Binding of human thrombin to human factor VIII:RAg

Area of Science:

• Hematology
• Biochemistry
• Molecular Biology

Background:

• Factor VIII related antigen (VIII:RAg) exists in various multimeric forms.
• Thrombin's interaction with VWF multimers is not fully understood.
• Understanding these interactions is crucial for hemostasis research.

Purpose of the Study:

• To investigate the binding capacity of inactivated radiolabeled alpha-thrombin to VIII:RAg multimers.
• To determine if thrombin's catalytic site is necessary for this binding.
• To compare thrombin binding patterns with anti-FVIII antibody binding.

Main Methods:

• Immune precipitation of VIII:RAg multimers from plasma and serum.
• Sodium dodecyl sulfate (SDS) agarose gel electrophoresis for multimer resolution.
• Binding assays using 125I-labeled phenyl-methyl sulphonyl fluoride (PMSF) inactivated alpha-thrombin.

Main Results:

• 125I-PMSF alpha-thrombin predominantly bound to four low molecular weight (LMW) VIII:RAg multimers in normal and hemophilia A plasma.
• Two VIII:RAg multimers in serum lost their capacity to bind thrombin.
• No binding was observed in plasma or serum from patients with severe von Willebrand's disease (vWd).

Conclusions:

• Thrombin binding to VIII:RAg multimers is specific and involves certain LMW forms.
• The binding is independent of the thrombin catalytic site.
• Similar binding patterns suggest shared binding sites for thrombin and anti-FVIII antibodies on VWF multimers.