Protein S

Protein S is a vitamin K-dependent plasma glycoprotein synthesized in the liver.

Protein S exists in two forms in the circulation: a free form and a complex form bound to complement protein C4b-binding protein.

Protein S is encoded by the PROS1 gene.

Gene location Chromosome 3.

It is partly homologous to other vitamin K-dependent plasma coagulation proteins, such as protein C and factors VII, IX, and X.

It may play a role in the protein functions as either a cofactor for activated protein C (APC) or in binding C4BP.

It functions as a cofactor to Protein C in the inactivation of Factors Va and VIIIa.

Protein S also binds to the nascent complement complex C5,6,7 and prevents this complex from inserting into a membrane, and prevents the inappropriate activation of the complement system, which would cause uncontrolled systemic inflammation.

Mutations in the PROS1 gene can lead to Protein S deficiency which is a rare blood disorder which can lead to an increased risk of thrombosis.

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