the grass-specific endotransglucosylase BdXTH8 preferentially uses MLG as a substrate, but also xyloglucan. BdXTH8 does not yield hydrolysis products separable by thin-layer chromatography when acting on xyloglucan or MLG. Mixed-linkage glucan (MLG) consists of several adjacent (1,4)-linked Glc residues separated by a single (1,3)-glucosyl linkage that occurs every third or fourth residue
MLG:xyloglucan endotransglucosylase, MXE, catalyses a reaction similar to XET activity, EC 2.4.1.207, which catalyses the endocleavage of xyloglucan as donor substrate and the creation of a glycosidic link between the newly formed potentially reducing terminus and the nonreducing terminus of another xyloglucan or xyloglucan oligosaccharide molecule as acceptor substrate, but uses mixed-linkage (1->3), (1->4)-beta-D-glucan, MLG,s as a donor substrate as opposed to xyloglucan, cleavage specificity, overview
MLG:xyloglucan endotransglucosylase, MXE, catalyses a reaction similar to XET activity, EC 2.4.1.207, which catalyses the endocleavage of xyloglucan as donor substrate and the creation of a glycosidic link between the newly formed potentially reducing terminus and the nonreducing terminus of another xyloglucan or xyloglucan oligosaccharide molecule as acceptor substrate, but uses mixed-linkage (1->3), (1->4)-beta-D-glucan, MLG,s as a donor substrate as opposed to xyloglucan, cleavage specificity, overview
attack of the site of hetero-trans-beta-glucanase (HTG) on one of its donor substrates, mixed-linkage (1->3),(1->4)-beta-D-glucan (MLG, from Equisetum arvense or Hordeum vulgare) is investigated with radioactive oligosaccharides of xyloglucan as the acceptor substrate. Analysis of the structure of the mixed-linkage glucan:xyloglucan endotransglucosylase (MXE) reaction product formed with [3H]XXXGol as the acceptor substrate and barley MLG as the donor substrate via digestion of the product with lichenase, method, overview. MXE forms a (Glc2)-XXXGol disaccharide product, which further analysis reveals as GGXXXGol, where GG is cellobiose. The bond between the GG and the XXXGol moiety is also likely to be a beta-(1->4)-bond because it can be cleaved by cellobiohydrolase. When the tetradecasaccharide [3H]XXXGXXXGol is used as an acceptor substrate, the single radioactive product is GG[3H]XXXGXXXGol. MXE has attached MLG to the non-reducing terminal heptasaccharide subunit alone. Identification of the bond initially cleaved by MXE activity
bifunctional xyloglucan endotransglucosylase, EC 2.4.1.207, and mixed-linkage glucan:xyloglucan endotransglucosylase, ratio of the activities is 1:7, respectively
transcriptional profiling, BdXTH8, along with the other three genes in the grass-specific clade, is expressed in tissues that accumulate high amounts of MLG. BdXTH8 is highly coexpressed with the transcription factor BdTHX2 in addition to BdTHX1. BdXTH8 and BdTHX2 both have higher expression in elongating internodes and elongating leaf tissue than that in endosperm, while BdTHX1 shows expression in elongating internodes and endosperm tissues
no activity in Equisetum arvense strobili and total extracts of these organs, vegetative lateral shoot extracts of Equisetum arvense contain high MXE activity
to confirm the transcriptome data, the expression pattern of FvXTH9 is examined by quantitative real-time PCR in fruit at different ripening stages as well as in leaf and flower tissues. FvXTH9 is highly expressed in fully developed green fruit, whereas its expression level dropped in later stages. A high expression level of FvXTH9 is also determined in flowers, whereas its mRNA abundance is very low in all other tissues investigated. The expression pattern of FvXTH6 during fruit development resembled that of FvXTH9. FvXTH9 shows the highest expression level in green receptacles
Brachypodium distachyon shoots regenerated from transformed calli overexpressing BdTHX1 show an abnormal arrangement of vascular tissue and seedling-lethal phenotypes. These results indicate that the transcription factor BdTHX1 likely plays an important role in MLG biosynthesis and restructuring by regulating the expression of BdCSLF6 and BdXTH8
BdXTH8 is a member of this grass-specific clade of GH16 genes in Brachypodium distachyon. Gene BdXTH8 encodes a grass-specific glycoside hydrolase family 16 endotransglucosylase/hydrolase. BdXTH8 is a poalean XTH that preferentially exhibits MXE (EC 2.4.1.B52), a hetero-transglycosylase activity
mixed-linkage glucan:xyloglucan endotransglucosylase (MXE) is one of the three activities of the recently characterised hetero-trans-beta-glucanase (HTG), which among land plants is known only from Equisetum species. The enzyme MXE belongs to the GH16 family
