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Galactomannan (Guar; Medium Viscosity)

Galactomannan Guar Medium Viscosity P-GGMMV
Product code: P-GGMMV
€155.00

4 g

Prices exclude VAT

Available for shipping

Content: 4 g
Shipping Temperature: Ambient
Storage Temperature: Ambient
Physical Form: Powder
Stability: > 10 years under recommended storage conditions
CAS Number: 11078-30-1
Source: Guar
Molecular Weight: 380,000
Purity: > 98%
Viscosity: 8 dL/g
Monosaccharides (%): Galactose: Mannose = 38: 62
Main Chain Glycosidic Linkage: β-1,4 and α-1,6
Substrate For (Enzyme): endo-1,4-β-Mannanase

High purity Galactomannan (Guar; Medium Viscosity) for use in research, biochemical enzyme assays and in vitro diagnostic analysis.

Documents
Certificate of Analysis
Safety Data Sheet
Booklet
Publications
Megazyme publication
Galactomannan changes in developing Gleditsia Triacanthos Seeds.

Mallett, I., McCleary, B. V. & Matheson, N. K. (1987). Phytochemistry, 26(7), 1889-1894.

Galactomannan has been extracted from the endosperm of seeds of Gleditsia triacanthos (honey locust) at different stages of development, when the seed was accumulating storage material. Properties of the different samples have been studied. The molecular size distribution became more disperse as galactomannan accumulated and the galactose: mannose ratio decreased slightly. Some possible reasons for these changes are discussed.

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Megazyme publication
Effect of galactose-substitution-patterns on the interaction properties of galactomannas.

Dea, I. C. M., Clark, A. H. & McCleary, B. V. (1986). Carbohydrate Research, 147(2), 275-294.

A range of galactomannans varying widely in the contents of D-galactose have been compared for self-association and their interaction properties with agarose and xanthan. Whereas, in general, the most interactive galactomannans are those in which the (1→4)-β-D-mannan chain is least substituted by α-D-galactosyl stubs, evidence is presented which indicates that the distribution of D-galactosyl groups along the backbone (fine structure) can have a significant effect on the interaction properties. For galactomannans containing <30% of D-galactose, those which contain a higher frequency of unsubstituted blocks of intermediate length in the β-D-mannan chain are most interactive. For galactomannans containing >40% of D-galactose, those which contain a higher frequency of exactly alternating regions in the β-D-mannan chain are most interactive. This selectivity, on the basis of galactomannan fine-structure, in mixed polysaccharide interactions in vitro could mimic the selectivity of binding of branched plant-cell-wall polysaccharides in biological systems.

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Megazyme publication

Effect of the molecular fine structure of galactomannans on their interaction properties - the role of unsubstituted sides.

Dea, I. C. M., Clark, A. H. & McCleary, B. V. (1986). Food Hydrocolloids, 1(2), 129-140.

A range of galactomannans varying widely in the content of D-galactose have been compared for self-association, and their interaction properties with agarose and xanthan. The results presented indicate that in general the most interactive galactomannans are those in which the D-mannan main chain bears fewest D-galactose stubs, and confirm that the distribution of D-galactose groups along the main chain can have a significant effect on the interactive properties of the galactomannans. It has been shown that freeze — thaw precipitation of galactomannans requires regions of totally unsubstituted D-mannose residues along the main chain, and that a threshold for significant freeze — thaw precipitation occurs at a weight-average length of totally unsubstituted residues of approximately six. For galactomannans having structures above this threshold their interactive properties with other polysaccharides are controlled by structural features associated with totally unsubstituted regions of the D-mannan backbone. In contrast, for galactomannans below this threshold, their interactive properties are controlled by structural features associated with unsubstituted sides of D-mannan backbone.

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Megazyme publication
The fine structures of carob and guar galactomannans.

McCleary, B. V., Clark, A. H., Dea, I. C. M. & Rees, D. A. (1985). Carbohydrate Research, 139, 237-260.

