Testing the Hydration Status of the Shaker-K Channel Voltage Sensor Domain with Sugars

Abstract

Voltage gated K-channels are formed by two well defined domains: the Pore Domain (PD), which is responsible for the K+ ions conduction process, and the Voltage Sensor Domain (VSD), which sense the transmembrane potential due to the presence of several charged moieties. VSD moves upon activation such that ∼4 net positive charges translocate across the membrane. The molecular details of such movement have been subject of intense controversy. We asked if part of the charges are hydrated at the resting and activated states, and if they change their hydration status during voltage activation. We measured the gating currents of a constitutively closed Shaker-V478W in macro patches of Xenopus oocytes in the presence of internal, external, or symmetric 2M Sucrose to reduce the water availability for eventual VSD hydration. Our results are consistent with the idea that some charged residues are hydrated when exposed to the cytosol at resting, dehydrate before translocation and rehydrate externally in the activated conformation. These suggest that water plays an important role stabilizing charged moieties in both, the resting and active conformation, revealing a novel role for water in the voltage sensing process.ID-F is a MECESUP Fellow. We thank to Iniciativa Cientifica Milenio (P09-022-F) and Fondecyt 1120819.