrolysis of spruce GGM revealed that an acetylated hexotriose was the shortest acetylated oligosaccharide produced by CjMan5A, whereas CjMan26A generated acetylated hexobiose as well as diacetylated oligosaccharides. A low degree of native acetylation did not significantly inhibit the enzymatic action. However, a high degree of chemical acetylation resulted in decreased hydrolyzability of mannan substrates, where reduced substrate solubility seemed to reduce enzyme activity.

CONCLUSIONS

Our findings demonstrate that the two mannanases from C. japonicus have different cleavage patterns on linear and decorated mannan polysaccharides, including the abundant and industrially important resource spruce GGM. CjMan26A released higher amounts of fermentable sugars suitable for biofuel production, while CjMan5A, producing higher amounts of oligosaccharides, could be a good candidate for the production of oligomeric platform chemicals and food additives. Furthermore, chemical acetylation of mannan polymers was found to be a potential strategy for limiting the biodegradation of mannan-containing materials.

Extraction, purification and characterization of water soluble galactomannans from Mimosa pudica seeds

Water soluble galactomannans from seed endosperm of Mimosa pudica L. was extracted and characterized (Fig. 1). Nuclear magnetic resonance spectroscopy and Gas Chromatography results revealed the presence of 4-linked mannose backbone with galactose side chains linked at the C6 position. Scanning Electron Micrographs showed smooth, elongated and irregular granular structure of galactomannan. Structural analysis by Attenuated total reflection infrared spectroscopy presented the Mannose to Galactose ratio while the X-ray diffraction studies showed the presences of A-type crystalline pattern of the galactomannan. Thermo Gravitimetric Analysis showed the three steps weight loss event and determined the thermal stability. The results showed that the extracted polysaccharides are typically amorphous, thermally stable and have desirable properties for industrial applications.

Pathogenesis and Inhibition of Flaviviruses from a Carbohydrate Perspective

Flaviviruses are enveloped, positive single stranded ribonucleic acid (RNA) viruses with various routes of transmission. While the type and severity of symptoms caused by pathogenic flaviviruses vary from hemorrhagic fever to fetal abnormalities, their general mechanism of host cell entry is similar. All pathogenic flaviviruses, such as dengue virus, yellow fever virus, West Nile virus, Japanese encephalitis virus, and Zika virus, bind to glycosaminglycans (GAGs) through the putative GAG binding sites within their envelope proteins to gain access to the surface of host cells. GAGs are long, linear, anionic polysaccharides with a repeating disaccharide unit and are involved in many biological processes, such as cellular signaling, cell adhesion, and pathogenesis. Flavivirus envelope proteins are N-glycosylated surface proteins, which interact with C-type lectins, dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) through their glycans. In this review, we discuss both host and viral surface receptors that have the carbohydrate components, focusing on the surface interactions in the early stage of flavivirus entry. GAG-flavivirus envelope protein interactions as well as interactions between flavivirus envelope proteins and DC-SIGN are discussed in detail. This review also examines natural and synthetic inhibitors of flaviviruses that are carbohydrate-based or carbohydrate-targeting. Both advantages and drawbacks of these inhibitors are explored, as are potential strategies to improve their efficacy to ultimately help eradicate flavivirus infections.

Kinetic properties and substrate inhibition of α-galactosidase from Aspergillus niger

The recombinant AglB produced by Pichia pastoris exhibited substrate inhibition behavior for the hydrolysis of p-nitrophenyl α-galactoside, whereas it hydrolyzed the natural substrates, including galactomanno-oligosaccharides and raffinose family oligosaccharides, according to the Michaelian kinetics. These contrasting kinetic behaviors can be attributed to the difference in the dissociation constant of second substrate from the enzyme and/or to the ability of the leaving group of the substrates. The enzyme displays the grater kcat/Km values for hydrolysis of the branched α-galactoside in galactomanno-oligosaccharides than that of raffinose and stachyose. A sequence comparison suggested that AglB had a shallow active-site pocket, and it can allow to hydrolyze the branched α-galactosides, but not linear raffinose family oligosaccharides.

