Helix breaking transition in the S4 of HCN channel is critical for hyperpolarization-dependent gating

Kasimova, Marina A.; Tewari, Debanjan; Cowgill, John; Ursuleaz, Willy Carrasquel; Lin, Jenna L.; Delemotte, Lucie; Chanda, Baron

doi:10.7554/elife.53400

Cited by 57 publications

(61 citation statements)

References 85 publications

(134 reference statements)

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“…Consequently, the VSD was trapped in a presumably activated state, characterized by a kink in S4 at the level of the disulfide bridge and a sliding movement of the external part of S4 towards the intracellular side ( 25 ). Similar conformational changes were observed in MD simulations of the HCN voltage-sensor domain under membrane hyperpolarization ( 26 ). The breaking of the S4 helix in two smaller helices was suggested to be essential to hyperpolarization gating.…”

Section: Discussionsupporting

confidence: 75%

“…The resulting sliding movement of the kinked S4 helix towards the intracellular space provides a more consensual explanation to the avidin accessibility experiments. Similar conformational changes were recently observed in the VSD of HCN, a channel activated by hyperpolarization ( 25, 26 ). The breaking of S4 observed in the VSD of KvAP reveals that this transition is not specific to hyperpolarization gating.…”

Section: Introductionsupporting

confidence: 83%

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The voltage-sensing mechanism of the KvAP channel involves breaking of the S4 helix

Bignucolo

Bernèche

2019

Preprint

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7Voltage-gated ion channels allow ion permeation upon changes of the membrane 8 electrostatic potential (Vm). Each subunit of these tetrameric channels is composed of six 9 transmembrane helices, of which the anti-parallel helix bundle S1-S4 constitutes the voltage-10 sensor domain (VSD) and S5-S6 forms the pore domain. Here, using molecular dynamics 11 (MD) simulations, we report novel responses of the archaebacterial potassium channel KvAP 12 to cell polarization. We show that the S4 helix, which is straight in the experimental crystal 13 structure solved under depolarized conditions (Vm ~ 0), breaks into two segments when the 14 cell is polarized (Vm << 0) , and reversibly forms a single straight helix following 15 depolarization of the cell (Vm =0). The outermost segment of S4 translates along the normal 16 to the membrane, bringing new perspective to previously paradoxical accessibility 17 experiments that were initially thought to imply the displacement of the whole VSD across 18 the membrane. Our simulations of KvAP reveal that the breaking of S4 under polarization is 19 not a feature unique to hyperpolarization activated channel, as might be suggested by recent 20 cryo-EM structures and MD simulations of the HCN channel. 21 22 23 2/18

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Section: Discussionsupporting

confidence: 75%

Section: Introductionsupporting

confidence: 83%

The voltage-sensing mechanism of the KvAP channel involves breaking of the S4 helix

Bignucolo

Bernèche

2019

Preprint

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“…Consistent with this hypothesis, coexpression of the PD with the VSD lacking the Cterminal end of the S4 resulted in cNMP modulated but voltage-independent channels (33) and cross-linking the S4 and S5 could lock the channels in the "locked-open" or "locked-closed" states (35,36). More recent structural analysis of the cross-linked HCN1 channels and molecular dynamics simulations indicated that during the hyperpolarization-dependent gating the S4 helix breaks into two helices (31,37). Since the HCND forms direct interactions with the VSD, it could also contribute to the VSD movement during the voltage-dependent gating.…”

Section: Discussionmentioning

confidence: 72%

HCN domain is required for HCN channel expression and couples voltage- and cAMP-dependent gating mechanisms

Wang

Blanco

Hayoz

et al. 2020

Preprint

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Hyperpolarization-activated cyclic nucleotidegated (HCN) channels are major regulators of synaptic plasticity, and rhythmic activity in the heart and brain. Opening of HCN channels requires membrane hyperpolarization and is further facilitated by intracellular cyclic nucleotides (cNMPs).In HCN channels, membrane hyperpolarization is sensed by the membrane-spanning voltage sensor domain (VSD) and the cNMP-dependent gating is mediated by the intracellular cyclic nucleotidebinding domain (CNBD) connected to the poreforming S6 transmembrane domain via the Clinker. Previous functional analysis of HCN channels suggested a direct or allosteric coupling between the voltage-and cNMPdependent activation mechanisms. However, the specifics of the coupling were unclear. The first cryo-EM structure of an HCN1 channel revealed that a novel structural element, dubbed HCN domain (HCND), forms a direct structural link between the VSD and Clinker/CNBD. In this study, we investigated the functional significance of the HCND. Deletion of the HCND prevented surface expression of HCN2 channels. Based on the HCN1 structure analysis, we identified R237 and G239 residues on the S2 of the VSD that form direct interactions with I135 on the HCND. Disrupting these interactions abolished HCN2 currents. We then identified three residues on the C-linker/CNBD (E478, Q382 and H559) that form direct interactions with residues R154 and S158 on the HCND. Disrupting these interactions affected both voltage-and cAMPdependent gating of HCN2 channels. These findings indicate that the HCND is necessary for the surface expression of HCN channels, and provides a functional link between the voltage-and cAMP-dependent mechanisms of HCN channel gating.Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels are peculiar members of the voltage-gated potassium channel superfamily. Unlike other potassium channels, which are depolarization-activated and highly selective for K + , HCN channels are activated by membrane hyperpolarization and permeate both Na + and K + (1,2). The opening of HCN channels is further facilitated by cyclic nucleotides (1-3).

