Ashton A W, Boehm M K, Johnson D J, Kemball-Cook G, Perkins S J
Department of Biochemistry and Molecular Biology, Royal Free Hospital School of Medicine, London, U. K.
Biochemistry. 1998 Jun 2;37(22):8208-17. doi: 10.1021/bi972574v.
Factor VIIa (FVIIa) is a soluble four-domain plasma serine protease coagulation factor that forms a tight complex with the two extracellular domains of the transmembrane protein tissue factor in the initiating step of blood coagulation. To date, there is no crystal structure for free FVIIa. X-ray and neutron scattering data in solution for free FVIIa and the complex between FVIIa and soluble tissue factor (sTF) had been obtained for comparison with crystal structures of the FVIIa-sTF complex and of free factor IXa (FIXa). The solution structure of free FVIIa as derived from scattering data is consistent with the extended domain arrangement of FVIIa seen in the crystal structure of its complex with sTF, but is incompatible with the bent, less extended domain conformation seen in the FIXa crystal structure. The FVIIa scattering curve is also compatible with a subset of 317 possible extended structures derived from a constrained automated conformational search of 15 625 FVIIa domain models. Thus, the scattering data support extended domain models for FVIIa free in solution. Similar analyses showed that the solution scattering derived and crystal structures of the FVIIa-sTF complex were in good agreement. An automated constrained search for allowed structures for the complex in solution based on scattering curves showed that only a small family of compact models gave good agreement, namely those in which FVIIa and sTF interact closely over a large surface area. The general utility of this approach for structural analysis of heterodimeric complexes in solution is discussed. Analytical ultracentrifugation data and the modeling of these data were consistent with the scattering results. It is concluded that in solution FVIIa has an extended or elongated domain structure, which allows rapid interaction with sTF over a large surface area to form a high-affinity complex.
凝血因子VIIa（FVIIa）是一种可溶性的四结构域血浆丝氨酸蛋白酶凝血因子，在血液凝固的起始步骤中，它与跨膜蛋白组织因子的两个细胞外结构域形成紧密复合物。迄今为止，尚无游离FVIIa的晶体结构。已获得游离FVIIa以及FVIIa与可溶性组织因子（sTF）复合物在溶液中的X射线和中子散射数据，用于与FVIIa - sTF复合物及游离因子IXa（FIXa）的晶体结构进行比较。从散射数据推导得到的游离FVIIa的溶液结构与在其与sTF复合物的晶体结构中所见的FVIIa的延伸结构域排列一致，但与在FIXa晶体结构中所见的弯曲、延伸程度较小的结构域构象不兼容。FVIIa散射曲线也与从15625个FVIIa结构域模型的受限自动构象搜索中得到的317种可能的延伸结构中的一个子集相兼容。因此，散射数据支持溶液中游离FVIIa的延伸结构域模型。类似分析表明，FVIIa - sTF复合物的溶液散射推导结构与晶体结构高度吻合。基于散射曲线对溶液中复合物允许结构进行的自动受限搜索表明，只有一小类紧密模型能给出较好的吻合度，即那些FVIIa和sTF在大表面积上紧密相互作用的模型。讨论了这种方法对溶液中异二聚体复合物进行结构分析的普遍实用性。分析超速离心数据及其建模与散射结果一致。得出的结论是，在溶液中FVIIa具有延伸或拉长的结构域结构，这使得它能够在大表面积上与sTF快速相互作用，形成高亲和力复合物。
