Keratin Sulfate (KS) is the only sulfated GAGs that do not contain uronic acids. It consists of repeating disaccharide Galb1-4GlcNAc linked by β-1,3 glycosidic bonds. During the biosynthesis of KS, glycosyltransferases and sulfotransferases work together in sequence to alternately add Gal and GlcNAc to the acceptor GlcNAc residue at the reducing end of KS chain, resulting in chain elongation. Both Gal and GlcNAc in KS chain can undergo sulfation at C6, but it occurs more frequently on GlcNAc than on Gal. The sulfation degree of KS is heterogeneous, including non-sulfated domains, low sulfated domains with only 6-O-sulfated GlcNAc residues, and highly sulfated domains with both 6-O-sulfated Gal and GlcNAc residues. Like other GAGs, it is these variable sulfated domains that determine the interaction properties of KS with ligands such as growth factors, morphogens, and cytokines, and thus determine the biological functions of KS. Different types of KS can be isolated and prepared from animal cornea, cartilage and egg white, but few are commercialized.

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