Thrombosis and Atherosclerosis Research Institute, Hamilton, Ontario L8L 2X2, Canada; Departments of Medical Sciences, Hamilton, Ontario L8L 2X2, Canada.
Thrombosis and Atherosclerosis Research Institute, Hamilton, Ontario L8L 2X2, Canada; Medicine, Hamilton, Ontario L8L 2X2, Canada.
J Biol Chem. 2013 Jun 7;288(23):16862-16871. doi: 10.1074/jbc.M113.464750. Epub 2013 Apr 23.
Batroxobin is a thrombin-like serine protease from the venom of Bothrops atrox moojeni that clots fibrinogen. In contrast to thrombin, which releases fibrinopeptide A and B from the NH2-terminal domains of the Aα- and Bβ-chains of fibrinogen, respectively, batroxobin only releases fibrinopeptide A. Because the mechanism responsible for these differences is unknown, we compared the interactions of batroxobin and thrombin with the predominant γA/γA isoform of fibrin(ogen) and the γA/γ' variant with an extended γ-chain. Thrombin binds to the γ'-chain and forms a higher affinity interaction with γA/γ'-fibrin(ogen) than γA/γA-fibrin(ogen). In contrast, batroxobin binds both fibrin(ogen) isoforms with similar high affinity (Kd values of about 0.5 μM) even though it does not interact with the γ'-chain. The batroxobin-binding sites on fibrin(ogen) only partially overlap with those of thrombin because thrombin attenuates, but does not abrogate, the interaction of γA/γA-fibrinogen with batroxobin. Furthermore, although both thrombin and batroxobin bind to the central E-region of fibrinogen with a Kd value of 2-5 μM, the α(17-51) and Bβ(1-42) regions bind thrombin but not batroxobin. Once bound to fibrin, the capacity of batroxobin to promote fibrin accretion is 18-fold greater than that of thrombin, a finding that may explain the microvascular thrombosis that complicates envenomation by B. atrox moojeni. Therefore, batroxobin binds fibrin(ogen) in a manner distinct from thrombin, which may contribute to its higher affinity interaction, selective fibrinopeptide A release, and prothrombotic properties.
巴曲酶是一种来自莫氏矛头蝮蛇毒的纤维蛋白原凝血酶样丝氨酸蛋白酶。与分别从纤维蛋白原 Aα-和 Bβ-链的 NH2-末端结构域释放纤维蛋白肽 A 和 B 的凝血酶不同，巴曲酶仅释放纤维蛋白肽 A。由于导致这些差异的机制尚不清楚，我们比较了巴曲酶和凝血酶与纤维蛋白（原）的主要 γA/γA 同工型以及带有扩展 γ 链的 γA/γ'变体的相互作用。凝血酶与 γ'-链结合，并与 γA/γ'-纤维蛋白（原）形成比 γA/γA-纤维蛋白（原）更高亲和力的相互作用。相比之下，巴曲酶以相似的高亲和力（约 0.5 μM 的 Kd 值）结合两种纤维蛋白（原）同工型，尽管它不与 γ'-链相互作用。纤维蛋白（原）上的巴曲酶结合位点与凝血酶的结合位点部分重叠，因为凝血酶减弱但不消除 γA/γA-纤维蛋白原与巴曲酶的相互作用。此外，尽管凝血酶和巴曲酶都以 2-5 μM 的 Kd 值结合纤维蛋白原的中央 E 区，但 α(17-51)和 Bβ(1-42)区结合凝血酶而不结合巴曲酶。一旦结合到纤维蛋白上，巴曲酶促进纤维蛋白堆积的能力比凝血酶高 18 倍，这一发现可能解释了莫氏矛头蝮蛇毒中毒引起的微血管血栓形成。因此，巴曲酶以与凝血酶不同的方式结合纤维蛋白（原），这可能有助于其更高的亲和力相互作用、选择性纤维蛋白肽 A 释放和促血栓形成特性。