The distribution of D-galactosyl groups along the D-mannan backbone (fine structure) of carob and guar galactomannans has been studied by a computer analysis of the amounts and structures of oligosaccharides released on hydrolysis of the polymers with two highly purified β-D-mannanases isolated from germinated guar seed and from Aspergillus niger cultures. Computer programmes were developed which accounted for the specific subsite-binding requirements of the β-D-mannanases and which simulated the synthesis of galactomannan by processes in which the D-galactosyl groups were transferred to the growing D-mannan chain in either a statistically random manner or as influenced by nearest-neighbour/second-nearest-neighbour substitution. Such a model was chosen as it is consistent with the known pattern of synthesis of similar polysaccharides, for example, xyloglucan; also, addition to a preformed mannan chain would be unlikely, due to the insoluble nature of such polymers. The D-galactose distribution in carob galactomannan and in the hot- and cold-water-soluble fractions of carob galactomannan has been shown to be non-regular, with a high proportion of substituted couplets, lesser amounts of triplets, and an absence of blocks of substitution. The probability of sequences in which alternate D-mannosyl residues are substituted is low. The probability distribution of block sizes for unsubstituted D-mannosyl residues indicates that there is a higher proportion of blocks of intermediate size than would be present in a galactomannan with a statistically random D-galactose distribution. Based on the almost identical patterns of amounts of oligosaccharides produced on hydrolysis with β-D-mannanase, it appears that galactomannans from seed of a wide range of carob varities have the same fine-structure. The D-galactose distribution in guar-seed galactomannan also appears to be non-regular, and galactomannans from different guar-seed varieties appear to have the same fine-structure.

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Megazyme publication
β-D-mannosidase from Helix pomatia.

McCleary, B. V. (1983). Carbohydrate Research, 111(2), 297-310.

β-D-Mannosidase (β-D-mannoside mannohydrolase EC 3.2.1.25) was purified 160-fold from crude gut-solution of Helix pomatia by three chromatographic steps and then gave a single protein band (mol. wt. 94,000) on SDS-gel electrophoresis, and three protein bands (of almost identical isoelectric points) on thin-layer iso-electric focusing. Each of these protein bands had enzyme activity. The specific activity of the purified enzyme on p-nitrophenyl β-D-mannopyranoside was 1694 nkat/mg at 40° and it was devoid of α-D-mannosidase, β-D-galactosidase, 2-acet-amido-2-deoxy-D-glucosidase, (1→4)-β-D-mannanase, and (1→4)-β-D-glucanase activities, almost devoid of α-D-galactosidase activity, and contaminated with <0.02% of β-D-glucosidase activity. The purified enzyme had the same Km for borohydride-reduced β-D-manno-oligosaccharides of d.p. 3-5 (12.5mM). The initial rate of hydrolysis of (1→4)-linked β-D-manno-oligosaccharides of d.p. 2-5 and of reduced β-D-manno-oligosaccharides of d.p. 3-5 was the same, and o-nitrophenyl, methylumbelliferyl, and naphthyl β-D-mannopyranosides were readily hydrolysed. β-D-Mannobiose was hydrolysed at a rate ~25 times that of 61-α-D-galactosyl-β-D-mannobiose and 63-α-D-galactosyl-β-D-mannotetraose, and at ~90 times the rate for β-D-mannobi-itol.

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Megazyme publication
Enzymic interactions in the hydrolysis of galactomannan in germinating guar: The role of exo-β-mannanase.

McCleary, B. V. (1983). Phytochemistry, 22(3), 649-658.

Hydrolysis of galactomannan in endosperms of germinating guar is due to the combined action of three enzymes, α-galactosidase, β-mannanase and exo-β-mannanase. α-Galactosidase and exo-β-mannanase activities occur both in endosperm and cotyledon tissue but β-mannanase occurs only in endosperms. On seed germination, β-mannanase and endospermic α-galactosidase are synthesized and activity changes parallel galactomannan degradation. Galactomannan degradation and synthesis of these two enzymes are inhibited by cycloheximide. In contrast, endospermic exo-β-mannanase is not synthesized on seed germination, but rather is already present throughout endosperm tissue. It has no action on native galactomannan. α-Galactosidase, β-mannanase and exo-β-mannanase have been purified to homogeneity and their separate and combined action in the hydrolysis of galactomannan and effect on the rate of uptake of carbohydrate by cotyledons, studied. Results obtained indicated that these three activities are sufficient to account for galactomannan degradation in vivo and, further, that all three are required. Cotyledons contain an active exo-β-mannanase and sugar-uptake experiments have shown that cotyledons can absorb mannobiose intact, indicating that this enzyme is involved in the complete degradation of galactomannan on seed germination.

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Megazyme publication
Characterisation of the oligosaccharides produced on hydrolysis of galactomannan with β-D-mannase.

McCleary, B. V., Nurthen, E., Taravel, F. R. & Joseleau, J. P. (1983). Carbohydrate Research, 118, 91-109.

