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Posttranslational modifications of fibromodulin
P Antonsson1, D Heinegård, A Oldberg
1Department of Medical and Physiological Chemistry, University of Lund, Sweden.
The Journal of Biological Chemistry
|September 5, 1991
Summary
Fibromodulin, a protein found in cartilage, tendon, and sclera, contains tyrosine sulfate residues in its N-terminal region. This modification, along with keratan sulfate chain substitution, occurs in various cell types, not just chondrocytes.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Fibromodulin is a leucine-rich repeat proteoglycan found in connective tissues.
- Previous studies suggested fibromodulin is primarily synthesized by chondrocytes.
Purpose of the Study:
- To investigate the post-translational modifications of fibromodulin, specifically tyrosine sulfation and keratan sulfate substitution.
- To determine the cellular origins and tissue distribution of modified fibromodulin.
Main Methods:
- Analysis of fibromodulin produced by tracheal chondrocytes, tendon fibroblasts, sclera fibroblasts, and transfected Chinese hamster ovary (CHO) cells.
- Site-directed mutagenesis to create fibromodulin variants lacking the N-terminal region.
- Digestion with N-glycosidase F to analyze oligosaccharide chains.
Main Results:
- Tyrosine sulfate residues were identified in the N-terminal region of fibromodulin from various sources, including transfected CHO cells.
- Fibromodulin lacking the N-terminal 52 amino acids showed no tyrosine sulfation.
- Keratan sulfate chain substitution was observed in fibromodulin from chondrocytes, tendon fibroblasts, sclera fibroblasts, and tendon tissue.
- N-glycosidase F digestion confirmed the presence of N-glycosidically linked oligosaccharides, some extended to keratan sulfate chains.
Conclusions:
- Fibromodulin undergoes tyrosine sulfation in its N-terminal domain, a modification present in multiple cell types.
- Keratan sulfate substitution is not exclusive to chondrocytes and occurs in fibromodulin synthesized by fibroblasts and found in tendon.
- Fibromodulin contains N-glycosidically linked oligosaccharides, with some extending into keratan sulfate chains, across cartilage, tendon, and sclera.