Isolation and characterisation of hemicelluloses from sunflower hulls

Chamomile tea: Source of a glucuronoxylan with antinociceptive, sedative and anxiolytic-like effects

Chamomile is one of the most ancient medicinal herbs known to mankind and among its traditional uses are the calming effects. However, few studies explored its effects on the central nervous system (CNS). In this study we further proceed with structural elucidation of polysaccharides from chamomile tea. A highly substituted 4-O-methyl-glucuronoxylan (fraction SN-50R) was purified and chemically characterized, presenting Xyl:GlcA ratio of 1.7:1, M_w of 500 kDa and total sugar content of 98%. Its bioactivity on pain and on CNS was explored. Animals treated with SN-50R presented antinociceptive effect and a dose-dependent decrease in the number of crossings in the activity chamber and in the open field test, as well as a significant reduction in the number of marbles buried when compared to control. These results suggest that SN-50R presented sedative and anxiolytic-like effects and may be contributing for the calming effects obtained by chamomile tea ingestion.

Chemical structure and rheological studies of arabinoglucuronoxylans from the Cercidium praecox exudate brea gum

The structure of the arabinoglucuronoxylans from brea gum was elucidated through an chemical and NMR spectroscopical analysis. They are composed of xylose, arabinose, glucuronic acid and 4-O-methylglucuronic acid in a molar ratio 1:0.44:0.16:0.22. The structure consists of a central chain of (1→4)-β-d-xylopyranose of which ca.70% are susbstituted in C2 with single stubs of others sugars (β-d-Xylp, α-d-GlcpA and 4-O-Me-α-d-GlcpA), with disaccharides (α-l-Arap-(1→2)-4-O-Me-α-d-GlcpA-(1→, α-l-Arap-(1→2)-α-d-GlcpA-(1→, β-l-Araf-(1→3)-α-l-Araf-(1→ and α-l-Araf-(1→3)-α-l-Araf-(1→5), and possibly with trisaccharides of xylose. The determination of the location of the acetyl groups and their quantification in these arabinoglucuronoxylans has been achieved for the first time. Brea gum presents a higher thickening effect than gum arabic in 5% aqueous solution, demonstrating its potential usefulness for food and pharmaceutical applications.

A gel-state 2D-NMR method for plant cell wall profiling and analysis: a model study with the amorphous cellulose and xylan from ball-milled cotton linters

Amorphous cellulose and xylan structures were analyzed using high-resolution 2D-NMR, and the NMR data were obtained in a DMSO-d₆/pyridine-d₅ (4 : 1) solvent system.

Degradation of wheat straw by Fibrobacter succinogenes S85: a liquid- and solid-state nuclear magnetic resonance study

Wheat straw degradation by Fibrobacter succinogenes was monitored by nuclear magnetic resonance (NMR) spectroscopy and chemolytic methods to investigate the activity of an entire fibrolytic system on an intact complex substrate. In situ solid-state NMR with 13C cross-polarization magic angle spinning was used to monitor the modification of the composition and structure of lignocellulosic fibers (of 13C-enriched wheat straw) during the growth of bacteria on this substrate. There was no preferential degradation either of amorphous regions of cellulose versus crystalline regions or of cellulose versus hemicelluloses in wheat straw. This suggests either a simultaneous degradation of the amorphous and crystalline parts of cellulose and of cellulose and hemicelluloses by the enzymes or degradation at the surface at a molecular scale that cannot be detected by NMR. Liquid-state two-dimensional NMR experiments and chemolytic methods were used to analyze in detail the various sugars released into the culture medium. An integration of NMR signals enabled the quantification of oligosaccharides produced from wheat straw at various times of culture and showed the sequential activities of some of the fibrolytic enzymes of F. succinogenes S85 on wheat straw. In particular, acetylxylan esterase appeared to be more active than arabinofuranosidase, which was more active than alpha-glucuronidase. Finally, cellodextrins did not accumulate to a great extent in the culture medium.

Cloning, characterization, and functional expression of the Klebsiella oxytoca xylodextrin utilization operon (xynTB) in Escherichia coli

Escherichia coli is being developed as a biocatalyst for bulk chemical production from inexpensive carbohydrates derived from lignocellulose. Potential substrates include the soluble xylodextrins (xyloside, xylooligosaccharide) and xylobiose that are produced by treatments designed to expose cellulose for subsequent enzymatic hydrolysis. Adjacent genes encoding xylobiose uptake and hydrolysis were cloned from Klebsiella oxytoca M5A1 and are functionally expressed in ethanologenic E. coli. The xylosidase encoded by xynB contains the COG3507 domain characteristic of glycosyl hydrolase family 43. The xynT gene encodes a membrane protein containing the MelB domain (COG2211) found in Na(+)/melibiose symporters and related proteins. These two genes form a bicistronic operon that appears to be regulated by xylose (XylR) and by catabolite repression in both K. oxytoca and recombinant E. coli. Homologs of this operon were found in Klebsiella pneumoniae, Lactobacillus lactis, E. coli, Clostridium acetobutylicum, and Bacillus subtilis based on sequence comparisons. Based on similarities in protein sequence, the xynTB genes in K. oxytoca appear to have originated from a gram-positive ancestor related to L. lactis. Functional expression of xynB allowed ethanologenic E. coli to metabolize xylodextrins (xylosides) containing up to six xylose residues without the addition of enzyme supplements. 4-O-methylglucuronic acid substitutions at the nonreducing termini of soluble xylodextrins blocked further degradation by the XynB xylosidase. The rate of xylodextrin utilization by recombinant E. coli was increased when a full-length xynT gene was included with xynB, consistent with xynT functioning as a symport. Hydrolysis rates were inversely related to xylodextrin chain length, with xylobiose as the preferred substrate. Xylodextrins were utilized more rapidly by recombinant E. coli than K. oxytoca M5A1 (the source of xynT and xynB). XynB exhibited weak arabinosidase activity, 3% that of xylosidase.

