STRUCTURE OF INTERGRIN CYTOPLASMIC DOMAIN ALBB3

血小板整合素αIIbbeta3的内向外信号已经得到了最清楚的证明：在未经刺激的血小板中，αIIbbeta3以一种“潜伏的”非功能状态存在--它不结合其丰富的血液中的配体，如纤维蛋白原，而当受到激动剂(如凝血酶和ADP)的刺激时，αIIbbeta3经历构象变化，随后被激活到高亲和力配体结合状态。这种构象变化被认为首先发生在αIIbbeta3的细胞质区域，然后通过跨膜区传播到细胞外区域，导致高亲和力的配体结合。AlphaIIbbeta3胞质结构域从封闭的非活性状态到开放的活性状态的构象转换的分子细节仍然知之甚少。最近的研究表明，当αIIbbeta3不活跃时，胞质尾巴相互作用，并与二价阳离子形成三元胞质结构域复合体。另一方面，AlphaIIb和/或Beta3尾上的选择性突变导致了结构性活性受体，这表明这些活性突变体的细胞质结构域采用了与野生型不同的构象。因此，这个建议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转导。

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.