Liu Q, Matsueda G, Brown E, Frojmovic M
Department of Physiology, McGill University, Montreal, Quebec, Canada.
Biochim Biophys Acta. 1997 Dec 5;1343(2):316-26. doi: 10.1016/s0167-4838(97)00130-1.
It has been clear that only the carboxyl terminus of fibrinogen (Fg) gamma chain is required for the initial binding of Fg from solution to its GPIIbIIIa (glycoprotein IIb and IIIa) receptor on activated platelets, whereas the two RGD sites on the A alpha chain do not play any role. In this study, we examined the role of these three putative adhesive domains on Fg already bound to its receptors in mediating platelet aggregation. Activated platelets were first incubated with Fg to let the Fg bind, then with monoclonal antibodies (mAb) to block the putative adhesive domains, and the platelet suspension was then sheared or stirred to induce aggregation. The mAb 4A5, which recognizes the last four amino acid residues (AGDV) in a dodecapeptide (H12) on the carboxyl terminus of the Fg gamma chain, markedly inhibited platelet aggregation. Z69/8, a mAb whose epitope is also on the dodecapeptide but does not recognize the AGDV residues, did not have any inhibitory effect on aggregation. The anti-RGDS and anti-RGDF mAbs did not affect both macro- and micro-aggregation at all, whether tested singly or together. These results demonstrate that, similar to the situation for the initial binding of soluble Fg, only the gamma chain carboxyl terminus with the AGDV residues are needed for platelet-bound Fg to support aggregation, while the RGD sites on the A alpha chain do not seem to be required.
已经明确的是，纤维蛋白原（Fg）γ链的羧基末端是溶液中的Fg与活化血小板上的糖蛋白IIbIIIa（GPIIb和IIIa）受体初始结合所必需的，而Aα链上的两个RGD位点不起任何作用。在本研究中，我们研究了Fg上已与其受体结合的这三个假定的粘附结构域在介导血小板聚集中的作用。首先将活化的血小板与Fg孵育以使Fg结合，然后用单克隆抗体（mAb）阻断假定的粘附结构域，然后剪切或搅拌血小板悬浮液以诱导聚集。识别Fgγ链羧基末端十二肽（H12）中最后四个氨基酸残基（AGDV）的单克隆抗体4A5显著抑制血小板聚集。Z69/8是一种表位也在该十二肽上但不识别AGDV残基的单克隆抗体，对聚集没有任何抑制作用。抗RGDS和抗RGDF单克隆抗体无论单独测试还是一起测试，对宏观和微观聚集均无影响。这些结果表明，与可溶性Fg初始结合的情况类似，血小板结合的Fg支持聚集仅需要带有AGDV残基的γ链羧基末端，而Aα链上似乎不需要RGD位点。
