Department of Molecular Biology, Division of Structural Biology, University of Salzburg, 5020 Salzburg, Austria.
Department of Molecular Biology, Division of Structural Biology, University of Salzburg, 5020 Salzburg, Austria.
Structure. 2009 Dec 9;17(12):1669-1678. doi: 10.1016/j.str.2009.10.011.
Human coagulation factor IX serves both to maintain and to control blood coagulation. The dual function of this hemophilic factor is implemented by a tiered activation mechanism. Processed two-chain factor IXa is catalytically silent; only together with its cofactor VIIIa does factor IXa form the highly potent Xase complex. The detailed mechanism of this secondary activation has remained elusive so far. Here we present the crystal structures of Xase-like factor IXa mutants with several-thousand-fold activity enhancement that mimic the secondary activation by Xase formation. The structures reveal how cofactor-triggered and substrate-assisted modulations in the factor IXa 99- and 60-loops cooperate in S4 through S2' formation, allowing for productive substrate recognition. We could further physically map and visualize a distinct communication line, along which agonists such as Ca(2+) direct their effects to the active site and vice versa.
人凝血因子 IX 既具有维持作用又具有控制作用血液凝固。这种血友病因子的双重功能是通过分层激活机制实现的。经过处理的双链因子 IXa 没有催化活性；只有与辅助因子 VIIIa 一起，因子 IXa 才能形成高效的 Xase 复合物。迄今为止，这种二次激活的详细机制仍难以捉摸。在这里，我们展示了具有数千倍活性增强的 Xase 样因子 IXa 突变体的晶体结构，这些突变体模拟了由 Xase 形成的二次激活。这些结构揭示了辅助因子触发和底物辅助调节因子 IXa 的 99-和 60-环如何通过 S4 到 S2' 的形成进行合作，从而允许进行有效的底物识别。我们还可以进一步在物理上进行映射和可视化一个独特的通讯线路，沿着该线路，激动剂（如 Ca(2+)）将它们的作用直接导向活性位点，反之亦然。
