Structural and functional analysis of the interaction between vitronectin and the thrombin-antithrombin pair

Vitronectin is a multifunctional glycoprotein found both in the circulation and in the extracellular matrix. Circulating vitronectin is in monomeric form while matrix and tissue associated vitronectin tend to form multimers. Interacts with a wide variety of ligands that are involved in control of diverse processes including coagulation and fibrinolysis. Some target macromolecules that interact with vitronectin are heparin, PAI-1, thrombin-antithrombin pair, collagen, integrin receptors (on the cell surfaces), and urokinase plasminogen activator receptor (uPAR). Recently, a computational model of vitronectin was proposed using threading method. This model showed that vitronectin is made up of an N-terminal somatomedin-β domain, a central β-propeller hemopexin homology domain, and a C-terminal heparin-binding domain. β-propeller domain has been found in other proteins and it has been reported to be important in protein-protein interactions. Vitronectin is known to interact with the thrombin-antithrombin pair and mediates the removal of this inactive complex from the circulation. Although there has been extensive research performed concerning vitronectin interaction with the thrombin-antithrombin pair, questions about how this interaction takes place and what the consequences of this association have not been fully understood. The purpose of this study was to use techniques of molecular biology and analytical chemistry to analyze hemopexin homology region of vitronectin and ultimately elucidate the functional contribution of this region to the whole protein. Also, preliminary work concerning association of vitronectin with the thrombin- antithrombin pair has been performed using enzyme linked immunoabsorbant assays and fluorescence labeling. Results of these studies indicate that vitronectin forms complexes with the thrombin-antithrombin pair through ionic interactions and the interaction of vitronectin with the thrombin-antithrombin pair results in multimerization.