The pH-sensitive structure of the C-terminal domain of voltage-gated proton channel and the thermodynamic characteristics of Zn²⁺ binding to this domain.

The voltage-gated proton channel Hv1 is strongly sensitive to Zn(2+). The H(+) conduction is decreased at a high concentration of Zn(2+) and Hv1 channel closing is slowed by the internal application of Zn(2+). Although the recent studies demonstrated that Zn(2+) interacts with the intracellular C-terminal domain, the binding sites and details of the interaction remain unknown. Here, we studied the pH-dependent structural stability of the intracellular C-terminal domain of human Hv1 and showed that Zn(2+) binds to His(244) and His(266) residues. The thermodynamics signature of Zn(2+) binding to the two sites was investigated by isothermal titration calorimetry. The binding of Zn(2+) to His(244) (mutant H266A) and His(266) (mutant H244A) were an endothermic heat reaction and an exothermic heat reaction, respectively.