Department of Molecular Biophysics & Physiology

The properties and biological functions of ion channels are long-term interests of Tom DeCoursey's laboratory. A major focus in recent years is the voltage-gated proton channel {Table}. Modulation of the voltage-dependence of this channel by pHo and pHi ensures that it opens only when the electrochemical gradient for H+ is outward (in most species). In other words, when the proton channel opens, it extrudes acid from cells. In a long collaboration with Dr. Vladimir V. Cherny and others, tThe Ganghe behavior of proton channels has been explored in alveolar epithelial cells and in white blood cells (human neutrophils and eosinophils). Immune cells engulf (phagocytose) bacteria and kill parasites by secreting reactive oxygen species (e.g., ChloroxTM). The enzyme responsible for these heroic actions is NADPH oxidase.  This enzyme moves electrons across the cell membrane to form superoxide anion near the invading critters. We measure the electron movement directly as an electrical current. For each electron that leaves, one proton stays in the cell. To prevent massive depolarization as well as acidification, protons exit the cell through proton channels.  Without H+ efflux, the killing process would be interrupted prematurely. Fortunately, proton channels are activated, relieving the cell of excess acid {Respiratory Burst figure; cartoon modified to show stoichiometry}, and preventing depolarization. The discovery of proton channels has been a great boon to cells, who until this time had to use other, less efficient means of extruding acid.
    Identification of proton channel genes in 2006 has transformed the field.  More functions are described each year, and structure-function studies are appearing.  The channel was shown to be a dimer, with conduction pathway in each protomer.  The dimer gates cooperatively - both protomers need to move before either conducts. New genes (eight confirmed, dozens speculated) are appearing at a high rate.  The proton channel resists efforts to crystallize it. The first
crystal structure was reported in 2014 by Takeshita et al, is likely closed, and is of a chimera with a Voltage-Sensing Phosphatase. James Letts' valiant efforts to determine the open structure of HV1 (a chimera with KVAP) can be found in his PhD dissertation, which also nicely shows that Asp112 mutants have severely compromised H+ flux!
HV1 triggers the flash in bioluminescent dinoflagellates (Smith et al, 2011), which were recently active in Tasmania

Quick summaries of proton channel lore:

{NSF summary of first dinoflagellate proton channel gene}

{Invited SciTopics entry on proton channels}

{Wikipedia entry on voltage-gated proton channels}

{Summary of recent Hv1 studies with special reference to phagocytes, by Boris Musset, in German!}

Susan M.E. Smith produced this phylogenetic tree showing known and predicted proton channels.  The length of each branch indicates the degree of difference from its neighbors.Phylogenetic tree

Other Items of Interest: Recent International Conferences 

Telluride: Proton Transfer in Biology, July, 2018