Treatment of hot-water-soluble carob galactomannan with β-D-mannanases from A. niger or lucerne seed affords an array of D-galactose-containing β-D-mannosaccharides as well as β-D-manno-biose, -triose, and -tetraose (lucerne-seed enzyme only). The D-galactose-containing β-D-mannosaccharides of d.p. 3–9 produced by A. niger β-D-mannanase have been characterised, using enzymic, n.m.r., and chemical techniques, as 61-α-D-galactosyl-β-D-mannobiose, 61-α-D-galactosyl-β-D-mannotriose, 63,64-di-α-D-galactosyl-β-D-mannopentaose (the only heptasaccharide), and 63,64-di-α-D-galactosyl-β-D-mannohexaose, 64,65-di-α-D-galactosyl-β-D-mannohexaose, and 61, 63,64-tri-α-D-galactosyl-β-D-mannopentaose (the only octasaccharides). Four nonasaccharides have also been characterised. Penta- and hexa-saccharides were absent. Lucerne-seed β-D-mannanase produced the same branched tri-, tetra- and hepta-saccharides, and also penta- and hexa-saccharides that were characterised as 61-α-D-galactosyl-β-D-mannotetraose, 63-α-D-galactosyl-β-D-mannotetraose, 61,63-di-α-D-galactosyl-β-D-mannotetraose, 63-α-D-galactosyl-β-D-mannopentaose, and 64-α-D-galactosyl-β-D-mannopentaose. None of the oligosaccharides contained a D-galactose stub on the terminal D-mannosyl group nor were they substituted on the second D-mannosyl residue from the reducing terminal.

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Megazyme publication
Action patterns and substrate-binding requirements of β-D-mannanase with mannosaccharides and mannan-type polysaccharides.

McCleary, B. V. & Matheson, N. K. (1983). Carbohydrate Research, 119, 191-219.

Purified (1→4)-β-D-mannanase from Aspergillus niger and lucerne seeds has been incubated with mannosaccharides and end-reduced (1→4)-β-D-mannosaccharides and, from the products of hydrolysis, a cyclic reaction-sequence has been proposed. From the heterosaccharides released by hydrolysis of the hot-water-soluble fraction of carob galactomannan by A. niger β-D-mannanase, a pattern of binding between the β-D-mannan chain and the enzyme has been deduced. The products of hydrolysis with the β-D-mannanases from Irpex lacteus, Helix pomatia, Bacillus subtilis, and lucerne and guar seeds have also been determined, and the differences from the action of A. niger β-D-mannanase related to minor differences in substrate binding. The products of hydrolysis of glucomannan are consistent with those expected from the binding pattern proposed from the hydrolysis of galactomannan.

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Megazyme publication
Purification and properties of a β-D-mannoside mannohydrolase from guar.

McCleary, B. V. (1982), Carbohydrate Research, 101(1), 75-92.

A β-D-mannoside mannohydrolase enzyme has been purified to homogeneity from germinated guar-seeds. Difficulties associated with the extraction and purification appeared to be due to an interaction of the enzyme with other protein material. The purified enzyme hydrolysed various natural and synthetic substrates, including β-D-manno-oligosaccharides and reduced β-D-manno-oligosaccharides of degree of polymerisation 2 to 6, as well as p-nitrophenyl, naphthyl, and methylumbelliferyl β-D-mannopyranosides. The preferred, natural substrate was β-D-mannopentaose, which was hydrolysed at twice the rate of β-D-mannotetraose and five times the rate of β-D-mannotriose. This result, together with the observation that α-D-mannose is released on hydrolysis, indicates that the enzyme is an exo-β-D-mannanase.

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Megazyme publication
Preparative–scale isolation and characterisation of 61-α-D-galactosyl-(1→4)-β-D-mannobiose and 62-α-D-galactosyl-(1→4)-β-D-mannobiose.

McCleary, B. V., Taravel, F. R. & Cheetham, N. W. H. (1982). Carbohydrate Research, 104(2), 285-297.

N.m.r., enzymic, and chemical techniques have been used to characterise the D-galactose-containing tri- and tetra-saccharides produced on hydrolysis of carob and L. leucocephala D-galacto-D-mannans by Driselase β-D-mannanase. These oligosaccharides were shown to be exclusively 61-α-D-galactosyl-β-D-mannobiose and 61-α-D-galactosyl-β-D-mannotriose. Furthermore, these were the only D-galactose-containing tri- and tetra-saccharides produced on hydrolysis of carob D-galacto-D-mannan by β-D-mannanases from other sources, including Bacillus subtilis, Aspergillus niger, Helix pomatia gut solution, and germinated legumes. Acid hydrolysis of lucerne galactomannan yielded 61-α-D-galactosyl-β-D-mannobiose and 62-α-D-galactosyl-β-D-mannobiose.

