Huang Kai, Zhao Wei, Gao Yongxiang, Wei Wenqing, Teng Maikun, Niu Liwen
Hefei National Laboratory for Physical Sciences at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui, People's Republic of China.
Acta Crystallogr Sect F Struct Biol Cryst Commun. 2011 Aug 1;67(Pt 8):862-5. doi: 10.1107/S1744309111022548. Epub 2011 Jul 13.
Snake-venom thrombin-like enzymes (SVTLEs) are serine proteases that are widely distributed in snakes from the Crotalinae subfamily of the Viperidae. In contrast to other snake-venom serine proteases, they have a biochemical activity similar to that of thrombin and play an important role in the process of blood coagulation. However, SVTLEs cannot activate factor VIII, which is essential in blood-clot stabilization. Consequently, blood clots produced by SVTLEs are not stable and are cleared rapidly. This characteristic makes SVTLEs attractive as potential candidates for antithrombotic therapy. Saxthrombin, an SVTLE from Gloydius saxatilis, was purified and crystallized to obtain a high-quality crystal, from which data were acquired to 1.43 Å resolution. Preliminary X-ray diffraction analysis showed that the crystal belonged to space group C2, with unit-cell parameters a = 94.2, b = 52.2, c = 50.1 Å, β = 96.7°. The crystal structure was determined by molecular replacement and the final R factor was 18.69%; the R(free) was 20.01%. This is the first report of a crystal structure of an SVTLE. Saxthrombin belongs to the typical α/β-hydrolase fold of serine proteases. Its structure was compared with those of thrombin and other snake-venom serine proteases. The observed differences in the amino-acid composition of the loops surrounding the active site appear to contribute to different surface-charge distributions and thus alter the shape of the active-site cleft, which may explain the differences in substrate affinity.
蛇毒类凝血酶（SVTLEs）是丝氨酸蛋白酶，广泛分布于蝰蛇科蝮亚科的蛇类中。与其他蛇毒丝氨酸蛋白酶不同，它们具有与凝血酶相似的生化活性，在血液凝固过程中起重要作用。然而，SVTLEs不能激活凝血因子VIII，而凝血因子VIII在血凝块稳定中至关重要。因此，由SVTLEs产生的血凝块不稳定且会迅速清除。这一特性使SVTLEs成为抗血栓治疗潜在候选药物。从岩栖蝮蛇中纯化并结晶出一种蛇毒类凝血酶——岩栖蝮蛇凝血酶，获得了高质量晶体，并采集了分辨率达1.43 Å的数据。初步X射线衍射分析表明，该晶体属于空间群C2，晶胞参数为a = 94.2、b = 52.2、c = 50.1 Å，β = 96.7°。通过分子置换法确定了晶体结构，最终R因子为18.69%；R（free）为20.01%。这是关于蛇毒类凝血酶晶体结构的首次报道。岩栖蝮蛇凝血酶属于丝氨酸蛋白酶典型的α/β-水解酶折叠结构。将其结构与凝血酶及其他蛇毒丝氨酸蛋白酶的结构进行了比较。活性位点周围环的氨基酸组成上观察到的差异似乎导致了不同的表面电荷分布，从而改变了活性位点裂隙的形状，这可能解释了底物亲和力的差异。
