Abstract
The voltage-gated proton channel Hv1 is expressed in a variety of cells, including macrophages, sperm, and lung epithelial cells. Hv1 is gated by both the membrane potential and the difference between the intra- and extracellular pH (ΔpH). The coupling of voltage- and ∆pH-sensing is such that Hv1 opens only when the electrochemical proton gradient is outwardly directed. However, the molecular mechanism of this coupling is not known. Here, we investigate the coupling between voltage- and ΔpH-sensing of Ciona intestinalis proton channel (ciHv1) using patch-clamp fluorometry (PCF) and proton uncaging. We show that changes in ΔpH can induce conformational changes of the S4 voltage sensor. Our results are consistent with the idea that S4 can detect both voltage and ΔpH.
Highlights
The voltage-gated proton channel Hv1 is expressed in a variety of cells, including macrophages, sperm, and lung epithelial cells
Hv1 sustains the production of reactive oxygen species by NADPH oxidase (NOX) a ctivity[4,8,9], which depolarizes the membrane and acidifies the cytosol
We provide direct evidence that the S4 segment alters its conformation in response to changes in ΔpH, suggesting that S4 serves as both voltage- and ΔpH-sensor
Summary
The voltage-gated proton channel Hv1 is expressed in a variety of cells, including macrophages, sperm, and lung epithelial cells. The coupling of voltage- and ∆pH-sensing is such that Hv1 opens only when the electrochemical proton gradient is outwardly directed. Classical voltage-gated ion channels comprise a voltage-sensor domain (VSD), consisting of four transmembrane segments, S1–S4, and a pore domain (PD), consisting of two transmembrane segments (S5 and S6). Four subunits assemble such that the four PDs form a central pore. An important functional consequence of ΔpH sensing in Hv1 is outward rectification: the channel only opens when the electrochemical gradient is directed towards the extracellular side (see[25] for an exception). Our results suggest that S4 is the main voltage sensor, but that S4 serves as a ΔpH sensor
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