Hydrolysis of wheat flour arabinoxylan, acid-debranched wheat flour arabinoxylan and arabino-xylo-oligosaccharides by β-xylanase, α-L-arabinofuranosidase and β-xylosidase.
McCleary, B. V., McKie, V. A., Draga, A., Rooney, E., Mangan, D. & Larkin, J. (2015). Carbohydrate Research, 407, 79-96.
A range of α-L-arabinofuranosyl-(1-4)-β-D-xylo-oligosaccharides (AXOS) were produced by hydrolysis of wheat flour arabinoxylan (WAX) and acid debranched arabinoxylan (ADWAX), in the presence and absence of an AXH-d3 α-L-arabinofuranosidase, by several GH10 and GH11 β-xylanases. The structures of the oligosaccharides were characterised by GC-MS and NMR and by hydrolysis by a range of α-L-arabinofuranosidases and β-xylosidase. The AXOS were purified and used to characterise the action patterns of the specific α-L-arabinofuranosidases. These enzymes, in combination with either Cellvibrio mixtus or Neocallimastix patriciarum β -xylanase, were used to produce elevated levels of specific AXOS on hydrolysis of WAX, such as 32-α-L-Araf-(1-4)-β-D-xylobiose (A3X), 23-α-L-Araf-(1-4)-β-D-xylotriose (A2XX), 33-α-L-Araf-(1-4)-β-D-xylotriose (A3XX), 22-α-L-Araf-(1-4)-β-D-xylotriose (XA2X), 32-α-L-Araf (1-4)-β-D-xylotriose (XA3X), 23-α-L-Araf-(1-4)-β-D-xylotetraose (XA2XX), 33-α-L-Araf-(1-4)-β-D-xylotetraose (XA3XX), 23 ,33-di-α-L-Araf-(1-4)-β-D-xylotriose (A2+3XX), 23,33-di-α-L-Araf-(1-4)-β-D-xylotetraose (XA2+3XX), 24,34-di-α-L-Araf-(1-4)-β-D-xylopentaose (XA2+3XXX) and 33,34-di-α-L-Araf-(1-4)-β-D-xylopentaose (XA3A3XX), many of which have not previously been produced in sufficient quantities to allow their use as substrates in further enzymic studies. For A2,3XX, yields of approximately 16% of the starting material (wheat arabinoxylan) have been achieved. Mixtures of the α-L-arabinofuranosidases, with specific action on AXOS, have been combined with β-xylosidase and β-xylanase to obtain an optimal mixture for hydrolysis of arabinoxylan to L-arabinose and D-xylose.
Cloning and characterization of arabinoxylan arabinofuranohydrolase-D3 (AXHd3) from Bifidobacterium adolescentis DSM20083.
Van den Broek, L. A. M., Lloyd, R. M., Beldman, G., Verdoes, J. C., McCleary, B. V. & Voragen, A. G. J. (2005). Applied Microbiology and Biotechnology, 67(5), 641-647.
Arabinoxylan arabinofuranohydrolase-D3 (AXHd3) from Bifidobacterium adolescentis releases only C3-linked arabinose residues from double-substituted xylose residues. A genomic library of B. adolescentis DSM20083 was screened for the presence of the axhD3 gene. Two plasmids were identified containing part of the axhD3 gene. The nucleotide sequences were combined and three open reading frames (ORFs) were found. The first ORF showed high homology with xylanases belonging to family 8 of the glycoside hydrolases and this gene was designated xylA. The second ORF was the axhD3 gene belonging to glycoside hydrolase family 43. The third (partial) ORF coded for a putative carboxylesterase. The axhD3 gene was cloned and expressed in Escherichia coli. Several substrates were employed in the biochemical characterization of recombinant AXHd3. The enzyme showed the highest activity toward wheat arabinoxylan oligosaccharides. In addition, β-xylanase from Trichoderma sp. was able to degrade soluble wheat arabinoxylan polymer to a higher extent, after pretreatment with recombinant AXHd3. Arabinoxylan oligosaccharides incubated with a combination of recombinant AXHd3 and an α-L-arabinofuranosidase from Aspergillus niger did not result in a higher maximal release of arabinose than incubation with these enzymes separately.
