Antithrombin III – coagulation factor Xa axis (ATIII-FXa axis)

The Antithrombin III – coagulation factor Xa axis is a fundamental regulatory pathway in the human coagulation cascade responsible for maintaining hemostatic balance. Antithrombin III (ATIII), a serine protease inhibitor (serpin), naturally neutralizes coagulation factor Xa (FXa) by forming a stable, inactive 1:1 complex, thereby preventing the conversion of prothrombin to thrombin (UniProt: P01008, P00742). While this interaction occurs endogenously, its rate is accelerated by over 1,000-fold in the presence of heparin or synthetic pentasaccharides like fondaparinux, which bind to ATIII and induce a critical conformational change in its reactive center loop (PubMed: 11368157). This axis serves as the primary therapeutic target for indirect anticoagulants used to treat and prevent venous thromboembolism, pulmonary embolism, and acute coronary syndromes (StatPearls: Anticoagulation). Clinical monitoring of drugs targeting this axis is typically performed using the anti-Xa activity assay, which measures the functional capacity of the ATIII-drug complex to inhibit FXa (PubMed: 25079453). Dysregulation of this axis, such as hereditary antithrombin deficiency, leads to a severe hypercoagulable state and significantly increased risk of life-threatening thrombotic events. Consequently, pharmacological modulation of the ATIII-FXa axis remains a cornerstone of modern antithrombotic therapy.

Other names

Antithrombin-Factor Xa complexATIII-FXa interactionHeparin-Antithrombin-Factor Xa pathwaySERPINC1-F10 axis

Potentiation of antithrombin III-mediated neutralization of factor Xa through allosteric activation or a template mechanism.