protein S

Protein S is a vitamin K-dependent, anticoagulant glycoprotein that plays a role in blood clotting. It enhances the ability of protein C to inactivate factors V and VIII, which are crucial for coagulation. A deficiency in protein S is linked to an increased risk of venous thrombosis, a condition where blood clots form in deep veins.1

The hemostatic process, which prevents excessive bleeding, involves platelets, endothelial cells, and blood-clotting proteins. Protein S is part of the complex system that regulates this process. It works alongside activated protein C to inactivate factors VIII and V, helping to prevent inappropriate clot formation. The synthesis of protein S, like other vitamin K-dependent clotting proteins, occurs in the liver.2