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3??-helix conformation facilitates the transition of a voltage sensor S4 segment toward the down state.

ABSTRACT: The activation of voltage-gated ion channels is controlled by the S4 helix, with arginines every third residue. The x-ray structures are believed to reflect an open-inactivated state, and models propose combinations of translation, rotation, and tilt to reach the resting state. Recently, experiments and simulations have independently observed occurrence of 3(10)-helix in S4. This suggests S4 might make a transition from ?- to 3(10)-helix in the gating process. Here, we show 3(10)-helix structure between Q1 and R3 in the S4 segment of a voltage sensor appears to facilitate the early stage of the motion toward a down state. We use multiple microsecond-steered molecular simulations to calculate the work required for translating S4 both as ?-helix and transformed to 3(10)-helix. The barrier appears to be caused by salt-bridge reformation simultaneous to R4 passing the F233 hydrophobic lock, and it is almost a factor-two lower with 3(10)-helix. The latter facilitates translation because R2/R3 line up to face E183/E226, which reduces the requirement to rotate S4. This is also reflected in a lower root mean-square deviation distortion of the rest of the voltage sensor. This supports the 3(10) hypothesis, and could explain some of the differences between the open-inactivated- versus activated-states.

SUBMITTER: Schwaiger CS

PROVIDER: S-EPMC3059565 | biostudies-literature | 2011 Mar

REPOSITORIES: biostudies-literature

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3₁₀-helix conformation facilitates the transition of a voltage sensor S4 segment toward the down state.

Schwaiger Christine S CS Bjelkmar Pär P Hess Berk B Lindahl Erik E

Biophysical journal 20110301 6

The activation of voltage-gated ion channels is controlled by the S4 helix, with arginines every third residue. The x-ray structures are believed to reflect an open-inactivated state, and models propose combinations of translation, rotation, and tilt to reach the resting state. Recently, experiments and simulations have independently observed occurrence of 3(10)-helix in S4. This suggests S4 might make a transition from α- to 3(10)-helix in the gating process. Here, we show 3(10)-helix structure ...[more]

PMID: 21402026

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Project description:Slow deactivation of hERG channels is critical for preventing cardiac arrhythmia yet the mechanistic basis for the slow gating transition is unclear. Here, we characterized the temporal sequence of events leading to voltage sensor stabilization upon membrane depolarization. Progressive increase in step depolarization duration slowed voltage-sensor return in a biphasic manner (τfast = 34 ms, τslow = 2.5 s). The faster phase of voltage-sensor return slowing correlated with the kinetics of pore opening. The slower component occurred over durations that exceeded channel activation and was consistent with voltage sensor relaxation. The S4-S5 linker mutation, G546L, impeded the faster phase of voltage sensor stabilization without attenuating the slower phase, suggesting that the S4-S5 linker is important for communications between the pore gate and the voltage sensor during deactivation. These data also demonstrate that the mechanisms of pore gate-opening-induced and relaxation-induced voltage-sensor stabilization are separable. Deletion of the distal N-terminus (Δ2-135) accelerated off-gating current, but did not influence the relative contribution of either mechanism of stabilization of the voltage sensor. Lastly, we characterized mode-shift behavior in hERG channels, which results from stabilization of activated channel states. The apparent mode-shift depended greatly on recording conditions. By measuring slow activation and deactivation at steady state we found the "true" mode-shift to be ∼15 mV. Interestingly, the "true" mode-shift of gating currents was ∼40 mV, much greater than that of the pore gate. This demonstrates that voltage sensor return is less energetically favorable upon repolarization than pore gate closure. We interpret this to indicate that stabilization of the activated voltage sensor limits the return of hERG channels to rest. The data suggest that this stabilization occurs as a result of reconfiguration of the pore gate upon opening by a mechanism that is influenced by the S4-S5 linker, and by a separable voltage-sensor intrinsic relaxation mechanism.

Dataset Information

3??-helix conformation facilitates the transition of a voltage sensor S4 segment toward the down state.

Publications

3₁₀-helix conformation facilitates the transition of a voltage sensor S4 segment toward the down state.

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