Keratan Sulfate Structure
Like other glycosaminoglycans keratan sulfate is a linear polymer that consists of a repeating disaccharide unit. Keratan sulfate occurs as a proteoglycan (PG) in which KS chains are attached to cell-surface or extracellular matrix proteins, termed core proteins. KS core proteins include Lumican, Keratocan, Mimecan, Fibromodulin, PRELP, Osteoadherin and Aggrecan.
The basic repeating disaccharide unit within keratan sulfate is -3Galβ1-4GlcNAcβ1-. This can be sulfated at carbon position 6 (C6) of either or both the Gal or GlcNAc monosaccharides. However, the detailed primary structure of specific KS types are best considered to be composed of three regions:
- A linkage region, at one end of which the KS chain is linked to the core protein.
- A repeat region, composed of the -3Galβ1-4GlcNAcβ1- repeating disaccharide unit and
- A chain capping region, occurring at the opposite end of the KS chain to the protein linkage region.
The monosaccharide mannose is found within the linkage region of keratan sulfate type I (KSI). Disaccharides within the repeating region of KSII may be fucosylated and N-Acetylneuraminic acid caps the end of all keratan sulfate type II (KSII) chains and up to 70% of KSI type chains.
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