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Inhibition of Thrombin Formation by Active Site Mutated (S360A) Activated Protein C

På svenska

Author

  • Gerry A. F. Nicolaes
  • Paul E. Bock
  • Kenneth Segers
  • Karin C. A. A. Wildhagen
  • Björn Dahlbäck
  • Jan Rosing

Summary, in English

Activated protein C (APC) down-regulates thrombin formation through proteolytic inactivation of factor Va (FVa) by cleavage at Arg(506) and Arg(306) and of factor VIIIa (FVIIIa) by cleavage at Arg(336) and Arg(562). To study substrate recognition by APC, active site-mutated APC (APC(S360A)) was used, which lacks proteolytic activity but exhibits anticoagulant activity. Experiments in model systems and in plasma show that APC(S360A), and not its zymogen protein C(S360A), expresses anticoagulant activities by competing with activated coagulation factors X and IX for binding to FVa and FVIIIa, respectively. APC(S360A) bound to FVa with a K-D of 0.11 +/- 0.05 nM and competed with active site-labeled Oregon Green activated coagulation factor X for binding to FVa. The binding of APC(S360A) to FVa was not affected by protein S but was inhibited by prothrombin. APC(S360A) binding to FVa was critically dependent upon the presence of Arg(506) and not Arg(306) and additionally required an active site accessible to substrates. Inhibition of FVIIIa activity by APC(S360A) was > 100-fold less efficient than inhibition of FVa. Our results show that despite exosite interactions near the Arg(506) cleavage site, binding of APC(S360A) to FVa is almost completely dependent on Arg(506) interacting with APC(S360A) to form a nonproductive Michaelis complex. Because docking of APC to FVa and FVIIIa constitutes the first step in the inactivation of the cofactors, we hypothesize that the observed anticoagulant activity may be important for in vivo regulation of thrombin formation.

Publishing year

2010

Language

English

Pages

22888-22898

Publication/Series

Journal of Biological Chemistry

Volume

285

Issue

30

Document type

Journal article

Publisher

American Society for Biochemistry and Molecular Biology

Topic

  • Medicinal Chemistry

Status

Published

Research group

  • Clinical Chemistry, Malmö

ISBN/ISSN/Other

  • ISSN: 1083-351X