scholarly journals The HCN domain couples voltage gating and cAMP response in hyperpolarization-activated cyclic nucleotide-gated channels

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Alessandro Porro ◽  
Andrea Saponaro ◽  
Federica Gasparri ◽  
Daniel Bauer ◽  
Christine Gross ◽  
...  
Keyword(s):  
Cyclic Nucleotide ◽  
Channel Gating ◽  
Hcn Channels ◽  
Structural Mechanism ◽  
Cyclic Nucleotide Gated Channels ◽  
Channel Opening ◽  
Mode Of Operation ◽  
Voltage Dependent ◽  
Upward Displacement ◽  
Voltage Sensing Domain

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels control spontaneous electrical activity in heart and brain. Binding of cAMP to the cyclic nucleotide-binding domain (CNBD) facilitates channel opening by relieving a tonic inhibition exerted by the CNBD. Despite high resolution structures of the HCN1 channel in the cAMP bound and unbound states, the structural mechanism coupling ligand binding to channel gating is unknown. Here we show that the recently identified helical HCN-domain (HCND) mechanically couples the CNBD and channel voltage sensing domain (VSD), possibly acting as a sliding crank that converts the planar rotational movement of the CNBD into a rotational upward displacement of the VSD. This mode of operation and its impact on channel gating are confirmed by computational and experimental data showing that disruption of critical contacts between the three domains affects cAMP- and voltage-dependent gating in three HCN isoforms.

scholarly journals Effects of Ultraviolet Modification on the Gating Energetics of Cyclic Nucleotide–Gated Channels

2000 ◽  
Vol 116 (2) ◽  
pp. 253-282 ◽  
Author(s):  
Thomas R. Middendorf ◽  
Richard W. Aldrich
Keyword(s):  
Cyclic Nucleotide ◽  
Channel Gating ◽  
Quantum Yields ◽  
Open Probability ◽  
Current Increase ◽  
Cyclic Nucleotide Gated Channels ◽  
Channel Opening ◽  
High Concentrations ◽  
Current Reduction ◽  
Opposing Effects

Middendorf et al. (Middendorf, T.R., R.W. Aldrich, and D.A. Baylor. 2000. J. Gen. Physiol. 116:227–252) showed that ultraviolet light decreases the current through cloned cyclic nucleotide–gated channels from bovine retina activated by high concentrations of cGMP. Here we probe the mechanism of the current reduction. The channels' open probability before irradiation, Po(0), determined the sign of the change in current amplitude that occurred upon irradiation. UV always decreased the current through channels with high initial open probabilities [Po(0) > 0.3]. Manipulations that promoted channel opening antagonized the current reduction by UV. In contrast, UV always increased the current through channels with low initial open probabilities [Po(0) ≤ 0.02], and the magnitude of the current increase varied inversely with Po(0). The dual effects of UV on channel currents and the correlation of both effects with Po(0) suggest that the channels contain two distinct classes of UV target residues whose photochemical modification exerts opposing effects on channel gating. We present a simple model based on this idea that accounts quantitatively for the UV effects on the currents and provides estimates for the photochemical quantum yields and free energy costs of modifying the UV targets. Simulations indicate that UV modification may be used to produce and quantify large changes in channel gating energetics in regimes where the associated changes in open probability are not measurable by existing techniques.

scholarly journals Structural mechanism of voltage-dependent gating in an isolated voltage-sensing domain

2014 ◽  
Vol 21 (3) ◽  
pp. 244-252 ◽  
Author(s):  
Qufei Li ◽  
Sherry Wanderling ◽  
Marcin Paduch ◽  
David Medovoy ◽  
Abhishek Singharoy ◽  
...  
Keyword(s):  
Voltage Sensing ◽  
Structural Mechanism ◽  
Voltage Dependent ◽  
Voltage Sensing Domain

scholarly journals Hyperpolarization-activated cyclic-nucleotide-gated channels potentially modulate axonal excitability at different thresholds

2017 ◽  
Vol 118 (6) ◽  
pp. 3044-3050 ◽  
Author(s):  
Dinushi Weerasinghe ◽  
Parvathi Menon ◽  
Steve Vucic
Keyword(s):  
Cyclic Nucleotide ◽  
Neurological Diseases ◽  
Lower Threshold ◽  
Resting Membrane Potential ◽  
Hcn Channels ◽  
Motor Axons ◽  
Cyclic Nucleotide Gated Channels ◽  
Sensory Axons ◽  
Current Threshold ◽  
Axonal Excitability

Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels mediate differences in sensory and motor axonal excitability at different thresholds in animal models. Importantly, HCN channels are responsible for voltage-gated inward rectifying ( Ih) currents activated during hyperpolarization. The Ih currents exert a crucial role in determining the resting membrane potential and have been implicated in a variety of neurological disorders, including neuropathic pain. In humans, differences in biophysical properties of motor and sensory axons at different thresholds remain to be elucidated and could provide crucial pathophysiological insights in peripheral neurological diseases. Consequently, the aim of this study was to characterize sensory and motor axonal function at different threshold. Median nerve motor and sensory axonal excitability studies were undertaken in 15 healthy subjects (45 studies in total). Tracking targets were set to 20, 40, and 60% of maximum for sensory and motor axons. Hyperpolarizing threshold electrotonus (TEh) at 90–100 ms was significantly increased in lower threshold sensory axons times ( F = 11.195, P < 0.001). In motor axons, the hyperpolarizing current/threshold ( I/ V) gradient was significantly increased in lower threshold axons ( F = 3.191, P < 0.05). The minimum I/ V gradient was increased in lower threshold motor and sensory axons. In conclusion, variation in the kinetics of HCN isoforms could account for the findings in motor and sensory axons. Importantly, assessing the function of HCN channels in sensory and motor axons of different thresholds may provide insights into the pathophysiological processes underlying peripheral neurological diseases in humans, particularly focusing on the role of HCN channels with the potential of identifying novel treatment targets. NEW & NOTEWORTHY Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels, which underlie inward rectifying currents ( Ih), appear to mediate differences in sensory and motor axonal properties. Inward rectifying currents are increased in lower threshold motor and sensory axons, although different HCN channel isoforms appear to underlie these changes. While faster activating HCN channels seem to underlie Ih changes in sensory axons, slower activating HCN isoforms appear to be mediating the differences in Ih conductances in motor axons of different thresholds. The differences in HCN gating properties could explain the predilection for dysfunction of sensory and motor axons in specific neurological diseases.

scholarly journals Hydrophobic gasket mutation produces gating pore currents in closed human voltage-gated proton channels

2019 ◽  
Vol 116 (38) ◽  
pp. 18951-18961 ◽  
Author(s):  
Richard Banh ◽  
Vladimir V. Cherny ◽  
Deri Morgan ◽  
Boris Musset ◽  
Sarah Thomas ◽  
...  
Keyword(s):  
Proton Channel ◽  
Voltage Gated ◽  
Closed State ◽  
Channel Opening ◽  
Proton Current ◽  
Voltage Dependent ◽  
Current Flows ◽  
Voltage Gated Ion Channels ◽  
Dynamics Simulations ◽  
Voltage Sensing Domain

The hydrophobic gasket (HG), a ring of hydrophobic amino acids in the voltage-sensing domain of most voltage-gated ion channels, forms a constriction between internal and external aqueous vestibules. Cationic Arg or Lys side chains lining the S4 helix move through this “gating pore” when the channel opens. S4 movement may occur during gating of the human voltage-gated proton channel, hHV1, but proton current flows through the same pore in open channels. Here, we replaced putative HG residues with less hydrophobic residues or acidic Asp. Substitution of individuals, pairs, or all 3 HG positions did not impair proton selectivity. Evidently, the HG does not act as a secondary selectivity filter. However, 2 unexpected functions of the HG in HV1 were discovered. Mutating HG residues independently accelerated channel opening and compromised the closed state. Mutants exhibited open–closed gating, but strikingly, at negative voltages where “normal” gating produces a nonconducting closed state, the channel leaked protons. Closed-channel proton current was smaller than open-channel current and was inhibited by 10 μM Zn2+. Extreme hyperpolarization produced a deeper closed state through a weakly voltage-dependent transition. We functionally identify the HG as Val109, Phe150, Val177, and Val178, which play a critical and exclusive role in preventing H+ influx through closed channels. Molecular dynamics simulations revealed enhanced mobility of Arg208 in mutants exhibiting H+ leak. Mutation of HG residues produces gating pore currents reminiscent of several channelopathies.

scholarly journals CryoEM structure of a prokaryotic cyclic nucleotide-gated ion channel

