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 (HV1) that lacks a discernible pore domain but is sufficient for expression of a voltage-sensitive proton-selective ion channel activity. Hv1 currents are activated at depolarizing voltages, sensitive to the transmembrane pH gradient, H+-selective, and Zn2+-sensitive. Mutagenesis of Hv1 identified three arginine residues in S4 that regulate channel gating and two histidine residues that are required for extracellular inhibition of Hv1 by Zn2+. Hv1 is expressed in immune tissues and manifests the characteristic properties of native proton conductances (). In phagocytic leukocytes4, are required to support the oxidative burst that underlies microbial killing by the innate immune system4,5. The data presented here identify Hv1 as a long-sought voltage-gated H+ channel and establish Hv1 as the founding member of a family of mammalian VSD proteins.
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We thank T. DeCoursey, C. Miller, R. MacKinnon and P. Bezanilla for comments on the manuscript, and K.-H. Lee for technical assistance. This work was supported by the Sandler Program for Asthma Research and the Howard Hughes Medical Institute.
Hv1 amino acid sequence and expression profile.
a, Human tissue Western blot probed with 4234 antibody (5 µg/ml) demonstrates expression of native Hv1 protein (~32 kDa) in immune tissues. b, Western blot of total cell lysates prepared from Jurkat (lane 1) or HEK-293T cells transfected with the indicated cDNA (lanes 3-5). c, in HL-60 cells, Hv1 protein appeared to be increased when cells were cultured in the presence of 1.3% DMSO (lane 2).
a, Hv1-like currents were not detectable in HM1 cells. b, Native GvH+ in a DMSO-differentiated HL-60 cell. c, Temperature dependence of Hv1 currents. d, Monoexponential fits of τACT from the same cell as shown in panel c illustrate strong temperature-dependence of Hv1 kinetics. e, R205A currents. f, R208A currents. g, R211A currents.
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Cell Research (2016)