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Megazyme publication

An enzymic technique for the quantitation of galactomannan in guar Seeds.

McCleary, B. V. (1981). Lebensmittel-Wissenschaft & Technologie, 14, 56-59.

An enzymic technique has been developed for the rapid and accurate quantitation of the galactomannan content of guar seeds and milling fractions. The technique involves the measurement of the galactose component of galactomannans using galactose dehydrogenase. The galactomannans are converted to galactose and manno-oligosaccharides using partially purified enzymes from a commercial preparation and from germinated guar seeds. Simple procedures have been devised for the preparation of these enzymes. Application of the technique to a number of guar varieties gave values for the galactomannan content ranging from 22.7 to 30.8% of seed weight.

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Megazyme publication
Modes of action of β-mannanase enzymes of diverse origin on legume seed galactomannans.

McCleary, B. V. (1979). Phytochemistry, 18(5), 757-763.

β-Mannanase activities in the commercial enzyme preparations Driselase and Cellulase, in culture solutions of Bacillus subtilis (TX1), in commercial snail gut (Helix pomatia) preparations and in germinated seeds of lucerne, Leucaena leucocephala and honey locust, have been purified by substrate affinity chromatography on glucomannan-AH-Sepharose. On isoelectric focusing, multiple protein bands were found, all of which had β-mannanase activity. Each preparation appeared as a single major band on SDS-polyacrylamide gel electrophoresis. The enzymes varied in their final specific activities, Km values, optimal pH, isoelectric points and pH and temperature stabilities but had similar MWs. The enzymes have different abilities to hydrolyse galactomannans which are highly substituted with galactose. The preparations Driselase and Cellulase contain β-mannanases which can attack highly substituted galactomannans at points of single unsubstituted D-mannosyl residues if the D-galactose residues in the vicinity of the bond to be hydrolysed are all on only one side of the main chain.

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Megazyme publication
Galactomannans and a galactoglucomannan in legume seed endosperms: Structural requirements for β-mannanase hydrolysis.

McCleary, B. V., Matheson, N. K. & Small, D. B. (1976). Phytochemistry, 15(7), 1111-1117.

A series of galactomannans with varying degrees of galactose substitution have been extracted from the endosperms of legume seeds with water and alkali and the amount of substitution required for water solubility has been determined. Some were heterogeneous with respect to the degree of galactose substitution. The structural requirements for hydrolysis by plant β-mannanase have been studied using the relative rates and extents of hydrolysis of these galactomannans. A more detailed examination of the products of hydrolysis of carob galactomannan has been made. At least two contiguous anhydromannose units appear to be needed for scission. This is similar to the requirement for hydrolysis by microbial enzymes. Judas tree (Cercis siliquastrum) endosperm contained a polysaccharide with a unique composition for a legume seed reserve. Gel chromatography and electrophoresis on cellulose acetate indicated homogeneity. Hydrolysis with a mixture of β-mannanase and α-galactosidase gave a glucose-mannose disaccharide and acetolysis gave a galactose-mannose. These results, as well as the pattern of hydrolysis by β-mannanase were consistent with a galactoglucomannan structure.

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Megazyme publication
Galactomannan structure and β-mannanase and β-mannosidase activity in germinating legume seeds.

McCleary, B. V. & Matheson, N. K. (1975). Phytochemistry, 14(5-6), 1187-1194.

Structural changes in galactomannan on germination of lucerne, carob, honey locust, guar and soybean seeds, as measured by viscosity, elution volumes on gel filtration and ultra-centrifugation were slight consistent with a rapid and complete hydrolysis of a molecule once hydrolysis of the mannan chain starts. β-Mannanase activity increased and then decreased, paralleling galactomannan depletion. Multiple forms of β-mannanase were isolated and these were located in the endosperm. β-Mannanase had limited ability to hydrolyse galactomannans with high galactose contents. Seeds containing these galactomannans had very active α-galactosidases. β-Mannosidases were present in both endosperm and cotyledon-embryo and could be separated chromatographically. The level of activity was just sufficient to account for mannose production from manno-oligosaccharides.

