The proteoglycans aggrecan and Versican form networks with fibulin-2 through their lectin domain binding.
Aggrecan, versican, neurocan, and brevican are important components of the extracellular matrix in various tissues. Their amino-terminal globular domains bind to hyaluronan, but the function of their carboxyl-terminal globular domains has long remained elusive. A picture is now emerging where the C-type lectin motif of this domain mediates binding to other extracellular matrix proteins. We here demonstrate that aggrecan, versican, and brevican lectin domains bind fibulin-2, whereas neurocan does not. As expected for a C-type lectin, the interactions are calcium-dependent, with K(D) values in the nanomolar range as measured by surface plasmon resonance. Solid phase competition assays with previously identified ligands demonstrated that fibulin-2 and tenascin-R bind the same site on the proteoglycan lectin domains. Fibulin-1 has affinity for the common site on versican but may bind to a different site on the aggrecan lectin domain. By using deletion mutants, the interaction sites for aggrecan and versican lectin domains were mapped to epidermal growth factor-like repeats in domain II of fibulin-2. Affinity chromatography and solid phase assays confirmed that also native full-length aggrecan and versican bind the lectin domain ligands. Electron microscopy confirmed the mapping and demonstrated that hyaluronan-aggrecan complexes can be cross-linked by the fibulins.
Olin
A I
AI
Department of Cell and Molecular Biology, Section for Connective Tissue Biology, Lund University, BMC Plan C12, SE-221 84 Lund, Sweden.
Mörgelin
M
M
Sasaki
T
T
Timpl
R
R
Heinegård
D
D
Aspberg
A
A
D053674:Aggrecans; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D011508:Chondroitin Sulfate Proteoglycans / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D003432:Cross-Linking Reagents; D019281:Dimerization; D016326:Extracellular Matrix Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D007700:Kinetics; D037102:Lectins; D037181:Lectins, C-Type; D008322:Mammals; D011509:Proteoglycans / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D020349:Surface Plasmon Resonance; D053675:Versicans
D053674:Aggrecans; D002135:Calcium-Binding Proteins; D011508:Chondroitin Sulfate Proteoglycans; D003432:Cross-Linking Reagents; D016326:Extracellular Matrix Proteins; D037102:Lectins; D037181:Lectins, C-Type; D011509:Proteoglycans; D011993:Recombinant Fusion Proteins; C084612:fibulin 2; D053675:Versicans; D000469:Alkaline Phosphatase