Unitary conductance of the voltage-sensitive proton channel HV1
Sprache des Vortragstitels:
The voltage-sensitive proton selective channel HV1 is
ubiquitously present in mammalian tissues. An aqueous pore
provides the proton pathway. Intervening amino acid side chains
render the channel impermeable to water . Based on the hydrogen
bonds formed between the permeating water molecules and the
channel wall, HV1 would otherwise exhibit a water conductance
comparable to aquaporins [2, 3]. The proton wire involves Grotthusslike
proton hopping on top of intraluminal water molecules and
titratable amino acids. Other proton-selective molecules engaged in
bioenergetics possess a similar proton-conducting mechanism.
Conceivably, HV1 exploits one or more of the arginines from the
voltage sensor as part of the proton wire. Yet, proton release from
arginines is slow, provided the side chain pKa in the channel lumen
remains at the bulk level. It may limit the proton transport rate to
roughly 10 protons per second. Here we tested the hypothesis by
reconstituting the purified proton channel into lipid vesicles. We
used pHluorin to tag the channel and measure intravesicular pH.
Fluorescence correlation spectroscopy served to measure channel
density . Accounting for the number of channels per vesicle allows
extracting the unitary channel conductance. The latter confirms the
role of amino acids in proton transfer.
We thank the European Union?s Horizon 2020 research and
innovation program (Marie Sk?odowska-Curie grant agreement No.