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C4b-binding protein protects coagulation factor Va from inactivation by activated protein C
R H van de Poel1, J C Meijers, J Rosing
1Thrombosis and Haemostasis Laboratory, Department of Haematology, University Medical Center, and Institute of Biomembranes, Utrecht University, Utrecht, The Netherlands.
Biochemistry
|November 23, 2000
Summary
Complement factor C4B-binding protein (C4BP) protects factor Va (FVa) from inactivation by activated protein C (APC). This protection is independent of protein S and involves direct interaction of C4BP's alpha-chains.
Area of Science:
- Biochemistry
- Hemostasis
- Complement System
Background:
- Factor Va (FVa) is a crucial coagulation cofactor.
- Activated protein C (APC) inactivates FVa, regulating blood coagulation.
- Protein S acts as a cofactor for APC-mediated FVa inactivation.
Purpose of the Study:
- To investigate the effect of C4BP on APC-mediated FVa inactivation.
- To determine the role of protein S in C4BP's effect on FVa inactivation.
- To elucidate the mechanism of C4BP's interaction with FVa and APC.
Main Methods:
- Kinetics of FVa inactivation by APC were measured.
- Experiments were conducted in the absence and presence of protein S.
- Monoclonal antibodies and recombinant proteins were used to probe interactions.
Main Results:
- C4BP abrogated protein S cofactor activity and protected FVa from APC-mediated inactivation.
- C4BP's protective effect on FVa was independent of protein S.
- C4BP alpha-chains directly interact with FVa and/or APC, mediating protection.
Conclusions:
- C4BP directly inhibits APC-mediated FVa inactivation through its alpha-chains.
- This protein S-independent mechanism highlights a novel regulatory role for C4BP in coagulation.
- C4BP may play a significant role in modulating thrombotic processes.