BINDING-SITES ON NATIVE AND MULTIMERIC VITRONECTIN EXHIBIT SIMILAR AFFINITY FOR HEPARIN - THE INFLUENCE OF SELF-ASSOCIATION AND MULTIVALENCE ON LIGAND-BINDING

A previously accepted model for the morphoregulatory activity of vitro nectin is based on the idea that the heparin-binding site is buried wi thin the circulating, monometric form of vitronectin and that it is ex posed on conversion to the multimeric form by denaturation or incorpor ation into the extracellular matrix. New evidence indicates that the h eparin-binding sites ave similarly exposed in the two forms of vitrone ctin and supports an alternative model for apparently altered heparin affinity. Differences in the heparin-binding properties of circulating and matrix-associated vitronectin result from an increased number of binding sites on the multivalent matrix form. By analogy with other in stances in which multivalent binding interactions increase functional affinity for carbohydrates or lectins, the self-association of vitrone ctin into a multimeric form allows effective neutralization of heparin at the endothelial surface in the vicinity of a thrombus. (C) 1998, E lsevier Science Inc.