STRUCTURE OF INTERGRIN CYTOPLASMIC DOMAIN ALBB3

血小板整合素alphaIIbbeta3的由内到外的信号传导已被最清楚地证明：在未受刺激的血小板中，alphaIIbbeta3以“潜伏”的非活性状态存在——它不结合其丰富的血源性配体，如纤维蛋白原，而在激动剂（如凝血酶和ADP）的刺激下，alphaIIbbeta3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alphaIIbbeta3的细胞质区域，然后通过跨膜区域传播到细胞外区域，导致高亲和力配体结合。alphaIIbbeta3细胞质结构域从“封闭非活性形式”到“开放活性状态”的构象转变的分子细节仍然知之甚少。最近的研究表明，当失活时，alphaIIbbeta3的细胞质尾部相互作用并与二价阳离子形成三元细胞质结构域复合物。另一方面，α iib和/或β a3尾部的选择性突变导致受体组成性活性，这表明这些活性突变体的细胞质结构域与野生型的构象不同。因此，本提案的总体目标是通过确定alphaIIbbeta3细胞质结构域及其“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.