The von Willebrand factor-reducing activity of thrombospondin-1 is located in the calcium-binding/C-terminal sequence and requires a free thiol at position 974.
Plasma von Willebrand factor (VWF) is a multimeric protein that mediates adhesion of platelets to sites of vascular injury; however, only the very large VWF multimers are effective in promoting platelet adhesion in flowing blood. The multimeric size of VWF can be controlled by the glycoprotein, thrombospondin-1 (TSP-1), which facilitates reduction of the disulfide bonds that hold VWF multimers together. The TSP family of extracellular glycoproteins consists of 5 members in vertebrates, TSP-1 through TSP-4 and TSP-5/COMP. TSP-1 and TSP-2 are structurally similar trimeric proteins composed of disulfide-linked 150-kDa monomers. Recombinant pieces of TSP-1 and TSP-2 incorporating combinations of domains that span the entire subunit were produced in insect cells and examined for VWF reductase activity. VWF reductase activity was present in the Ca(++)-binding repeats and C-terminal sequence of TSP-1, but not of TSP-2. Alkylation of Cys974 in the C-terminal TSP-1 construct, which is a serine in TSP-2, ablated VWF reductase activity. These results imply that the reductase function of TSP-1 centers around Cys974 in the C-terminal sequence.
D000478:Alkylation; D001665:Binding Sites; D006801:Humans; D008301:Maleimides / Q000494:pharmacology; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000378:metabolism; D019700:Thrombospondin 1 / Q000737:chemistry / Q000378:metabolism*; D019699:Thrombospondins / Q000378:metabolism*; D014841:von Willebrand Factor / Q000378:metabolism*; D000099262:Thrombospondin 2
D008301:Maleimides; D010446:Peptide Fragments; D011994:Recombinant Proteins; D013438:Sulfhydryl Compounds; D019700:Thrombospondin 1; D019699:Thrombospondins; D014841:von Willebrand Factor; D000099262:Thrombospondin 2