Water movement in voltage-gated proton channel (HV1).

Abstract

To date, the permeation mechanism of the Hv1 channel has been controversial, due to the lack of an open structure. Besides the selectivity filter (SF), several studies have shown that the highly conserved S4 asparagine is important for the channel's proton conduction. The protons’ conduction mechanism cannot be separated from the nature of water; thus, using electrophysiological techniques, we evaluated how different mutations directed to the N264 site of the CiHv1 channel affect the proton conduction properties, and these results were contrasted with classical MD simulations in which we explore how the hydration profiles, and the dipole angle of H2O molecules along the protein change with the different N264 mutations. We observed that the super-conductive N264E construct has a favorable electrostatic profile and the H2O molecules near the SF had more freedom of movement and showed more dipole angle configurations, whereas low-conductive N264R had an unfavorable electrostatic profile and a virtually dry zone near the SF. Hv1-injected X. laevis oocytes showed an increased osmotic permeability coefficient. These experiments suggest the presence of water fluxes though the Hv1 channel. With the results of this study, we were able to increase the understanding on the H+ conduction in Hv1 channels and we proposed a new model that takes into consideration water movement. Thus, in our model we propose that the Hv1 conduction possesses two main components: (1) the H2O configurations along the protein and (2) the electrostatic profile, and the proton permeation mechanism occurs in a non-Grotthuss manner, probably accompanied by water fluxes at least at higher voltage structure configurations.