Journal of Biological Chemistry
Volume 274, Issue 9, 26 February 1999, Pages 5777-5781
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CELL BIOLOGY AND METABOLISM
Association of the Aggrecan Keratan Sulfate-rich Region with Collagen in Bovine Articular Cartilage*

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Aggrecan, the predominant large proteoglycan of cartilage, is a multidomain macromolecule with each domain contributing specific functional properties. One of the domains contains the majority of the keratan sulfate (KS) chain substituents and a protein segment with a proline-rich hexapeptide repeat sequence. The function of this domain is unknown but the primary structure suggests a potential for binding to collagen fibrils. We have examined binding of aggrecan fragments encompassing the KS-rich region in a solid-phase assay. A moderate affinity (apparent K d = 1.1 μm) for isolated collagen II, as well as collagen I, was demonstrated. Enzymatic digestion of the KS chains did not alter the capacity of the peptide to bind to collagen, whereas cleavage of the protein core abolished the interaction. The distribution of the aggrecan KS-rich region in bovine tarsometatarsal joint cartilage was investigated using immunoelectron microscopy. Immunoreactivity was relatively low in the superficial zone and higher in the intermediate and deep zones of the uncalcified cartilage. Within the pericellular and territorial matrix compartments the epitopes representing the aggrecan KS-rich region were detected preferentially near or at collagen fibrils. Along the fibrils, epitope reactivity was non-randomly distributed, showing preference for the gap region within the d-period. Our data suggest that collagen fibrils interact with the KS-rich regions of several aggrecan monomers aligned within a proteoglycan aggregate. The fibril could therefore serve as a backbone in at least some of the aggrecan complexes.

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*

This study was supported by grants from the Swedish Medical Research Council, the Swedish Medical Association (12231-020A), the Swedish Association against Rheumatism, Inga Britt and Arne Lundberg's Research Foundation, Axel and Margaret Ax:son Johnson's Foundation, Loo and Hans Osterman's Foundation, Anna-Greta Crafoord's Foundation, King Gustaf V's 80 year Anniversary Foundation, Signe and Reinhold Sund's Foundation for Rheumatologic Research, Ulla and Gustaf af Ugglas' Foundation, the Bank of Sweden Tercentenary Foundation, Clas Groschinky's Foundation, Ragnhild and Einar Lundström's Memorial Foundation, Sigurd and Elsa Golje's Memorial Foundation, Alfred Österlund's Foundation, Greta and Johan Kock's Foundations, Gunand Bertil Stohne's Foundation and from Karolinska Institutet, Stockholm.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.