THE STRUCTURE OF THE KERATAN SULFATE CHAINS ATTACHED TO FIBROMODULIN FROM HUMAN ARTICULAR-CARTILAGE

The small keratan sulphate proteoglycan, fibromodulin, has been isolat ed from pooled human articular cartilage. The main chain repeat region and the chain caps from the attached N-linked keratan sulphate chains have been fragmented by keratanase II digestion, and the oligosacchar ides generated have been reduced and isolated. Their structures and ab undance have been determined by high pH anion-exchange chromatography. These regions of the keratan sulphate from human articular cartilage fibromodulin have been found to have the following general structure: [GRAPHICS] Significantly, both alpha(2-6)- and alpha(2-3)-linked N-ace tyl-neuraminic acid have been found in the capping oligosaccharides. F ucose, which is alpha(1-3)-linked as a branch to N-acetylglucosamine, has also been found along the length of the repeat region and in the c apping region. The chains, which have been found to be very highly sul phated, are short; the length of the repeat region and chain caps is c a. nine disaccharides. These data demonstrate that the structure of th e N-linked keratan sulphate chains of human articular cartilage fibrom odulin is similar, in general, to articular cartilage derived O-linked keratan sulphate chains. Further, the general structure of the kerata n sulphate chains attached to human articular cartilage fibromodulin h as been found to be generally similar to that of both bovine and equin e articular cartilage fibromodulin.