Understanding gating kinetics in Cys-loop receptors

点击翻译按钮获取中文摘要

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.