Cornea, keratan sulfate

As shown in Figure 48-8, the keratan sulfates consist of repeating Gal-GlcNAc disaccharide units containing sulfate attached to the 6 position of GlcNAc or occasionally of Gal. Type 1 is abundant in cornea, and type II is found along with chondroitin sulfate attached to hyaluronic acid in loose connective tissue. Types I and II have different attachments to protein (Figure 48—8). 

The second polysaccharide present in cartilage proteogylcan is keratan sulfate. It is generally found in shorter chains than chondroitin sulfate with an average molecular weight of about 20,000 Da. It is also found in the cornea of the eye. 

As well as chondroitin sulfate, other glycosaminoglycans, such as keratan sulfate, with shorter chains (Mr = 2,500-5,000) are found in cartilage (Fig. 5-22). N-linked oligosaccharides similar to those found in glycoproteins are also present. Note that keratan sulfate in other tissues, e.g., intervertebral disk or cornea, has a longer chain (Mr= 10,000-25,000) and may have a different oligosaccharide link to the core protein. 

Nilsson B, Nakazawa K, Hassell JR, Newsome DA, Hascall VC. Structure of oligosaccharides and the hnkage region between keratan sulfate and the core protein on proteoglycans from monkey cornea. J. Biol. Chem. 1983 258(10) 6056—6063. 

Christner JE, Distler JJ, Jourdian GW. Biosynthesis of keratan sulfate - purification and properties of a galactosyltransferase from bovine cornea. Arch. Biochem. Biophys. 1979 192(2) 548-558. 

Keratan sulfate constitutes approximately half the total mucopolysaccharide fraction of bovine cornea, where it was isolated originally by Meyer et al. (M16). It occurs fairly widely in animal connective tissues, and its presence has been reported in nucleus pulposus (G2), aorta (B17), and costal cartilage (M20). Unlike the acid mucopolysaccharides described previously, keratan sulfate contains no uronic acid residue but is comprised of V-acetyl-n-glucosamine, D-galactose, and sulfate, in equimolar ratio. The small amount of L-fucose detected in acidic... 

Keratan sulfate consists of the disaccharide, iV-acetyl-lactosamine, linked /3-(1 3) to the D-galactopyranose residue of the next iV-acetyl-lactosamine unit. Keratan sulfate is the most heterogeneous of the glycosaminoglycans, with variable sulfate content linked to C-4 or C-6 of the D-galactop)Tanose residue in lactosamine, and small amounts of L-fucose (6-deoxy-L-galactose), D-mannose, and iV-acetyl-neuraminic acid residues [93] (also see Sects. 10.2 and O 14 on the occurrence of iV-acetyl-D-neuraminic acid and L-fucose in other systems). Keratan sulfate is found in the cornea, on the surfaces of erythrocytes, in cartilage, and in bone. 

Keratan sulfate (4,000 to 19,000) D-Glucosamine None (but contains D-Galactose) 6-0-sulfate on both carbohydrate residues Cartilage, cornea, intervertebral disks... 

The keratan and chondroitin/dermatan sulfate levels in normal human corneas and corneas affected by macular corneal dystrophies types I and II were compared (10). The results revealed that the keratan sulfate chain size was reduced and chain sulfation was absent in type I, and that sulfation of both GlcNAc and Gal was significantly reduced in type II. The chondroitin/dermatan sulfate chain sizes were also decreased in all diseased corneas, and the contents of 4- and... 

Macular corneal dystrophy types I and II have also been characterized histo-chemically. In normal corneas, high levels of sulfated keratan sulfate were detected in the stroma. Bowman s layer, and Descemet s membrane with low levels in the keratocytes, epithelium, and endothelium. Furthermore, in normal corneas, negligible levels of labeling for A-acetyllactosamine (unsulfated keratan sulfate) were detected. In macular corneal dystrophy type I corneas, sulfated keratan sulfate... 

Edward DP, Thonar EJ, Srinivasan M, Yue BJ, Tso MO. Macular dystrophy of the cornea. A systemic disorder of keratan sulfate metabolism. Ophthalmology 1990 97 1194-1200. 

Keratan sulfate is highly expressed in the cornea, bones, brain, and the ECM. 

Animal models suggest that keratan sulfate together with dermatan sulfate regulates the water content in the cornea (136). In mice, macrophages do not adhere to any surface that is coated with keratan sulfate-enriched luminican... 

Type IV Morquio-Ullrich syndrome (probably more than one allelic form) Severe bone changes of distinctive type, cloudy cornea, aortic regurgitation Homozygous for Morquio-Ullrich gene Keratan sulfate Unknown... 

V-Acetyl-D-galactosamine (D-GalpNAc, AN) OH OH HO NHCOCH3 D-GalNAc is found in mucopolysaccharide such as chondroitin (cartilage) keratan sulfate (cornea) and dermatan sulfate (skin). In 0-glycoproteins, GalNAc provides attachment to serine. 

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