Vitamin K-dependent coagulation factors (II, VII, IX, X) and regulatory proteins (C, S) (VKD proteins)

The Vitamin K-dependent (VKD) proteins comprise a group of essential blood-clotting factors (II, VII, IX, and X) and anticoagulant regulatory proteins (C and S) synthesized primarily in the liver (StatPearls: NBK441838). These proteins require a post-translational modification known as gamma-carboxylation of glutamic acid residues to become biologically active (PubMed: 22516726). This process is catalyzed by gamma-glutamyl carboxylase and requires the reduced form of Vitamin K as a mandatory cofactor. The resulting gamma-carboxyglutamic acid (Gla) residues enable these proteins to bind calcium ions, which facilitates their attachment to negatively charged phospholipid surfaces on platelets and endothelial cells (UniProt: P00734). This membrane binding is a prerequisite for the assembly of coagulation complexes and the subsequent generation of thrombin. Clinically, these proteins are the primary targets of Vitamin K antagonists, such as warfarin, which inhibit the enzyme Vitamin K epoxide reductase (VKORC1) to prevent the recycling of Vitamin K (NIH: MedlinePlus). By reducing the availability of functional VKD factors, these drugs provide effective anticoagulation for conditions like atrial fibrillation and venous thromboembolism, though they require careful monitoring due to a narrow therapeutic window and significant bleeding risks (PubMed: 11591428).

Other names

Vitamin K-dependent clotting factorsGla-domain proteinsProthrombin complexFactors II, VII, IX, X, Protein C, and Protein S

Vitamin K antagonists (VKAs) target these proteins indirectly by inhibiting Vitamin K epoxide reductase (VKORC1), which prevents the regeneration of reduced Vitamin K (StatPearls: NBK441838). Reduced Vitamin K is a necessary cofactor for the gamma-glutamyl carboxylase enzyme, which performs post-translational gamma-carboxylation of glutamic acid residues on these factors. Without this modification, the proteins cannot bind calcium or phospholipid membranes, rendering them functionally inactive and thus inhibiting the coagulation cascade (PubMed: 11591428).