Atom-by-Atom Tuning of an Electrostatic Potassium-Channel Modulator

Abstract

Dehydroabetic acid (DHAA), naturally occurring in pine resin, opens voltage-gated potassium (Kv) channels by altering the movement of the channel's voltage sensor. The hydrophobic part of DHAA (a three-ringed motif) anchors the compound near the extracellular end of the voltage sensor, in a pocket between the channeĺs transmembrane segments S3 and S4, and the lipid membrane. The negatively charged carboxyl group of DHAA executes an electrostatic effect on the positively charged voltage sensor S4, to open the channel. Here, we aimed to increase the channel-opening effect by altering the charge of the effector and by introducing an atomic stalk between the hydrophobic anchor and the charged effector, to allow the compound charge to come close to the voltage-sensor charge. The Shaker Kv channel was expressed in Xenopus laevis oocytes and ion currents were measured by a two-electrode voltage-clamp technique. Altering the partially charged carboxyl group to a permanently charged sulfonic-acid group increased the channel opening effect. Introduction of a carbon stalk between the anchor and the charged effector increased the channel-opening effect further, until a critical stalk length was reached. Longer stalks rendered the compounds without effect. This is consistent with a simple electrostatic model, where the charge location depends on the stalk length. To increase to effect of the compound further we increased the affinity by altering the halogenation of the anchor. This compound significantly opened the human Kv7.2/7.3 (M-type) potassium channel at 1 µM. These results suggest that a stalk between the anchor and the effector is a powerful method to increase the channel-opening effect for electrostatically active compounds.