Identification of SVTCG in thrombospondin as the conformation-dependent, high affinity binding site for its receptor, CD36.
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Thrombospondin (TSP) binds to its cellular receptor, CD36 (glycoprotein IV or IIIb), and participates in many adhesive cell interactions. We have shown that the CD36-TSP interaction occurs in a stepwise, conformation-dependent process. CD36 sequence 139-155 binds TSP and induces a second CD36-binding site, which binds CD36 sequence 93-110 with high affinity. To characterize this high affinity CD36-binding site on TSP, an anti-TSP monoclonal antibody (mAb), 7A-1e, was identified that showed augmentation of TSP binding in the presence of CD36 peptide P139-155. Purified mAb 7A-1e IgG specifically blocked both P139-155-augmented CD36 binding and P139-155-dependent CD36 peptide P93-110 binding to TSP, indicating that the binding sites on TSP for mAb 7A-1e and P93-110 are closely related. mAb 7A-1e IgG inhibited collagen-induced platelet aggregation in platelet-rich plasma. SVTCG is a cell adhesive motif in TSP. Both mAb 7A-1e and P93-110 specifically bound to a TSP peptide containing SVTCG, and the binding of mAb 7A-1e or P93-110 to TSP was inhibited by soluble SCTCG peptide. The SVTCG cell adhesive domain in TSP is the conformation-dependent, high affinity binding site for CD36 sequence 93-110.
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