Characterization of indigestible carbohydrates in various fractions from wheat processing.
Haskå, L., Nyman, M. & Andersson, R. (2010). Cereal Chemistry, 87(2), 125-130.
Fractions rich in indigestible carbohydrates, such as fructan and arabinoxylan, are obtained as by-products when ethanol, starch, and gluten are produced from wheat flour. Today, these fractions are used as animal feed. However, these components may have positive physiological effects in humans. In this study, the content of indigestible carbohydrates in distillers' grains and process streams from the wet fractionation of wheat flour was determined. The fractions were further characterized by ethanol extractability analysis, anion-exchange chromatography, NMR, and size-exclusion chromatography. One fraction from wet fractionation contained (g/100 g, db) 6.0 ± 1.0 fructan and 10.3 ± 1.1 dietary fiber (66 ± 4% arabinoxylan), while distillers' grains contained 20.7 g/100 g (db) dietary fiber (30% arabinoxylan). In addition to indigestible carbohydrates from wheat, distillers' grains contained β-(1→3) and β-(1→6) glucans and mannoproteins from the yeast and low molecular weight carbohydrates mainly composed of arabinose. The use of endoxylanase in wet fractionation decreased the molecular weight of the arabinoxylans and increased the arabinose to xylose ratio but had no effect on the fructans. In conclusion, waste streams from industrial wheat processing were enriched in fructan, arabinoxylan, and other indigestible carbohydrates. However, the physiological effects of these fractions require further investigation.
Molecular characterization and solution properties of enzymatically tailored arabinoxylans.
Pitkänen, L., Tuomainen, P., Virkki, L. & Tenkanen, M. (2011). International Journal of Biological Macromolecules, 49(5), 963-969.
Two α-L-arabinofuranosidases with different substrate specificities were used to modify the arabinose-to-xylose ratio of cereal arabinoxylans: one enzyme (AXH-m) removed the L-arabinofuranosyl substituents from the monosubstituted xylopyranosyl residues and the other (AXH-d3) the (1 → 3)-linked L-arabinofuranosyl units from the disubstituted xylopyranosyl residue. In this study, we noticed that not only the arabinose-to-xylose ratio but also the position of the arabinofuranosyl substituents affects the water-solubility of arabinoxylans. The AXH-d3 treatment had no significant effect on the solution conformation of arabinoxylans, but the density of the arabinoxylan molecules decreased in DMSO solution after AXH-m modification. The possible heterogeneity of arabinoxylans complicated the interpretation of data describing the macromolecular properties of the enzymatically modified samples.
Specific enzymatic tailoring of wheat arabinoxylan reveals the role of substitution on xylan film properties.
Heikkinen, S. L., Mikkonen, K. S., Pirkkalainen, K., Serimaa, R., Joly, C. & Tenkanen, M. (2013). Carbohydrate Polymers, 92(1), 733-740.
To increase understanding of the applicability of agro biomass by-products as biodegradable film formers, the effect of wheat arabinoxylan (WAX) fine structure on film properties was studied by applying specific enzyme modifications. WAX was selectively modified to mimic the natural variations of different arabinoxylans, particularly the degree of mono and disubstitution of α-L-arabinofuranosyl (Araf) units in β-D-xylopyranosyl (Xylp) backbone residues. The resulting modified WAX samples had similar arabinose-to-xylose (Ara/Xyl) ratios, but they differed in the number of unsubstituted Xylp units. The substitution of WAX was found to affect, in particular, tensile strength, crystallinity, and oxygen permeability properties of the films, as statistically significant decreases in tensile strength and oxygen permeability took place after WAX de-branching. An increase in the number of unsubstituted Xylp units decreased the temperature of relaxation of small-scale molecular motions of WAX (β-relaxation) and increased the degree of crystallinity of the films.
Adsorption of arabinoxylan on cellulosic surfaces: influence of degree of substitution and substitution pattern on adsorption characteristics.
Köhnke, T., Östlund, Å. & Brelid, H. (2011). Biomacromolecules, 12(7), 2633-2641.