TEMPO-mediated oxidation on galactomannan: Gal/Man ratio and chain flexibility dependence

Guar (GG) and locust bean (LBG) galactomannans (GMs) oxidation at C-6 was performed with catalyst TEMPO, in which the reaction progress was monitored by consume of NaOH solution. The products were characterized by spectroscopic analysis, infrared, and (1)H-nuclear magnetic resonance, confirming the presence of aldehydes groups as intermediate of reaction to carboxylic acid. From high performance anion exchange chromatography with pulsed amperometric detection Man/Gal molar ratio was determined and demonstrated a preference to oxidize Man during the reaction on both GMs, following a first order kinetics of oxidation. The comparative macromolecular behavior of native and oxidized GMs was obtained through the analysis by high performance size exclusion chromatography, and the persistence length (Lp) was 6nm and 4nm to native LBG and GG, respectively. A more accessible OH-6 at mannose residue in LBG could be related with a two times faster reaction than GG. The selective oxidation with catalyst TEMPO proved to be efficient to increase the flexibility of the GMs during oxidation. Short reaction time and β-elimination process were mainly observed to LBG, probably due to a more favorable oxidation access to the polysaccharide main chain.

Guar gum as a promising starting material for diverse applications: A review

Guar gum is the powdered endosperm of the seeds of the Cyamopsis tetragonolobus which is a leguminous crop. The endosperm contains a complex polysaccharide called galactomannan, which is a polymer of d-galactose and d-mannose. This hydroxyl group rich polymer when added to water forms hydrogen bonding imparting significant viscosity and thickening to the solution. Due to its thickening, emulsifying, binding and gelling properties, quick solubility in cold water, wide pH stability, film forming ability and biodegradability, it finds applications in large number of industries. In last few decades a lot of research has been done on guar gum to fit it into particular application, as such or by its structural modifications. This review gives an overview of the nature, chemistry and properties of guar gum and discusses recent developments in its modifications and applications in major industries like hydraulic fracturing, explosives, food, agriculture, textile, paper, cosmetics, bioremediation, drug delivery, medical and pharmaceuticals. This article would help researchers engaged in biopolymer area and other end-users who want to begin research in natural polysaccharides.

Physicochemical and thermomechanical characterization of tara gum edible films: effect of polyols as plasticizers

The aim of this study was to evaluate tara gum as edible film material as well as the influence of polyols as plasticizers on the properties of the films. Thermomechanical, physicochemical and barrier properties were determined as a function of plasticizer type and concentration. Glycerol, sorbitol and PEG 400 were used in the range of 0.075-0.3g/tarag. Glycerol was the best plasticizer in terms of mechanical properties with the highest elongation (16-44%) and resistance (45-90 MPa). Sorbitol presented the best barrier properties with the lowest hydrophilicity and water vapour permeability (0.24-0.34 g mm m(-2)h(-1) kPa(-1)). Fourier transform infrared (FTIR) spectroscopy showed no significant effect on the structure of the polysaccharide. Dynamic mechanical analysis (DMA) revealed that incorporation of plasticizers increased the mobility of the polymer chains and reduced the glass transition and melting temperature by 30 and 100 °C respectively.

Role of glycoside phosphorylases in mannose foraging by human gut bacteria

To metabolize both dietary fiber constituent carbohydrates and host glycans lining the intestinal epithelium, gut bacteria produce a wide range of carbohydrate-active enzymes, of which glycoside hydrolases are the main components. In this study, we describe the ability of phosphorylases to participate in the breakdown of human N-glycans, from an analysis of the substrate specificity of UhgbMP, a mannoside phosphorylase of the GH130 protein family discovered by functional metagenomics. UhgbMP is found to phosphorolyze β-D-Manp-1,4-β-D-GlcpNAc-1,4-D-GlcpNAc and is also a highly efficient enzyme to catalyze the synthesis of this precious N-glycan core oligosaccharide by reverse phosphorolysis. Analysis of sequence conservation within family GH130, mapped on a three-dimensional model of UhgbMP and supported by site-directed mutagenesis results, revealed two GH130 subfamilies and allowed the identification of key residues responsible for catalysis and substrate specificity. The analysis of the genomic context of 65 known GH130 sequences belonging to human gut bacteria indicates that the enzymes of the GH130_1 subfamily would be involved in mannan catabolism, whereas the enzymes belonging to the GH130_2 subfamily would rather work in synergy with glycoside hydrolases of the GH92 and GH18 families in the breakdown of N-glycans. The use of GH130 inhibitors as therapeutic agents or functional foods could thus be considered as an innovative strategy to inhibit N-glycan degradation, with the ultimate goal of protecting, or restoring, the epithelial barrier.

