C4b-binding protein protects coagulation factor Va from inactivation by activated protein C. 2000

R H van de Poel, and J C Meijers, and J Rosing, and G Tans, and B N Bouma
Thrombosis and Haemostasis Laboratory, Department of Haematology, University Medical Center, and Institute of Biomembranes, Utrecht University, Utrecht, The Netherlands.

We investigated the effect of C4BP on APC-mediated inactivation of factor Va (FVa) in the absence and presence of protein S. FVa inactivation was biphasic (k(506) = 4.4 x 10(8) M(-)(1) s(-)(1), k(306) = 2.7 x 10(7) M(-)(1) s(-)(1)), and protein S accelerated Arg(306) cleavage approximately 10-fold. Preincubation of protein S with C4BP resulted in a total abrogation of protein S cofactor activity. C4BP also protected FVa from inactivation by APC in the absence of protein S. Control experiments with CLB-PS13, a monoclonal anti-protein S antibody, indicated that inhibition of FVa inactivation by C4BP was not mediated through contaminating traces of protein S in our reaction systems. Protection of FVa was prevented by a monoclonal antibody directed against the C4BP alpha-chain. Recombinant rC4BPalpha comprised of only alpha-chains also protected FVa, but in the presence of protein S, the level of protection was decreased, since rC4BPalpha lacks the beta-chain responsible for C4BP binding to protein S. A truncated C4BP beta-chain (SCR-1+2) inhibited protein S cofactor activity, but had no effect on FVa inactivation by APC in the absence of protein S. In conclusion, C4BP protects FVa from APC-catalyzed cleavage in a protein S-independent way through direct interactions of the alpha-chaims of C4BP with FVa and/or APC.

UI MeSH Term Description Entries
D007668 Kidney Body organ that filters blood for the secretion of URINE and that regulates ion concentrations. Kidneys
D011485 Protein Binding The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments. Plasma Protein Binding Capacity,Binding, Protein
D011486 Protein C A vitamin-K dependent zymogen present in the blood, which, upon activation by thrombin and thrombomodulin exerts anticoagulant properties by inactivating factors Va and VIIIa at the rate-limiting steps of thrombin formation.
D011951 Receptors, Complement Molecules on the surface of some B-lymphocytes and macrophages, that recognize and combine with the C3b, C3d, C1q, and C4b components of complement. Complement Receptors,Complement Receptor,Complement Receptor Type 1,Receptor, Complement
D011994 Recombinant Proteins Proteins prepared by recombinant DNA technology. Biosynthetic Protein,Biosynthetic Proteins,DNA Recombinant Proteins,Recombinant Protein,Proteins, Biosynthetic,Proteins, Recombinant DNA,DNA Proteins, Recombinant,Protein, Biosynthetic,Protein, Recombinant,Proteins, DNA Recombinant,Proteins, Recombinant,Recombinant DNA Proteins,Recombinant Proteins, DNA
D002460 Cell Line Established cell cultures that have the potential to propagate indefinitely. Cell Lines,Line, Cell,Lines, Cell
D003169 Complement Inactivator Proteins Serum proteins that negatively regulate the cascade process of COMPLEMENT ACTIVATION. Uncontrolled complement activation and resulting cell lysis is potentially dangerous for the host. The complement system is tightly regulated by inactivators that accelerate the decay of intermediates and certain cell surface receptors. Complement Cytolysis Inhibiting Proteins,Complement Cytolysis Inhibitor Proteins,Complement Inactivating Proteins,Serum Complement Inactivators,Complement Inactivators, Serum,Inactivating Proteins, Complement,Inactivator Proteins, Complement,Inactivators, Serum Complement,Proteins, Complement Inactivating,Proteins, Complement Inactivator
D004789 Enzyme Activation Conversion of an inactive form of an enzyme to one possessing metabolic activity. It includes 1, activation by ions (activators); 2, activation by cofactors (coenzymes); and 3, conversion of an enzyme precursor (proenzyme or zymogen) to an active enzyme. Activation, Enzyme,Activations, Enzyme,Enzyme Activations
D005973 Glutamine A non-essential amino acid present abundantly throughout the body and is involved in many metabolic processes. It is synthesized from GLUTAMIC ACID and AMMONIA. It is the principal carrier of NITROGEN in the body and is an important energy source for many cells. D-Glutamine,L-Glutamine,D Glutamine,L Glutamine
D006023 Glycoproteins Conjugated protein-carbohydrate compounds including MUCINS; mucoid, and AMYLOID glycoproteins. C-Glycosylated Proteins,Glycosylated Protein,Glycosylated Proteins,N-Glycosylated Proteins,O-Glycosylated Proteins,Glycoprotein,Neoglycoproteins,Protein, Glycosylated,Proteins, C-Glycosylated,Proteins, Glycosylated,Proteins, N-Glycosylated,Proteins, O-Glycosylated

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