Understanding gating kinetics in Cys-loop receptors

配体门控离子通道是存在于全身的蛋白质，介导突触发生的快速细胞间通讯。它们是控制许多重要过程所必需的，包括那些对记忆和学习以及肌肉控制至关重要的过程。因此，这些受体与包括癫痫和痉挛在内的一系列神经系统疾病有关也就不足为奇了。为了执行它们的功能，这些蛋白质必须在与神经递质结合时改变构象(形状)，以便允许离子进入或离开细胞。这个过程是一个非常动态的过程，通道处于关闭或开放状态之间的运动速度直接支撑着中枢神经系统的行为。尽管取得了巨大的进展，但在分子水平上，这些受体到底如何改变构象(形状)以及控制整体动态反应的因素仍然知之甚少。在这项提案中，我们将试图通过检查甘氨酸受体作为关键的通道蛋白来解决这个最基本的问题。这种结构通常是通过结晶学获得的，通道的功能行为通常是通过电生理实验记录通道的电活动来监测的。要在结构和功能之间建立联系，并阐明有关基础动力学的关键信息，最合适和最有用的工具是分子模拟和计算模型。我们希望尝试和理解的关键问题之一是，为什么非常相似的激动剂(打开通道的化合物)会产生非常不同的功能反应？例如，与丙氨酸相比，甘氨酸受体对甘氨酸的反应明显更强(总电流更大)，丙氨酸分子的不同之处只有一个甲基的存在(与甘氨酸中的单个氢原子相比)。为了回答这类问题，我们可以等待更多的结构信息(通过结晶学)，但不能保证在不久的将来就能解决高分辨率结构，无论如何，我们希望了解几种不同激动剂的行为。此外，我们以前的数据表明，即使当激动剂与受体结合时，激动剂也可能具有相当大的流动性，并表现出多种结合模式(可能导致其功能的复杂性)。因此，为了解决这类问题，我们建议使用各种分子动力学方法。这些模拟可以提供工作假说，这些假说可以通过我们与伦敦大学学院同事的持续合作进行测试。反过来，在伦敦大学学院进行的功能实验可以用分子模拟来探索，以便提供对结果的洞察，否则可能很难合理化。我们的建议利用分子模拟的能力来提供原子水平的细节，说明是什么控制了结合位点对不同化合物的反应方式。如果我们不仅要扩展我们对离子通道行为的基本知识，而且要有机会在未来开发针对这些类型的蛋白质的化合物作为各种神经疾病的治疗方法，那么对这一点的充分理解是必要的。

Ligand-gated ion channels are proteins that are present throughout the body and mediate the fast cell-to-cell communication that occurs at the synapses. They are necessary for controlling many important processes including those fundamental to memory and learning as well as muscle control. It is therefore perhaps unsurprising that these receptors have been implicated in a range of neurological conditions including epilepsy and spasticity. In order to perform their function, these proteins must, upon binding a neurotransmitter, change conformation (shape) in order to allow ions to pass into or out of the cell. This process is a very dynamic one and the speeds of movement between the channel being in closed or open states directly underpins the behaviour of the central nervous system.Despite huge progress, exactly how these receptors change conformation (shape) and what factors control the overall dynamic response remain very poorly understood at the molecular level. In this proposal, we will try and address this most fundamental of questions, via examination of the glycine receptor as a key example channel protein. The structure is usually obtained by crystallography and the functional behavior of the channel is usually monitored by recoding the channel's electrical activity via electrophysiological experiments. To make the link between structure and function and to elucidate key information about the underling dynamics, the most appropriate and useful tool is molecular simulation and computational modelling.One of the key questions we wish to try and understand is exactly why do very similar agonists (compounds that open the channel) give very different functional responses? For example, the response of the glycine receptor to glycine is significantly stronger (larger overall current) compared to alanine, a molecule that differs only by the presence of a methyl group (compared to a single hydrogen atom in glycine). In order to answer this kind of question, we could wait for more structural information (via crystallography), but there is no guarantee that a high-resolution structure will be solved in the near future and regardless, we would like to understand the behaviour of several different agonists. Furthermore, our previous data suggests that even when bound to the receptor, agonists may be quite mobile and exhibit multiple binding modes (perhaps contributing to their functional complexity). Thus, in order to address these kinds of questions we are proposing to using various molecular dynamics methodologies. These simulations can provide working hypotheses which can be tested via our on-going collaboration with colleagues at UCL. In turn, the functional experiments performed at UCL can be explored with molecular simulation in order to provide insight into results that might otherwise be difficult to rationalize. Our proposal utilizes the power of molecular simulations to provide atomic-level detail of what controls the way the binding site behaves in response to different compounds. A full understanding of this is necessary if we are to not only extend our fundamental knowledge of ion channel behavior but also to have any chance of developing compounds that target these kinds of proteins in the future as treatments for various neurological conditions.