Populus endo-beta-mannanase PtrMAN6 plays a role in coordinating cell wall remodeling with suppression of secondary wall thickening through generation of oligosaccharide signals

Endo-1,4-β-mannanase is known to able to hydrolyze mannan-type polysaccharides in cell wall remodeling, but its function in regulating wall thickening has been little studied. Here we show that a Populus endo-1,4-β-mannanase gene, named PtrMAN6, suppresses cell wall thickening during xylem differentiation. PtrMAN6 is expressed specifically in xylem tissue and its encoded protein localizes to developing vessel cells. Overexpression of PtrMAN6 enhanced wall loosening as well as suppressed secondary wall thickening, whilst knockdown of its expression promoted secondary wall thickening. Transcriptional analysis revealed that PtrMAN6 overexpression downregulated the transcriptional program of secondary cell wall thickening, whilst PtrMAN6 knockdown upregulated transcriptional activities toward secondary wall formation. Activity of PtrMAN6 hydrolysis resulted in the generation of oligosaccharide compounds from cell wall polysaccharides. Application of the oligosaccharides resulted in cellular and transcriptional changes that were similar to those found in PtrMAN6 overexpressed transgenic plants. Overall, our results demonstrated that PtrMAN6 plays a role in hydrolysis of mannan-type wall polysaccharides to produce oligosaccharides that may serve as signaling molecules to suppress cell wall thickening during wood xylem cell differentiation.

Dietary roles of non-starch polysaccharides in human nutrition: a review

Nonstarch polysaccharides (NSPs) occur naturally in many foods. The physiochemical and biological properties of these compounds correspond to dietary fiber. Nonstarch polysaccharides show various physiological effects in the small and large intestine and therefore have important health implications for humans. The remarkable properties of dietary NSPs are water dispersibility, viscosity effect, bulk, and fermentibility into short chain fatty acids (SCFAs). These features may lead to diminished risk of serious diet related diseases which are major problems in Western countries and are emerging in developing countries with greater affluence. These conditions include coronary heart disease, colo-rectal cancer, inflammatory bowel disease, breast cancer, tumor formation, mineral related abnormalities, and disordered laxation. Insoluble NSPs (cellulose and hemicellulose) are effective laxatives whereas soluble NSPs (especially mixed-link β-glucans) lower plasma cholesterol levels and help to normalize blood glucose and insulin levels, making these kinds of polysaccharides a part of dietary plans to treat cardiovascular diseases and Type 2 diabetes. Moreover, a major proportion of dietary NSPs escapes the small intestine nearly intact, and is fermented into SCFAs by commensal microflora present in the colon and cecum and promotes normal laxation. Short chain fatty acids have a number of health promoting effects and are particularly effective in promoting large bowel function. Certain NSPs through their fermented products may promote the growth of specific beneficial colonic bacteria which offer a prebiotic effect. Various modes of action of NSPs as therapeutic agent have been proposed in the present review. In addition, NSPs based films and coatings for packaging and wrapping are of commercial interest because they are compatible with several types of food products. However, much of the physiological and nutritional impact of NSPs and the mechanism involved is not fully understood and even the recommendation on the dose of different dietary NSPs intake among different age groups needs to be studied.

An overview of mannan structure and mannan-degrading enzyme systems

Hemicellulose is a complex group of heterogeneous polymers and represents one of the major sources of renewable organic matter. Mannan is one of the major constituent groups of hemicellulose in the wall of higher plants. It comprises linear or branched polymers derived from sugars such as D-mannose, D-galactose, and D-glucose. The principal component of softwood hemicellulose is glucomannan. Structural studies revealed that the galactosyl side chain hydrogen interacts to the mannan backbone intramolecularly and provides structural stability. Differences in the distribution of D-galactosyl units along the mannan structure are found in galactomannans from different sources. Acetyl groups were identified and distributed irregularly in glucomannan. Some of the mannosyl units of galactoglucomannan are partially substituted by O-acetyl groups. Some unusual structures are found in the mannan family from seaweed, showing a complex system of sulfated structure. Endohydrolases and exohydrolases are involved in the breakdown of the mannan backbone to oligosaccharides or fermentable sugars. The main-chain mannan-degrading enzymes include beta-mannanase, beta-glucosidase, and beta-mannosidase. Additional enzymes such as acetyl mannan esterase and alpha-galactosidase are required to remove side-chain substituents that are attached at various points on mannan, creating more sites for subsequent enzymatic hydrolysis. Mannan-degrading enzymes have found applications in the pharmaceutical, food, feed, and pulp and paper industries. This review reports the structure of mannans and some biochemical properties and applications of mannan-degrading enzymes.

