Zn2+-Binding to the Voltage-Gated Proton Channel Hv1/VSOP

The voltage-gated proton channel (Hv1/VSOP) is inhibited by Zn2+, of which the binding site is located in the extracellular region. We utilized attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy to examine the coordination structure by monitoring protein structural changes induced by Zn2+-binding. The Zn2+-induced difference ATR-FTIR spectra of Hv1 showed IR features that can be assigned to the histidine C5-N1 and carboxylate-COO- stretches as well as amide I changes likely in alpha-helical peptide bonds. Analysis of vibrational frequencies indicated that the Zn2+ is coordinated by the anionic carboxylate with monodentate mode and by the histidine at N1 (N tau) position of the neutral imidazole form. Combined with quantum chemical calculations, the most probable coordination structure was proposed as a tetrahedral geometry with ligands of carboxylate and imidazole groups in addition to a water molecule.