Abstract

The dissipation of acute acid loads by the voltage-gated proton channel (Hv1) relies on regulating the channel's open probability by the voltage and the ApH across the membrane (ApH = pHex - pHin). Using monomeric Ciona-Hv1, we asked whether ApHdependent gating is produced during the voltage sensor activation or permeation pathway opening. A leftward shift of the conductance-voltage (G-V) curve was produced at higher ApH values in the monomeric channel. Next, we measured the voltage sensor pH dependence in the absence of a functional permeation pathway by recording gating currents in the monomeric nonconducting D160N mutant. Increasing the ApH leftward shifted the gating charge-voltage (Q-V) curve, demonstrating that the ApHdependent gating in Hv1 arises by modulating its voltage sensor. We fitted our data to a model that explicitly supposes the Hv1 voltage sensor free energy is a function of both the proton chemical and the electrical potential. The parameters obtained showed that around 60% of the free energy stored in the ApH is coupled to the Hv1 voltage sensor activation. Our results suggest that the molecular mechanism underlying the Hv1 ApH dependence is produced by protons, which alter the free-energy landscape around the voltage sensor domain. We propose that this alteration is produced by accessibility changes of the protons in the Hv1 voltage sensor during activation.