Intrinsic aqueduct orifices facilitate K+ channel gating.

The ion-conducting pore of potassium channels, which can open and close to regulate ion passage, was at long thought to be a one-dimensional pore structure with a water-filled central cavity. Here, we find four orifices in the KcsA potassium channel, which are perpendicular to the pore and stretch out from the cavity. Equilibrium molecular dynamics simulations show that water molecules can flow between the cavity and orifices. Targeted molecular dynamics simulations show that during the opening process, water molecules can move into the cavity through the orifices to facilitate channel gating, whereas blocking the aqueduct orifices makes the channel difficult to open.