凝血酶原是因子 XI 与血小板表面结合以及凝血酶介导血小板激活因子 XI 过程中的一种辅助因子。

Prothrombin is a cofactor for the binding of factor XI to the platelet surface and for platelet-mediated factor XI activation by thrombin.

作者信息

Baglia F A, Walsh P N

机构信息

The Sol Sherry Thrombosis Research Center, Department of Medicine, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.

出版信息

Biochemistry. 1998 Feb 24;37(8):2271-81. doi: 10.1021/bi972113+.

DOI:10.1021/bi972113+

PMID:9485373

Abstract

To study the physiological significance of thrombin as an initiator of intrinsic blood coagulation, activated human platelets were compared with dextran sulfate as a surface for thrombin-catalyzed factor XI activation. Activated gel-filtered platelets promoted factor XI activation by thrombin at initial rates 2-5-fold greater than dextran sulfate in the presence of high molecular weight kininogen (HK, 45 nM), ZnCl2 (25 microM), and CaCl2 (2 mM), conditions optimal for factor XI binding to platelets. Physiological concentrations of HK (636 nM) inhibited factor XI activation by thrombin in a concentration-dependent manner, and this inhibition was reversed by prothrombin (1-3 microM) and by prothrombin fragment 1.2 (PF1.2), but not by prothrombin fragment 1 (PF1). Since prothrombin and PF1.2 (but not PF1) also displaced HK from its binding site on the Apple 1 domain of factor XI, we conclude that the Kringle II domain of prothrombin competes with HK for binding to the Apple 1 domain of factor XI. Prothrombin (1-3 microM) and PF1.2 (but not PF1) in the presence of CaCl2 (2 mM) were able to replace HK (45 nM) in the presence of ZnCl2 (25 microM) as a cofactor for the specific, reversible, high-affinity (Kd approximately 25 nM) binding of factor XI to 947 +/- 150 sites per platelet. This binding is mediated by residues Asn 235-Arg 266 in the Apple 3 domain since a conformationally constrained, synthetic peptide analogue of this sequence inhibits both factor XI binding to activated platelets and platelet-mediated, thrombin-catalyzed factor XI activation in the presence of prothrombin and CaCl2. Finally, prothrombin (1.2 microM) and CaCl2 (2 mM) could substitute for HK (45 nM) and ZnCl2 (25 microM) in promoting optimal rates of thrombin-catalyzed factor XI activation on the platelet surface, thereby initiating the intrinsic coagulation pathway by mechanisms completely independent of the contact phase proteins, factor XII, HK, and prekallikrein.

摘要

为研究凝血酶作为内源性血液凝固启动因子的生理意义，将活化的人血小板与硫酸葡聚糖作为凝血酶催化因子XI活化的表面进行了比较。在高分子量激肽原（HK，45 nM）、ZnCl2（25 μM）和CaCl2（2 mM）存在的情况下，活化的凝胶过滤血小板促进凝血酶对因子XI的活化，其初始速率比硫酸葡聚糖高2 - 5倍，这些条件是因子XI与血小板结合的最佳条件。生理浓度的HK（636 nM）以浓度依赖的方式抑制凝血酶对因子XI的活化，而凝血酶原（1 - 3 μM）和凝血酶原片段1.2（PF1.2）可逆转这种抑制作用，但凝血酶原片段1（PF1）则不能。由于凝血酶原和PF1.2（但不是PF1）也能将HK从其在因子XI苹果1结构域的结合位点上置换下来，我们得出结论，凝血酶原的kringle II结构域与HK竞争结合因子XI的苹果1结构域。在CaCl2（2 mM）存在的情况下，凝血酶原（1 - 3 μM）和PF1.2（但不是PF1）能够替代在ZnCl2（25 μM）存在时的HK（45 nM），作为因子XI与每个血小板947±150个位点特异性、可逆、高亲和力（Kd约为25 nM）结合的辅因子。这种结合是由苹果3结构域中的Asn 235 - Arg 266残基介导的，因为该序列的构象受限合成肽类似物在凝血酶原和CaCl2存在的情况下，既抑制因子XI与活化血小板的结合，也抑制血小板介导的凝血酶催化因子XI的活化。最后，凝血酶原（1.2 μM）和CaCl2（2 mM）可以替代HK（45 nM）和ZnCl2（25 μM），在血小板表面促进凝血酶催化因子XI活化的最佳速率，从而通过完全独立于接触相蛋白、因子XII、HK和前激肽释放酶的机制启动内源性凝血途径。