title: CD36 peptides enhance or inhibit CD36-thrombospondin binding. A two-step process of ligand-receptor interaction.
abstract: CD36 (glycoprotein IV or IIIB) is an integral plasma membrane protein of wide cellular distribution and functions as a receptor site for thrombospondin (TSP), an adhesive protein important in cell-cell and cell-matrix interactions. OKM5, a monoclonal anti-CD36 antibody, has been reported to block CD36 cell adhesive functions suggesting that the OKM5 epitope on CD36 is functionally important. A panel of 10 synthetic CD36 peptides was made. One peptide, P139-155, specifically inhibited the immunoadsorption of CD36 by OKM5, and P139-155 was directly immunoadsorbed by OKM5, indicating that CD36 sequence 139-155 represents part of the OKM5 epitope. TSP bound to immobilized P139-155 in a dose-dependent and saturable manner. Surprisingly, P139-155 significantly augmented, instead of inhibited, binding of CD36 to TSP. This peptide did not induce platelet aggregation but augmented ADP- and collagen-induced aggregation in platelet-rich plasma. Another CD36 peptide, P93-110, which had no effect on OKM5 immunoadsorption, blocked binding of CD36 to immobilized TSP and partially inhibited collagen-induced platelet aggregation. P93-110 by itself did not bind to TSP; however, in the presence of P139-155, there was a marked enhancement of P93-110 binding to TSP, with a stoichiometry consistent with the trimeric nature of TSP. The data suggest that CD36-TSP interaction is a two-step process; the sequence 139-155 region of CD36 binds first to TSP, triggering a change in TSP to reveal a second site, which binds the 93-110 region of CD36 with high affinity. CD36 peptides can be used as stimulators or inhibitors in cellular adhesive events involving TSP-CD36 interaction. Conformational changes leading to the exposure or activation of high affinity binding sites may occur in both the receptor and the ligand upon cell-cell and cell-matrix adhesion.
authors.affiliation: Division of Hematology, Stanford University School of Medicine, California 94305.
authors.forename: L L
authors.initials: LL
authors.lastname: Leung
authors.forename: W X
authors.initials: WX
authors.lastname: Li
authors.forename: J L
authors.initials: JL
authors.lastname: McGregor
authors.forename: G
authors.initials: G
authors.lastname: Albrecht
authors.forename: R J
authors.initials: RJ
authors.lastname: Howard
mesh_terms: D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000187:drug effects / Q000378:metabolism*; D001665:Binding Sites; D001792:Blood Platelets / Q000502:physiology; D018955:CD36 Antigens; D002462:Cell Membrane / Q000502:physiology; D006801:Humans; D007700:Kinetics; D008961:Models, Structural; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000494:pharmacology*; D010974:Platelet Aggregation / Q000187:drug effects; D010980:Platelet Membrane Glycoproteins / Q000187:drug effects / Q000378:metabolism*; D019699:Thrombospondins
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D018955:CD36 Antigens; D010446:Peptide Fragments; D010980:Platelet Membrane Glycoproteins; D019699:Thrombospondins