This study presents results that show that the fine structure of arabinoxylan affects its interaction with cellulosic surfaces, an important understanding when designing and evaluating properties of xylan–cellulose-based materials. Arabinoxylan samples, with well-defined structures, were prepared from a wheat flour arabinoxylan with targeted enzymatic hydrolysis. Turbidity measurements and analyses using NMR diffusometry showed that the solubility and the hydrodynamic properties of arabinoxylan are determined not only by the degree of substitution but also by the substitution pattern. On the basis of results obtained from adsorption experiments on microcrystalline cellulose particles and on cellulosic model surfaces investigated with quartz crystal microbalance with dissipation monitoring, it was also found that arabinoxylan adsorbs irreversibly on cellulosic surfaces and that the adsorption characteristics, as well as the properties of the adsorbed layer, are controlled by the fine structure of the xylan molecule.
Enzyme kinetics and identification of the rate-limiting step of enzymatic arabinoxylan degradation.
Rasmussen, L. E., Xu, C., Sørensen, J. F., Nielsen, M. K. & Meyer, A. S. (2012). Biochemical Engineering Journal, 69, 8-16.
This study investigated the kinetics of multi-enzymatic degradation of soluble wheat arabinoxylan by monitoring the release of xylose and arabinose during designed treatments with mono-component enzymes at different substrate concentrations. The results of different combinations of α-L-arabinofuranosidases (EC 184.108.40.206), one derived from Aspergillus niger (AFAn) and one from Bifidobacterium adolescentis (AFBa), respectively, a β-xylosidase (EC 220.127.116.11) from Trichoderma reesei, and an engineered D11F/R122D variant of Bacillus subtilis XynA endo-1,4-β-xylanase (EC 18.104.22.168) were examined. The two selected α-L-arabinofuranosidases catalyze liberation of arabinose residues linked 1 → 3 to singly (AFAn) or doubly (AFBa) substituted xyloses in arabinoxylan, respectively. When added to arabinoxylan at equimolar levels, the AFBa enzyme catalyzed the release of more arabinose, i.e. had a higher rate constant than AFAn, but with respect to the xylose release, AFAn– as expected – exhibited a better synergistic effect than AFBa with β-xylosidase. This synergistic effect with AFAn was estimated to increase the number of β-xylosidase catalyzed cuts from ~3 (with β-xylosidase alone) to ~7 in each arabinoxylan substrate molecule. However, the synergistic effects between β-xylosidase and the α-L-arabinofuranosidases on the xylose release were low as compared to the effect of xylanase addition with β-xylosidase, which increased the xylose release by ~25 times in 30 min, to a yield equivalent to ~104 β-xylosidase catalyzed cuts in each arabinoxylan substrate molecule. At equimolar addition levels of the four enzymes, the xylanase activity was thus rate-limiting for the β-xylosidase catalyzed depolymerization to release xylose from arabinoxylan. The work provides clues to design efficient enzymatic degradation of arabinoxylan into fermentable monosaccharides.
A glucurono(arabino)xylan synthase complex from wheat contains members of the GT43, GT47, and GT75 families and functions cooperatively.
Zeng, W., Jiang, N., Nadella, R., Killen, T. L., Nadella, V. & Faik, A. (2010). Plant Physiology, 154(1), 78-97.
Glucuronoarabinoxylans (GAXs) are the major hemicelluloses in grass cell walls, but the proteins that synthesize them have previously been uncharacterized. The biosynthesis of GAXs would require at least three glycosyltransferases (GTs): xylosyltransferase (XylT), arabinosyltransferase (AraT), and glucuronosyltransferase (GlcAT). A combination of proteomics and transcriptomics analyses revealed three wheat (Triticum aestivum) glycosyltransferase (TaGT) proteins from the GT43, GT47, and GT75 families as promising candidates involved in GAX synthesis in wheat, namely TaGT43-4, TaGT47-13, and TaGT75-4. Coimmunoprecipitation experiments using specific antibodies produced against TaGT43-4 allowed the immunopurification of a complex containing these three GT proteins. The affinity-purified complex also showed GAX-XylT, GAX-AraT, and GAX-GlcAT activities that work in a cooperative manner. UDP Xyl strongly enhanced both AraT and GlcAT activities. However, while UDP arabinopyranose stimulated the XylT activity, it had only limited effect on GlcAT activity. Similarly, UDP GlcUA stimulated the XylT activity but had only limited effect on AraT activity. The [14C]GAX polymer synthesized by the affinity-purified complex contained Xyl, Ara, and GlcUA in a ratio of 45:12:1, respectively. When this product was digested with purified endoxylanase III and analyzed by high-pH anion-exchange chromatography, only two oligosaccharides were obtained, suggesting a regular structure. One of the two oligosaccharides has six Xyls and two Aras, and the second oligosaccharide contains Xyl, Ara, and GlcUA in a ratio of 40:8:1, respectively. Our results provide a direct link of the involvement of TaGT43-4, TaGT47-13, and TaGT75-4 proteins (as a core complex) in the synthesis of GAX polymer in wheat.
