Pike A C, Brzozowski A M, Roberts S M, Olsen O H, Persson E
Structural Biology Laboratory, Chemistry Department, University of York, York YO10 5DD, United Kingdom.
Proc Natl Acad Sci U S A. 1999 Aug 3;96(16):8925-30. doi: 10.1073/pnas.96.16.8925.
Factor VIIa (EC 3.4.21.21) is a trypsin-like serine protease that plays a key role in the blood coagulation cascade. On injury, factor VIIa forms a complex with its allosteric regulator, tissue factor, and initiates blood clotting. Although the structure of the binary complex has already been determined [Banner, D. W., D'Arcy, A., Chène, C., Winkler, F. K., Guha, A., Konigsberg, W. H., Nemerson, Y. & Kirchhofer, D. (1996) Nature (London) 380, 41-46], the conformational effects of cofactor binding to factor VIIa are not known in detail because of a lack of structural information on free factor VIIa. Here we report the structure of gamma-carboxyglutamic acid-domainless human coagulation factor VIIa at a resolution of 2.8 A. The molecule adopts an extended conformation within the crystal similar to that previously observed for the full-length protein in complex with tissue factor. Detailed comparison of free and tissue factor-bound factor VIIa reveals several structural differences. The binding mode of the active-site inhibitor D-Phe-Phe-Arg methyl ketone differs in the two structures, suggesting a role for the cofactor in substrate recognition. More importantly, a surface-exposed alpha-helix in the protease domain (residues 307-312), which is located at the cofactor recognition site, is distorted in the free form of factor VIIa. This subtle structural difference sheds light on the mechanism of the dramatic tissue factor-induced enhancement of factor VIIa activity.
凝血因子VIIa（EC 3.4.21.21）是一种类胰蛋白酶丝氨酸蛋白酶，在血液凝固级联反应中起关键作用。受伤时，凝血因子VIIa与其变构调节剂组织因子形成复合物，启动血液凝固。尽管二元复合物的结构已经确定[班纳，D.W.，达西，A.，谢内，C.，温克勒，F.K.，古哈，A.，科尼格斯伯格，W.H.，内默森，Y. & 基尔希霍费尔，D.（1996年）《自然》（伦敦）380，41 - 46]，但由于缺乏游离凝血因子VIIa的结构信息，辅因子与凝血因子VIIa结合的构象效应尚不清楚。在此，我们报告了无γ-羧基谷氨酸结构域的人凝血因子VIIa的结构，分辨率为2.8埃。该分子在晶体中呈伸展构象，类似于先前观察到的与组织因子结合的全长蛋白的构象。游离和与组织因子结合的凝血因子VIIa的详细比较揭示了几个结构差异。活性位点抑制剂D-苯丙氨酸-苯丙氨酸-精氨酸甲基酮在两种结构中的结合模式不同，表明辅因子在底物识别中起作用。更重要的是，位于辅因子识别位点的蛋白酶结构域中的一个表面暴露的α-螺旋（残基307 - 312）在凝血因子VIIa的游离形式中发生扭曲。这种细微的结构差异揭示了组织因子诱导的凝血因子VIIa活性显著增强的机制。
