A new platelet receptor specific to type III collagen - Type III collagen-binding protein

Platelet interaction with type III collagen is mediated by several platelet receptors that recognize specific sequences in collagen. We previously des cribed an octapeptide KP*GEP*GPK within the alpha(1)III-CB4 fragment that b inds to platelets and specifically inhibits platelet aggregation induced by type III collagen. In this study, we demonstrated that the octapeptide pre vented platelet contact and spreading on type III collagen and subendotheli um under static and flow conditions. Platelets adhered to the immobilized o ctapeptide, and antibodies directed against other platelet collagen recepto rs (glycoprotein (GP) Ia/IIa, GP IV, p65, p47) did not impair this adhesion . The platelet octapeptide receptor was identified by ligand blotting as a protein doublet with molecular masses of 68 and 72 kDa and does not corresp ond to any other already known platelet collagen receptors (GP Ia, GP TV GP VI, and p65), Our results indicate that a specific type III collagen recep tor, expressed on the platelet surface, is involved in the first stages of platelet type III collagen interaction.