Interior pH Sensing Residue of Human Voltage-Gated Proton Channel H_v1 is Histidine 168

The molecular mechanisms governing the human voltage-gated proton channel hH_v1 remain elusive. Here we used membrane-enabled hybrid-solvent continuous constant pH molecular dynamics (CpHMD) simulations with pH replica exchange to further evaluate the recently obtained structural models of hH_v1 in hyperpolarized (closed channel) and depolarized (open channel) states (Geragotelis, Tobias et al., Proc. Natl. Acad. Sci. USA 2020) and explore potential pH-sensing residues. The CpHMD titration at a set of symmetric pH conditions revealed three residues that can gain or lose protons upon channel depolarization. Among them residue H168 at the intracellular end of the S3 helix switches from the deprotonated to the protonated state and its protonation is correlated with the increased tilting of the S3 helix during the transition from the hyper-to the depolarized state. Thus, the simulation data suggest H168 as an interior pH sensor, in support of a recent finding based on electrophysiological experiments of H_v1 mutants (Cherny, DeCoursey et al., J. Gen. Physiol. 2018). Our work represents an important step towards deciphering the pH-dependent gating mechanism of hH_v1.