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Megazyme publication
α-D-galactosidase activity and galactomannan and galactosylsucrose oligosaccharide depletion in germinating legume seeds.

McCleary, B. V. & Matheson, N. K. (1974). Phytochemistry, 13(9), 1747-1757.

Germinating seeds of lucerne, guar, carob and soybean initially depleted raffinose series oligosaccharides and then galactomannan. This depletion was accompanied by a rapid increase and then a decrease in α-galactosidase levels. Lucerne and guar contained two α-galactosidase activities, carob three and soybean four. One of these in each plant, from its location in the endosperm, time of appearance and kinetic behaviour, appeared to be primarily involved in galactomannan hydrolysis. This enzyme in lucerne had MW of 23 000 and could not be separated from β-mannanase by (NH4)2SO4 fractionation, DEAE, CM or SE-cellulose chromatography or gel filtration, but only by polyacrylamide gel electrophoresis. In guar, carob and soybean, it could be separated by ion-exchange chromatography and gel filtration. In lucerne, carob and guar most of the total increase in activity was due to this enzyme. The other α-galactosidases had MWs of about 35 000 and could be separated from β-mannanase by dissection, ion exchange cellulose chromatography and gel filtration. They were located in the cotyledon-embryo and appeared to be primarily involved in galactosylsucrose oligosaccharide hydrolysis.

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Publication
A novel α-galactosidase from Fusarium oxysporum and its application in determining the structure of the gum arabic side chain.

Maruta, A., Yamane, M., Matsubara, M., Suzuki, S., Nakazawa, M., Ueda, M. & Sakamoto, T. (2017). Enzyme and Microbial Technology, 103, 25-33.

We previously reported that Fusarium oxysporum 12S produces two bifunctional proteins, FoAP1 and FoAP2, with α-D-galactopyranosidase (GPase) and β-L-arabinopyranosidase (APase) activities. The aim of this paper was to purify a third GPase, FoGP1, from culture supernatant of F. oxysporum 12S, to characterize it, and to determine its mode of action towards gum arabic. A cDNA encoding FoGP1 was cloned and the protein was overexpressed in Escherichia coli. Module sequence analysis revealed the presence of a GH27 domain in FoGP1. The recombinant enzyme (rFoGP1) showed a GPase/APase activity ratio of 330, which was quite different from that of FoAP1 (1.7) and FoAP2 (0.2). Among the natural substrates tested, rFoGP1 showed the highest activity towards gum arabic. In contrast to other well-characterized GPases, rFoGP1 released a small amount of galactose from α-galactosyl oligosaccharides such as raffinose and exhibited no activity toward galactomannans, which are highly substituted with α-galactosyl side chains. This indicated that FoGP1 is an unusual type of GPase. rFoGP1 released 30% of the total galactose from gum arabic, suggesting the existence of a large number of α-galactosyl residues at the non-reducing ends of gum arabic side chains. Together, rFoGP1 and α-L-arabinofuranosidase released four times more arabinose than α-L-arabinofuranosidase acting alone. This suggested that a large number of α-L-arabinofuranosyl residues is capped by α-galactosyl residues. 1H NMR experiments revealed that rFoGP1 hydrolyzed the α-1,3-galactosidic linkage within the side chain structure of [α-D-Galp-(1 → 3)-α-L-Araf-(1 → ] in gum arabic. In conclusion, rFoGP1 is highly active toward α-1,3-galactosyl linkages but negligibly or not active toward α-1,6-galactosyl linkages. The novel FoGP1 might be used to modify the physical properties of gum arabic, which is an industrially important polysaccharide used as an emulsion stabilizer and coating agent.

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Publication
Purification and Characterization of a Thermostable β-Mannanase from Bacillus subtilis BE-91: Potential Application in Inflammatory Diseases.

Cheng, L., Duan, S., Feng, X., Zheng, K., Yang, Q. & Liu, Z. (2016). BioMed Research International, 2016, In Press.

β-mannanase has shown compelling biological functions because of its regulatory roles in metabolism, inflammation, and oxidation. This study separated and purified the β-mannanase from Bacillus subtilis BE-91, which is a powerful hemicellulose-degrading bacterium using a “two-step” method comprising ultrafiltration and gel chromatography. The purified β-mannanase (about 28.2 kDa) showed high specific activity (79, 859.2 IU/mg). The optimum temperature and pH were 65°C and 6.0, respectively. Moreover, the enzyme was highly stable at temperatures up to 70°C and pH 4.5-7.0. The β-mannanase activity was significantly enhanced in the presence of Mn2+, Cu2+, Zn2+, Ca2+, Mg2+, and Al3+, and strongly inhibited by Ba2+, and Pb2+. Km and Vmax values for locust bean gum were 7.14 mg/mL and 107.5 µmol/min/mL versus 1.749 mg/mL and 33.45 µ mol/min/mL for Konjac glucomannan, respectively. Therefore, β-mannanase purified by this work shows stability at high temperatures and in weakly acidic or neutral environments. Based on such data, the β-mannanase will have potential applications as a dietary supplement in treatment of inflammatory processes.

