Calcium-driven regulation of voltage-sensing domains in BK channels

Lorenzo-Ceballos, Yenisleidy; Carrasquel-Ursulaez, Willy; Castillo, Karen; Álvarez, Osvaldo; Latorre, Ramón

doi:10.7554/elife.44934

Cited by 13 publications

(20 citation statements)

References 55 publications

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“…S1 ). Gating charges were calculated by integrating the early gating currents elicited by the voltage steps using a previously reported procedure that excludes charge displacements associated with channel opening ( 21 , 38 – 40 ) ( SI Appendix, Materials and Methods ). Since the half-activation voltages (

) of mutants R207Q and R210Q were largely leftward shifted ( Fig.…”

Section: Resultsmentioning

confidence: 99%

Mechanism of voltage sensing in Ca ²⁺ - and voltage-activated K ⁺ (BK) channels

Carrasquel-Ursulaez

Segura

Díaz-Franulic

et al. 2022

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

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In neurosecretion, allosteric communication between voltage sensors and Ca 2+ binding in BK channels is crucially involved in damping excitatory stimuli. Nevertheless, the voltage-sensing mechanism of BK channels is still under debate. Here, based on gating current measurements, we demonstrate that two arginines in the transmembrane segment S4 (R210 and R213) function as the BK gating charges. Significantly, the energy landscape of the gating particles is electrostatically tuned by a network of salt bridges contained in the voltage sensor domain (VSD). Molecular dynamics simulations and proton transport experiments in the hyperpolarization-activated R210H mutant suggest that the electric field drops off within a narrow septum whose boundaries are defined by the gating charges. Unlike Kv channels, the charge movement in BK appears to be limited to a small displacement of the guanidinium moieties of R210 and R213, without significant movement of the S4.

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) of mutants R207Q and R210Q were largely leftward shifted ( Fig.…”

Section: Resultsmentioning

confidence: 99%

Mechanism of voltage sensing in Ca ²⁺ - and voltage-activated K ⁺ (BK) channels

Carrasquel-Ursulaez

Segura

Díaz-Franulic

et al. 2022

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

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“…In the absence of L390P mutations, our observations that RCK1 Ca 2+ sites acting alone make a greater contribution to Ca 2+ activation than Ca 2+ bowl sites acting alone, and that the sum of ΔV1/2 0→100 µM Ca for RCK1 Ca 2+ sites alone and Ca 2+ bowl sites alone can exceed ΔV1/2 0→100 µM Ca for WT channels has been described previously (47,48). Also observed by others have been equal contributions of the RCK1 Ca 2+ site and Ca 2+ bowl to left shifts in V1/2 (7,8,49), and equal contributions of these sites to decreasing the free energy necessary to activate voltage sensors (43). The reason for the apparent differences in the relative contributions from the two types of Ca 2+ sites is not known.…”

Section: Disruption Of the αB Helix Decreases High Affinity Ca 2+ Senmentioning

confidence: 66%

“…The αB Helix/VSD Interface is Required for Effective Voltage and Ca 2+ Activation of BK Channels. Functional studies have suggested that voltage and Ca 2+ sensors of BK channels interact, as summarized in the Introduction (6,13,15,28,30,40,41,43,44), and that the AC (N-lobe) region of the CTD is involved (25,51). Structural studies have identified a potential structural pathway to couple Ca 2+ sensors in the CTD with voltage sensors in the TMD (16,17,31).…”

Section: Discussionmentioning

confidence: 99%

“…Ca 2+ binding alters VSD rearrangement (42). Ca 2+ sensor occupancy left shifts the Q-V curves, with strong allosteric coupling between Ca 2+ -binding sites and voltage sensors (43). Strong correlations have been observed between VSD rearrangements and conformational changes in the CTD, which support a pathway that couples Ca 2+ binding to channel opening through the voltage sensor (44).…”

Section: Introductionmentioning

confidence: 87%

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Coupling of Ca²⁺and voltage activation in BK channels through the αB helix/voltage sensor interface

