Voltage and pH difference across the membrane control the S4 voltage-sensor motion of the Hv1 proton channel

Schladt, Moritz; Berger, Thomas

doi:10.1038/s41598-020-77986-z

Cited by 17 publications

(26 citation statements)

References 51 publications

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“…In conclusion, the unique voltage and pH gating in the hHv1 channel is based on the spontaneous, voltage-dependent structural transitions of the S4 segment, which facilitate its pH dependent dynamic interactions with both the intra-(H168) and extracellular (H140) pH sensors. Our gating model (Fig 5) also explains the most recent patch-clamp fluorometry data and gating current from Hv channels, which showed that the conformation transitions of the S4 segment are dependent on both intraand extracellular pHs (17,28).…”

Section: Discussionsupporting

confidence: 68%

Structural dynamics determine voltage and pH gating in human voltage-gated proton channel

Han

Peng

Vance

et al. 2021

Preprint

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Voltage-gated ion channels are key players of electrical signaling in cells. As a unique subfamily, voltage-gated proton (Hv) channels are standalone voltage sensors without separate ion conductive pores. They are gated by both voltage and transmembrane proton gradient (i.e ΔpH), serving as acid extruders in most cells. Amongst their many functions, Hv channels are known to regulate the intracellular pH of human spermatozoa and compensate for the charge and pH imbalances caused by NADPH oxidases in phagocytes. Like the canonical voltage sensors, the Hv channel is a bundle of 4 helices (named S1 through S4), with the S4 segment carrying 3 positively charged Arg residues. Extensive structural and electrophysiological studies on voltage-gated ion channels generally agree on an outwards movement of the S4 segment upon activating voltage, but the real time conformational transitions are still unattainable. With purified human voltage-gated proton (hHv1) channel reconstituted in liposomes, we have examined its conformational dynamics at different voltage and pHs using the single molecule fluorescence resonance energy transfer (smFRET). Here we provided the first glimpse of real time conformational trajectories of the hHv1 voltage sensor and showed that both voltage and pH gradient shift the conformational dynamics of the S4 segment to control channel gating. Our results suggested the biological gating is determined by the conformational distributions of the hHv1 voltage sensor, rather than the conformational transitions between the presumptive ‘resting’ and ‘activated’ conformations. We further identified H140 as the key residue sensing extracellular pH and showed that both the intracellular and extracellular pH sensors act on the voltage sensing S4 segment to enrich the resting conformations. Taken together, we proposed a model that explains the mechanisms underlying voltage and pH gating in Hv channels, which may also serve as a general framework to understand the voltage sensing and gating in other voltage-gated ion channels.

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Section: Discussionsupporting

confidence: 68%

Structural dynamics determine voltage and pH gating in human voltage-gated proton channel

Han

Peng

Vance

et al. 2021

Preprint

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“…The intra- and extracellular pHs modify the stability of inward resting conformations by altering the protonation states of the pH-sensing residues that may directly or indirectly interact with the S4 segment in hHv1 channels. The gating model we proposed also explains the most recent patch-clamp fluorometry data and gating current from Hv channels ( Figure 5B ), which showed that the conformation transitions of the S4 segment are dependent on both intra- and extracellular pHs ( Carmona, 2021 ; Schladt and Berger, 2020 ).…”

Section: Discussionsupporting

confidence: 64%

Structural dynamics determine voltage and pH gating in human voltage-gated proton channel