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Publication
Understanding how noncatalytic carbohydrate binding modules can display specificity for xyloglucan.

Luís, A. S., Venditto, I., Temple, M. J., Rogowski, A., Baslé, A., Xue, J., Knox, J. P., Prates, J. A. M., Ferreira, L. M. A., Fontes, C. M. G. A., Najmudin, S. & Gilbert, H. J. (2013). Journal of Biological Chemistry, 288(7), 4799-4809.

Plant biomass is central to the carbon cycle and to environmentally sustainable industries exemplified by the biofuel sector. Plant cell wall degrading enzymes generally contain noncatalytic carbohydrate binding modules (CBMs) that fulfil a targeting function, which enhances catalysis. CBMs that bind β-glucan chains often display broad specificity recognizing β1,4-glucans (cellulose), β1,3-β1,4-mixed linked glucans and xyloglucan, a β1,4-glucan decorated with α-1,6-xylose residues, by targeting structures common to the three polysaccharides. Thus, CBMs that recognize xyloglucan target the β1,4-glucan backbone and only accommodate the xylose decorations. Here we show that two closely related CBMs, CBM65A and CBM65B, derived from EcCel5A, a Eubacterium cellulosolvens endoglucanase, bind to a range of β-glucans but, uniquely, display significant preference for xyloglucan. The structures of the two CBMs reveal a β-sandwich fold. The ligand binding site comprises the β-sheet that forms the concave surface of the proteins. Binding to the backbone chains of β-glucans is mediated primarily by five aromatic residues that also make hydrophobic interactions with the xylose side chains of xyloglucan, conferring the distinctive specificity of the CBMs for the decorated polysaccharide. Significantly, and in contrast to other CBMs that recognize β-glucans, CBM65A utilizes different polar residues to bind cellulose and mixed linked glucans. Thus, Gln106 is central to cellulose recognition, but is not required for binding to mixed linked glucans. This report reveals the mechanism by which β-glucan-specific CBMs can distinguish between linear and mixed linked glucans, and show how these CBMs can exploit an extensive hydrophobic platform to target the side chains of decorated β-glucans.

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Publication
Family 42 carbohydrate-binding modules display multiple arabinoxylan-binding interfaces presenting different ligand affinities.

Ribeiro, T., Santos-Silva, T., Alves, V. D., Dias, F. M. V., Luís, A. S., Prates, J. A. M., Ferraira, L. M. A., Romao, M. J. & Fontes, C. M. G. A. (2010). Biochimica et Biophysica Acta (BBA)-Proteins and Proteomics, 1804(10), 2054-2062.

Enzymes that degrade plant cell wall polysaccharides display a modular architecture comprising a catalytic domain bound to one or more non-catalytic carbohydrate-binding modules (CBMs). CBMs display considerable variation in primary structure and are grouped into 59 sequence-based families organized in the Carbohydrate-Active enZYme (CAZy) database. Here we report the crystal structure of CtCBM42A together with the biochemical characterization of two other members of family 42 CBMs from Clostridium thermocellum. CtCBM42A, CtCBM42B and CtCBM42C bind specifically to the arabinose side-chains of arabinoxylans and arabinan, suggesting that various cellulosomal components are targeted to these regions of the plant cell wall. The structure of CtCBM42A displays a beta-trefoil fold, which comprises 3 sub-domains designated as α, β and γ. Each one of the three sub-domains presents a putative carbohydrate-binding pocket where an aspartate residue located in a central position dominates ligand recognition. Intriguingly, the γ sub-domain of CtCBM42A is pivotal for arabinoxylan binding, while the concerted action of β and γ sub-domains of CtCBM42B and CtCBM42C is apparently required for ligand sequestration. Thus, this work reveals that the binding mechanism of CBM42 members is in contrast with that of homologous CBM13s where recognition of complex polysaccharides results from the cooperative action of three protein sub-domains presenting similar affinities.

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