Zamarron C, Ginsberg M H, Plow E F
Committee on Vascular Biology, Research Institute of Scripps Clinic, La Jolla, California 92037.
J Biol Chem. 1991 Aug 25;266(24):16193-9.
The interaction of fibrinogen with membrane glycoprotein GPIIb-IIIa regulates platelet aggregation. This ligand:integrin receptor interaction elicits conformational changes in GPIIb-IIIa as evidenced by the induction of ligand-induced binding sites which are recognized by antibodies that react selectively with the occupied receptor. The dynamic nature of these conformational changes is now demonstrated by the identification and characterization of a receptor-induced binding site (RIBS) elicited in fibrinogen bound to GPIIb-IIIa. A monoclonal antibody to fibrinogen, anti-Fg-RIBS-I, failed to bind to nonstimulated platelets in the presence or absence of fibrinogen. However, when platelets were stimulated with an agonist, the antibody reacted with platelet-bound fibrinogen even in the presence of a marked excess of unbound fibrinogen. A key element of the RIBS epitope has been precisely localized to residues 373-385 of the gamma chain of fibrinogen. Conformational elements also are important in defining the epitope. Fab fragments of the antibody inhibited platelet aggregation. As these fragments also inhibited fibrin polymerization, a commonality between these two diverse functions of fibrinogen in thrombus formation is indicated. In general, antibodies to RIBS and ligand-induced binding site provide unique probes for characterizing ligand:receptor interactions.
纤维蛋白原与膜糖蛋白GPIIb-IIIa的相互作用调节血小板聚集。这种配体：整合素受体相互作用引发了GPIIb-IIIa的构象变化，这可通过诱导配体诱导的结合位点得到证明，这些位点可被选择性地与占据的受体反应的抗体识别。现在，通过鉴定和表征在与GPIIb-IIIa结合的纤维蛋白原中引发的受体诱导结合位点（RIBS），证明了这些构象变化的动态性质。一种针对纤维蛋白原的单克隆抗体，抗Fg-RIBS-I，在有无纤维蛋白原的情况下均不能与未刺激的血小板结合。然而，当用激动剂刺激血小板时，即使存在大量过量的未结合纤维蛋白原，该抗体也能与血小板结合的纤维蛋白原发生反应。RIBS表位的一个关键元件已被精确地定位到纤维蛋白原γ链的373-385位残基。构象元件在定义表位方面也很重要。该抗体的Fab片段抑制血小板聚集。由于这些片段也抑制纤维蛋白聚合，这表明纤维蛋白原在血栓形成中的这两种不同功能之间存在共性。一般来说，针对RIBS和配体诱导结合位点的抗体为表征配体：受体相互作用提供了独特的探针。
