Organic Chemistry; Neuroscience; Ligand-gated Ion Channels; Serotonin 5-HT3 Receptor; Fluorescence Spectroscopy; Electrophysiology; Synthetic Chemistry; Binding Assay; Biophysical Tools; Post-photoaffinity Modifications; Antagonists
Simonin Jonathan, Vernekar Sanjeev Kumar V., Thompson Andrew J., Hothersall Daniel J., Connolly Christopher N., Lummis Sarah C. R., Lochner Martin (2011), High-affinity Fluorescent Ligands for the 5-HT3 Receptor, in Bioorganic & Medicinal Chemistry Letters
, 22(2), 1151-1155.
Lochner Martin (2010), Expanding the Small Molecular Toolbox to Study Big Biomolecular Machines, in Chimia
, 64(4), 241-246.
Quek Gracia X. J., Lin Diana, Halliday Jill I., Absalom Nathan, Ambrus Joseph I., Thompson Andrew J., Lochner Martin, Lummis Sarah C. R., McLeod Malcolm D., Chebib Mary (2010), Identifying the Binding Site of Novel Methyllycaconitine (MLA) Analogs at a4b2 Nicotinic Acetylcholine Receptors, in ACS Chemical Neuroscience
, 1(12), 796-809.
Ligand-gated ion channels are protein complexes located at nerve terminals, also called synapses. They are responsible for the rapid transmission of nerve impulses from one nerve cell to the next one. The crucial physiological importance of ligand-gated ion channels becomes apparent when their function is impaired. In fact, numerous mutations in ligand-gated ion channel genes are known to cause neurological diseases. In addition, ligand-gated ion channels are the site of action of many therapeutic drugs.The ligand-gated ion channels work when small organic molecules (neurotransmitters) are released into the synaptic cleft from the pre-synaptic cell and bind to the ligand-gated ion channel resulting in a conformational transition from a non-conducting "closed" state to a conducting "open" state. High ion flux across the biological membrane in the open channel state triggers further events in the post-synaptic cell and finally leads to the generation of a new action potential and transmission of the nerve impulse.There is evidence that small molecules which block or activate channel function specifically may be useful for treatment of certain psychiatric disorders such as anxiety, drug-dependence, schizophrenia and cognitive dysfunction. Although there have been considerable achievements in the past ten years to solve the exact three-dimensional structure of these large proteins the structures are not accurate enough to allow rational structure-based drug design. As a result many different libraries of compounds are being synthesised and have to be tested against the ion channel receptors. Current screening methods are time consuming and some even rely on using radioactive compounds.The aim of this proposal is to develop novel synthetic biophysical tools which will aid our understanding of the function of these ion channel receptors but also allow their selective chemical modification. These proposed chemical modifications will yield semi-synthetic ion channels with added biophysical properties (e.g. fluorescence). Such fluorescent ion channel receptors would be very powerful tools in sophisticated fluorescence spectroscopy studies determining how small molecules interact with these huge multi-subunit proteins and how they activate them. Furthermore, the added biophysical properties of the modified ion channels will be exploited in a binding assay which is based on detection of fluorescence and hence could be used for screening of drugs targeting ion channels. Another goal of the proposed research is the generation of small libraries of compounds which fit the common molecular signature of ion channel activators and inhibitors but which have more natural product-like structures. Such libraries would be screened with the newly developed assay and positive hits will be further analysed for their influence on ion channel function using electrophysiology experiments. The proposed novel methodologies shall be developed on the serotonin 5-HT3 ion channel receptor which is one of the simplest ligand-gated ion channels. The concept would then be expanded to other more complex ion channels and cell-surface receptors (e.g. G-protein coupled receptors). Due to its highly interdisciplinary nature the proposed work is likely to attract interest from researchers in other fields such as biology, pharmacology and spectroscopy. The chance of success is high with the prospect of yielding a new and highly rewarding angle to look at ion channel function. Whereas in the past ion channels have purely been studied using physiological and biochemical methods the proposed research involves intelligent molecular design to develop a tool for studying the binding of small organic molecules to ion channels which also gives an element of structural and functional information. This will lead to a better understanding of ion channel function and reveal details of their structure which will ultimately lead to better and more selective drugs.