Galactoglucomannans increase cell population density and alter the protoxylem/metaxylem tracheary element ratio in xylogenic cultures of Zinnia

Xylogenic cultures of zinnia (Zinnia elegans) provide a unique opportunity to study signaling pathways of tracheary element (TE) differentiation. In vitro TEs differentiate into either protoxylem (PX)-like TEs characterized by annular/helical secondary wall thickening or metaxylem (MX)-like TEs with reticulate/scalariform/pitted thickening. The factors that determine these different cell fates are largely unknown. We show here that supplementing zinnia cultures with exogenous galactoglucomannan oligosaccharides (GGMOs) derived from spruce (Picea abies) xylem had two major effects: an increase in cell population density and a decrease in the ratio of PX to MX TEs. In an attempt to link these two effects, the consequence of the plane of cell division on PX-MX differentiation was assessed. Although GGMOs did not affect the plane of cell division per se, they significantly increased the proportion of longitudinally divided cells differentiating into MX. To test the biological significance of these findings, we have determined the presence of mannan-containing oligosaccharides in zinnia cultures in vitro. Immunoblot assays indicated that beta-1,4-mannosyl epitopes accumulate specifically in TE-inductive media. These epitopes were homogeneously distributed within the thickened secondary walls of TEs when the primary cell wall was weakly labeled. Using polysaccharide analysis carbohydrate gel electrophoresis, glucomannans were specifically detected in cell walls of differentiating zinnia cultures. Finally, zinnia macroarrays probed with cDNAs from cells cultured in the presence or absence of GGMOs indicated that significantly more genes were down-regulated rather than up-regulated by GGMOs. This study constitutes a major step in the elucidation of signaling mechanisms of PX- and MX-specific genetic programs in zinnia.

Plant glycoside hydrolases involved in cell wall polysaccharide degradation

The cell wall plays a key role in controlling the size and shape of the plant cell during plant development and in the interactions of the plant with its environment. The cell wall structure is complex and contains various components such as polysaccharides, lignin and proteins whose composition and concentration change during plant development and growth. Many studies have revealed changes in cell walls which occur during cell division, expansion, and differentiation and in response to environmental stresses; i.e. pathogens or mechanical stress. Although many proteins and enzymes are necessary for the control of cell wall organization, little information is available concerning them. An important advance was made recently concerning cell wall organization as plant enzymes that belong to the superfamily of glycoside hydrolases and transglycosidases were identified and characterized; these enzymes are involved in the degradation of cell wall polysaccharides. Glycoside hydrolases have been characterized using molecular, genetic and biochemical approaches. Many genes encoding these enzymes have been identified and functional analysis of some of them has been performed. This review summarizes our current knowledge about plant glycoside hydrolases that participate in the degradation and reorganisation of cell wall polysaccharides in plants focussing particularly on those from Arabidopsis thaliana.

A novel xyloglucan from seeds of Afzelia africana Se. Pers.—extraction, characterization, and conformational properties

This paper is the first multi-scale characterization of the xyloglucan extracted from seeds of the African tree Afzelia africana Se. Pers. It describes the extraction and characterization of this polysaccharide in terms of both primary monosaccharide and oligosaccharide composition. It also includes a study of the seed morphology. Morphological characterization includes optical, transmission, and scanning electron microscopy. The polysaccharide exists in thickened cell walls of the cotyledonary cells, and the extracted xyloglucan is structurally quite similar to those from tamarind seed and detarium. Nevertheless there are some subtle differences in the fine structure, particularly in the oligomeric xyloglucan composition. The chain flexibility of the polysaccharide is also discussed in the light of our recent measurements reported elsewhere [Biomacromolecules2004, 5, 2384-2391].

