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

2020 ◽  
Vol 117 (25) ◽  
pp. 14512-14521
Author(s):  
Yanyan Geng ◽  
Zengqin Deng ◽  
Guohui Zhang ◽  
Gonzalo Budelli ◽  
Alice Butler ◽  
...  
Keyword(s):  
Structural Changes ◽  
Cell Types ◽  
Bk Channels ◽  
Voltage Sensor ◽  
Membrane Excitability ◽  
Gating Currents ◽  
Sensor Interface ◽  
Pore Opening ◽  
Helical Turn ◽  
Voltage Activation

Large-conductance Ca2+and voltage-activated K+(BK) channels control membrane excitability in many cell types. BK channels are tetrameric. Each subunit is composed of a voltage sensor domain (VSD), a central pore-gate domain, and a large cytoplasmic domain (CTD) that contains the Ca2+sensors. While it is known that BK channels are activated by voltage and Ca2+, and that voltage and Ca2+activations interact, less is known about the mechanisms involved. We explore here these mechanisms 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 Horrigan, Cui, and Aldrich model indicated a decreased coupling between voltage sensors and pore gate. Proline mutations decreased Ca2+activation for both Ca2+bowl and RCK1 Ca2+sites, suggesting that both high-affinity Ca2+sites transduce their effect, at least in part, through the αB helix. Mg2+activation 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 wild type, without other notable differences in the CTD, indicating that structural changes from the mutation were confined to the αB helix. These findings indicate that an intact αB helix/VSD interface is required for effective coupling of Ca2+binding and voltage depolarization to pore opening and that shared Ca2+and voltage transduction pathways involving the αB helix may be involved.

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

2020 ◽  
Author(s):  
Yanyan Geng ◽  
Zengqin Deng ◽  
Guohui Zhang ◽  
Gonzalo Budelli ◽  
Alice Butler ◽  
...  
Keyword(s):  
Modular Design ◽  
Cell Types ◽  
Cytoplasmic Domain ◽  
Bk Channels ◽  
Bk Channel ◽  
Voltage Sensor ◽  
Membrane Excitability ◽  
Gating Currents ◽  
Voltage Sensors ◽  
Voltage Activation

AbstractLarge conductance Ca2+ 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 Ca2+ sensors. While it is known that BK channels are activated by voltage and Ca2+, and that voltage and Ca2+ 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 Ca2+ activation for both Ca2+ bowl and RCK1 Ca2+ sites, suggesting that both high affinity Ca2+ sites transduce their effect, at least in part, through the αB helix. Mg2+ 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 Ca2+ binding and voltage depolarization to pore opening, and that shared Ca2+ and voltage transduction pathways involving the αB helix may be involved.SignificanceLarge conductance BK (Slo1) K+ channels are activated by voltage, Ca2+, and Mg2+ 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 Ca2+ sensors. Previous observations suggest that voltage and Ca2+ 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 Ca2+, suggesting that these processes may share common allosteric activation pathways. Such knowledge should help explain disease processes associated with BK channel dysfunction.

scholarly journals Heme Regulates Allosteric Activation of the Slo1 BK Channel

2005 ◽  
Vol 126 (1) ◽  
pp. 7-21 ◽  
Author(s):  
Frank T. Horrigan ◽  
Stefan H. Heinemann ◽  
Toshinori Hoshi
Keyword(s):  
Divalent Cations ◽  
Ionic Currents ◽  
Bk Channels ◽  
Bk Channel ◽  
Voltage Sensor ◽  
Gating Currents ◽  
Calcium Dependent ◽  
Channel Opening ◽  
Activation Gate ◽  
Voltage Dependent

