O-linked glycosylation

O-linked glycans are a common covalent modification of serine and threonine residues of mammalian glycoproteins. The most common type of O-linked glycans found on secreted mammalian glycoproteins and mucins (proteins conjugated to carbohydrate) is from the addition of N-acytylgalactosamine (GalNac) to serine or threonine residues. The Core 1 structure is generated by the addition of galactose b1-3 to this GalNAc. The Core 2 structure is generated by the further addition of N-acetyl-glucosamine b1-6 to the N-acetyl-galactosamine on the Core 1 structure. In total eight different O-linked glycans core structures have been identified and all of these can be further elongated by the addition of a number of monosaccharides including sialic acids.