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Fibrinogen gamma' chain binds thrombin exosite II.
R S Lovely1, M Moaddel, D H Farrell
1Department of Pathology, School of Medicine, Oregon Health and Science University, Portland, Oregon 97239-3098, USA.
Journal of Thrombosis and Haemostasis : JTH
|July 23, 2003
Summary
Researchers identified a high-affinity thrombin-binding site on the gammaA/gamma' fibrinogen isoform. This binding occurs via exosite II, leaving the active site accessible, which may explain fibrin-bound thrombin
Area of Science:
- Biochemistry
- Molecular Biology
- Hematology
Background:
- Fibrinogen is a key protein in blood coagulation.
- Alternative processing of fibrinogen generates the gammaA/gamma' isoform.
- Thrombin is a critical enzyme in the coagulation cascade.
Purpose of the Study:
- To characterize the high-affinity thrombin-binding site on the gammaA/gamma' fibrinogen isoform.
- To elucidate the mechanism of thrombin binding to this fibrinogen variant.
Main Methods:
- Characterization of a synthetic peptide corresponding to the gamma' chain carboxyl terminus.
- Determination of thrombin binding affinity (Kd) using the synthetic peptide.
- Competitive binding studies utilizing hirudin peptides, heparin, and DNA aptamers.
Main Results:
- A high-affinity thrombin-binding site was identified between gamma' 414 and 427.
- Sulfated tyrosines (Tyr418 and Tyr422) are crucial for maximum peptide binding.
- Thrombin binds to the gamma' peptide via exosite II, not exosite I.
Conclusions:
- Thrombin binding to the gamma' chain occurs through exosite II, preserving exosite I accessibility.
- This binding mechanism may explain the retained enzymatic activity of fibrin-bound thrombin.
- The interaction could also account for the heparin resistance observed in fibrin-bound thrombin.