Voltage-gated proton channel

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Identifiers
SymbolHv
TCDB1.A.51
OPM superfamily8
OPM protein3wkv

Voltage-gated proton channels are ion channels that have the unique property of opening with depolarization, but in a strongly pH-sensitive manner.[1] The result is that these channels open only when the electrochemical gradient is outward, such that their opening will only allow protons to leave cells. Their function thus appears to be acid extrusion from cells.[2]

Another important function occurs in phagocytes (e.g. eosinophils, neutrophils, and macrophages) during the respiratory burst. When bacteria or other microbes are engulfed by phagocytes, the enzyme NADPH oxidase assembles in the membrane and begins to produce reactive oxygen species (ROS) that help kill bacteria.[3] NADPH oxidase is electrogenic,[4] moving electrons across the membrane, and proton channels open to allow proton flux to balance the electron movement electrically.[5] The functional expression of Hv1 in phagocytes has been well characterized in mammals, and recently in zebrafish,[6] suggesting its important roles in the immune cells of mammals and non-mammalian vertebrates. A group of small molecule inhibitors of the Hv1 channel are shown as chemotherapeutics and anti-inflammatory agents.[7]

When activated, the voltage-gated proton channel HV1 can allow up to 100,000 hydrogen ions across the membrane each second.[8] Whereas most voltage-gated ion channels contain a central pore that is surrounding by alpha helices and the voltage-sensing domain (VSD), voltage-gated hydrogen channels contain no central pore,[9] so their voltage-sensing regions (VSD) carry out the job of bringing acidic protons across the membrane. As mentioned, these voltage-gated hydrogen channels only carry outward current, meaning they are used to move acidic protons out of the membrane. As a result, the opening of voltage-gated hydrogen channels usually hyperpolarize the cell membrane, or makes the membrane potential more negative.

A recent discovery has shown that the voltage-gated proton channel Hv1 is highly expressed in human breast tumor tissues that are metastatic, but not in non-metastatic breast cancer tissues.[10] Because it has also been found to be highly expressed in other cancer tissues,[11] the study of the voltage-gated proton channel has led many scientists to wonder what its importance is in cancer metastasis. However, much is still being discovered concerning the structure and function of the voltage-gated proton channel.

Known types[edit]

References[edit]

  1. ^ Cherny VV, Markin VS, DeCoursey TE (June 1995). "The voltage-activated hydrogen ion conductance in rat alveolar epithelial cells is determined by the pH gradient". The Journal of General Physiology. 105 (6): 861–96. CiteSeerX 10.1.1.282.2439. doi:10.1085/jgp.105.6.861. PMID 7561747.
  2. ^ Decoursey TE (April 2003). "Voltage-gated proton channels and other proton transfer pathways". Physiological Reviews. 83 (2): 475–579. doi:10.1152/physrev.00028.2002. PMID 12663866.
  3. ^ Babior BM (March 1999). "NADPH oxidase: an update" (PDF). Blood. 93 (5): 1464–76. PMID 10029572.
  4. ^ Henderson LM, Chappell JB, Jones OT (September 1987). "The superoxide-generating NADPH oxidase of human neutrophils is electrogenic and associated with an H+ channel" (PDF). The Biochemical Journal. 246 (2): 325–9. PMID 2825632.
  5. ^ Murphy R, DeCoursey TE (August 2006). "Charge compensation during the phagocyte respiratory burst". Biochimica et Biophysica Acta. Bioenergetics (published 2006-08-08). 1757 (8): 996–1011. doi:10.1016/j.bbabio.2006.01.005. PMID 16483534.
  6. ^ Ratanayotha A, Kawai T, Higashijima SI, Okamura Y (August 2017). "Molecular and functional characterization of the voltage-gated proton channel in zebrafish neutrophils". Physiological Reports. 5 (15): e13345. doi:10.14814/phy2.13345. PMID 28774948.
  7. ^ Hong L, Pathak MM, Kim IH, Ta D, Tombola F (January 2013). "Voltage-sensing domain of voltage-gated proton channel Hv1 shares mechanism of block with pore domains". Neuron. 77 (2): 274–87. doi:10.1016/j.neuron.2012.11.013. PMC 3559007. PMID 23352164.
  8. ^ DeCoursey TE, Hosler J (March 2014). "Philosophy of voltage-gated proton channels". Journal of the Royal Society, Interface. 11 (92): 20130799. doi:10.1098/rsif.2013.0799. PMC 3899857. PMID 24352668.
  9. ^ DeCoursey TE, Morgan D, Musset B, Cherny VV (August 2016). "Insights into the structure and function of HV1 from a meta-analysis of mutation studies". The Journal of General Physiology. 148 (2): 97–118. doi:10.1085/jgp.201611619. PMC 4969798. PMID 27481712.
  10. ^ Wang Y, Li SJ, Pan J, Che Y, Yin J, Zhao Q (August 2011). "Specific expression of the human voltage-gated proton channel Hv1 in highly metastatic breast cancer cells, promotes tumor progression and metastasis". Biochemical and Biophysical Research Communications. 412 (2): 353–9. doi:10.1016/j.bbrc.2011.07.102. PMID 21821008.
  11. ^ Wang Y, Wu X, Li Q, Zhang S, Li SJ (2013). "Human voltage-gated proton channel hv1: a new potential biomarker for diagnosis and prognosis of colorectal cancer". PLOS One. 8 (8): e70550. doi:10.1371/journal.pone.0070550. PMC 3734282. PMID 23940591.