Hemicellulose

Ebringerová, Anna; Hromàdková, Zdenka; Heinze, Thomas

doi:10.1007/b136816

Cited by 477 publications

(388 citation statements)

References 359 publications

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“…Birch is also employed as a soil improver and for reforestation of degraded soils. HW hemicelluloses are mainly composed of acetyl-4-O-methylglucuronoxylan, with glucomannans and other compounds in lower amounts (Ebringerová et al 2005). Native birch xylan consists of a backbone of β(1-4)-D-xylopyranosyl units, with O-acetyl substituent at positions C2 (23.7%), C3 (22.5%), or C2,3 (9.5%).…”

Section: Introductionmentioning

confidence: 99%

Furfural production from birch hemicelluloses by two-step processing: a potential technology for biorefineries

et al. 2016

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Birch samples were subjected to non-isothermal autohydrolysis to obtain a solution of hemicellulosic saccharides and a solid phase mainly made up of cellulose and lignin. Based on kinetic modeling, operational conditions were identified which give rise to soluble saccharides and furfural derived from xylan in a yield of 80.5%. The soluble mixture was supplemented with 1% sulfuric acid and heated (directly or in the presence of methyl isobutyl ketone, MIBK) for furfural production. MIBK is used as an extraction agent to limit furfural consumption by side reactions. Operating in single phase at 170°C, up to 44.8% of the potential substrates were converted into furfural. In experiments performed in biphasic media, the effects of MIBK were assessed by empirical modeling and about 75% of the potential substrates were converted under selected conditions.

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Section: Introductionmentioning

confidence: 99%

Furfural production from birch hemicelluloses by two-step processing: a potential technology for biorefineries

et al. 2016

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“…Although the organization of these various components in the cell wall is not well understood, the increased cross-linking apparently contributes to the recalcitrance of the cell wall (6,7). Xylans are structurally diverse between taxonomic groups (4,8). The most basal form of xylan is a main chain that lacks substitutions as seen in the green alga Caulerpa that has β-1,3-D-xylan in place of cellulose, and the red seaweeds Palmariales and Nemaliales that have a mixed linkage β-(1,3-1,4)-D-xylose backbone (8).…”

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confidence: 99%

“…Xylans are structurally diverse between taxonomic groups (4,8). The most basal form of xylan is a main chain that lacks substitutions as seen in the green alga Caulerpa that has β-1,3-D-xylan in place of cellulose, and the red seaweeds Palmariales and Nemaliales that have a mixed linkage β-(1,3-1,4)-D-xylose backbone (8). Xylans of embryophytes have a β-1,4-linked xylose backbone.…”

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confidence: 99%

XAX1 from glycosyltransferase family 61 mediates xylosyltransfer to rice xylan

Chiniquy

Sharma

Schultink

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

176

161

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Xylan is the second most abundant polysaccharide on Earth and represents an immense quantity of stored energy for biofuel production. Despite its importance, most of the enzymes that synthesize xylan have yet to be identified. Xylans have a backbone of β-1,4–linked xylose residues with substitutions that include α-(1→2)–linked glucuronosyl, 4- O -methyl glucuronosyl, and α-1,2- and α-1,3-arabinofuranosyl residues. The substitutions are structurally diverse and vary by taxonomy, with grass xylan representing a unique composition distinct from dicots and other monocots. To date, no enzyme has yet been identified that is specific to grass xylan synthesis. We identified a xylose-deficient loss-of-function rice mutant in Os02g22380, a putative glycosyltransferase in a grass-specific subfamily of family GT61. We designate the mutant xax1 for x ylosyl a rabinosyl substitution of x ylan 1. Enzymatic fingerprinting of xylan showed the specific absence in the mutant of a peak, which was isolated and determined by 1 H-NMR to be (β-1,4-Xyl) 4 with a β-Xyl p -(1→2)-α-Ara f -(1→3). Rice xax1 mutant plants are deficient in ferulic and coumaric acid, aromatic compounds known to be attached to arabinosyl residues in xylan substituted with xylosyl residues. The xax1 mutant plants exhibit an increased extractability of xylan and increased saccharification, probably reflecting a lower degree of diferulic cross-links. Activity assays with microsomes isolated from tobacco plants transiently expressing XAX1 demonstrated xylosyltransferase activity onto endogenous acceptors. Our results provide insight into grass xylan synthesis and how substitutions may be modified for increased saccharification for biofuel generation.

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“…Xylan is a hemicellulosic component of cell walls and one of the most abundant polysaccharides in nature (Ebringerova et al, 2005;Scheller and Ulvskov, 2010). Its prevalence and structure differ markedly between dicots and grasses; in the former, it constitutes only about 5% of the polysaccharide of primary cell walls, whereas it is typically 30% of the polysaccharide of grass primary cell walls (Carpita, 1996;Scheller and Ulvskov, 2010).…”

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confidence: 99%

RNA Interference Suppression of Genes in Glycosyl Transferase Families 43 and 47 in Wheat Starchy Endosperm Causes Large Decreases in Arabinoxylan Content

et al. 2013

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The cell walls of wheat (Triticum aestivum) starchy endosperm are dominated by arabinoxylan (AX), accounting for 65% to 70% of the polysaccharide content. Genes within two glycosyl transferase (GT) families, GT43 (IRREGULAR XYLEM9 [IRX9] and IRX14) and GT47 (IRX10), have previously been shown to be involved in the synthesis of the xylan backbone in Arabidopsis, and close homologs of these have been implicated in the synthesis of xylan in other species. Here, homologs of IRX10 TaGT47_2 and IRX9 TaGT43_2, which are highly expressed in wheat starchy endosperm cells, were suppressed by RNA interference (RNAi) constructs driven by a starchy endosperm-specific promoter. The total amount of AX was decreased by 40% to 50% and the degree of arabinosylation was increased by 25% to 30% in transgenic lines carrying either of the transgenes. The cell walls of starchy endosperm in sections of grain from TaGT43_2 and TaGT47_2 RNAi transgenics showed decreased immunolabeling for xylan and arabinoxylan epitopes and approximately 50% decreased cell wall thickness compared with controls. The proportion of AX that was water soluble was not significantly affected, but average AX polymer chain length was decreased in both TaGT43_2 and TaGT47_2 RNAi transgenics. However, the long AX chains seen in controls were absent in TaGT43_2 RNAi transgenics but still present in TaGT47_2 RNAi transgenics. The results support an emerging picture of IRX9-like and IRX10-like proteins acting as key components in the xylan synthesis machinery in both dicots and grasses. Since AX is the main component of dietary fiber in wheat foods, the TaGT43_2 and TaGT47_2 genes are of major importance to human nutrition.

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Hemicellulose

Cited by 477 publications

References 359 publications

Furfural production from birch hemicelluloses by two-step processing: a potential technology for biorefineries

Furfural production from birch hemicelluloses by two-step processing: a potential technology for biorefineries

XAX1 from glycosyltransferase family 61 mediates xylosyltransfer to rice xylan

RNA Interference Suppression of Genes in Glycosyl Transferase Families 43 and 47 in Wheat Starchy Endosperm Causes Large Decreases in Arabinoxylan Content

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