The structure and function of normal and mutated collagen IX
1University of Oulu, Faculty of Medicine, Department of Medical Biochemistry and Molecular Biology
2University of Oulu, Biocenter Oulu
|Online Access:||PDF Full Text (PDF, 0.8 MB)|
|Persistent link:|| http://urn.fi/urn:isbn:9789514286544
|Publish Date:|| 2007-12-11
|Thesis type:||Doctoral Dissertation
|Defence Note:||Academic dissertation to be presented, with the assent of the Faculty of Medicine of the University of Oulu, for public defence in Auditorium F101 of the Department of Physiology (Aapistie 7), on December 21st, 2007, at 1 p.m.
Professor Yrjö Konttinen
Docent Asta Pirskanen
Collagen IX belongs to the superfamily of collagenous proteins and is present on the surface of the heterotypic collagen fibrils that are predominantly composed of collagen II, and also collagen XI. The major sites of expression of collagen IX include the articular cartilage, intervertebral disc, inner ear and the vitreous body of the eye.
Previous reports have indicated that mutations in the genes encoding the three polypeptide chains of collagen IX may lead to intervertebral disc disease and multiple epiphyseal dysplasia, a chondrodysplasia characterized by early onset osteoarthritis. These observations and results from genetically modified mouse lines suggest that collagen IX is crucial in the maintenance of the long-term integrity of tissues. However, the structure-function relationship as well as detailed information concerning the functional roles of this protein has remained unclear.
Recombinant human collagen IX was obtained using an insect cell expression system. Besides full-length molecules, five truncated variants of collagen IX were produced to examine chain association and trimerization. Contrary to previous observations, it was shown that the COL1 and NC1 domains are not essential for trimerization. Instead, they seem to play an important role in the specificity of chain selection. The results also suggest that the N-terminal domains, NC3 or COL3, are required for complete folding and stabilization of collagen IX molecules, implicating cooperativity between different domains in the folding process.
Collagen IX was found to mediate cell adhesion and bind efficiently to collagen receptor integrins α1β1, α2β1, α10β1 and α11β1. The binding was found to represent a novel type of mechanism, and the binding site of the integrin I domain was located at the N-terminal end of the COL3 domain in collagen IX. The obtained results suggest that the FACITs may play an important role as mediators of cell adhesion to collagen fibrils.
Antibodies binding to human recombinant collagen IX were measured among 53 patients with seropositive rheumatoid arthritis (RA). These autoantibodies were significantly elevated among the RA patients when compared to the controls, suggesting that autoantibodies to collagen IX show diagnostic potential in early RA. However, no association was found between the antibody levels and outcome.
Acta Universitatis Ouluensis. D, Medica
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