In vitro and in vivo antiviral properties of sulfated galactomannans against yellow fever virus (BeH111 strain) and dengue 1 virus (Hawaii strain)

Two galactomannans, one extracted from seeds of Mimosa scabrella, having a mannose to galactose ratio of 1.1, and another with a 1.4 ratio from seeds of Leucaena leucocephala, were sulfated. The products from M. scabrella (BRS) and L. leucocephala (LLS) had a degree of sulfation of 0.62 and 0.50, and an average molecular weight of 620x10(3) and 574x10(3) gmol(-1), respectively. Their activities against yellow fever virus (YFV; BeH111 strain) and dengue 1 virus (DEN-1; Hawaii strain) were evaluated. This was carried out in young mice following intraperitoneal infection with YFV. At a dose of 49 mgkg(-1), BRS and LLS gave protection against death in 87.7 and 96.5% of the mice, respectively. When challenged with 37.5 LD50 of YFV, mice previously inoculated with BRS+virus or LLS+virus, showed 93.3 and 100% resistance, respectively, with neutralization titers similar to mice injected with 25 LD50 of formaldehyde-inactivated YFV. In vitro experiments with YFV and DEN-1 in C6/36 cell culture assays in 24-well microplates showed that concentrations that produced a 100-fold decrease in virus titer of YFV were 586 and 385 mgl(-1) for BRS and LLS, respectively. For DEN-1 they were 347 and 37 mgl(-1), respectively. Sulfated galactomannans, thus demonstrate in vitro and in vivo activity against flaviviruses.

Purification and characterization of alpha-galactosidase from a thermophilic fungus Thermomyces lanuginosus

An extracellular alpha-galactosidase was purified to electrophoretic homogeneity from a locust bean gum-spent culture fluid of a mannanolytic strain of the thermophilic fungus Thermomyces lanuginosus. Molecular mass of the enzyme is 57 kDa. The pure enzyme which has a glycoprotein nature, afforded several forms on IEF, indicating its microheterogeneity. Isoelectric point of the major form was 5.2. Enzyme is the most active against aryl alpha-D-galactosides but efficiently hydrolyzed alpha-glycosidically linked non-reducing terminal galactopyranosyl residues occurring in natural substrates such as melibiose, raffinose, stachyose, and fragments of galactomannan. In addition, the enzyme is able to catalyze efficient degalactosylation of polymeric galactomannans leading to precipitation of the polymers. Stereochemical course of hydrolysis of two substrates, 4-nitrophenyl alpha-galactopyranoside and galactosyl(1)mannotriose, followed by (1)H NMR spectroscopy, pointed out the alpha-anomer of D-galactose was the primary product of hydrolysis from which the beta-anomer was formed by mutarotation. Hence the enzyme is a retaining glycosyl hydrolase. In accord with its retaining character the enzyme catalyzed transgalactosylation from 4-nitrophenyl alpha-galactopyranoside as a glycosyl donor. Amino acid sequence alignment of N-terminal and two internal sequences suggested that the enzyme is a member of family 27 of glycosyl hydrolases.

A water-soluble galactomannan from the seeds of Phoenix dactylifera L

A water-soluble polysaccharide, isolated from the seeds of dates, has been investigated using methylation, periodate and CrO(3) oxidation, NMR spectroscopy, and reaction with Bandeiraea simplicifolia lectin and alpha-D-galactosidase. The polysaccharide consists of a backbone composed of (1-->4)-beta-D-mannopyranosyl residues and carries a single (1-->6)-alpha-linked D-galactopyranosyl residue.

Real-time monitoring of enzymatic hydrolysis of galactomannans

Enzymatic hydrolysis was monitored in real-time using time dependent static light scattering (TDSLS) for a variety of galactomannans from native Brazilian flora. alpha-Galactosidase, which strips only the (1-6)alpha-D galactose side groups, and beta-mannanase, which hydrolyses only the (1-4)beta-D mannan main chain into oligosaccharides were investigated separately and in combination. The time-dependent signatures matched those describing side-chain stripping for galactosidase, whereas those resulting from the action of mannanase followed the signature typical of random backbone cleavage. Use of both enzymes together required that the TDSLS theory of polymer degradation be extended to the case where random backbone cleavage sites appear as side chains are stripped by the first enzyme. Whereas galactosidase allowed mannanase to access more backbone cleavage sites as time passes, leading to a higher degree of hydrolysis, there was no increase in rate constants. The distribution of random fragments in the case of mannanase digestion alone followed reasonably well the predictions for random cleavage of a single-strand polymer with a restricted number of cleavage sites. The fragment distributions were evaluated by size exclusion chromatography.