Large conductance calcium-dependent (Slo1 BK) channels are allosterically activated by membrane depolarization and divalent cations, and possess a rich modulatory repertoire. Recently, intracellular heme has been identified as a potent regulator of Slo1 BK channels (Tang, X.D., R. Xu, M.F. Reynolds, M.L. Garcia, S.H. Heinemann, and T. Hoshi. 2003. Nature. 425:531–535). Here we investigated the mechanism of the regulatory action of heme on heterologously expressed Slo1 BK channels by separating the influences of voltage and divalent cations. In the absence of divalent cations, heme generally decreased ionic currents by shifting the channel's G–V curve toward more depolarized voltages and by rendering the curve less steep. In contrast, gating currents remained largely unaffected by heme. Simulations suggest that a decrease in the strength of allosteric coupling between the voltage sensor and the activation gate and a concomitant stabilization of the open state account for the essential features of the heme action in the absence of divalent ions. At saturating levels of divalent cations, heme remained similarly effective with its influence on the G–V simulated by weakening the coupling of both Ca2+ binding and voltage sensor activation to channel opening. The results thus show that heme dampens the influence of allosteric activators on the activation gate of the Slo1 BK channel. To account for these effects, we consider the possibility that heme binding alters the structure of the RCK gating ring and thereby disrupts both Ca2+- and voltage-dependent gating as well as intrinsic stability of the open state.

scholarly journals Mode shift of the voltage sensors in Shaker K+ channels is caused by energetic coupling to the pore domain

2011 ◽  
Vol 137 (5) ◽  
pp. 455-472 ◽  
Author(s):  
Georges A. Haddad ◽  
Rikard Blunck
Keyword(s):  
Conformational Change ◽  
Mechanical Load ◽  
Voltage Sensor ◽  
Charge Movement ◽  
Gating Currents ◽  
Mode Shift ◽  
Voltage Sensors ◽  
Pore Opening ◽  
Voltage Gated Ion Channels ◽  
Pore Domain

The voltage sensors of voltage-gated ion channels undergo a conformational change upon depolarization of the membrane that leads to pore opening. This conformational change can be measured as gating currents and is thought to be transferred to the pore domain via an annealing of the covalent link between voltage sensor and pore (S4-S5 linker) and the C terminus of the pore domain (S6). Upon prolonged depolarizations, the voltage dependence of the charge movement shifts to more hyperpolarized potentials. This mode shift had been linked to C-type inactivation but has recently been suggested to be caused by a relaxation of the voltage sensor itself. In this study, we identified two ShakerIR mutations in the S4-S5 linker (I384N) and S6 (F484G) that, when mutated, completely uncouple voltage sensor movement from pore opening. Using these mutants, we show that the pore transfers energy onto the voltage sensor and that uncoupling the pore from the voltage sensor leads the voltage sensors to be activated at more negative potentials. This uncoupling also eliminates the mode shift occurring during prolonged depolarizations, indicating that the pore influences entry into the mode shift. Using voltage-clamp fluorometry, we identified that the slow conformational change of the S4 previously correlated with the mode shift disappears when uncoupling the pore. The effects can be explained by a mechanical load that is imposed upon the voltage sensors by the pore domain and allosterically modulates its conformation. Mode shift is caused by the stabilization of the open state but leads to a conformational change in the voltage sensor.

scholarly journals The BK channel gating ring is strongly coupled to the voltage sensor

2018 ◽  
Author(s):  
Pablo Miranda ◽  
Miguel Holmgren ◽  
Teresa Giraldez
Keyword(s):  
Conformational Changes ◽  
Bk Channels ◽  
Bk Channel ◽  
Voltage Sensor ◽  
Voltage Sensitivity ◽  
Divalent Ions ◽  
Gating Currents ◽  
Open Probability ◽  
Voltage Dependent ◽  
Tightly Coupled

ABSTRACTThe open probability of large conductance voltage- and calcium-dependent potassium (BK) channels is regulated allosterically by changes in the transmembrane voltage and intracellular concentration of divalent ions (Ca2+ and Mg2+). The divalent cation sensors reside within the gating ring formed by eight Regulator of Conductance of Potassium (RCK) domains, two from each of the four channel subunits. Overall, the gating ring contains 12 sites that can bind Ca2+ with different affinities. Using patch-clamp fluorometry, we have shown robust changes in FRET signals within the gating ring in response to divalent ions and voltage, which do not directly track open probability. Only the conformational changes triggered through the RCK1 binding site are voltage-dependent in presence of Ca2+. Because the gating ring is outside the electric field, it must gain voltage sensitivity from coupling to the voltage-dependent channel opening, the voltage sensor or both. Here we demonstrate that alterations of voltage sensor dynamics known to shift gating currents produce a cognate shift in the gating ring voltage dependence, whereas changing BK channels’ relative probability of opening had little effect. These results strongly suggest that the conformational changes of the RCK1 domain of the gating ring are tightly coupled to the voltage sensor function, and this interaction is central to the allosteric modulation of BK channels.

