Keratan sulfates (KSs) are sulfated polymers of N-acetyllactosamine structured by repeating (1 3)--D-galactose-(1 4)--D-N-acetylglucosamine units, which are generally sulfated at position C6 of the hexosamine and/or galactosamine. They are mostly covalently bound to core proteins of KS-bearing proteoglycans (PGs), but a few non-proteoglycan KS-substituted macromolecules have been described, and their attachment to protein backbones occurs primarily through an N-linkage involving glucosamine binding to an asparagine residue These are referred to type I KSs and are characteristic of the corneal ECM. KS chains may also be bound to proteins through an O-glycosidic linkage between galactosamine and a serine or threonine residue, i.e. referred to as type II KSs and highly represented in articular cartilage ECM. Phosphocan and other KS-containing PGs of the brain may also carry KS chains attached to the core protein through an alternative mannose-serine/threonine linkage.

One of the complexities of KSs is the variable degree of chain branching (i.e. bi-antennary in the cornea and more intricate branching in skeletal KS), which together with the variable extent and positioning of the sulfate groups and the relative frequency, linkage and type of capping fucose and/or neuraminic acid residues, creates a spectrum of putative functionally diverse KS moieties. For instance, sialic acid residues may coincidently, or in an alternated fashion be present in an (1-3), (2-3) or (2-6)-linkage, and may or may not associate with (1-3)-linked fucoses.

References:
Magro, M., et.al., 2003. Proteomic and post-proteomic characterization of keratan sulfate-glycanated isoforms of thyroglobulin and transferrin uniquely elaborated by papillary thyroid carcinoma. Am J. Pathol. 163, 183-196.

Keratan sulfates (KSs) are sulfated polymers of N-acetyllactosamine structured by repeating (1 3)--D-galactose-(1 4)--D-N-acetylglucosamine units, which are generally sulfated at position C6 of the hexosamine and/or galactosamine. They are mostly covalently bound to core proteins of KS-bearing proteoglycans (PGs), but a few non-proteoglycan KS-substituted macromolecules have been described, and their attachment to protein backbones occurs primarily through an N-linkage involving glucosamine binding to an asparagine residue These are referred to type I KSs and are characteristic of the corneal ECM. KS chains may also be bound to proteins through an O-glycosidic linkage between galactosamine and a serine or threonine residue, i.e. referred to as type II KSs and highly represented in articular cartilage ECM. Phosphocan and other KS-containing PGs of the brain may also carry KS chains attached to the core protein through an alternative mannose-serine/threonine linkage.

One of the complexities of KSs is the variable degree of chain branching (i.e. bi-antennary in the cornea and more intricate branching in skeletal KS), which together with the variable extent and positioning of the sulfate groups and the relative frequency, linkage and type of capping fucose and/or neuraminic acid residues, creates a spectrum of putative functionally diverse KS moieties. For instance, sialic acid residues may coincidently, or in an alternated fashion be present in an (1-3), (2-3) or (2-6)-linkage, and may or may not associate with (1-3)-linked fucoses.

References:
Magro, M., et.al., 2003. Proteomic and post-proteomic characterization of keratan sulfate-glycanated isoforms of thyroglobulin and transferrin uniquely elaborated by papillary thyroid carcinoma. Am J. Pathol. 163, 183-196.