Voltage‐gated proton channels: what's next?

DeCoursey, Thomas E.

doi:10.1113/jphysiol.2008.161703

Cited by 55 publications

(65 citation statements)

References 179 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…To know whether A206stop retains the properties of Hv channels, we assessed several hallmark properties of Hv channel currents, including proton permeation, zinc sensitivity, and pHdependent gating (26,27). We initially examined proton-exporting activity by measuring intracellular pH (pH in ) using a pH-sensitive ratiometric dye, BCECF, under whole-cell patch clamp.…”

Section: Resultsmentioning

confidence: 99%

Functionality of the voltage-gated proton channel truncated in S4

Sakata

Kurokawa

Nørholm

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

The voltage sensor domain (VSD) is the key module for voltage sensing in voltage-gated ion channels and voltage-sensing phosphatases. Structurally, both the VSD and the recently discovered voltage-gated proton channels (Hv channels) voltage sensor only protein (VSOP) and Hv1 contain four transmembrane segments. The fourth transmembrane segment (S4) of Hv channels contains three periodically aligned arginines (R1, R2, R3). It remains unknown where protons permeate or how voltage sensing is coupled to ion permeation in Hv channels. Here we report that Hv channels truncated just downstream of R2 in the S4 segment retain most channel properties. Two assays, site-directed cysteinescanning using accessibility of maleimide-reagent as detected by Western blotting and insertion into dog pancreas microsomes, both showed that S4 inserts into the membrane, even if it is truncated between the R2 and R3 positions. These findings provide important clues to the molecular mechanism underlying voltage sensing and proton permeation in Hv channels.ion conduction | membrane topology | membrane insertion | voltage sensor V oltage sensor domain (VSD) is a protein module that senses transmembrane voltage and regulates ion permeation through the pore (1-3) and phosphoinositide turnover by the phosphatase (4). The fourth transmembrane segment (S4) of VSD contains periodically aligned positively charged residues (arginine and lysine), which play a critical role in voltage sensing (1, 2). Recent analyses of the crystal structures of voltage-gated potassium channels (5, 6) showed that basic residues in S4 form salt bridges with negatively charged residues from other helices, and these salt bridges are formed at both sides of a hydrophobic residue such as phenylalanine. This suggests a focused electric field within a crevice surrounded by transmembrane helices (6), which would enable extracellular and intracellular aqueous environments to enter deeply into the membrane through a narrow crevice. One line of functional evidence for this narrow crevice is that mutation within the VSD creates an ion permeation pathway that is activated upon hyperpolarization (7−9). Such ion conduction is called an "omegacurrent" (9) or "gating pore current" (10). Similar conductances through the VSD are elicited in a mutated form of human voltagegated sodium channels (SCN4a) found in patients with periodic paralysis (11, 12) and in flatworm potassium channels (13).Recently, the protein, which consists solely of a VSD, was identified in tunicate, mouse (14) and human (15) and called voltage sensor only protein (VSOP) or Hv1. Mouse VSOP (mVSOP) is found within the phagosomes of white blood cells, and is essential for robust production of superoxide anions (16, 17) and maintenance of intracellular pH (18) in phagocytes. Despite the lack of a pore domain, these proteins function as voltage-gated proton channels (Hv channels) in heterologous expression systems (14,15) and when reconstituted into artificial membranes (19). S4 of both mVSOP and Hv1 contain three argini...

show abstract

Section: Resultsmentioning

confidence: 99%

Functionality of the voltage-gated proton channel truncated in S4

Sakata

Kurokawa

Nørholm

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

show abstract

“…We model Hv voltage-dependent gating with a two-state Boltzmann function with midpoint activation voltage V mid = 40 mV and valence 3 5; 15.…”

Section: Understanding the Time Course Of Fluorescence Decaymentioning

confidence: 99%

Functional Reconstitution of Purified Human Hv1 H+ Channels

Lee

Letts

MacKinnon

2009

Journal of Molecular Biology

101

View full text Add to dashboard Cite

Summary Voltage-dependent H+ (Hv) channels mediate proton conduction into and out of cells under the control of membrane voltage. Hv channels are unusual compared to voltage-dependent K+, Na+ and Ca2+ channels in that Hv channel genes encode a voltage sensor domain (VSD) without a pore domain. The H+ currents observed when Hv channels are expressed heterologously suggest that the VSD itself provides the pathway for proton conduction. In order to exclude the possibility that the Hv channel VSD assembles with an as yet unknown protein in the cell membrane as a requirement for H+ conduction we have purified Hv channels to homogeneity and reconstituted them into synthetic lipid liposomes. The Hv channel VSD by itself supports H+ flux.

show abstract

“…At present, no evidence even suggests that any other ion can permeate. Numerous studies in many cell types have demonstrated that when the dominant cation or anion in the bathing solution is changed, the measured reversal potential ( V rev ) does not change, after liquid junction potentials are corrected (56, 58, 200). Any small deviation of V rev from the Nernst potential for protons ( E H ), is therefore attributable to imperfect control of pH.…”

Section: Introductionmentioning

confidence: 99%

Voltage‐Gated Proton Channels

DeCoursey

2012

Comprehensive Physiology

Self Cite

View full text Add to dashboard Cite

Voltage‐gated proton channels, H V 1, have vaulted from the realm of the esoteric into the forefront of a central question facing ion channel biophysicists, namely, the mechanism by which voltage‐dependent gating occurs. This transformation is the result of several factors. Identification of the gene in 2006 revealed that proton channels are homologues of the voltage‐sensing domain of most other voltage‐gated ion channels. Unique, or at least eccentric, properties of proton channels include dimeric architecture with dual conduction pathways, perfect proton selectivity, a single‐channel conductance approximately 10 3 times smaller than most ion channels, voltage‐dependent gating that is strongly modulated by the pH gradient, ΔpH, and potent inhibition by Zn 2+ (in many species) but an absence of other potent inhibitors. The recent identification of H V 1 in three unicellular marine plankton species has dramatically expanded the phylogenetic family tree. Interest in proton channels in their own right has increased as important physiological roles have been identified in many cells. Proton channels trigger the bioluminescent flash of dinoflagellates, facilitate calcification by coccolithophores, regulate pH‐dependent processes in eggs and sperm during fertilization, secrete acid to control the pH of airway fluids, facilitate histamine secretion by basophils, and play a signaling role in facilitating B‐cell receptor mediated responses in B‐lymphocytes. The most elaborate and best‐established functions occur in phagocytes, where proton channels optimize the activity of NADPH oxidase, an important producer of reactive oxygen species. Proton efflux mediated by H V 1 balances the charge translocated across the membrane by electrons through NADPH oxidase, minimizes changes in cytoplasmic and phagosomal pH, limits osmotic swelling of the phagosome, and provides substrate H + for the production of H 2 O 2 and HOCl, reactive oxygen species crucial to killing pathogens. © 2012 American Physiological Society. Compr Physiol 2:1355‐1385, 2012.

show abstract

Voltage‐gated proton channels: what's next?

Cited by 55 publications

References 179 publications

Functionality of the voltage-gated proton channel truncated in S4

Functionality of the voltage-gated proton channel truncated in S4

Functional Reconstitution of Purified Human Hv1 H+ Channels

Voltage‐Gated Proton Channels

Contact Info

Product

Resources

About