Step-wise enzymatic preparation and structural characterization of singly and doubly substituted arabinoxylo-oligosaccharides with non-reducing end terminal branches.
Pastell, H., Tuomainen, P., Virkki, L. & Tenkanen, M. (2008). Carbohydrate Research, 343(18), 3049-3057.
Shearzyme (GH10 endo-1,4-β-D-xylanase) and two different α-L-arabinofuranosidases (AXH-m and AXH-d3) were used stepwise to manufacture arabinoxylo-oligosaccharides (AXOS) with α-L-Araf (1→2)-monosubstituted β-D-Xylp residues or α-L-Araf (1→2)- and (1→3) doubly substituted β-D-Xylp residues from wheat arabinoxylan (AX) in a rather straightforward way. Four major AXOS (d-I, d-II, m-I and m-II) were formed in two separate hydrolyses. The AXOS were purified and the structures were confirmed using TLC, HPAEC-PAD, MALDI-TOF-MS and 1D and 2D NMR spectroscopy. The samples were identified as d-I: α-L-Araf-(1→2)-[α-L-Araf-(1→3)]-β-D-Xylp-(1→4)-β-D-Xylp-(1→4)-D-Xylp, d-II: α-L-Araf-(1→2)-[α-L-Araf-(1→3)]-β-D-Xylp-(1→4)-D-Xylp, m-I: α-L-Araf-(1→2)-β-D-Xylp-(1→4)-β-D-Xylp-(1→4)-D-Xylp and m-II: α-L-Araf-(1→2)-β-D-Xylp-(1→4)-D-Xylp. To our knowledge, this is the first report on structural 1H and 13C NMR analysis of xylobiose-derived AXOS d-II and m-II. The latter compound has not been reported previously. The doubly substituted AXOS were produced for the first time in good yields, as d-I and d-II corresponded to 11.8 and 5.6 wt% of AX, respectively. Singly α-L-Araf (1→2)-substituted AXOS could also be prepared in similar yields by treating the doubly substituted AXOS further with AXH-d3.
Structural comparison of arabinoxylans from two barley side-stream fractions.
Pitkänen, L., Tuomainen, P., Virkki, L., Aseyev, V. & Tenkanen, M. (2008). Journal of Agricultural and Food Chemistry, 56(13), 5069-5077.
The structures of barley (Hordeum vulgare) arabinoxylans isolated from two industrial side fractions, barley husks (BH) and barley fiber (BF), were characterized. Arabinoxylans were extracted with saturated barium hydroxide after enzymatic pretreatment. Barium hydroxide was selective toward arabinoxylans, and only a minor amount of glucose-containing material was coextracted. Acid methanolysis followed by gas chromatography, 1H NMR spectroscopy, and specific enzymatic treatments followed by anion exchange chromatography with pulse amperometric detection (HPAEC-PAD) revealed that the chemical structure of barley husk arabinoxylan (BHAX) clearly differed from that of barley fiber arabinoxylan (BFAX). BFAX was more branched, containing more β-D-xylopyranosyl (β-D-Xylp) residues carrying α-L-arabinofuranosyl (α-L-Araf) units at both O-2 and O-3 positions. BHAX, on the other hand, contained more 2-O-β-D-Xylp-α-L-Araf substituents than BFAX. BHAX and BFAX also differed with respect to the hydrodynamic properties investigated with multidetector size exclusion chromatography. BFAX had a higher weight-average molar mass and larger hydrodynamic volume, the latter indicating less dense conformation than BHAX. Mn, Mw/Mn, Rh, and the Mark−Houwink a value were also determined for both arabinoxylans.