Department of Biological Sciences, Faculty of Science, National University of Singapore, Singapore 119260, Singapore.
Department of Biochemistry, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298, USA.
Sci Rep. 2016 Aug 25;6:32036. doi: 10.1038/srep32036.
Unwanted clots lead to heart attack and stroke that result in a large number of deaths. Currently available anticoagulants have some drawbacks including their non-specific actions. Therefore novel anticoagulants that target specific steps in the coagulation pathway are being sought. Here we describe the identification and characterization of a novel anticoagulant protein from the venom of Hemachatus haemachatus (African Ringhals cobra) that specifically inhibits factor X (FX) activation by the extrinsic tenase complex (ETC) and thus named as exactin. Exactin belongs to the three-finger toxin (3FTx) family, with high sequence identity to neurotoxins and low identity to the well-characterized 3FTx anticoagulants-hemextin and naniproin. It is a mixed-type inhibitor of ETC with the kinetic constants, Ki' and Ki determined as 30.62 ± 7.73 nM and 153.75 ± 17.96 nM, respectively. Exactin does not bind to the active site of factor VIIa and factor Xa based on its weak inhibition (IC50 ≫ 300 μM) to the amidolytic activities of these proteases. Exactin shows exquisite macromolecular specificity to FX activation as compared to factor IX activation by ETC. Exactin thus displays a distinct mechanism when compared to other anticoagulants targeting ETC, with its selective preference to ETC-FX [ES] complex.
不想要的血栓会导致心脏病发作和中风，从而导致大量死亡。目前可用的抗凝剂存在一些缺点，包括它们的非特异性作用。因此，正在寻找针对凝血途径特定步骤的新型抗凝剂。在这里，我们描述了从 Hemachatus haemachatus（非洲环颈眼镜蛇）毒液中鉴定和表征新型抗凝蛋白，该蛋白特异性抑制外源性 tenase 复合物（ETC）激活因子 X（FX），因此命名为 exactin。Exactin 属于三指毒素（3FTx）家族，与神经毒素具有高度序列同一性，与特征明确的 3FTx 抗凝剂-hemextin 和 naniproin 具有低同一性。它是 ETC 的混合类型抑制剂，动力学常数 Ki' 和 Ki 分别确定为 30.62 ± 7.73 nM 和 153.75 ± 17.96 nM。基于其对这些蛋白酶的酶解活性的弱抑制作用（IC50>300 μM），Exactin 不会与因子 VIIa 和因子 Xa 的活性位点结合。与 ETC 激活因子 IX 相比，Exactin 对 FX 激活具有出色的大分子特异性。因此，与其他针对 ETC 的抗凝剂相比，Exactin 显示出独特的机制，其对 ETC-FX [ES] 复合物具有选择性偏好。