Geng

Deng²,

Zhang³

et al. 2020

Preprint

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Office phone: 305 243-6236. AbstractLarge conductance Ca 2+ and voltage activated K + (BK) channels control membrane excitability in many cell types. BK channels are tetrameric. Each subunit is comprised of a voltage sensor domain (VSD), a central pore gate domain, and a large cytoplasmic domain (CTD) that contains the Ca 2+ sensors. While it is known that BK channels are activated by voltage and Ca 2+ , and that voltage and Ca 2+ activations interact, less is known about the mechanisms involved. We now explore mechanism by examining the gating contribution of an interface formed between the VSDs and the αB helices located at the top of the CTDs. Proline mutations in the αB helix greatly decreased voltage activation while having negligible effects on gating currents. Analysis with the HCA model indicated a decreased coupling between voltage sensors and pore gate. Proline mutations decreased Ca 2+ activation for both Ca 2+ bowl and RCK1 Ca 2+ sites, suggesting that both high affinity Ca 2+ sites transduce their effect, at least in part, through the αB helix. Mg 2+ activation was also decreased. The crystal structure of the CTD with proline mutation L390P showed a flattening of the first helical turn in the αB helix compared to WT, without other notable differences in the CTD, indicating structural change from the mutation was confined to the αB helix. These findings indicate that an intact αB helix/VSD interface is required for effective coupling of Ca 2+ binding and voltage depolarization to pore opening, and that shared Ca 2+ and voltage transduction pathways involving the αB helix may be involved. Slo1 channel | BK channel | Ca 2+ -activated K + channel | allosteric coupling | patch clamp SignificanceLarge conductance BK (Slo1) K + channels are activated by voltage, Ca 2+ , and Mg 2+ to modulate membrane excitability in neurons, muscle, and other cells. BK channels are of modular design, with pore-gate and voltage sensors as transmembrane domains and a large cytoplasmic domain CTD containing the Ca 2+ sensors. Previous observations suggest that voltage and Ca 2+ sensors interact, but less is known about this interaction and its involvement in the gating process. We show that a previously identified structural interface between the CTD and voltage sensors is required for effective activation by both voltage and Ca 2+ , suggesting that these processes may share common allosteric activation pathways. Such knowledge should help explain disease processes associated with BK channel dysfunction.

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“…While direct assessment of allosteric coupling between the VSD and CSD (parameter E) has historically been challenging, it was recently hypothesized that VSD-CSD coupling may have a substantial impact on voltage-dependent activation (Lorenzo-Ceballos et al, 2019;Hite et al, 2017). Consistent with this idea, although both Fit A and Fit B describe G-V-Ca 2+ relations similarly well at 0 µM NS11021 (Table 1), changing L 0 in Fit A better accounts for the observed effects of NS11021 at higher drug concentrations and contains an 18-fold greater value for parameter E than Fit B ( Fig.…”

Section: Limitations Of the Proposed Mechanismmentioning

confidence: 99%

Molecular mechanism of BK channel activation by the smooth muscle relaxant NS11021

Rockman

Vouga

Rothberg

2020

Journal of General Physiology

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Large-conductance Ca2+-activated K+ channels (BK channels) are activated by cytosolic calcium and depolarized membrane potential under physiological conditions. Thus, these channels control electrical excitability in neurons and smooth muscle by gating K+ efflux and hyperpolarizing the membrane in response to Ca2+ signaling. Altered BK channel function has been linked to epilepsy, dyskinesia, and other neurological deficits in humans, making these channels a key target for drug therapies. To gain insight into mechanisms underlying pharmacological modulation of BK channel gating, here we studied mechanisms underlying activation of BK channels by the biarylthiourea derivative, NS11021, which acts as a smooth muscle relaxant. We observe that increasing NS11021 shifts the half-maximal activation voltage for BK channels toward more hyperpolarized voltages, in both the presence and nominal absence of Ca2+, suggesting that NS11021 facilitates BK channel activation primarily by a mechanism that is distinct from Ca2+ activation. 30 µM NS11021 slows the time course of BK channel deactivation at −200 mV by ∼10-fold compared with 0 µM NS11021, while having little effect on the time course of activation. This action is most pronounced at negative voltages, at which the BK channel voltage sensors are at rest. Single-channel kinetic analysis further shows that 30 µM NS11021 increases open probability by 62-fold and increases mean open time from 0.15 to 0.52 ms in the nominal absence of Ca2+ at voltages less than −60 mV, conditions in which BK voltage sensors are largely in the resting state. We could therefore account for the major activating effects of NS11021 by a scheme in which the drug primarily shifts the pore-gate equilibrium toward the open state.

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Calcium-driven regulation of voltage-sensing domains in BK channels

Cited by 13 publications

References 55 publications

Mechanism of voltage sensing in Ca ²⁺ - and voltage-activated K ⁺ (BK) channels

Mechanism of voltage sensing in Ca ²⁺ - and voltage-activated K ⁺ (BK) channels

Coupling of Ca²⁺and voltage activation in BK channels through the αB helix/voltage sensor interface

Molecular mechanism of BK channel activation by the smooth muscle relaxant NS11021

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Calcium-driven regulation of voltage-sensing domains in BK channels

Cited by 13 publications

References 55 publications

Mechanism of voltage sensing in Ca 2+ - and voltage-activated K + (BK) channels

Mechanism of voltage sensing in Ca 2+ - and voltage-activated K + (BK) channels

Coupling of Ca2+and voltage activation in BK channels through the αB helix/voltage sensor interface

Molecular mechanism of BK channel activation by the smooth muscle relaxant NS11021

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Mechanism of voltage sensing in Ca ²⁺ - and voltage-activated K ⁺ (BK) channels

Mechanism of voltage sensing in Ca ²⁺ - and voltage-activated K ⁺ (BK) channels

Coupling of Ca²⁺and voltage activation in BK channels through the αB helix/voltage sensor interface