[ANT3_HUMAN] Defects in SERPINC1 are the cause of antithrombin III deficiency (AT3D) [MIM:613118]. AT3D is an important risk factor for hereditary thrombophilia, a hemostatic disorder characterized by a tendency to recurrent thrombosis. AT3D is classified into 4 types. Type I: characterized by a 50% decrease in antigenic and functional levels. Type II: has defects affecting the thrombin-binding domain. Type III: alteration of the heparin-binding domain. Plasma AT-III antigen levels are normal in type II and III. Type IV: consists of miscellaneous group of unclassifiable mutations. [:]                     [:]            
[ANT3_HUMAN] Most important serine protease inhibitor in plasma that regulates the blood coagulation cascade. AT-III inhibits thrombin, matriptase-3/TMPRSS7, as well as factors IXa, Xa and XIa. Its inhibitory activity is greatly enhanced in the presence of heparin.
Publication Abstract from PubMed
Antithrombin is unique among the serpins in that it circulates in a native conformation that is kinetically inactive toward its target proteinase, factor Xa. Activation occurs upon binding of a specific pentasaccharide sequence found in heparin that results in a rearrangement of the reactive center loop removing constraints on the active center P1 residue. We determined the crystal structure of an activated antithrombin variant, N135Q S380C-fluorescein (P14-fluorescein), in order to see how full activation is achieved in the absence of heparin and how the structural effects of the substitution in the hinge region are translated to the heparin binding region. The crystal structure resembles native antithrombin except in the hinge and heparin binding regions. The absence of global conformational change allows for identification of specific interactions, centered on Glu(381) (P13), that are responsible for maintenance of the solution equilibrium between the native and activated forms and establishes the existence of an electrostatic link between the hinge region and the heparin binding region. A revised model for the mechanism of the allosteric activation of antithrombin is proposed.
The conformational activation of antithrombin. A 2.85-A structure of a fluorescein derivative reveals an electrostatic link between the hinge and heparin binding regions.,Huntington JA, McCoy A, Belzar KJ, Pei XY, Gettins PG, Carrell RW J Biol Chem. 2000 May 19;275(20):15377-83. PMID:10809774
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.