Han

Peng

Vance

et al. 2022

eLife

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Voltage-gated ion channels are key players of electrical signaling in cells. As a unique subfamily, voltage-gated proton (Hv) channels are standalone voltage sensors without separate ion conductive pores. Hv channels are gated by both voltage and transmembrane proton gradient (i.e ∆pH), serving as acid extruders in most cells. Amongst their many functions, Hv channels are known for regulating the intracellular pH of human spermatozoa and compensating for the charge and pH imbalances caused by NADPH oxidases in phagocytes. Like the canonical voltage sensors, Hv channels are a bundle of 4 helices (named S1 through S4), with the S4 segment carrying 3 positively charged Arg residues. Extensive structural and electrophysiological studies on voltage-gated ion channels, in general, agree on an outwards movement of the S4 segment upon activating voltage, but the real-time conformational transitions are still unattainable. With purified human voltage-gated proton (hHv1) channels reconstituted in liposomes, we have examined its conformational dynamics, including the S4 segment at different voltage and pHs using single-molecule fluorescence resonance energy transfer (smFRET). Here, we provide the first glimpse of real-time conformational trajectories of the hHv1 voltage sensor and show that both voltage and pH gradient shift the conformational dynamics of the S4 segment to control channel gating. Our results indicate that the S4 segment transits among 3 major conformational states and kinetic analysis suggest that only the transitions between the inward and outward conformations are highly dependent on voltage and pH changes. Our smFRET studies uncover the stochastic conformational dynamics of S4 and demonstrate how voltage and pH shift its conformational distributions to regulate channel gating. Altogether, we propose a kinetic model that explains the mechanisms underlying voltage and pH gating in Hv channels, which may also serve as a general framework for understanding the voltage sensing and gating in other voltage-gated ion channels.

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“…ΔpH on H v 1-gating currents unknown. Recently, another report explored the pH sensitivity in the conductive CiH v 1 dimer using patch-clamp fluorometry (21). Tracking the S4 movements with fluorescence changes, they found that the S4 segment sensed the ΔpH imposed on the membrane.…”

Section: Discussionmentioning

confidence: 99%

“…In this regard, the H v 1 pH dependence has been challenging to understand, because it has mainly been studied by measuring the dimer's proton current; in fact, the pH dependence of these currents could be produced by modulating the channel cooperativity, voltage sensor activation, or channel opening. Indeed, there is evidence indicating that pH affects both the voltage sensor movement (20,21) and the channel's unitary conductance (22). Consequently, the simultaneous processes that occur during H v 1 gating obscure the source of this ΔpH dependence.…”

mentioning

confidence: 99%

The voltage sensor is responsible for ΔpH dependence in H _v 1 channels

Carmona

Fernández

Alvear-Arias

et al. 2021

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

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The dissipation of acute acid loads by the voltage-gated proton channel (Hv1) relies on regulating the channel’s open probability by the voltage and the ΔpH across the membrane (ΔpH = pHex − pHin). Using monomeric Ciona-Hv1, we asked whether ΔpH-dependent gating is produced during the voltage sensor activation or permeation pathway opening. A leftward shift of the conductance-voltage (G-V) curve was produced at higher ΔpH values in the monomeric channel. Next, we measured the voltage sensor pH dependence in the absence of a functional permeation pathway by recording gating currents in the monomeric nonconducting D160N mutant. Increasing the ΔpH leftward shifted the gating charge-voltage (Q-V) curve, demonstrating that the ΔpH-dependent gating in Hv1 arises by modulating its voltage sensor. We fitted our data to a model that explicitly supposes the Hv1 voltage sensor free energy is a function of both the proton chemical and the electrical potential. The parameters obtained showed that around 60% of the free energy stored in the ΔpH is coupled to the Hv1 voltage sensor activation. Our results suggest that the molecular mechanism underlying the Hv1 ΔpH dependence is produced by protons, which alter the free-energy landscape around the voltage sensor domain. We propose that this alteration is produced by accessibility changes of the protons in the Hv1 voltage sensor during activation.

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Voltage and pH difference across the membrane control the S4 voltage-sensor motion of the Hv1 proton channel

Cited by 17 publications

References 51 publications

Structural dynamics determine voltage and pH gating in human voltage-gated proton channel

Structural dynamics determine voltage and pH gating in human voltage-gated proton channel

Structural dynamics determine voltage and pH gating in human voltage-gated proton channel

The voltage sensor is responsible for ΔpH dependence in H _v 1 channels

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Voltage and pH difference across the membrane control the S4 voltage-sensor motion of the Hv1 proton channel

Cited by 17 publications

References 51 publications

Structural dynamics determine voltage and pH gating in human voltage-gated proton channel

Structural dynamics determine voltage and pH gating in human voltage-gated proton channel

Structural dynamics determine voltage and pH gating in human voltage-gated proton channel

The voltage sensor is responsible for ΔpH dependence in H v 1 channels

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The voltage sensor is responsible for ΔpH dependence in H _v 1 channels