The Structural Mechanism of K2P Channel Gating

Almost every single process in the human body is controlled at some level by electrical signals, from the way our hearts beat, the way our muscles move, to the way we think. These electrical signals are generated and controlled by ion channels which act as electrical 'switches' to control the selective movement of charged ions like potassium (K+) and sodium (Na+) into and out of the cell. They therefore play a fundamentally important role in normal cellular function and their dysfunction is known to result in a wide variety of disease states. The 'Two-Pore' or 'K2P' channels are a major subfamily of potassium channels found in many different tissues throughout the human body and are involved in many important physiological processes, in particular the control of electrical activity in nerve cells. However, in marked contrast to many other types of K+ ion channel, the molecular mechanisms which control K2P channel function and their 3D structure are still poorly understood. In an attempt to tackle this problem we have recently identified a range of high-affinity drugs which can be used as molecular tools to probe the structure of the K2P channel and the mechanisms by which they open and close. We have also identified an important difference between two particular K2P channels (TREK and TRESK) which now provides us with a fresh insight into how these channels function and why their gating mechanism is different to other types of K+ channel. In the proposed study we aim to exploit these exciting new findings and to use these molecular tools to investigate the structural mechanism of K2P channel gating. The proposed industrial partnership with Pfizer also provides us with access to a variety of chemical tools, expertise and resources that are not normally available in an academic environment and which place us in a unique position to be able to pursue these goals.

Two-pore-domain potassium (K2P) channels comprise a major and structurally distinct subset of the mammalian K+ channel superfamily, and underlie the background, or leak, currents that regulate the resting membrane potential and excitability of many mammalian cells. However, in contrast to many other classes of K+ channel, relatively little is known about the structural mechanisms of K2P channel gating. In particular it is unclear how different regulatory stimuli open the channel pore - do they open the channel at the helix bundle crossing or modify the proposed 'inactivation gate' at the selectivity filter? Also, it is unknown how these two gates are affected by the binding of different activatory ligands. We have recently identified a range of pharmacological tools which can be used to probe the structure and gating mechanism of the K2P channel pore. Using these tools our initial studies of TREK-1 indicate that the primary gating mechanism resides close to or within the selectivity filter and does not involve closure of the channel at the helix bundle crossing. We have also obtained evidence which indicates that a structural and functional asymmetry exists within the K2P channel pore, and that fundamental differences between the role of the pore-lining helices in TREK-1 and TRESK gating will provide an important insight into how the binding of regulatory ligands affects channel activity. This proposal aims to exploit these recent advances in order to probe the fundamental molecular mechanisms of K2P channel gating. To help with achieving these objectives the project involves an industrial partnership with Pfizer which provides unique access to a wide range of resources, expertise and new molecular tools.

The proposed study aims to enhance our basic knowledge of how an important class of ion channels function at the molecular level, and although the project is science-led and driven by a curiosity to understand the structural basis of K+ channel gating, the long-term potential impact of this work is significant. K2P channels are involved in many important physiological process and the future design of any novel therapeutic strategies to target these channels ultimately relies upon a fundamental understanding of the intimate relationship between their structure and their functional properties. In particular the TREK and TRESK K2P channels are now known to be involved in a variety of pain sensation pathways. They therefore represent potentially important and novel therapeutic targets for the treatment of pain. The social and economic impact of potential new developments in this area is therefore wide-ranging and will have obvious and long-lasting implications. In addition, the proposed study will not only help to raise the overall profile of industrially-sponsored basic academic research in the UK, but also establish a new academic collaboration between the two principal applicants. Other potential stakeholders include academic and industrial research groups who will benefit from the tools and reagents developed as part of this study. Closer to home, the PDRAs employed on this grant will also receive training in new areas to enhance their career development, and the project will provide an excellent training environment for research students at the University of Oxford and the Medway School of Pharmacy. This project would therefore represent a strategic investment in UK bioscience.