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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.
N-linked glycosylation is a very prevalent form of glycosylation and is important for the folding of many eukaryotic glycoproteins and for cell–cell and cell–extracellular matrix attachment. The N-linked glycosylation process occurs in eukaryotes in the lumen of the endoplasmic reticulum and widely in archaea, but very rarely in bacteria.
The different types of lipid-linked oligosaccharide (LLO) precursor produced in different organisms.. N-linked glycosylation is the attachment of an oligosaccharide, a carbohydrate consisting of several sugar molecules, sometimes also referred to as glycan, to a nitrogen atom (the amide nitrogen of an asparagine (Asn) residue of a protein), in a process called N-glycosylation, studied in ...
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]
An example of an O-linked oligosaccharide with β-Galactosyl-(1n3)-α-N-acetylgalactosaminyl-Ser/Thr. Oligosaccharides that participate in O-linked glycosylation are attached to threonine or serine on the hydroxyl group of the side chain. [7]
The modification is characterized by a β-glycosidic bond between the hydroxyl group of serine or threonine side chains and N-acetylglucosamine (GlcNAc). O-GlcNAc differs from other forms of protein glycosylation: (i) O-GlcNAc is not elongated or modified to form more complex glycan structures, (ii) O-GlcNAc is almost exclusively found on ...
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.
N-linked glycosylation starts in the endoplasmic reticulum with the addition of a precursor glycan. The precursor glycan is modified in the Golgi apparatus to produce complex glycan bound covalently to the nitrogen in an asparagine amino acid. In contrast, O-linked glycosylation is the sequential covalent addition of individual sugars onto the ...