Calcium indirectly regulates immunochemical reactivity and functional activities of the N-domain of thrombospondin-1.
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, alpha3beta1 integrin, tumor necrosis factor-alpha-stimulated gene-6 protein, and, to a lesser extent, alpha4beta1 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.
Calzada
Maria J
MJ
Laboratory of Pathology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, United States.
Kuznetsova
Svetlana A
SA
Sipes
John M
JM
Rodrigues
Rui G
RG
Cashel
Jo Anne
JA
Annis
Douglas S
DS
Mosher
Deane F
DF
Roberts
David D
DD
D000906:Antibodies / Q000276:immunology; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D002413:Cations, Divalent / Q000737:chemistry; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000378:metabolism; D000939:Epitopes / Q000276:immunology; D005353:Fibronectins / Q000378:metabolism; D006801:Humans; D007120:Immunochemistry; D039201:Integrin alpha3beta1 / Q000378:metabolism; D008024:Ligands; D011485:Protein Binding; D019700:Thrombospondin 1 / Q000276:immunology* / Q000378:metabolism*
D000906:Antibodies; D002413:Cations, Divalent; D015815:Cell Adhesion Molecules; D000939:Epitopes; D005353:Fibronectins; D039201:Integrin alpha3beta1; D008024:Ligands; D019700:Thrombospondin 1; D002118:Calcium