Xyloglucan is a hemicellulose that occurs in the primary cell wall of all vascular plants, however essential enzymes for xyloglucan metabolism, like XTH and β1→4-Glucan Synthase are found in Charophyceae algae. In many dicotyledonous plants, it is the most abundant hemicellulose in the primary cell wall. Xyloglucan binds to the surface of cellulose microfibrils and may link them together. It is the substrate of xyloglucan endotransglycosylase, which cuts and ligates xyloglucans, as a means of integrating new xyloglucans into the cell wall. It is also thought to be the substrate of alpha-expansin, which promotes cell wall enlargement.
Xyloglucan has a backbone of β1→4-linked glucose residues, most of which substituted with 1-6 linked xylose sidechains. The xylose residues are often capped with a galactose residue sometimes followed by a fucose residue. The specific structure of xyloglucan varies among plant families.
Xyloglucan is synthesized in Golgi trans cisternae and in the trans Golgi network (TGN) and is transported to the cell membrane by vesicles, where it is expelled and adsorbs on nascent cellulosic microfibrils.
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