STRUCTURE OF INTERGRIN CYTOPLASMIC DOMAIN ALBB3

由内而外的信号传导已被最清楚地证明为血小板整联蛋白α IIb β 3：在未刺激的血小板中，α IIb β 3以“潜伏”非活性状态存在-它不结合其丰富的血液携带的配体，如纤维蛋白原，而在用激动剂刺激时，如凝血酶和ADP，α IIb β 3经历构象变化，随后被激活为高亲和力配体结合状态。这种构象变化被认为首先发生在alphaIIbbeta 3的细胞质结构域中，然后通过跨膜区传播到细胞外结构域，导致高亲和力配体结合。α IIb β 3胞质结构域从其“封闭的非活性形式”到“开放的活性状态”的构象转变的分子细节仍然知之甚少。最近的研究表明，当α IIb β 3失活时，其胞质尾部相互作用，并与二价阳离子相互作用，形成三元胞质结构域复合物。另一方面，α IIb和/或β 3尾部的选择性突变导致组成型活性受体，这表明这些活性突变体的胞质结构域采用与野生型不同的构象。因此，这一建议的总体目标是通过确定α IIb β 3胞质结构域及其“活性”突变体的结构来深入了解构象诱导的整合素信号传导。

The inside-out signaling has been most clearly demonstrated for the platelet integrin alphaIIbbeta3: in unstimulated platelets, alphaIIbbeta3 exists in a "latent" noncompetent state - it does not bind its abundant blood-borne ligands such as fibrinogen, whereas upon stimulation with agonists, such as thrombin and ADP, alphaIIbbeta3 undergoes a conformational change and is subsequently activated to a high-affinity ligand binding state. This conformational change is thought to occur first in the cytoplasmic domain of alphaIIbbeta3, which then propagates through the transmembrane region to the extracellular domain resulting in high affinity ligand binding. The molecular details of the conformational transition for alphaIIbbeta3 cytoplasmic domain from its "closed inactive form" to the "open active state" remains poorly understood. It was recently shown that when inactive, the cytoplasmic tails of alphaIIbbeta3 interact with each other and with a divalent cation to form a ternary cytoplasmic domain complex. On the other hand, selective mutations on alphaIIb and/or beta3 tails result in constitutively active receptor, which suggests that the cytoplasmic domains of these active mutants adopt different conformation from the wild type. Thus the overall objective of this proposal is to gain insights into the conformation induced integrin signaling by determining structures of alphaIIbbeta3 cytoplasmic domain and its "active" mutants.