Two-pore domain potassium (K2P) channels conduct K+ ions across the plasma membrane of eukaryotic cells. They help to maintain the cellular resting potential and their modulation can tune cellular excitability (see the Perspective by Poulsen and Nissen). Miller and Long (p. 432) describe a high-resolution crystal structure of the human K2P channel K2P1 (TWIK-1) and Brohawn ef al. (p. 436) present a high-resolution structure of the lipid and mechanosensitive human channel TRAAK. In both structures an extracellular domain constricts the channel entrance so that K+ ions reach the selectivity filter through side portals. Openings in the transmembrane region expose the central cavity to the lipid bilayer and a helix is kinked so that its C-terminal part lies in the cytosol-membrane interface.
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