Bouton M C, Thurieau C, Guillin M C, Jandrot-Perrus M
Laboratoire de Recherche sur l'Hémostase et la Thrombose, Faculté de Médecine Xavier Bichat, Paris, France.
Thromb Haemost. 1998 Aug;80(2):310-5.
The interaction between GPIb and thrombin promotes platelet activation elicited via the hydrolysis of the thrombin receptor and involves structures located on the segment 238-290 within the N-terminal domain of GPIbalpha and the positively charged exosite 1 on thrombin. We have investigated the ability of peptides derived from the 269-287 sequence of GPIbalpha to interact with thrombin. Three peptides were synthesized, including Ibalpha 269-287 and two scrambled peptides R1 and R2 which are comparable to Ibalpha 269-287 with regards to their content and distribution of anionic residues. However, R2 differs from both Ibalpha 269-287 and R1 by the shifting of one proline from a central position to the N-terminus. By chemical cross-linking, we observed the formation of a complex between 125I-Ibalpha 269-287 and alpha-thrombin that was inhibited by hirudin, the C-terminal peptide of hirudin, sodium pyrophosphate but not by heparin. The complex did not form when gamma-thrombin was substituted for alpha-thrombin. Ibalpha 269-287 produced only slight changes in thrombin amidolytic activity and inhibited thrombin binding to fibrin. R1 and R2 also formed complexes with alpha-thrombin, modified slightly its catalytic activity and inhibited its binding to fibrin. Peptides Ibalpha 269-287 and R1 inhibited platelet aggregation and secretion induced by low thrombin concentrations whereas R2 was without effect. Our results indicate that Ibalpha 269-287 interacts with thrombin exosite 1 via mainly electrostatic interactions, which explains why the scrambled peptides also interact with exosite 1. Nevertheless, the lack of effect of R2 on thrombin-induced platelet activation suggests that proline 280 is important for thrombin interaction with GPIb.
糖蛋白Ib（GPIb）与凝血酶之间的相互作用通过凝血酶受体的水解促进血小板活化，且涉及GPIbα N端结构域238 - 290片段上的结构以及凝血酶上带正电荷的外位点1。我们研究了源自GPIbα 269 - 287序列的肽与凝血酶相互作用的能力。合成了三种肽，包括Ibalpha 269 - 287以及两种乱序肽R1和R2，它们在阴离子残基的含量和分布方面与Ibalpha 269 - 287相当。然而，R2与Ibalpha 269 - 287和R1的不同之处在于，有一个脯氨酸从中心位置移到了N端。通过化学交联，我们观察到125I - Ibalpha 269 - 287与α - 凝血酶之间形成了复合物，水蛭素、水蛭素C端肽、焦磷酸钠可抑制该复合物的形成，但肝素不能。用γ - 凝血酶替代α - 凝血酶时未形成复合物。Ibalpha 269 - 287仅使凝血酶酰胺水解活性发生轻微变化，并抑制凝血酶与纤维蛋白的结合。R1和R2也与α - 凝血酶形成复合物，对其催化活性有轻微修饰，并抑制其与纤维蛋白的结合。肽Ibalpha 269 - 287和R1抑制低浓度凝血酶诱导的血小板聚集和分泌，而R2则无此作用。我们的结果表明，Ibalpha 269 - 287主要通过静电相互作用与凝血酶外位点1相互作用，这解释了为什么乱序肽也能与外位点1相互作用。然而，R2对凝血酶诱导的血小板活化无作用，这表明脯氨酸280对于凝血酶与GPIb的相互作用很重要。