NMR structural determination of dissolved O-acetylated galactoglucomannan isolated from spruce thermomechanical pulp

Water-soluble O-acetylated galactoglucomannan (GGM) isolated from spruce thermomechanical pulp (TMP) by hot-water extraction was characterized by 1D and 2D (homo- and heteronuclear) NMR analysis. The backbone was found to consist of (1-->4)-linked mannopyranosyl and glucopyranosyl units in a ratio of 10:1.9-2.6. The mannopyranosyl units were acetylated at C-2 and C-3 with a degree of acetylation around 0.28-0.37 as determined by NMR. A slightly larger amount of 2-O-acetylated mannopyranosyl was detected when compared to the 3-O-acetylated component. Approximately every 10th mannopyranosyl unit was substituted at C-6 by a single alpha-galactopyranosyl unit. Fine structure determination based on sequence-specific chemical shift variations showed that the distribution of glycosyl residues is random. Small amounts of other minor polysaccharide species including xylans and galactans could also be identified by NMR.

Isolation and structure of D-xylans from pericarp seeds of Opuntia ficus-indica prickly pear fruits

Xylans were isolated from the pericarp of prickly pear seeds of Opuntia ficus-indica (OFI) by alkaline extraction, fractionated by precipitation and purified. Six fractions were obtained and characterized by sugar analysis and NMR spectroscopy. They were assumed to be (4-O-methyl-D-glucurono)-D-xylans, with 4-O-alpha-D-glucopyranosyluronic acid groups linked at C-2 of a (1-->4)-beta-D-xylan. The sugar composition and the 1H and 13C NMR spectra showed that their chemical structures were very similar, but with different proportions of D-Xyl and 4-O-Me-D-GlcA. Our results showed that, on average, the water soluble xylans have one nonreducing terminal residue of 4-O-methyl-D-glucuronic acid for every 11 to 14 xylose units, whereas in the water non-soluble xylans, xylose units can varied from 18 to 65 residues for one nonreducing terminal residue of 4-O-methyl-D-glucuronic acid.

Isolation and NMR characterisation of a (4-O-methyl-D-glucurono)-D-xylan from sugar beet pulp

Stable aqueous suspensions of purified and homogenised sugar beet pulp (SBP) cellulose were subjected to various TFA treatments which induced a flocculation of the suspension and the release of a number of polysaccharides. Among these, a 4-O-methyl glucuronoxylan was isolated and characterized by 1H and 13C NMR spectroscopy. In this polysaccharide the molar proportions of D-Xyl and 4-O-Me-D-GlcA were found to be 7:1. The presence of a glucuronoxylan at the surface of the cellulose microfibrils is very likely involved in the stability of the suspensions. To our knowledge, the presence of a 4-O-methyl-glucuronoxylan in the sugar beet cells has not been described previously.

(4-O-Methyl-alpha-D-glucurono)-D-xylan from Rudbeckia fulgida, var. sullivantii (Boynton et Beadle)

From the medicinal plant Rudbeckia fulgida, var. sillivantii (Boynton et Beadle) a low-molecular-mass (4-O-methyl-alpha-D-glucurono)-D-xylan was isolated by alkaline extraction, followed by ethanol precipitation, ion-exchange chromatography and gel filtration. The results of compositional and linkage analyses, supported by those of 1H and 13C NMR measurements of oligomers generated on partial acid hydrolysis, showed the (1-->4)-linked beta-D-xylopyranosyl backbone with about 18% of 4-O-methyl-D-glucuronic acid attached to O-2 of the xylose residues. From the mean distance of adjacent carboxyl groups, obtained from experimentally determined single-ion activity coefficients of calcium counterions, it followed that the uronic acid units are separated and distributed regularly along the xylan chain, i.e. approximately each sixth D-xylose unit bears a 4-O-methyl-D-glucuronic acid residue.

High-field NMR as a technique for the determination of polysaccharide structures

NMR spectroscopy has played a developing role in the study of polysaccharide structures for over 30 years. Many new bacterial polysaccharide repeat unit structures have recently been published as a result of the application of modern NMR techniques. NMR can also be used to elucidate the structures of both regular and heterogeneous polysaccharides from fungal and plant sources, as well as complex glycosaminoglycans of animal origin. In addition to covalent structure, conformation and dynamics of polysaccharides are susceptible to NMR analysis, both in solution and in the solid state. Improvements in NMR technology with potential applications to polysaccharide studies hold promise for the future.