Calcium indirectly regulates immunochemical reactivity and functional activities of the N-domain of thrombospondin-1

• Published in: Matrix biology 2008-05, Vol.27 (4), p.339-351
• Main Authors: Calzada, Maria J., Kuznetsova, Svetlana A., Sipes, John M., Rodrigues, Rui G., Cashel, Jo Anne, Annis, Douglas S., Mosher, Deane F., Roberts, David D.
• Format: Article
• Language: English
• Subjects: Antibodies - immunology; Calcium - chemistry; Calcium - metabolism; Calcium binding; Cations, Divalent - chemistry; Cell Adhesion; Cell Adhesion Molecules - metabolism; Conformational epitopes; Epitopes - immunology; Extracellular matrix; Fibronectins - metabolism; Humans; Immunochemistry; Integrin alpha3beta1 - metabolism; Integrin recognition; Ligands; Protein Binding; Thrombospondin 1 - immunology; Thrombospondin 1 - metabolism; Thrombospondin-1
• ISSN: 0945-053X; 1569-1802
• DOI: 10.1016/j.matbio.2007.12.002

Conformational changes induced in thrombospondin-1 by removal of calcium regulate interactions with some ligands of its N-modules. Because calcium binds primarily to elements of the C-terminal signature domain of thrombospondin-1, which are distant from the N-modules, such regulation was unexpected. To clarify the mechanism for this regulation, we compared ligand binding to the N-modules of thrombospondin-1 in the full-length protein and recombinant trimeric thrombospondin-1 truncated prior to the signature domain. Three monoclonal antibodies were identified that recognize the N-modules, two of which exhibit calcium-dependent binding to native thrombospondin-1 but not to the truncated trimeric protein. These antibodies or calcium selectively modulate interactions of fibronectin, heparin, sulfatide, α3β1 integrin, tumor necrosis factor-α-stimulated gene-6 protein, and, to a lesser extent, α4β1 integrin with native thrombospondin-1 but not with the truncated protein. These results indicate connectivity between calcium binding sites in the C-terminal signature domain and the N-modules of thrombospondin-1 that regulates ligand binding and functional activities of the N-modules.