On the galactosyl distribution of commercial galactomannans

A simple method was developed that enabled the enzymatic determination of the galactose distribution in galactomannans. endo-Mannanase of Aspergillus niger was used to degrade the galactomannan polymers and the degradation products were determined with high-performance anion-exchange chromatography. A whole range of commercial high-to-low substituted galactomannans was analyzed in this way. It was found that differences in the anion-exchange chromatograms reflected dissimilarities in the distribution of galactose and could be used directly to discern these dissimilarities. The differences among the various elution profiles were used to construct a similarity distance tree. In addition to this approach, the absolute amount of non-substituted mannose released by the enzyme was found to be a good discriminating factor. In this way, galactomannans with regular, blockwise, and randomly distributed galactose could be discerned. All guars and the highly substituted gum of Prosopis juliflora were found to have a blockwise distribution of galactose. For different batches of tara gum both random and blockwise distributions were found. Among batches of locust bean gum the greatest variation was observed: both random, blockwise, and ordered galactose distributions were present. Cassia gum was found to have a highly regular distribution of galactose.

Digestion of single crystals of mannan I by an endo-mannanase from Trichoderma reesei

The enzymatic degradation of single crystals of mannan I with the catalytic core domain of a beta-mannanase (EC 3.2.1.78 or Man5A) from Trichoderma reesei was investigated by transmission electron microscopy and electron diffraction. The enzyme attack took place at the edge of the crystals and progressed towards their centres. Quite remarkably the crystalline integrity of the crystals was preserved almost to the end of the digestion process. This behaviour is consistent with an endo-mechanism, where the enzyme interacts with the accessible mannan chains located at the crystal periphery and cleaves one mannan molecule at a time. The endo mode of digestion of the crystals was confirmed by an analysis of the soluble degradation products.

Role of galactomannan composition on the binary gel formation with xanthan

The influence of the galactomannan characteristic ratios (M/G) on the temperature of gelation (Tg) and the gel strength of mixtures of galactomannan with xanthan is reported. Two galactomannans were investigated: one highly substituted from the seeds of Mimosa scabrella (M/G = 11), and the other, less substituted, from the endosperm of Schizolobium parahybae, with (M/G = 30) [Ganter JLMS, Zawadzki-Baggio SF, Leitner SC, Sierakowski MR, Reicher F. J Carbohydr Chem 1993;12:753]. The xanthan:galactomannan systems (4:2 g l(-1), in 5 mM NaCl) showed a temperature of gel formation (Tg) of 24 degrees C for that of S. parahybae [Bresolin TMB, Milas M, Rinaudo M and Ganter JLMS. Int J Biol Macromol 1998;23:263] and 20 degrees C for the galactomannan of M. scabrella, determined by viscoelastic measurements and microcalorimetry. A Tg of 40-50 degrees C was found by Shatwell et al. [Shatwell KP, Sutherland IW, Ross-Murphy SB, Dea ICM. Carbohydr Polym 1991;14:29] for locust bean gum-LBG (M/G = 43). Lundin and Hermansson [Lundin L, Hermansson AM. Carbohydr Polym 1995;26:129] reported a difference of 13 degrees C for Tg of two LBG samples with M/G = 3 (40 degrees C) and 5 (53 degrees C), in mixtures with xanthan. It appears that the more substituted galactomannans have lower temperatures of gelation in the presence of xanthan. The mechanism of gelation depends also on the M/G ratio. For the lower values it involves only disordered xanthan chains in contrast to M/G ratios higher than 3. In addition, the presence of the galactomannan from M. scabrella increased slightly the temperature of the conformational change (Tm) of xanthan probably due to the ionic strength contribution of proteins (3.9%) present in the galactomannan. On the other hand, the galactomannans from S. parahybae, with 1.5% of proteins and M. scabrella, with 2.4% of protein, did not show this effect, the Tm of xanthan alone or in a mixture being practically unchanged.

