Protein C Activation — MFDS Part 1 MCQ
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Correct answer: E — Thrombin–thrombomodulin, with protein C presented by endothelial protein C receptor
Explanation lettering: C = shown as A · E = shown as C · A = shown as E
A is correct. Binding of thrombin to endothelial thrombomodulin alters thrombin's substrate specificity, allowing it to activate protein C efficiently; presentation of protein C by endothelial protein C receptor further enhances this reaction. Activated protein C, using protein S as a cofactor, proteolytically inactivates factors Va and VIIIa and limits further thrombin generation. The factor Xa–Va complex instead converts prothrombin to thrombin. Tissue plasminogen activator promotes conversion of plasminogen to plasmin during fibrinolysis. Antithrombin inhibits thrombin and factor Xa rather than activating protein C. Von Willebrand factor mediates platelet adhesion to exposed subendothelial collagen.
Reference: Ito T et al. Thrombomodulin: A key regulator of intravascular blood coagulation, fibrinolysis, and inflammation, and a treatment for disseminated intravascular coagulation. 2024. https://pubmed.ncbi.nlm.nih.gov/39694492/