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Related Experiment Videos

Platelet factor 4 stimulates thrombomodulin protein C-activating cofactor activity. A structure-function analysis

A Slungaard1, N S Key

  • 1Department of Medicine, University of Minnesota, Minneapolis 55455.

The Journal of Biological Chemistry
|October 14, 1994
PubMed
Summary
This summary is machine-generated.

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Platelet factor 4 (PF4) significantly enhances thrombomodulin

Area of Science:

  • Biochemistry and Molecular Biology
  • Hematology and Coagulation

Background:

  • Thrombomodulin (TM) is a cofactor protein crucial for generating activated protein C (APC), a key anticoagulant.
  • The interaction between TM, thrombin, and protein C regulates blood coagulation.

Purpose of the Study:

  • To investigate the effect of platelet factor 4 (PF4) on the cofactor activity of thrombomodulin (TM).
  • To elucidate the mechanism by which PF4 influences TM-mediated protein C activation.

Main Methods:

  • Assessed the cofactor activity of TM using rabbit and human TM variants (GAG+ and GAG- TM) in the presence of PF4.
  • Analyzed the kinetic parameters (Km, Kd) and calcium dependence of APC generation.
  • Utilized autofluorescence emission analysis to study protein C conformation changes.

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Main Results:

  • PF4 significantly stimulated TM cofactor activity (4-25 fold) for protein C activation.
  • PF4 reduced the Km for protein C by 30-fold, enhancing substrate affinity.
  • PF4 altered the calcium dependence of TM activity and induced heparin-reversible conformational changes in protein C.

Conclusions:

  • PF4 stimulates TM-mediated APC generation by electrostatically interacting with TM's glycosaminoglycan (GAG) and protein C's Gla domain.
  • This interaction enhances the affinity of the thrombin-TM complex for protein C.
  • PF4 may play a significant, previously unrecognized role in regulating blood clotting physiologically.