Distinct mechanisms of inhibition of Kv2 potassium channels by tetraethylammonium and RY785.

Abstract

Voltage-gated K⁺ channels play central roles in human physiology, in health, and disease. A repertoire of inhibitors that are both potent and specific would, therefore, be of great value. RY785 has been described as promising in this regard, as it selectively inhibits channels in the Kv2 subfamily with high potency. Its mechanism of action has not yet been determined at the molecular level, but functional studies indicate it differs from those of less specific inhibitors, such as quaternary-ammonium compounds or aminopyridines. To examine this mechanism at the single-molecule level, we have carried out a series of all-atom molecular dynamics simulations based on the structure of the Kv2.1 channel in the ion-conducting state. The simulations demonstrate both RY785 and tetraethylammonium spontaneously enter the channel interior through the cytoplasmic gate, but with distinct effects. Tetraethylammonium binds to a site adjacent to the selectivity filter, on the pore axis, thus blocking the flow of K⁺ ions. RY785, by contrast, binds to the channel walls, off-axis, and allows K⁺ flow while the gate remains open. This observation indicates RY785 inhibits Kv2.1 by fostering the occlusion of the gate, through a network of hydrophobic interactions therein, explaining why it also modulates the voltage-sensing mechanism of the channel, 3 nanometers away.