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Localization of the binding site on fibrin for the secondary binding site of thrombin
1Baker Laboratory of Chemistry, Cornell University, Ithaca, New York 14853-1301.
Insights
Researchers identified the central domain of fibrinogen as the location for thrombin
Area of Science:
- Biochemistry
- Protein-protein interactions
- Enzymology
Background:
- Thrombin plays a crucial role in blood coagulation by cleaving fibrinogen.
- Fibrinogen has multiple domains involved in interactions with thrombin.
- Understanding thrombin-fibrinogen interactions is key to elucidating coagulation mechanisms.
Purpose of the Study:
- To pinpoint the specific fibrinogen domain responsible for thrombin's secondary binding site.
- To identify the peptide regions within fibrinogen that mediate thrombin binding.
- To investigate the role of these interactions in thrombin's enzymatic activity on fibrinogen.
Main Methods:
- Affinity chromatography using immobilized fibrinogen fragments and active site inhibited thrombin.
- Competitive affinity chromatography to assess binding constants.
- Chromatography of isolated fibrinogen domains and peptide chains.
Main Results:
- Thrombin's secondary binding site is located within the central domain of fibrinogen.
- Common peptide regions (alpha(Gly17-Met51), beta(Val55-Met118), gamma(Tyr1-Lys53)) in central fragments bind thrombin.
- The alpha(Gly17-Lys78) peptide region of fibrinogen E contains a strong thrombin binding site.
Conclusions:
- The central domain of fibrinogen harbors the secondary binding site for thrombin.
- This interaction influences thrombin's cleavage specificity and fibrinopeptide release rate.
- The binding site on fibrinogen fragment E is distinct from its interaction site with cross-linked fibrin.
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 x D) itself does not bind to thrombin, whereas the D x DE complex remained attached to the column, suggesting that the binding site on fragment E for thrombin is distinct from its binding site for D x D.(ABSTRACT TRUNCATED AT 250 WORDS)