Elucidating the role of the intracellular pH sensing mechanism of TASK-2 K2P channel

Two-pore domain potassium (K2P) channels are responsible for maintaining the background conductance essential to the resting membrane potential. K2P channels assemble as dimers containing two pore-forming domains and four transmembrane segments per subunits. Two fenestrations connect the lipid membrane with the central conduction cavity, which can be open or closed depending of the movements of helix TM4. TALK subfamily of K2P channels is activated by alkaline extracellular pH and is formed by 3 members: TALK-1, TALK-2 and TASK-2. TASK-2 is also gated by intracellular pH (pHi), being closed by intracellular acidification and activated by increasing pHi. The neutralization of lysine positioned at the end of TM4 helix, and probably within the fenestrations, by a mutation to K245A abolishes pHi-gating . The molecular mechanism by which pHi-sensing K245 exerts its gating role is unknown. A possible mechanism suggest that K245 protonated is able to open the fenestrations and therefore close the channel. Through computational studies, we modeled the 3D structure of TASK-2 channel in both fenestration states, these models were used as a starting point to perform molecular dynamics simulations. The trajectories analysis reveals a good agreement between the pK1/2 of K245 obtained experimentally and the pKa predicted MOL2NET, 2018, 4, http://sciforum.net/conference/mol2net-04 2 when the fenestrations are closed. Besides, we proved that Norfluoxetine compound is a potent blocker of TASK-2 channels and its putative binding site is within the fenestrations (data not shown).