K2P2.1 (TREK-1)-activator complexes reveal a cryptic selectivity filter binding site

Polymodal thermo- and mechanosensitive two-pore domain potassium (K_2P) channels of the TREK subfamily generate 'leak' currents that regulate neuronal excitability, respond to lipids, temperature and mechanical stretch, and influence pain, temperature perception and anaesthetic responses. These dimeric voltage-gated ion channel (VGIC) superfamily members have a unique topology comprising two pore-forming regions per subunit. In contrast to other potassium channels, K_2P channels use a selectivity filter 'C-type' gate as the principal gating site. Despite recent advances, poor pharmacological profiles of K_2P channels limit mechanistic and biological studies. Here we describe a class of small-molecule TREK activators that directly stimulate the C-type gate by acting as molecular wedges that restrict interdomain interface movement behind the selectivity filter. Structures of K_2P2.1 (also known as TREK-1) alone and with two selective K_2P2.1 (TREK-1) and K_2P10.1 (TREK-2) activators-an N-aryl-sulfonamide, ML335, and a thiophene-carboxamide, ML402-define a cryptic binding pocket unlike other ion channel small-molecule binding sites and, together with functional studies, identify a cation-π interaction that controls selectivity. Together, our data reveal a druggable K_2P site that stabilizes the C-type gate 'leak mode' and provide direct evidence for K_2P selectivity filter gating.