Enhanced expression of a peanut agglutinin reactive O linked oligosaccharide on fibronectins from the synovial fluid of patients with rheumatic disease: quantitation, domain localization, and functional significance.

OBJECTIVE: To characterize the domain localization, quantitation, and functional binding consequences of an O linked oligosaccharide expressed on synovial fluid (SF) fibronectin (Fn).
METHODS: Identification and localization of the O linked oligosaccharide was performed by limited digestion of isolated SF Fn with a series of proteolytic enzymes followed by Western blotting with peroxidase labeled peanut agglutinin. Binding affinity to denatured collagen was performed utilizing a solid phase gelatin-binding assay. Quantitation was performed by measuring purified Fn in an antibody-lectin sandwich binding assay.
RESULTS: A desialyated O linked oligosaccharide was identified on the C-terminal 18 kDa segment of the SF Fn collagen-binding domain. These SF collagen-binding Fn fragments were more basic and had higher gelatin-binding affinities than corresponding plasma fibronectin fragments. Expression of this O linked oligosaccharide was highest on Fn isolated from osteoarthritic SF, followed by Fn isolated from rheumatoid arthritis SF, and finally normal human plasma.
CONCLUSION: Fn isolated from SF have glycosylation alterations that may influence their biologic properties in the diseased joint.