Probing chemical and conformational differences in the resting and active conformers of platelet integrin αIIbβ3
Probing chemical and conformational differences in the resting and active conformers of platelet integrin αIIbβ3
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DOI：
10.1074/jbc.275.10.7249
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发表时间：
2000-03-10
影响因子：
4.8
通讯作者：
Smith, JW
中科院分区：
文献类型：
--
作者：
Yan, B;Hu, DD;Smith, JW
整合素α（IIb）β（3）是介导血小板粘附和聚集的纤维蛋白原受体。血小板表面的α（IIb）β（3）的配体结合功能被生理刺激“激活”。可以从血小板裂解物中纯化两种形式的α（IIb）β（3），这些形式是血小板表面上发现的整联蛋白的静息（活化状态-1或AS-1）和活性（活化状态-2或AS-2）构象的复制品。在这里，纯化的AS-1和AS-2之间的差异进行了检查，以深入了解激活机制。提出了四个主要发现。1)纤维蛋白原和整合素之间的结合率（k（1））是AS-1和AS-2之间的关键差异。2)二价离子Mn ~（2+）虽然能增强AS-1的配体结合功能，但不能使AS-1转化为AS-2，因此Mn ~（2+）对整合素的作用与激活无关。3)肽质量指纹表明AS-1和AS-2的化学结构几乎相同，这对翻译后修饰是激活所必需的这一观点提出了质疑。4)α（IIb）β（3）的两种形式在三个位置具有显著的构象差异。这些包括α（IIb）重链和轻链的连接点、α（IIb）上的二价离子结合位点以及连接β（3）氨基末端与富含半胱氨酸结构域的二硫键结。这些观察结果表明，整合素被激活的一系列特定的构象重排的胞外域，增加配体协会的速度。
Integrin alpha(IIb)beta(3) is the fibrinogen receptor that mediates platelet adhesion and aggregation. The ligand binding function of alpha(IIb)beta(3) is "activated" on the platelet surface by physiologic stimuli. Two forms of alpha(IIb)beta(3) can be purified from platelet lysates, These forms are facsimiles of the resting (Activation State-1 or AS-1) and the active (Activation State-2 or AS-2) conformations of the integrin found on the platelet surface. Here, the differences between purified AS-1 and AS-2 were examined to gain insight into the mechanism of activation. Four major findings are put forth. 1) The association rate (k(1)) between fibrinogen and the integrin is a key difference between AS-1 and AS-2. 2) Although the divalent ion Mn2+ enhances the ligand binding function of AS-1, this ion is unable to convert AS-1 to AS-2, Therefore, its effect on integrin is unrelated to activation. 3) Peptide mass fingerprints indicate that the chemical structure of AS-1 and AS-2 are virtually identical, calling into question the idea that post-translational modifications are necessary for activation. 4) The two forms of alpha(IIb)beta(3) have significant conformational differences at three positions. These include the junction of the heavy and light chain of alpha(IIb), the divalent ion binding sites on alpha(IIb), and at a disulfide-bonded knot linking the amino terminus of beta(3) to the cysteine-rich domain. These observations indicate that integrin is activated by a series of specific conformational rearrangements in the ectodomain that increase the rate of ligand association.