Mediates the voltage-dependent proton permeability of excitable membranes. Forms a proton-selective channel through which protons may pass in accordance with their electrochemical gradient (By similarity). Less sensitive to zinc ions as compared to the mammalian homologs. Homodimer. The segment S4 is probably the voltage-sensor and is characterized by a series of positively charged amino acids at every third position. Unlike other voltage-gated ion channels it lacks the pore domain (By similarity). The C-terminal coiled coil region mediates homodimerization. Belongs to the hydrogen channel family.