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Keratan Sulfate Proteoglycans(KSPGs) are major components of the corneal stroma after collagen. It is believed that KSPG is involved in the process of corneal transparency. Many investigators have isolated, purified, and characterized KSPGs from monkey, bovine, rabbit, chicken, and human. There is no complete agreement on the number of isoforms of KSPGs present in different mammalian species. Nonetheless, extensive heterogeneety in the structures has been observed. The basis for such an heterogeneity is not clear at present. It may lie in the core proteins, in the glycosaminoglycans(GAGs). The core proteins may have different lengths and different amino acids sequence and may have different KS attachment sites. The GAG chains may differ in their chain length or the extent of sulfation. The KS chains may have also the bianeternary structure whereby two KS chains may be attached to a common linkage region via two mannose residues. The authors have attempted to answer some of these questions by isolating core proteins from KSPGs of bovine and chick corneal stromas. In order to do so, these investigators have taken novel approaches; i) Partially purified KSPG preparation was treated with keratanase, with trifluoromethyl sulfonic acid and N-glycanase in order to remove KS chains and oligosaccharide chains. The core proteins thus isolated were purifled by DEAE-Sephacel chromatography, SDSD-PAGE followed by transfer to nitrocellulose and elution. Three distinct core proteins of molecular sizes of 37 kDa(37A), 36 kDa(37B) and 25 kDa were isolated. ii) Identification of KS attachment sites on the core proteins was performed by use of specific endo-glycosidase from E. freundii which cleaves G1cNAc-GalKS linkage, leaving the linkage region with a bianternary structure and also leaving the non-reducing terminal N-acetyl-glucosamine available for accepting the galactose residue from UDP-Gal catalyzed by galactosyl-transferase. iii) Tryptic peptide mapping of three core proteins showed significant differences. Moreover, distribution of 3H-Gal labeled peptides as shown by reverse-phase chromatography revealed that 37 A core protein contained three major 3H-peptides indicating three KS attachment sites. 37B and 25 kDa core proteins contained only 3H-peptide suggesting only one KS attachment site. iv) Sialic acid residues on the linkage oligosaccharide portion of the labeled core proteins were selectively labeled with 3H soケ ラ タ ン硫 酸 プ ロテ オ グ リ カ ン(KSPG)は 角 膜 ス トロ ーマ

How Many Isoforms of Keratan Sulfate Proteoglycans are There?