scholarly journals Bipolar Switching by HCN Voltage Sensor Underlies Hyperpolarization Activation

2018 ◽  
Author(s):  
John Cowgill ◽  
Vadim A. Klenchin ◽  
Claudia Alvarez-Baron ◽  
Debanjan Tewari ◽  
Alexander Blair ◽  
...  
Keyword(s):  
Voltage Sensor ◽  
Hcn Channels ◽  
Hcn Channel ◽  
Sensor Interface ◽  
Bipolar Switching ◽  
Full Complement ◽  
Common Principle ◽  
Pore Opening ◽  
Voltage Gated Ion Channels ◽  
Common Architecture

SUMMARYDespite sharing a common architecture with archetypal voltage-gated ion channels (VGIC), the hyperpolarization- and cyclic AMP-activated ion (HCN) channels open upon hyperpolarization rather than depolarization. The basic motions of voltage sensor and pore gates are conserved implying that these domains are inversely coupled in HCN channels. Using structure-guided protein engineering, we systematically assembled an array of mosaic channels that display the full complement of voltage-activation phenotypes observed in the VGIC superfamily. Our studies reveal that the voltage-sensing S3b-S4 transmembrane segment of the HCN channel has an intrinsic ability to drive pore opening in either direction. Specific contacts at the pore-voltage sensor interface and unique interactions near the pore gate forces the HCN channel into a hERG-like inactivated state, thereby obscuring their opening upon depolarization. Our findings reveal an unexpected common principle underpinning voltage gating in the VGIC superfamily and identify the essential determinants of gating polarity.

Molecular structure of an open human KATP channel

2021 ◽  
Vol 118 (48) ◽  
pp. e2112267118
Author(s):  
Chen Zhao ◽  
Roderick MacKinnon
Keyword(s):  
Conformational Changes ◽  
Structural Changes ◽  
Inward Rectifier ◽  
Sulfonylurea Receptor ◽  
Membrane Excitability ◽  
Atp Binding Site ◽  
Area Reduction ◽  
Inward Rectifier Potassium Channel ◽  
Pore Opening ◽  
Inward Rectifier Channels

KATP channels are metabolic sensors that translate intracellular ATP/ADP balance into membrane excitability. The molecular composition of KATP includes an inward-rectifier potassium channel (Kir) and an ABC transporter–like sulfonylurea receptor (SUR). Although structures of KATP have been determined in many conformations, in all cases, the pore in Kir is closed. Here, we describe human pancreatic KATP (hKATP) structures with an open pore at 3.1- to 4.0-Å resolution using single-particle cryo-electron microscopy (cryo-EM). Pore opening is associated with coordinated structural changes within the ATP-binding site and the channel gate in Kir. Conformational changes in SUR are also observed, resulting in an area reduction of contact surfaces between SUR and Kir. We also observe that pancreatic hKATP exhibits the unique (among inward-rectifier channels) property of PIP2-independent opening, which appears to be correlated with a docked cytoplasmic domain in the absence of PIP2.

scholarly journals Deletion of cytosolic gating ring decreases gate and voltage sensor coupling in BK channels

2017 ◽  
Vol 149 (3) ◽  
pp. 373-387 ◽  
Author(s):  
Guohui Zhang ◽  
Yanyan Geng ◽  
Yakang Jin ◽  
Jingyi Shi ◽  
Kelli McFarland ◽  
...  
Keyword(s):  
Bk Channels ◽  
Bk Channel ◽  
Voltage Sensor ◽  
Voltage Sensitivity ◽  
Gating Currents ◽  
Voltage Sensors ◽  
Transmembrane Voltage ◽  
Wide Range ◽  
Activation Gate ◽  
Sensor Activation

