Multiple Activity Patterns of Acetylcholine Receptors

描述(由申请人提供)：神经肌肉突触上的信号需要乙酰胆碱受体(AChRs)的C(丢失通道)O(笔通道)‘门控’。这种变构转变的热力学基础是众所周知的：从神经末梢释放的递质分子与AChRs结合，与O与C的亲和力更高，从而增加了通道开放的可能性。CO内部的微观事件不太确定。我们将使用单通道动力学和phi值分析来探索AChR门的内部，并阐明该反应中的超快蛋白质重排。到目前为止，结果表明，AChRs从C到O经历了4个步骤。最先移动的氨基酸不是在递质结合部位，而是在连接亚基M2和M3螺旋的远距离膜结构域连接子中。此外，M2(所有子单元)中双门的解锁发生在最后2个门控激活步骤中。大多数侧链门控运动都是对只会产生局部能量后果的事件的重新安置。我们将研究AChR门控的两个新假设：1)结合位点和门之间的通信不是通过结构-机械过程，而是通过整个骨架的振动熵，以及2)变构通信始于激动剂与静息受体的低亲和力结合。

DESCRIPTION (provided by applicant): Signaling at the neuromuscular synapse requires C(losed-channel)O(pen-channel) 'gating' of acetylcholine receptors (AChRs). The thermodynamic foundation of this allosteric transition is well understood: transmitter molecules released from the nerve terminal bind to AChRs with higher affinity to O vs. C to increase the probability that the channel is Open. The microscopic events within CO are less certain. We will use single-channel kinetics and phi-value analysis to probe the interior of AChR gating and illuminate the ultra-fast protein rearrangements within this reaction. So far, results show that AChRs change from C-to-O in 4 steps. The first amino acids to move are not at the transmitter binding sites but in a distant membrane domain linker that joins the M2 and M3 helices of the subunit. Further, the unlocking of a double-gate in M2 (all subunits) occurs in the final 2 gating activation steps. Most side chain gating movements are 'resettling' events that have only local energetic consequences. We will investigate two new hypotheses for AChR gating: 1) communication between the binding sites and the gate is not by a structural-mechanical process but, rather, by the vibrational entropy of the entire backbone, and 2) allosteric communication commences with low-affinity binding of the agonist to the resting receptor.