Hantgan R R
Department of Biochemistry, Bowman Gray School of Medicine of Wake Forest University, Winston-Salem, NC 27103.
Biochim Biophys Acta. 1988 Jan 18;968(1):24-35. doi: 10.1016/0167-4889(88)90040-7.
The molecular basis of platelet-fibrin binding has been elucidated by studying interactions between platelets and protofibrils, soluble two-stranded polymers of fibrin which are intermediates on the fibrin assembly pathway. The fibrinogen degradation product, fragment D, has been used to block fibrin assembly, thus enabling the preparation of stable solutions of short protofibrils, composed of fewer than twenty fibrin monomer molecules per polymer. Fibrin protofibrils bound to ADP-activated platelets in a time- and concentration-dependent process which was effectively blocked by excess unlabelled fibrinogen, i.e., the binding was specific and appeared to involve a common receptor. ADP-stimulated cells bound approx. 3 micrograms of fibrin protofibrils/10(8) platelets, compared to 4 micrograms of fibrinogen/10(8) cells, following a 30-min incubation period at room temperature. Binding of both ligands was inhibited by high concentrations of fragment D, further indicating a similar mechanism. The kinetic data obtained were well described by an apparent first-order mechanism in which the rate constant for fibrin protofibril binding was found to be 5-fold slower than that measured for fibrinogen. Two monoclonal antibodies, each directed against the platelet glycoprotein IIb-IIIa complex, inhibited the binding of fibrin protofibrils and fibrinogen in a similar, concentration-dependent manner, providing strong evidence for a common receptor. Binding of GPRP-fibrin (soluble fibrin oligomers formed in the presence of 1 mM Gly-Pro-Arg-Pro) to ADP-stimulated platelets was also inhibited by a monoclonal antibody directed against the GPIIb-IIIa complex. Neither fibrin protofibrils nor fibrinogen bound to Glanzmann's thrombasthenic platelets, which lack normal quantities of functional glycoprotein IIb-IIIa complex, further supporting the hypothesis that fibrinogen and fibrin bind to a common platelet receptor present on the glycoprotein IIb-IIIa complex.
通过研究血小板与原纤维（纤维蛋白的可溶性双链聚合物，是纤维蛋白组装途径中的中间体）之间的相互作用，血小板 - 纤维蛋白结合的分子基础已得到阐明。纤维蛋白原降解产物片段D已被用于阻断纤维蛋白组装，从而能够制备由每个聚合物少于二十个纤维蛋白单体分子组成的稳定短原纤维溶液。纤维蛋白原纤维以时间和浓度依赖性过程与ADP激活的血小板结合，该过程被过量的未标记纤维蛋白原有效阻断，即这种结合是特异性的，并且似乎涉及共同的受体。在室温下孵育30分钟后，ADP刺激的细胞结合约3微克纤维蛋白原纤维/10⁸个血小板，而结合纤维蛋白原的量为4微克/10⁸个细胞。两种配体的结合均被高浓度的片段D抑制，进一步表明机制相似。所获得的动力学数据通过表观一级机制得到很好的描述，其中发现纤维蛋白原纤维结合的速率常数比纤维蛋白原测量的速率常数慢5倍。两种单克隆抗体，每种都针对血小板糖蛋白IIb-IIIa复合物，以相似的浓度依赖性方式抑制纤维蛋白原纤维和纤维蛋白原的结合，为共同受体提供了有力证据。针对GPIIb-IIIa复合物的单克隆抗体也抑制了GPRP - 纤维蛋白（在1 mM甘氨酰 - 脯氨酰 - 精氨酰 - 脯氨酸存在下形成的可溶性纤维蛋白寡聚物）与ADP刺激的血小板的结合。纤维蛋白原纤维和纤维蛋白原均不与缺乏正常量功能性糖蛋白IIb-IIIa复合物的Glanzmann血小板无力症血小板结合，进一步支持了纤维蛋白原和纤维蛋白与糖蛋白IIb-IIIa复合物上存在的共同血小板受体结合的假设。
