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.

scholarly journals Minimal molecular determinants of isoform-specific differences in efficacy in the HCN channel family

2018 ◽  
Vol 150 (8) ◽  
pp. 1203-1213 ◽  
Author(s):  
Claudia P. Alvarez-Baron ◽  
Vadim A. Klenchin ◽  
Baron Chanda
Keyword(s):  
Cyclic Nucleotide ◽  
Rhythmic Activity ◽  
Structural Similarity ◽  
Hcn Channels ◽  
Hcn Channel ◽  
Nucleotide Binding Domain ◽  
Functional Differences ◽  
Molecular Determinants ◽  
Voltage Dependent ◽  
Hcn1 Channels

Hyperpolarization-activated, cyclic nucleotide–gated (HCN) channels generate rhythmic activity in the heart and brain. Isoform-specific functional differences reflect the specializations required for the various roles that they play. Despite a high sequence and structural similarity, HCN isoforms differ greatly in their response to cyclic nucleotides. Cyclic AMP (cAMP) enhances the activity of HCN2 and HCN4 isoforms by shifting the voltage dependence of activation to more depolarized potentials, whereas HCN1 and HCN3 isoforms are practically insensitive to this ligand. Here, to determine the molecular basis for increased cAMP efficacy in HCN2 channels, we progressively mutate residues in the C-linker and cyclic nucleotide–binding domain (CNBD) of the mouse HCN2 to their equivalents in HCN1. We identify two clusters of mutations that determine the differences in voltage-dependent activation between these two isoforms. One maps to the C-linker region, whereas the other is in proximity to the cAMP-binding site in the CNBD. A mutant channel containing just five mutations (M485I, G497D, S514T, V562A, and S563G) switches cAMP sensitivity of full-length HCN2 to that of HCN1 channels. These findings, combined with a detailed analysis of various allosteric models for voltage- and ligand-dependent gating, indicate that these residues alter the ability of the C-linker to transduce signals from the CNBD to the pore gates of the HCN channel.

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 Mechanism of the Voltage Sensitivity of IRK1 Inward-rectifier K+ Channel Block by the Polyamine Spermine

2005 ◽  
Vol 125 (4) ◽  
pp. 413-426 ◽  
Author(s):  
Hyeon-Gyu Shin ◽  
Zhe Lu
Keyword(s):  
Steady State ◽  
Voltage Dependence ◽  
Ion Selectivity ◽  
Inward Rectifier ◽  
Selectivity Filter ◽  
K Channel ◽  
Voltage Sensitivity ◽  
Channel Block ◽  
Head Groups ◽  
Voltage Dependent

IRK1 (Kir2.1) inward-rectifier K+ channels exhibit exceedingly steep rectification, which reflects strong voltage dependence of channel block by intracellular cations such as the polyamine spermine. On the basis of studies of IRK1 block by various amine blockers, it was proposed that the observed voltage dependence (valence ∼5) of IRK1 block by spermine results primarily from K+ ions, not spermine itself, traversing the transmembrane electrical field that drops mostly across the narrow ion selectivity filter, as spermine and K+ ions displace one another during channel block and unblock. If indeed spermine itself only rarely penetrates deep into the ion selectivity filter, then a long blocker with head groups much wider than the selectivity filter should exhibit comparably strong voltage dependence. We confirm here that channel block by two molecules of comparable length, decane-bis-trimethylammonium (bis-QAC10) and spermine, exhibit practically identical overall voltage dependence even though the head groups of the former are much wider (∼6 Å) than the ion selectivity filter (∼3 Å). For both blockers, the overall equilibrium dissociation constant differs from the ratio of apparent rate constants of channel unblock and block. Also, although steady-state IRK1 block by both cations is strongly voltage dependent, their apparent channel-blocking rate constant exhibits minimal voltage dependence, which suggests that the pore becomes blocked as soon as the blocker encounters the innermost K+ ion. These findings strongly suggest the existence of at least two (potentially identifiable) sequentially related blocked states with increasing numbers of K+ ions displaced. Consequently, the steady-state voltage dependence of IRK1 block by spermine or bis-QAC10 should increase with membrane depolarization, a prediction indeed observed. Further kinetic analysis identifies two blocked states, and shows that most of the observed steady-state voltage dependence is associated with the transition between blocked states, consistent with the view that the mutual displacement of blocker and K+ ions must occur mainly as the blocker travels along the long inner pore.

