The Binding Site in β2-Glycoprotein I for ApoER2′ on Platelets Is Located in Domain V*
The Binding Site in β2-Glycoprotein I for ApoER2′ on Platelets Is Located in Domain V*
复制标题
血小板上 ApoER2 β2-糖蛋白 I 的结合位点位于结构域 V*
DOI：
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发表时间：
2005
影响因子：
4.8
通讯作者：
P. D. de Groot
中科院分区：
文献类型：
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作者：
M. van Lummel;M. Pennings;R. Derksen;R. Urbanus;B. Lutters;N. Kaldenhoven;P. D. de Groot
抗磷脂综合征是由针对β2-糖蛋白I（β2GPI）的自身抗体引起的。β2GPI的二聚化导致血小板向胶原沉积增加。我们发现低密度脂蛋白受体家族成员载脂蛋白E受体2′（apoER 2 ′）参与了二聚体β2GPI对血小板的激活。为了确定二聚体β2GPI的哪个结构域与apoER 2 ′相互作用，我们构建了二聚体β2GPI的结构域缺失突变体，缺失结构域I（ΔI）、II（ΔII）或V（ΔV），以及结构域V的磷脂（PL）插入环中W316 S取代的突变体。ΔI和ΔII延长凝血时间，全长二聚体β2GPI也是如此; ΔV对凝血时间没有影响。其次，ΔI和ΔII与阴离子PL结合，与全长二聚体β2GPI相当。ΔV和W316 S突变体与阴离子PL结合的亲和力降低。当全长二聚体β2GPI、ΔI或ΔII（平均增加150%）加入全血时，血小板与胶原的粘附显著增加。血浆β2GPI、ΔV或W316 S突变体未发现增加。免疫沉淀结果表明，全长二聚体β2GPI、ΔI、ΔII和W316 S突变体可与血小板上的apoER 2 ′相互作用。ΔV与apoER 2 ′无关。我们的结论是，结构域V既参与了β2GPI与阴离子PL的结合，又参与了与apoER 2 ′的相互作用以及随后的血小板活化。β2GPI与apoER 2 ′的结合位点与结构域V的疏水插入环不重叠。
The antiphospholipid syndrome is caused by autoantibodies directed against β2-glycoprotein I (β2GPI). Dimerization of β2GPI results in an increased platelet deposition to collagen. We found that apolipoprotein E receptor 2′ (apoER2′), a member of the low density lipoprotein receptor family, is involved in activation of platelets by dimeric β2GPI. To identify which domain of dimeric β2GPI interacts with apoER2′, we have constructed domain deletion mutants of dimeric β2GPI, lacking domain I (ΔI), II (ΔII), or V (ΔV), and a mutant with a W316S substitution in the phospholipid (PL)-insertion loop of domain V. ΔI and ΔII prolonged the clotting time, as did full-length dimeric β2GPI; ΔV had no effect on the clotting time. Second, ΔI and ΔII bound to anionic PL, comparable with full-length dimeric β2GPI. ΔV and the W316S mutant bound with decreased affinity to anionic PL. Platelet adhesion to collagen increased significantly when full-length dimeric β2GPI, ΔI, or ΔII (mean increase 150%) were added to whole blood. No increase was found with plasma β2GPI, ΔV, or the W316S mutant. Immunoprecipitation indicated that full-length dimeric β2GPI, ΔI, ΔII, and the W316S mutant can interact with apoER2′ on platelets. ΔV did not associate with apoER2′. We conclude that domain V is involved in both binding β2GPI to anionic PL and in interaction with apoER2′ and subsequent activation of platelets. The binding site in β2GPI for interaction with apoER2′ does not overlap with the hydrophobic insertion loop in domain V.