Gating Currents of Monomeric Hv Channel Reveals a Permeation Pathway Coupled to the Voltage Activation

Abstract

Recently, a family of voltage-gated proton channels, called (Hv) was cloned from different organisms. Hv channel shares a common structure with the Voltage Sensor Domain (VSD) of voltage-gated K channels. Despite off the high homology between Hv channel and the VSD, they have distant quaternary structures. Hv channel lacks a pore domain, and is fully functional either as a monomer or dimer. The S4 was proposed as the possible permeation pathway, resembling the omega current present in some mutants of Shaker K+ channel. However the permeation pathway is still elusive. Fluorescence experiments suggests that the voltage activation in Hv is in two steps, where the second step is a cooperative conformational change, involving interactions between subunits that opens both permeation pathways in a concerted way in the dimer. However, the relationship between the H+ pore, and the voltage sensor activation is not fully understood for the monomer. Here we presented the first Hv gating currents recordings from the monomeric Hv form (Hv-ΔNΔC). Interestingly, the voltage sensor activation precedes the H+ conduction, suggesting that voltage sensor and H+ pore, are two different structures allosterically coupled. The Q-V present a zδ of 1.6 e0, in agreement with previous experiments of voltage-clamp fluorometry. The data presented support the hypothesis that the channel opening is associated to a second conformational state of the voltage sensor, associated to an extremely slow component in the gating current. Supported by Fondecyt grants ACT 1104 and Fondecyt 1120802 to CG and 1110430 to R.L.