Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, C37
The Pore Structure and Gating Mechanism of K2P Channels
P. Piechotta1, M. Rapedius2, P. J. Stansfeld3, M. K. Bollepalli2, G. Ehrlich1, I. Andres-Enguix4, H. Fritzenschaft2, N. Decher5, M. S. Sansom3,6, S. J. Tucker4,6, T. Baukrowitz2
1. Dept Physiology, Friedrich Schiller University, Jena, Germany. 2. Dept Physiology, Christian Albrechts University, Kiel, Germany. 3. Dept Biochemistry, University of Oxford, Oxford, United Kingdom. 4. Dept Physics, University of Oxford, Oxford, United Kingdom. 5. Institute of Physiology and Pathophysiology, University of Marburg, Marburg, Germany. 6. OXION Ion Channel Initiative, University of Oxford, Oxford, United Kingdom.
Two-pore domain (K2P) potassium channels are important regulators of cellular electrical excitability. However, the structure of these channels and their gating mechanism, in particular the role of the bundle-crossing gate, are not well understood. Here we report that quaternary ammonium (QA) ions bind with high-affinity deep within the pore of TREK-1 and have free access to their binding site prior to channel activation by intracellular pH or pressure. This demonstrates that, unlike most other K+ channels, the bundle-crossing gate in this K2P channel is constitutively open. Furthermore, we used QA ions to probe the pore structure of TREK-1 by systematic scanning mutagenesis and comparison of these results to different possible structural models. This revealed that the TREK-1 pore most closely resembles the open-state structure of KvAP. We also found that mutations close to the selectivity filter and the nature of the permeant ion profoundly influence TREK-1 channel gating. These results demonstrate that the primary activation mechanisms in TREK-1 reside close to, or within the selectivity filter and do not involve gating at the cytoplasmic bundle-crossing.
Where applicable, experiments conform with Society ethical requirements