Antithrombin III–thrombin complex (TAT)

The Antithrombin III–thrombin complex (TAT) is a stable, inactive covalent complex formed when the serine protease inhibitor antithrombin III (ATIII) neutralizes thrombin (Factor IIa) (UniProt P01008, P00734). This interaction is a fundamental regulatory step in the coagulation cascade, preventing excessive clot formation by removing active thrombin from circulation (StatPearls, Physiology, Coagulation Cascade). While the complex itself is not a direct therapeutic target for drug binding, its formation is the primary pharmacological objective of anticoagulants such as heparin and low-molecular-weight heparins (LMWHs) (NCBI, Heparin Mechanism of Action). These drugs act as catalysts, binding to ATIII to increase its affinity for thrombin by several thousand-fold, thereby accelerating TAT formation. Clinically, TAT is recognized as a highly sensitive biomarker for the in vivo activation of coagulation, with elevated levels indicating a prothrombotic state or disseminated intravascular coagulation (DIC) (PubMed, PMID: 2518344). Consequently, monitoring TAT levels helps in assessing the risk of thrombotic events and the efficacy of anticoagulant therapy.

Other names

Thrombin–antithrombin complexTAT complexTATCAntithrombin–thrombin complex

Anticoagulant drugs like heparin bind to antithrombin III, inducing a conformational change that dramatically accelerates the formation of the inactive antithrombin III–thrombin complex, thereby inhibiting the coagulation cascade.