Guillin M C, Bezeaud A, Bouton M C, Jandrot-Perrus M
Laboratoire de Recherche sur l'Hémostase et la Thrombose, Faculté de Médecine Xavier Bichat, Paris, France.
Thromb Haemost. 1995 Jul;74(1):129-33.
A model of thrombin interaction with distinct substrates or ligands has been derived from the crystallographic studies of thrombin-inhibitors complexes, and buttressed by functional studies with mutant thrombins, thrombin proteolytic derivatives or antibodies against thrombin. The unique specificity of thrombin for its substrates and ligands may be ascribed to multiple interactions with both the active site cleft and exosite(s) distinct from the active site. Two prominent insertion loops around Trp 50 and Trp 148 project over the active site cleft and play an important role in the substrates selection. Several substrates (fibrinogen, thrombin receptor, heparin cofactor II) or ligands (thrombomodulin, glycoprotein Ib) interact with a large exosite located on the surface of the loop segment 65-76, mainly constituted of basic amino acids, designated anion binding exosite 1. Interaction with these various macromolecules appears to involve a limited number of residues within the large exosite 1. It is conceivable that exosite 1 contains distinct subsites, although most of them may overlap. A second basic exosite (anion binding exosite 2) is located close to the carboxy-terminal B chain helix. Exosite 2 interacts with heparin, the chondroitin sulfate moiety of thrombomodulin and prothrombin activation fragment 2. Interaction of ligands with either exosite 1 or exosite 2 leads to conformational changes of the thrombin molecule, that may be important determinants of thrombin specificity. Whether exosite 2 cooperates with exosite 1 for thrombin interaction with fibrin(ogen) or the thrombin receptor remains to be determined.
通过凝血酶-抑制剂复合物的晶体学研究，得出了凝血酶与不同底物或配体相互作用的模型，并得到了对突变凝血酶、凝血酶蛋白水解衍生物或抗凝血酶抗体的功能研究的支持。凝血酶对其底物和配体的独特特异性可能归因于其与活性位点裂隙以及与活性位点不同的外部位点的多重相互作用。围绕色氨酸50和色氨酸148的两个突出插入环突出于活性位点裂隙上方，并在底物选择中起重要作用。几种底物（纤维蛋白原、凝血酶受体、肝素辅因子II）或配体（血栓调节蛋白、糖蛋白Ib）与位于环段65-76表面的一个大的外部位点相互作用，该位点主要由碱性氨基酸组成，称为阴离子结合外部位点1。与这些各种大分子的相互作用似乎涉及大的外部位点1内有限数量的残基。可以想象，外部位点1包含不同的亚位点，尽管它们中的大多数可能重叠。第二个碱性外部位点（阴离子结合外部位点2）位于靠近羧基末端B链螺旋处。外部位点2与肝素、血栓调节蛋白的硫酸软骨素部分和凝血酶原激活片段2相互作用。配体与外部位点1或外部位点2的相互作用导致凝血酶分子的构象变化，这可能是凝血酶特异性的重要决定因素。外部位点2是否与外部位点1协同作用以实现凝血酶与纤维蛋白（原）或凝血酶受体的相互作用仍有待确定。
