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MetNet - plant pathway - xyloglucan biosynthesis
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Pathway details: xyloglucan biosynthesis


General info Interaction details Linked pathways Protein-protein interactions
Notes
  Pathway was created on Mon Jul 29, 2013.
 Contributed by aracyc:
General Background Xyloglucan is the major component of the in cell walls of dicotyledon type I and non-graminaceous monocotyledons plants. It also exists in some seeds of trees growing in the tropical zone. Xyloglucan interacts with cellulose microfibrils via hydrogen bonds to form a structural network that is assumed to play a key role in cell wall integrity. Cross-linking between the xyloglucan chains is a major factor in the stability of the resulting three-dimensional matrix |CITS: [Whitney95]|. Xyloglucan has a backbone of β-1,4-linked glucose residues, most of which are substituted in C-6 by α-D-xylosyl residues . Some of the xylosyl residues are further substituted by (1,2)-β-D-galactosyl residues, and some of the galactosyl residues are capped by (1,2)-α-L-fucose . A common terminology uses G for basic non-substituted glucosyl units within a xylosylglycan, X for glucose residues substituted by α-D-xylose, L for glucose residues substituted by α-D-xylose and β-D-galactose, and F for glucose residues substituted by α-D-xylose, β-D-galactose and α-L-fucose |CITS:[Fry93]|. Fucosyl residues are typically absent from seed xyloglucans but present on the xyloglucans in the vegatative portions of the same plant |CITS: [Mishra09]|. Most xylosylglucans consist of repeating heptasaccharide XXXG units. The average molecular weight of xyloglucan is more than 50 000 |CITS: [Mishra09]|. About This Pathway The biosynthesis of xyloglucan is still not well understood. It is well established that xyloglucan is assembled within Golgi stacks and transported in Golgi-derived vesicles to the cell wall. The glucan synthase that is involved in xyloglucan synthesis is likely encoded by gene, characterized from Nasturtium and Arabidopsis . Three xyloglucan 6-xylosyltransferase enzymes that catalyze the transfer of xylose from UDP-D-xylose onto β(1,4)-linked glucan chains have been reported from . Two of the enzymes ( and ) were shown to preferentially add one xylose to unsubstituted glucans at the second position from the non-reducing end. When using (GGGGGG), the preferred substrate, the enzymes produced mostly GGXGGG, with GGXXGG also formed after long incubations with a high substrate ratio |CITS: |. While the activity of the third enzyme, , has not been well characterized, it has been shown that a mutant lacking it shows a reduced xyloglucan content |CITS: . A xyloglucan galactosyltransferase () that attaches an α-L-D-galactose residue specifically to the third xylose residue within the XXXG core structure has been reported from Arabidopsis . Other galactosyltransferases may be necessary for galactosylation of other opsitions . Finally, the Arabidopsis () that attaches an α-L-fucose residue to the third xylose residue within the XXXG core structure has been identified and characterized ."
  Parts of this pathway occur in:   nucleus     cytosol  


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metabolite [20]
gene [12]
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