2017 ◽  
Vol 114 (17) ◽  
pp. 4430-4435 ◽  
Author(s):  
Zachary M. James ◽  
Andrew J. Borst ◽  
Yoni Haitin ◽  
Brandon Frenz ◽  
Frank DiMaio ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Cyclic Nucleotide ◽  
Sequence Similarity ◽  
Nucleotide Binding ◽  
Cardiac Pace ◽  
Hcn Channels ◽  
Cyclic Nucleotide Binding ◽  
Channel Opening ◽  
Cng Channel ◽  
Linker Domain

Cyclic nucleotide-gated (CNG) and hyperpolarization-activated cyclic nucleotide-regulated (HCN) ion channels play crucial physiological roles in phototransduction, olfaction, and cardiac pace making. These channels are characterized by the presence of a carboxyl-terminal cyclic nucleotide-binding domain (CNBD) that connects to the channel pore via a C-linker domain. Although cyclic nucleotide binding has been shown to promote CNG and HCN channel opening, the precise mechanism underlying gating remains poorly understood. Here we used cryoEM to determine the structure of the intact LliK CNG channel isolated from Leptospira licerasiae—which shares sequence similarity to eukaryotic CNG and HCN channels—in the presence of a saturating concentration of cAMP. A short S4–S5 linker connects nearby voltage-sensing and pore domains to produce a non–domain-swapped transmembrane architecture, which appears to be a hallmark of this channel family. We also observe major conformational changes of the LliK C-linkers and CNBDs relative to the crystal structures of isolated C-linker/CNBD fragments and the cryoEM structures of related CNG, HCN, and KCNH channels. The conformation of our LliK structure may represent a functional state of this channel family not captured in previous studies.

scholarly journals Hyperpolarization-activated cyclic nucleotide-gated channels in peripheral diaphragmatic lymphatics

2016 ◽  
Vol 311 (4) ◽  
pp. H892-H903 ◽  
Author(s):  
Daniela Negrini ◽  
Cristiana Marcozzi ◽  
Eleonora Solari ◽  
Elena Bossi ◽  
Raffaella Cinquetti ◽  
...  
Keyword(s):  
Cyclic Nucleotide ◽  
Cesium Chloride ◽  
Spontaneous Contraction ◽  
Hcn Channels ◽  
Contraction Frequency ◽  
Cyclic Nucleotide Gated Channels ◽  
Perfusion Chamber ◽  
Molecular Machinery ◽  
Pressure Changes ◽  
Zd 7288

Diaphragmatic lymphatic function is mainly sustained by pressure changes in the tissue and serosal cavities during cardiorespiratory cycles. The most peripheral diaphragmatic lymphatics are equipped with muscle cells (LMCs), which exhibit spontaneous contraction, whose molecular machinery is still undetermined. Hypothesizing that spontaneous contraction might involve hyperpolarization-activated cyclic nucleotide-gated (HCN) channels in lymphatic LMCs, diaphragmatic specimens, including spontaneously contracting lymphatics, were excised from 33 anesthetized rats, moved to a perfusion chamber containing HEPES-Tyrode's solution, and treated with HCN channels inhibitors cesium chloride (CsCl), ivabradine, and ZD-7288. Compared with control, exposure to 10 mM CsCl reduced (−65%, n = 13, P < 0.01) the contraction frequency (FL) and increased end-diastolic diameter (DL-d, +7.3%, P < 0.01) without changes in end-systolic diameter (DL-s). Ivabradine (300 μM) abolished contraction and increased DL-d (−14%, n = 10, P < 0.01) or caused an incomplete inhibition of FL ( n = 3, P < 0.01), leaving DL-d and DL-s unaltered. ZD-7288 (200 μM) completely ( n = 12, P < 0.01) abolished FL, while DL-d decreased to 90.9 ± 2.7% of control. HCN gene expression and immunostaining confirmed the presence of HCN1-4 channel isoforms, likely arranged in different configurations, in LMCs. Hence, all together, data suggest that HCN channels might play an important role in affecting contraction frequency of LMCs.

scholarly journals Gating of Cyclic Nucleotide Gated Channels is also Voltage Dependent

