CHARACTERIZATION OF THE LIGAND-BINDING ACTIVITIES OF VITRONECTIN - INTERACTION OF VITRONECTIN WITH LIPIDS AND IDENTIFICATION OF THE BINDINGDOMAINS FOR VARIOUS LIGANDS USING RECOMBINANT DOMAINS

Vitronectin is a multifunctional plasma glycoprotein which may regulat e the systems related to protease cascades such as the coagulation, fi brinolysis, and complement systems as well as cell adhesion. Solid-pha se assays and affinity chromatography on immobilized glycolipids indic ated that vitronectin purified under denaturing conditions bound to su lfatide (Gal(3-SO4)beta 1-1ceramide), cholesterol 3-sulfate, and vario us phospholipids, but not gangliosides. Only the unfolded or multimeri c form of vitronectin bound to sulfatide, suggesting a conformational dependency of the binding activity, while vitronectin bound to cholest erol 3-sulfate regardless of its conformational state. The recombinant domains of human vitronectin and mutants with certain domains deleted were separately expressed in E. coli as fusion proteins. Using the re combinants, sulfatide-, phosphatidylserine-, cholesterol 3-sulfate-, T ype I collagen-, heparin-, and beta-endorphin-binding activities were found to be attributable to hemopexin domain 2 and hemopexin domain 1. The possibility was suggested that the presence of a somatomedin doma in and/or connecting region flanking hemopexin domain 1 inactivated it s heparin binding. De-N-glycosylation of plasma vitronectin significan tly affected the cholesterol sulfate-and collagen-binding activities, although its effects were opposite. These findings suggest that divers e ligand-binding activities could be attributed to pexin family motifs but that the interdomain interactions and glycosylations modulate the ligand binding activities of vitronectin.