Hydrolytic properties of a beta-mannosidase purified from Aspergillus niger

A beta-mannosidase was purified to homogeneity from the culture filtrate of Aspergillus niger. A specific activity of 500 nkat mg-1 and a 53-fold purification was achieved using ammonium sulfate precipitation, anion-exchange chromatography, and gel filtration. The isolated enzyme has an isoelectric point of 5.0 and appears to be a dimer composed of two 135-kDa subunits. It is a glycoprotein and contains 17% N-linked carbohydrate by weight. Maximal activity was observed at pH 2.4 5.0 and at 70 degrees C. The beta-mannosidase hydrolyzed beta-1,4-linked manno-oligosaccharides of degree of polymerization (DP) 2-6 and also released mannose from polymeric ivory nut mannan and galactomannan. The Km and Vmax values for p-nitrophenyl-beta-D-mannopyranoside were 0.30 mM and 500 nkat mg-1, respectively. Hydrolysis of D-galactose substituted manno-oligosaccharides showed that the beta-mannosidase was able to cleave up to, but not beyond, a side group. An internal peptide sequence of 15 amino acids was highly similar to that of an Aspergillus aculeatus beta-mannosidase belonging to family 2 of glycosyl hydrolases.

Hybrid affinity chromatography of alpha-galactosidase from Verbascum thapsus L

Purification of alpha-galactosidase from the roots of Verbascum thapsus L. was difficult to achieve using conventional methods due to the presence of coloured contaminants. A newly developed procedure, hybrid affinity chromatography, which was based on a mixed matrix separation procedure, using a substrate analogue and an immobilized metal affinity matrix as ligands, respectively, allowed the purification of this enzyme with good recovery. The method should be applicable to other proteins as well.

Substrate specificities of alpha-galactosidases from yeasts

Twenty-nine strains of yeasts, which are capable of using galactose, melibiose, or raffinose, were screened for alpha-galactosidase production. Among the strains, 5 produced intracellular and extracellular alpha-galactosidases, and 2 produced only intracellular enzyme. Substrate specificities of these enzymes were explored using 6(3)-alpha-D-galactosyl-1,4-beta-D-mannotriose and 6(3)-alpha-D-galactosyl-1,4-beta-D-mannotetraose. All enzymes liberated the terminal galactose from 6(3)-alpha-D-galactosyl-1,4-beta-D-mannotriose, but did not the stub galactose from 6(3)-alpha-D-galactosyl-1,4-beta-D-mannotetraose.

Microorganisms and enzymes involved in the degradation of plant fiber cell walls

One of natures most important biological processes is the degradation of lignocellulosic materials to carbon dioxide, water and humic substances. This implies possibilities to use biotechnology in the pulp and paper industry and consequently, the use of microorganisms and their enzymes to replace or supplement chemical methods is gaining interest. This chapter describes the structure of wood and the main wood components, cellulose, hemicelluloses and lignins. The enzyme and enzyme mechanisms used by fungi and bacteria to modify and degrade these components are described in detail. Techniques for how to assay for these enzyme activities are also described. The possibilities for biotechnology in the pulp and paper industry and other fiber utilizing industries based on these enzymes are discussed.

Evolution and kinetics of monosaccharides, disaccharides and alpha-galactosides during germination of lentils

The effect of light and seed rinsing during the germination of lentil seeds (Lens culinaris var. vulgaris, cultivar Magda-20) on the level of monosaccharides, disaccharides and alpha-galactosides (raffinose, ciceritol and stachyose) was investigated. The total soluble sugar content corresponded to about 9% of the mature seed weight, about 65% of which was alpha-galactosides. Germination brought about a large decrease in alpha-galactosides: 18% to 40% losses after 3 days and 100% after 6 days. However, glucose, which was not detected in ungerminated seeds, as well as fructose and sucrose gradually increased during germination. The content of alpha-galactosides decreased more rapidly when germinating seeds were given 6 h light per day, but under these conditions there was also a major reduction in the levels of fructose, glucose and sucrose. Seeds rinsed daily showed a greater reduction of alpha-galactosides and an increase in the levels of fructose, glucose and sucrose. When seeds were germinated for 10 days in the dark with daily rinsing, the content of alpha-galactosides decreased gradually during the first 4 days and they were not detected after 6 days. Under these conditions, fructose, glucose and sucrose, which represented about 3% of the mature seed weight, started increasing after day 2 and represented more than 13% of the germinated seed dry weight after 10 days.