Thromb Haemost 2007; 97(06): 899-906
DOI: 10.1160/TH06-12-0697
Blood Coagulation, Fibrinolysis and Cellular Haemostasis
Schattauer GmbH

Calcium-binding sites of the thrombin-thrombomodulin-protein C complex: Possible implications for the effect of platelet factor 4 on the activation of vitamin K-dependent coagulation factors

Likui Yang
1   Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, Saint Louis, Missouri, USA
,
Alireza R. Rezaie
1   Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, Saint Louis, Missouri, USA
› Author Affiliations
Financial support: The research discussed here in was supported by grants awarded by the National Heart, Lung, and Blood Institute of the National Institutes of Health (HL 62565 and HL 68571 to ARR).
Further Information

Publication History

Received 06 December 2006

Accepted after resubmission 05 March 2007

Publication Date:
27 November 2017 (online)

Summary

The Ca2+-dependence of protein C activation by thrombin in complex with thrombomodulin (TM) containing chondroitin sulfate (CS) exhibits saturation at ~0.5–1 mM Ca2+, but withTM lacking CS, it has a distinct optimum at ~0.1 mM Ca2+. Since the substrate protein C has multiple Ca2+-binding sites, and the cofactor TM also interacts with Ca2+, the basis for differences in Ca2+ effect on protein C activation by thrombin in complex with TM containing or lacking CS is not known. In this study, by using full-length and Gla-domainless mutants of protein C whose activation by thrombin is independent of either Ca2+ or both Ca2+ and TM, we demonstrate that i) the Ca2+ occupancy of a high-affinity binding site in TM is essential for the high-affinity interaction of the cofactor with thrombin, ii) the Ca2+ occupancy of a binding site (KD ~50 μM) in the catalytic domain of protein C is required for the substrate recognition by the thrombin-TM complex, however, at this concentration of Ca2+ the Gla domain of protein C is not folded properly and thus interacts with exosite-2 of thrombin in complex with TM that lacks CS but not withTM that contains CS, and finally iii) platelet factor 4 can nonspecifically interact with the Gla domain of protein C and other coagulation factors to influence their activation only at subphysiological concentrations of Ca2+.

 
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