Huntington J A, Gettins P G
Department of Biochemistry and Molecular Biology, College of Medicine, University of Illinois at Chicago 60612-4316, USA.
Biochemistry. 1998 Mar 10;37(10):3272-7. doi: 10.1021/bi972182o.
Regulation of the inhibitory activity of antithrombin, the principal inhibitor of the blood-clotting proteinases factor Xa and thrombin, is accomplished by binding to heparin. We report here an antithrombin variant in which serine at position 380, 14 residues N-terminal from the reactive bond and at a hinge point in the structure, was replaced by cysteine to test a proposed mechanism of heparin activation of antithrombin as an inhibitor of factor Xa. By derivatization of this cysteine with a bulky group, fluorescein, the antithrombin became permanently and fully activated toward reaction with factor Xa in a manner analogous to heparin activation, albeit as a substrate. These findings establish a structural basis for the mechanism of heparin activation of antithrombin against factor Xa in agreement with that proposed from an X-ray structure of antithrombin.
抗凝血酶是血液凝固蛋白酶因子Xa和凝血酶的主要抑制剂，其抑制活性的调节是通过与肝素结合来实现的。我们在此报告一种抗凝血酶变体，其中位于反应键N端14个残基处且处于结构铰链点的380位丝氨酸被半胱氨酸取代，以测试所提出的肝素激活抗凝血酶作为因子Xa抑制剂的机制。通过用一个庞大基团荧光素对该半胱氨酸进行衍生化，抗凝血酶以类似于肝素激活的方式，尽管作为底物，对与因子Xa的反应永久性地且完全地被激活。这些发现为抗凝血酶针对因子Xa的肝素激活机制建立了结构基础，这与从抗凝血酶的X射线结构所提出的机制一致。