Sweet taste transduction in hamster: sweeteners and cyclic nucleotides depolarize taste cells by reducing a K+ current

1996 ◽  
Vol 75 (3) ◽  
pp. 1256-1263 ◽  
Author(s):  
T. A. Cummings ◽  
C. Daniels ◽  
S. C. Kinnamon
Keyword(s):  
Cyclic Nucleotides ◽  
Cyclic Nucleotide ◽  
Taste Receptor ◽  
Reversal Potential ◽  
Taste Cell ◽  
K Channel ◽  
Cyclic Monophosphate ◽  
Taste Cells ◽  
Voltage Dependent ◽  
K Current

1. The gigaseal voltage-clamp technique was used to record responses of hamster taste receptor cells to synthetic sweeteners and cyclic nucleotides. Voltage-dependent currents and steady-state currents were monitored during bath exchanges of saccharin, two high-potency sweeteners, 8-chlorophenylthio-adenosine 3',5'-cyclic monophosphate (8cpt-cAMP), and dibutyryl-guanosine 3',5'-cyclic monophosphate (db-cGMP). 2. Of the 237 fungiform taste cells studied, only one in eight was sweet responsive. Outward currents, both voltage-dependent and resting, were reduced by all of the sweeteners tested in sweet-responsive taste cells, whereas these currents were unaffected by sweeteners in sweet-unresponsive taste cells. 3. In every sweet-responsive cell tested, 8cpt-cAMP and db-cGMP mimicked the response to the sweeteners, but neither nucleotide elicited responses in sweet-unresponsive cells. Thus there was a one-to-one correlation between sweet responsivity and cyclic nucleotide responsivity. 4. Sweet responses showed cross adaptation with cyclic nucleotide responses. This indicates that the same ion channel is modulated by sweeteners and cyclic nucleotides. 5. The sweetener- and cyclic nucleotide-blocked current had an apparent reversal potential of -50 mV, which was close to the potassium reversal potential in these experiments. In addition, there was no effect of sweeteners and cyclic nucleotides in the presence of the K+ channel blocker tetraethylammonium bromide (TEA). These data suggest that block of a resting, TEA-sensitive K+ current is the final common step leading to taste cell depolarization during sweet transduction. 6. These data, together with data from a previous study (Cummings et al. 1993), suggest that both synthetic sweeteners and sucrose utilize second-messenger pathways that block a resting K+ conductance to depolarize the taste cell membrane.

scholarly journals Allosteric Regulation of the Cyclic Nucleotide-Binding Domain in HCN Channels

2015 ◽  
Vol 108 (2) ◽  
pp. 192a-193a
Author(s):  
Hannah A. DeBerg ◽  
Shahidul M. Islam ◽  
Michael C. Puljung ◽  
Benoit Roux ◽  
William N. Zagotta ◽  
...  
Keyword(s):  
Cyclic Nucleotide ◽  
Allosteric Regulation ◽  
Nucleotide Binding ◽  
Binding Domain ◽  
Hcn Channels ◽  
Nucleotide Binding Domain ◽  
Cyclic Nucleotide Binding ◽  
Cyclic Nucleotide Binding Domain

scholarly journals S4 Movement in a Mammalian HCN Channel

2003 ◽  
Vol 123 (1) ◽  
pp. 21-32 ◽  
Author(s):  
Sriharsha Vemana ◽  
Shilpi Pandey ◽  
H. Peter Larsson
Keyword(s):  
Voltage Sensor ◽  
K Channel ◽  
Hcn Channels ◽  
Dependent Manner ◽  
Hcn Channel ◽  
Voltage Range ◽  
Kv Channels ◽  
State Dependent ◽  
Voltage Dependent ◽  
Hcn1 Channels

