Vitamin K-dependent protein S (Protein S)

Vitamin K-dependent protein S (also known as Protein S or PROS) is a plasma glycoprotein synthesized in the liver that acts as a critical cofactor for activated protein C in the degradation of coagulation factors Va and VIIIa, thereby exerting a key regulatory effect on blood coagulation and thrombosis prevention. Approximately 60% of circulating protein S is bound to C4b-binding protein (C4BP) and inactive, while 40% remains free and functionally active as a cofactor[4][6]. Beyond coagulation, protein S participates in the clearance of apoptotic cells by bridging phospholipids on the surface of dying cells to phagocytes, facilitating non-inflammatory removal[3][4]. Mutations or deficiencies in protein S (PROS1 gene) confer a high risk for venous thromboembolism and rare, severe inherited thrombophilias. Protein S is not a direct therapeutic drug target (i.e., no drugs selectively modulate or block it), but its levels and function are clinically significant in managing coagulation disorders and monitoring anticoagulant therapy[4][6].

Other names

PROSPROS1Protein SVitamin K-dependent plasma protein S

Acts as a cofactor for activated protein C to degrade coagulation factors Va and VIIIa; indirectly involved in regulation of coagulation and clearance of apoptotic cells[1][3][4]