Identification of SVTCG in thrombospondin as the conformation-dependent, high affinity binding site for its receptor, CD36.

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.