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O-linked glycosylation is the attachment of a sugar molecule to the oxygen atom of serine (Ser) or threonine (Thr) residues in a protein. O -glycosylation is a post-translational modification that occurs after the protein has been synthesised.
Oligosaccharides that participate in O-linked glycosylation are attached to threonine or serine on the hydroxyl group of the side chain. [7] O-linked glycosylation occurs in the Golgi apparatus, where monosaccharide units are added to a complete polypeptide chain. Cell surface proteins and extracellular proteins are O-glycosylated. [10]
O-linked glycans attached to the hydroxyl oxygen of serine, threonine, tyrosine, hydroxylysine, or hydroxyproline side-chains, or to oxygens on lipids such as ceramide. Phosphoglycans linked through the phosphate of a phosphoserine. C-linked glycans, a rare form of glycosylation where a sugar is added to a carbon on a tryptophan side-chain.
The most common method of glycosylation of N-linked glycoproteins is through the reaction between a protected glycan and a protected Asparagine. [5] Similarly, an O-linked glycoprotein can be formed through the addition of a glycosyl donor with a protected Serine or Threonine. [5] These two methods are examples of natural linkage. [5]
Glycosidic bonds of the form discussed above are known as O-glycosidic bonds, in reference to the glycosidic oxygen that links the glycoside to the aglycone or reducing end sugar. In analogy, one also considers S-glycosidic bonds (which form thioglycosides ), where the oxygen of the glycosidic bond is replaced with a sulfur atom.
In the case of branched oligosaccharides, meaning that the structure contains at least one monosaccharide residue linked to more than two other monosaccharide residues, terms designating the branches should be listed in square brackets, with the longest linear chain (the parent chain) written without square brackets. [3]
This area becomes saturated with hundreds of O-linked oligosaccharides. N-linked oligosaccharides are also found on mucins, but in less abundance than O-linked sugars.
Carbohydrates consist of "hydrated carbon", i.e. [CH 2 O]n. Monosaccharides are a carbohydrate that cannot be hydrolyzed into a simpler carbohydrate and are the building blocks of oligosaccharides and polysaccharides. Oligosaccharides are linear or branched chains of monosaccharides attached to one another via glycosidic linkages. The number of ...