a trihelix family transcription factor is associated with key genes in mixed-linkage glucan accumulation. Brachypodium distachyon trihelix family transcription factor (BdTHX1) is highly coexpressed with the Brachypodium distachyon CSLF6 gene (BdCSLF6), which suggests that BdTHX1 is involved in the regulation of mixed-linkage glucan (MLG) biosynthesis. The gene encoding a grass-specific glycoside hydrolase family 16 endotransglucosylase/hydrolase (BdXTH8) is bound by BdTHX1. BdTHX1 directly binds to an intronic region of BdCSLF6 and also to the 3' proximal region of BdXTH8. BdTHX1 likely plays an important role in MLG biosynthesis and restructuring by regulating the expression of BdCSLF6 and BdXTH8. BdTHX1 may regulate genes related to cell wall assembly or restructuring such as BdXTH8, and misregulation of BdTHX1 is detrimental to Brachypodium distachyon development
enzymes FvXTH9 and FvXTH6 display xyloglucan endotransglucosylase (XET, EC 2.4.1.207) activity towards various acceptor substrates using xyloglucan as the donor substrate. FvXTH9 also shows activity of mixed-linkage glucan:xyloglucan endotransglucosylase (MXE) and cellulose:xyloglucan endotransglucosylase (CXE). XTHs (xyloglucan endotransglucosylases/hydrolases) can catalyse the endolytic cleavage of xyloglucan polymers and the rejoining of the newly generated reducing ends to other xyloglucan molecules, which is referred to as xyloglucan endotransglucosylase (XET) activity. In addition, XTHs can also show xyloglucan endohydrolase (XEH) activity, where water is used as an acceptor, and thus the xyloglucan molecule is hydrolysed
among land-plant hemicelluloses, xyloglucan is ubiquitous, whereas mixed-linkage (1->3), (1->4)-beta-D-glucan, i.e. MLG, is confined to the Poales and Equisetales. The enzyme MLG:xyloglucan endotransglucosylase, MXE, grafts MLGto xyloglucan. MLG is absent in the most immature cells tested (callus culture) and highly prevalent in older tissues, whereas xyloglucan content is higher in young tissues
among land-plant hemicelluloses, xyloglucan is ubiquitous, whereas mixed-linkage (1->3), (1->4)-beta-D-glucan, i.e. MLG, is confined to the Poales and Equisetales. The enzyme MLG:xyloglucan endotransglucosylase, MXE, grafts MLGto xyloglucan. MLG is absent in the most immature cells tested (callus culture) and highly prevalent in older tissues, whereas xyloglucan content is higher in young tissues
BdXTH8 exhibits predominantly MLG:xyloglucan endotransglucosylase activity, a hetero-transglycosylation reaction, and can thus produce MLG-xyloglucan covalent bonds. It also has a lower xyloglucan:xyloglucan endotransglucosylase activity. Mixed-linkage glucan (MLG) is a polysaccharide that is highly abundant in grass endosperm cell walls and present at lower amounts in other tissues. BdXTH8 does not exhibit appreciable cellulose:xyloglucan endotransglucosylase (CXE) activity, with either insoluble (paper) cellulose or water-soluble cellulose acetate as donor substrate. The enzyme's main role in vivo is likely to be the making and/or breaking of MLG-xyloglucan covalent bonds that stably link two hemicelluloses of the grass cell wall and thus contribute to grass cell wall assembly and/or loosening
FvXTH9 and also FvXTH6 might promote strawberry fruit ripening by the modification of cell wall components. The level of anthocyanins such as pelargonidin-3-O-glucoside and pelargonidin-3-O-(6'-malonyl)-glucoside is significantly higher in the infiltrated fruits, similar to citric acid and ascorbic acid
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CRYSTALLIZATION (Commentary)
ORGANISM
UNIPROT
LITERATURE
homology modeling of structure suggests that key amino acid substitutions Trp-Pro, Gly-Ser and Arg-Leu are responsible for the evolution of HTGs specificity from the xyloglucan-acting homo-transglycanases
in constructed BdTHX1 RNA1 knockdown lines of Brachypodium distachyon, the expression of BdTHX1 and BdXTH8 is downregulated, and the transcript abundance of BdCSLF6 is not significantly changed. In the four lines, the expression of BdTHX1, BdCSLF6, and BdXTH8 show the same pattern in the T0, T1, and T2 generation
Fragaria x ananassa cv. Elsanta fruits infiltrated with FvXTH9 and FvXTH6 ripen faster and show decreased firmness compared with the empty vector control pBI121
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CLONED (Commentary)
ORGANISM
UNIPROT
LITERATURE
BdTHX1, transcriptional profiling, recombinant expression of BdXTH8(amino acids 25-301), without the N-terminal signal peptide, in Pichia pastoris as a secreted protein using a Pichia pastoris signal sequence
phylogenetic tree of xyloglucan endotransglucosylase/hydrolases (XTHs) from different species, overexpression of FvXTH9 in Fragaria x ananassa cv. Elsanta fruits, coexpression with FvXTH6, recombinant expression in Nicotiana tabacum cv. Samsum Agrobacterium tumefaciens GV3101/pSoup transfection system for localization studies, recombinant expression of His-tagged enzyme in Saccharomyces cerevisiae INVSc1 cells