Large conductance Ca2+-activated K+ channels (BK channels) gate open in response to both membrane voltage and intracellular Ca2+. The channel is formed by a central pore-gate domain (PGD), which spans the membrane, plus transmembrane voltage sensors and a cytoplasmic gating ring that acts as a Ca2+ sensor. How these voltage and Ca2+ sensors influence the common activation gate, and interact with each other, is unclear. A previous study showed that a BK channel core lacking the entire cytoplasmic gating ring (Core-MT) was devoid of Ca2+ activation but retained voltage sensitivity (Budelli et al. 2013. Proc. Natl. Acad. Sci. USA. http://dx.doi.org/10.1073/pnas.1313433110). In this study, we measure voltage sensor activation and pore opening in this Core-MT channel over a wide range of voltages. We record gating currents and find that voltage sensor activation in this truncated channel is similar to WT but that the coupling between voltage sensor activation and gating of the pore is reduced. These results suggest that the gating ring, in addition to being the Ca2+ sensor, enhances the effective coupling between voltage sensors and the PGD. We also find that removal of the gating ring alters modulation of the channels by the BK channel’s β1 and β2 subunits.

Neuronal mRNA Translation in Addiction

2018 ◽  
Author(s):  
Emma Puighermanal ◽  
Emmanuel Valjent
Keyword(s):  
Structural Changes ◽  
Drugs Of Abuse ◽  
Mrna Translation ◽  
Cell Types ◽  
Behavioral Changes ◽  
Translational Machinery ◽  
Addictive Drugs ◽  
Specific Mrnas ◽  
Cell Type Specific ◽  
Future Work

Addictive drugs trigger persistent synaptic and structural changes in the neuronal reward circuits that are thought to underlie the development of drug-adaptive behavior. While transcriptional and epigenetic modifications are known to contribute to these circuit changes, accumulating evidence indicates that altered mRNA translation is also a key molecular mechanism. This chapter reviews recent studies demonstrating how addictive drugs alter protein synthesis and/or the translational machinery and how this leads to neuronal circuit remodeling and behavioral changes. Future work will determine precisely which neuronal circuits and cell types participate in these changes. The chapter summarizes current methodologies for identifying cell type-specific mRNAs whose translation is affected by drugs of abuse and gives recent examples of the mechanistic insights into addiction they provide.

scholarly journals Subunit-Specific Effect of the Voltage Sensor Domain on Ca2+ Sensitivity of BK Channels

2008 ◽  
Vol 94 (12) ◽  
pp. 4678-4687 ◽  
Author(s):  
Huanghe Yang ◽  
Guohui Zhang ◽  
Jingyi Shi ◽  
Urvi S. Lee ◽  
Kelli Delaloye ◽  
...  
Keyword(s):  
Specific Effect ◽  
Bk Channels ◽  
Voltage Sensor ◽  
Voltage Sensor Domain

scholarly journals Intercellular calcium signalling between chondrocytes and synovial cells in co-culture

1998 ◽  
Vol 329 (3) ◽  
pp. 681-687 ◽  
Author(s):  
Paola D'ANDREA ◽  
Alessandra CALABRESE ◽  
Micaela GRANDOLFO
Keyword(s):  
Gap Junctions ◽  
Intercellular Communication ◽  
Structural Changes ◽  
Articular Chondrocytes ◽  
Cell Metabolism ◽  
Second Messengers ◽  
Calcium Signalling ◽  
Cell Types ◽  
Synovial Cells ◽  
Cell Coupling

Intercellular communication allows the co-ordination of cell metabolism between tissues as well as sensitivity to extracellular stimuli. Paracrine stimulation and cell-to-cell coupling through gap junctions induce the formation of complex cellular networks that favour the intercellular exchange of nutrients and second messengers. Heterologous intercellular communication was studied in co-cultures of articular chondrocytes and HIG-82 synovial cells by measuring mechanically induced cytosolic changes in Ca2+ ion levels by digital fluorescence video imaging. In confluent co-cultures, mechanical stimulation induced intercellular Ca2+ waves that propagated to both cell types with similar kinetics. Intercellular wave spreading was inhibited by 18α-glycyrrhetinic acid and by treatments inhibiting the activation of purinoreceptors, suggesting that intercellular signalling between these two cell types occurs both through gap junctions and ATP-mediated paracrine stimulation. In rheumatoid arthritis the formation of the synovial pannus induces structural changes at the chondrosynovial junction, where chondrocyte and synovial cells come into close apposition: these results provide the first evidence for direct intercellular communication between these two cell types.

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