2012 ◽  
Vol 102 (3) ◽  
pp. 130a ◽  
Author(s):  
Arin Marchesi ◽  
Monica Mazzolini ◽  
Vincent Torre
Keyword(s):  
Cyclic Nucleotide ◽  
Cyclic Nucleotide Gated Channels ◽  
Voltage Dependent

scholarly journals Insights into the molecular mechanism for hyperpolarization-dependent activation of HCN channels

2018 ◽  
Vol 115 (34) ◽  
pp. E8086-E8095 ◽  
Author(s):  
Galen E. Flynn ◽  
William N. Zagotta
Keyword(s):  
Ion Channels ◽  
Cyclic Nucleotide ◽  
Electromechanical Coupling ◽  
Canonical Model ◽  
Hcn Channels ◽  
Voltage Gated ◽  
Kv Channels ◽  
Recovery From Inactivation ◽  
Voltage Dependent ◽  
Pore Domain

Hyperpolarization-activated, cyclic nucleotide-gated (HCN) ion channels are both voltage- and ligand-activated membrane proteins that contribute to electrical excitability and pace-making activity in cardiac and neuronal cells. These channels are members of the voltage-gated Kv channel superfamily and cyclic nucleotide-binding domain subfamily of ion channels. HCN channels have a unique feature that distinguishes them from other voltage-gated channels: the HCN channel pore opens in response to hyperpolarizing voltages instead of depolarizing voltages. In the canonical model of electromechanical coupling, based on Kv channels, a change in membrane voltage activates the voltage-sensing domains (VSD) and the activation energy passes to the pore domain (PD) through a covalent linker that connects the VSD to the PD. In this investigation, the covalent linkage between the VSD and PD, the S4-S5 linker, and nearby regions of spHCN channels were mutated to determine the functional role each plays in hyperpolarization-dependent activation. The results show that: (i) the S4-S5 linker is not required for hyperpolarization-dependent activation or ligand-dependent gating; (ii) the S4 C-terminal region (S4C-term) is not necessary for ligand-dependent gating but is required for hyperpolarization-dependent activation and acts like an autoinhibitory domain on the PD; (iii) the S5N-term region is involved in VSD–PD coupling and holding the pore closed; and (iv) spHCN channels have two voltage-dependent processes, a hyperpolarization-dependent activation and a depolarization-dependent recovery from inactivation. These results are inconsistent with the canonical model of VSD–PD coupling in Kv channels and elucidate the mechanism for hyperpolarization-dependent activation of HCN channels.

scholarly journals Structural Mechanism of Voltage-Dependent Gating in an Isolated Voltage-Sensing Domain

2013 ◽  
Vol 104 (2) ◽  
pp. 196a
Author(s):  
Qufei Li ◽  
Sherry Wanderling ◽  
Marcin Paduch ◽  
David Medovoy ◽  
Carlos Villalba-Galea ◽  
...  
Keyword(s):  
Voltage Sensing ◽  
Structural Mechanism ◽  
Voltage Dependent ◽  
Voltage Sensing Domain

scholarly journals Structural insights into the mechanisms of CNBD channel function

2017 ◽  
Vol 150 (2) ◽  
pp. 225-244 ◽  
Author(s):  
Zachary M. James ◽  
William N. Zagotta
Keyword(s):  
Cyclic Nucleotide ◽  
Ion Selectivity ◽  
K Channel ◽  
Hcn Channels ◽  
Nucleotide Binding Domain ◽  
Physiological Processes ◽  
Structural Framework ◽  
Voltage Dependent ◽  
Compare And Contrast ◽  
Structural Insights

Cyclic nucleotide-binding domain (CNBD) channels are a family of ion channels in the voltage-gated K+ channel superfamily that play crucial roles in many physiological processes. CNBD channels are structurally similar but functionally very diverse. This family includes three subfamilies: (1) the cyclic nucleotide-gated (CNG) channels, which are cation-nonselective, voltage-independent, and cyclic nucleotide-gated; (2) the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, which are weakly K+ selective, hyperpolarization-activated, and cyclic nucleotide-gated; and (3) the ether-à-go-go-type (KCNH) channels, which are strongly K+ selective, depolarization-activated, and cyclic nucleotide-independent. Recently, several high-resolution structures have been reported for intact CNBD channels, providing a structural framework to better understand their diverse function. In this review, we compare and contrast the recent structures and discuss how they inform our understanding of ion selectivity, voltage-dependent gating, and cyclic nucleotide–dependent gating within this channel family.

Sign in / Sign up

Export Citation Format

Share Document