Hyperpolarization-activated, cyclic nucleotide–gated ion channels (HCN) mediate an inward cation current that contributes to spontaneous rhythmic firing activity in the heart and the brain. HCN channels share sequence homology with depolarization-activated Kv channels, including six transmembrane domains and a positively charged S4 segment. S4 has been shown to function as the voltage sensor and to undergo a voltage-dependent movement in the Shaker K+ channel (a Kv channel) and in the spHCN channel (an HCN channel from sea urchin). However, it is still unknown whether S4 undergoes a similar movement in mammalian HCN channels. In this study, we used cysteine accessibility to determine whether there is voltage-dependent S4 movement in a mammalian HCN1 channel. Six cysteine mutations (R247C, T249C, I251C, S253C, L254C, and S261C) were used to assess S4 movement of the heterologously expressed HCN1 channel in Xenopus oocytes. We found a state-dependent accessibility for four S4 residues: T249C and S253C from the extracellular solution, and L254C and S261C from the internal solution. We conclude that S4 moves in a voltage-dependent manner in HCN1 channels, similar to its movement in the spHCN channel. This S4 movement suggests that the role of S4 as a voltage sensor is conserved in HCN channels. In addition, to determine the reason for the different cAMP modulation and the different voltage range of activation in spHCN channels compared with HCN1 channels, we constructed a COOH-terminal–deleted spHCN. This channel appeared to be similar to a COOH-terminal–deleted HCN1 channel, suggesting that the main functional differences between spHCN and HCN1 channels are due to differences in their COOH termini or in the interaction between the COOH terminus and the rest of the channel protein in spHCN channels compared with HCN1 channels.

scholarly journals A synthetic peptide that prevents cAMP regulation in mammalian hyperpolarization-activated cyclic nucleotide-gated (HCN) channels

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Andrea Saponaro ◽  
Francesca Cantini ◽  
Alessandro Porro ◽  
Annalisa Bucchi ◽  
Dario DiFrancesco ◽  
...  
Keyword(s):  
Cyclic Nucleotide ◽  
Rational Design ◽  
Structural Model ◽  
Hcn Channels ◽  
Nucleotide Binding Domain ◽  
Novel Approach ◽  
A Cell ◽  
The Central Nervous System ◽  
The Brain ◽  
Adrenergic Activation

Binding of TRIP8b to the cyclic nucleotide binding domain (CNBD) of mammalian hyperpolarization-activated cyclic nucleotide-gated (HCN) channels prevents their regulation by cAMP. Since TRIP8b is expressed exclusively in the brain, we envisage that it can be used for orthogonal control of HCN channels beyond the central nervous system. To this end, we have identified by rational design a 40-aa long peptide (TRIP8bnano) that recapitulates affinity and gating effects of TRIP8b in HCN isoforms (hHCN1, mHCN2, rbHCN4) and in the cardiac current If in rabbit and mouse sinoatrial node cardiomyocytes. Guided by an NMR-derived structural model that identifies the key molecular interactions between TRIP8bnano and the HCN CNBD, we further designed a cell-penetrating peptide (TAT-TRIP8bnano) which successfully prevented β-adrenergic activation of mouse If leaving the stimulation of the L-type calcium current (ICaL) unaffected. TRIP8bnano represents a novel approach to selectively control HCN activation, which yields the promise of a more targeted pharmacology compared to pore blockers.

scholarly journals Transfer of Voltage Independence from a Rat Olfactory Channel to the Drosophila Ether-à-go-go K+ Channel

1997 ◽  
Vol 109 (3) ◽  
pp. 301-311 ◽  
Author(s):  
Chih-Yung Tang ◽  
Diane M. Papazian
Keyword(s):  
Cyclic Nucleotide ◽  
Voltage Sensor ◽  
K Channel ◽  
Voltage Range ◽  
Voltage Gated ◽  
Cyclic Nucleotide Gated Channels ◽  
Voltage Dependent ◽  
Relative Stabilization ◽  
Voltage Gated Ion Channels ◽  
S4 Segment

The S4 segment is an important part of the voltage sensor in voltage-gated ion channels. Cyclic nucleotide-gated channels, which are members of the superfamily of voltage-gated channels, have little inherent sensitivity to voltage despite the presence of an S4 segment. We made chimeras between a voltage-independent rat olfactory channel (rolf) and the voltage-dependent ether-à-go-go K+ channel (eag) to determine the basis of their divergent gating properties. We found that the rolf S4 segment can support a voltage-dependent mechanism of activation in eag, suggesting that rolf has a potentially functional voltage sensor that is silent during gating. In addition, we found that the S3-S4 loop of rolf increases the relative stability of the open conformation of eag, effectively converting eag into a voltage-independent channel. A single charged residue in the loop makes a significant contribution to the relative stabilization of the open state in eag. Our data suggest that cyclic nucleotide-gated channels such as rolf contain a voltage sensor which, in the physiological voltage range, is stabilized in an activated conformation that is permissive for pore opening.

Sign in / Sign up

Export Citation Format

Share Document