Localization of a fibrin polymerization site

Area of Science:

• Biochemistry
• Molecular Biology
• Hematology

Background:

• Fibrin clot formation is crucial for hemostasis.
• Thrombin cleaves fibrinogen to initiate fibrin monomer polymerization.
• Polymerization involves interactions between fibrinogen's NH2-terminal and COOH-terminal (Fragment D) regions.

Purpose of the Study:

• To isolate and characterize a peptide that inhibits fibrin monomer polymerization.
• To identify the specific binding sites and interactions involved in fibrin polymerization.
• To elucidate the role of the gamma chain remnant of fibrinogen Fragment D1 in clot formation.

Main Methods:

• Isolation of a peptide from fibrinogen Fragment D1.
• Inhibition assays for fibrin monomer polymerization using thrombin and batroxobin.
• Binding studies using thrombin-treated disulfide knot and fibrin monomer.
• Determination of peptide sequences (NH2-terminal and COOH-terminal).

Main Results:

• A D1 peptide was isolated that binds to the NH2-terminal region of fibrinogen and inhibits polymerization.
• The peptide reduces polymerization rate and extent, increasing lag time.
• Binding occurs at approximately two sites per fibrin monomer, suggesting a site revealed by fibrinopeptide A removal.
• The gamma 373-410 region of fibrinogen contains a polymerization site complementary to the NH2-terminal site.

Conclusions:

• The D1 peptide acts as a polymerization inhibitor by blocking key interaction sites.
• Fibrinopeptide A removal exposes a polymerization site on the fibrin NH2-terminus.
• The gamma 373-410 region is critical for fibrin polymerization, offering a target for modulating clot formation.