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 humans, 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', 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 channels. Here we describe a mammalian VSD protein (H(V)1) that lacks a discernible pore domain but is sufficient for expression of a voltage-sensitive proton-selective ion channel activity. H(v)1 currents are activated at depolarizing voltages, sensitive to the transmembrane pH gradient, H+-selective, and Zn2+-sensitive. Mutagenesis of H(v)1 identified three arginine residues in S4 that regulate channel gating and two histidine residues that are required for extracellular inhibition of H(v)1 by Zn2+. H(v)1 is expressed in immune tissues and manifests the characteristic properties of native proton conductances (G(vH+)). In phagocytic leukocytes, G(vH+) are required to support the oxidative burst that underlies microbial killing by the innate immune system. The data presented here identify H(v)1 as a long-sought voltage-gated H+ channel and establish H(v)1 as the founding member of a family of mammalian VSD proteins.

The cytoplasmic coiled-coil mediates cooperative gating temperature sensitivity in the voltage-gated H+ channel Hv1

“…Hv1/VSOP is a minimal voltage-gated ion channel that has only four transmembrane regions (S1-S4), which comprise a voltage-sensor domain 1,2 . In addition, a C-terminal cytoplasmic domain consisting of ~55 residues is well conserved among species (Fig.…”

“…H v1/VSOP is a recently discovered voltage-gated H + channel (Hv) 1,2 that is expressed in immunocytes and is involved in the production of reactive oxygen species in phagocytes [3][4][5] and the antigen response in B lymphocytes 6 . Hv1/VSOP has fourtransmembrane segments that correspond to the voltage-sensor domain (S1-S4) of other voltage-gated channels 1,2 , it does not have a canonical pore domain, and the voltage-sensor domain is thought to act as both the voltage-sensor and the H + -permeation pathway 7 .…”

Nox enzymes, ROS, and chronic disease: An example of antagonistic pleiotropy

“…In addition, macrophages (but possibly not neutrophils) produce large production of NO during phagocytosis; when NO reacts with superoxide, it generates the highly cytotoxic chemical species peroxinitrite (HONO) [7]. The activity of the phagocyte NADPH-oxidase also triggers opening of proton [8][9][10][11] and possibly potassium channels [3], that are proposed to change the ionic environment of the phagosome thereby activating microbicidal proteases and contributing to microbial killing [3]. Regardless of the precise mechanisms, it is clear from the inherited condition chronic granulomatous disease (CGD) that mutations resulting in defects in ROS generation by the respiratory burst oxidase are associated with an inability of phagocytes to kill bacteria and other microbes [12], convincingly demonstrating a role for the Nox2 system in innate immunity mediated by professional phagocytes.…”

Do Hv1 proton channels regulate the ionic and redox homeostasis of phagosomes?

“…However, subsequent studies from BKCa-deficient mice refuted this finding and showed that the antibacterial activity of human granulocytes and mouse neutrophils requires proton channels but not BKCa channels (Femling et al, 2006;Essin et al, 2007). The BKCa channel paper was eventually retracted (Retraction, 2010) and the cloning in 2006 of the HVCN1 gene coding for the Hv1 proton channel (Ramsey et al, 2006;Sasaki et al, 2006) enabled to test the role of Hv1 channels in antibacterial defense. Studies from mice lacking Hv1 proton channels (Ramsey et al, 2009;Morgan et al, 2009;El Chemaly et al, 2010) clearly established that Hv1 proton channels provide most of the charge compensation during the respiratory burst (see the Fig.…”

“…Multiple functions were proposed for proton channels, but these remained speculative until the cloning of the Hv1 protein by two separate laboratories (Ramsey et al, 2006;Sasaki et al, 2006) and the generation of Hv1 knockout mice offered the possibility to test the physiological role of proton channels. Structure-function studies revealed that Hv1 channels are dimers that gate cooperatively (Gonzalez et al, 2010;Musset et al, 2010;Tombola et al, 2010), with each monomer containing a separate conduction pathway and voltage sensor (Koch et al, 2008;Lee et al, 2008;Tombola et al, 2008).…”