Localization of the binding site on fibrin for the secondary binding site of thrombin

Publisher Website
Google Scholar
Abstract
Affinity chromatography of active site inhibited thrombin on immobilized fragments derived from the central (desAB-NDSK) and terminal (D1) globular domains of fibrinogen revealed that the site responsible for the binding of thrombin at its secondary fibrin binding site is located in the central domain. Chromatography of various domains of the central nodule (desAB-NDSK, fibrinogen E, and fibrin E) having nonidentical amino acid sequences showed that all of these fragments are capable of binding to PMSF-thrombin-Sepharose, suggesting that the thrombin binding site resides within the peptide regions common to all of these fragments: .alpha.(Gly17-Met51), .beta.(Val55-Met118), and .gamma.(Tyr1-Lys53). Competitive affinity chromatography of the same binding domains revealed that there is no detectable difference in their binding constants to PMSF-thrombin-Sepharose, indicating that the .alpha.(Lys52-Lys78), .beta.(Gly15-Lys54)/(Tyr119-Lys122), and .gamma.(Thr54-Met78) peptide segments do not contribute significantly to the binding of thrombin. Chromatography of the isolated chains of fibrinogen E showed that the .alpha.(Gly17-Lys78) peptide region itself contains a strong binding site for PMSF-thrombin-Sepharose. The location of the binding site suggests that the secondary site interaction may play an important role in determining the cleavage specificity of thrombin on fibrinogen and can affect the rate of release of the fibrinopeptides. Affinity chromatography of fragments prepared from polymerized fibrin showed that cross-linked DD (D .times. D) itself does not bind to thrombin, whereas the D .times. DE complex remained attached to the column, suggesting that the binding site on fragment E fo thrombin is distinct from its binding site for D .times. D. Thus, the interaction between D .times. D and E during polymerization is not likely to release thrombin from fibrin. The possible consequences of the fibrin-thrombin interaction on the mechanism of fibrin polymerization and factor XIII activation are discussed.