A voltage-gated proton-selective channel lacking the pore domain

Abstract

Voltage changes across the cell membrane control the gating of many cation-selective ion channels. Conserved from bacteria to humans¹, the voltage-gated-ligand superfamily of ion channels are encoded as polypeptide chains of six transmembrane-spanning segments (S1–S6). S1–S4 functions as a self-contained voltage-sensing domain (VSD), in essence a positively charged lever that moves in response to voltage changes. The VSD ‘ligand’ transmits force via a linker to the S5–S6 pore domain ‘receptor’², thereby opening or closing the channel. The ascidian VSD protein Ci-VSP gates a phosphatase activity rather than a channel pore, indicating that VSDs function independently of ion channels³. Here we describe a mammalian VSD protein (H_V1) that lacks a discernible pore domain but is sufficient for expression of a voltage-sensitive proton-selective ion channel activity. H_v1 currents are activated at depolarizing voltages, sensitive to the transmembrane pH gradient, H⁺-selective, and Zn²⁺-sensitive. Mutagenesis of H_v1 identified three arginine residues in S4 that regulate channel gating and two histidine residues that are required for extracellular inhibition of H_v1 by Zn²⁺. H_v1 is expressed in immune tissues and manifests the characteristic properties of native proton conductances ($G_{{\text{vH}}^{+}}$). In phagocytic leukocytes⁴, $G_{{\text{vH}}^{+}}$ are required to support the oxidative burst that underlies microbial killing by the innate immune system^4,5. The data presented here identify H_v1 as a long-sought voltage-gated H⁺ channel and establish H_v1 as the founding member of a family of mammalian VSD proteins.