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“…Using a combination of long molecular dynamics (MD) simulations with the depolarized human HCN1 cryo-EM structure (Lee and MacKinnon, 2017) as template, as well as functional studies with HCN-eag chimeras, a hyperpolarizationinduced break in the S4 helix of the VSD was observed. This break originated two sub-helices and placing the lower sub-helix in an orientation almost parallel to the membrane plane as a surrogate S4-S5 helix (Kasimova et al, 2019). The breaking transition seemed to be important for HCN1 hyperpolarizationdependent activation.…”

Section: New Structural and Functional Data Regarding Allosteric Inflmentioning

confidence: 97%

“…The breaking transition seemed to be important for HCN1 hyperpolarizationdependent activation. Strikingly, the hydrophobicity of the amino acid following the breakpoint determined the gating polarity of some chimeric channels, changing it from a depolarization-to a hyperpolarization-dependent activation, opening the possibility that divergence of both types of channels could have occurred through a single point mutation in the S4 segment (Kasimova et al, 2019). The presence of the interfacial S4 sub-helix following the aforementioned S4 helix break, has been demonstrated in the recent cryo-EM structure of the HCN1 channel with the VSD chemically trapped in a hyperpolarized conformation by reversible, metal-mediated cross bridging (Lee and MacKinnon, 2019).…”

Section: New Structural and Functional Data Regarding Allosteric Inflmentioning

confidence: 99%

The EAG Voltage-Dependent K+ Channel Subfamily: Similarities and Differences in Structural Organization and Gating

et al. 2020

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EAG (ether-à-go-go or KCNH) are a subfamily of the voltage-gated potassium (Kv) channels. Like for all potassium channels, opening of EAG channels drives the membrane potential toward its equilibrium value for potassium, thus setting the resting potential and repolarizing action potentials. As voltage-dependent channels, they switch between open and closed conformations (gating) when changes in membrane potential are sensed by a voltage sensing domain (VSD) which is functionally coupled to a pore domain (PD) containing the permeation pathway, the potassium selectivity filter, and the channel gate. All Kv channels are tetrameric, with four VSDs formed by the S1-S4 transmembrane segments of each subunit, surrounding a central PD with the four S5-S6 sections arranged in a square-shaped structure. Structural information, mutagenesis, and functional experiments, indicated that in "classical/Shaker-type" Kv channels voltagetriggered VSD reorganizations are transmitted to PD gating via the a-helical S4-S5 sequence that links both modules. Importantly, these Shaker-type channels share a domain-swapped VSD/PD organization, with each VSD contacting the PD of the adjacent subunit. In this case, the S4-S5 linker, acting as a rigid mechanical lever (electromechanical lever coupling), would lead to channel gate opening at the cytoplasmic S6 helices bundle. However, new functional data with EAG channels split between the VSD and PD modules indicate that, in some Kv channels, alternative VSD/PD coupling mechanisms do exist. Noticeably, recent elucidation of the architecture of some EAG channels, and other relatives, showed that their VSDs are non-domain swapped. Despite similarities in primary sequence and predicted structural organization for all EAG channels, they show marked kinetic differences whose molecular basis is not completely understood. Thus, while a common general architecture may establish the gating system used by the EAG channels and the physicochemical coupling of voltage sensing to gating, subtle changes in that common structure, and/or allosteric influences of protein domains relatively distant from the central gating machinery, can crucially influence the gating Frontiers in Pharmacology | www.frontiersin.org

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Helix breaking transition in the S4 of HCN channel is critical for hyperpolarization-dependent gating

Cited by 57 publications

References 85 publications

The voltage-sensing mechanism of the KvAP channel involves breaking of the S4 helix

The voltage-sensing mechanism of the KvAP channel involves breaking of the S4 helix

HCN domain is required for HCN channel expression and couples voltage- and cAMP-dependent gating mechanisms

The EAG Voltage-Dependent K+ Channel Subfamily: Similarities and Differences in Structural Organization and Gating

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