title: Type IX collagen interacts with fibronectin providing an important molecular bridge in articular cartilage.
abstract: Type IX collagen is covalently bound to the surface of type II collagen fibrils within the cartilage extracellular matrix. The N-terminal, globular noncollagenous domain (NC4) of the α1(IX) chain protrudes away from the surface of the fibrils into the surrounding matrix and is available for molecular interactions. To define these interactions, we used the NC4 domain in a yeast two-hybrid screen of a human chondrocyte cDNA library. 73% of the interacting clones encoded fibronectin. The interaction was confirmed using in vitro immunoprecipitation and was further characterized by surface plasmon resonance. Using whole and pepsin-derived preparations of type IX collagen, the interaction was shown to be specific for the NC4 domain with no interaction with the triple helical collagenous domains. The interaction was shown to be of high affinity with nanomolar K(d) values. Analysis of the fibronectin-interacting clones indicates that the constant domain is the likely site of interaction. Type IX collagen and fibronectin were shown to co-localize in cartilage. This novel interaction between the NC4 domain of type IX collagen and fibronectin may represent an in vivo interaction in cartilage that could contribute to the matrix integrity of the tissue.
authors.affiliation: Research Centre, Smith & Nephew, York Science Park, Heslington, York YO10 5DF, United Kingdom.
authors.forename: Philippa
authors.initials: P
authors.lastname: Parsons
authors.forename: Sophie J
authors.initials: SJ
authors.lastname: Gilbert
authors.forename: Anne
authors.initials: A
authors.lastname: Vaughan-Thomas
authors.forename: David A
authors.initials: DA
authors.lastname: Sorrell
authors.forename: Rebecca
authors.initials: R
authors.lastname: Notman
authors.forename: Mark
authors.initials: M
authors.lastname: Bishop
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Hayes
authors.forename: Deborah J
authors.initials: DJ
authors.lastname: Mason
authors.forename: Victor C
authors.initials: VC
authors.lastname: Duance
mesh_terms: D000818:Animals; D002356:Cartilage / Q000378:metabolism; D002358:Cartilage, Articular / Q000378:metabolism*; D002460:Cell Line; D019902:Chondrocytes / Q000378:metabolism; D024081:Collagen Type IX / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D051379:Mice; D016133:Polymerase Chain Reaction; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D020798:Two-Hybrid System Techniques
chemical_list: D024081:Collagen Type IX; D018076:DNA, Complementary; D005353:Fibronectins; D011994:Recombinant Proteins