scholarly journals Models of the Structure and Voltage-Gating Mechanism of the Shaker K+ Channel

2004 ◽  
Vol 87 (4) ◽  
pp. 2116-2130 ◽  
Author(s):  
Stewart R. Durell ◽  
Indira H. Shrivastava ◽  
H. Robert Guy
Keyword(s):  
Voltage Gating ◽  
K Channel ◽  
Gating Mechanism

scholarly journals Structural Basis for pH-Gating of the K+ Channel TWIK1 at the Selectivity Filter

2021 ◽  
Author(s):  
Toby S Turney ◽  
Vivian Li ◽  
Stephen G Brohawn
Keyword(s):  
Conformational Changes ◽  
Pancreatic Beta Cells ◽  
Low Ph ◽  
Selectivity Filter ◽  
Structural Basis ◽  
K Channel ◽  
Open Conformation ◽  
Gating Mechanism ◽  
Lipid Nanodiscs ◽  
Pore Domain

TWIK1 is a widely expressed pH-gated two-pore domain K+ channel (K2P) that contributes to cardiac rhythm generation and insulin release from pancreatic beta cells. TWIK1 displays unique properties among K2Ps including low basal activity and inhibition by extracellular protons through incompletely understood mechanisms. Here, we present cryo-EM structures of TWIK1 in lipid nanodiscs at high and low pH that reveal a novel gating mechanism at the K+ selectivity filter. At high pH, TWIK1 adopts an open conformation. At low pH, protonation of an extracellular histidine results in a cascade of conformational changes that close the channel by sealing the top of the selectivity filter, displacing the helical cap to block extracellular ion access pathways, and opening gaps for lipid block of the intracellular cavity. These data provide a mechanistic understanding for extracellular pH-gating of TWIK1 and show how diverse mechanisms have evolved to gate the selectivity filter of K+ channels.

The Ca-activated K channel of human red cells: All or none behaviour of the Ca2+-gating mechanism

Cell Calcium ◽  
1983 ◽  
Vol 4 (5-6) ◽  
pp. 511-517 ◽  
Author(s):  
V.L. Lew ◽  
S. Muallem ◽  
Carol A. Seymour
Keyword(s):  
Red Cells ◽  
K Channel ◽  
Gating Mechanism ◽  
Human Red Cells

Molecular site for nucleotide binding on an ATP-sensitive renal K+ channel (ROMK2)

1996 ◽  
Vol 271 (2) ◽  
pp. F275-F285 ◽  
Author(s):  
C. M. McNicholas ◽  
Y. Yang ◽  
G. Giebisch ◽  
S. C. Hebert
Keyword(s):  
Channel Gating ◽  
Direct Interaction ◽  
K Channel ◽  
Amino Terminus ◽  
Atp Binding Site ◽  
Gating Mechanism ◽  
Alternatively Spliced ◽  
Carboxy Terminal ◽  
Apical Membranes

ATP-sensitive, inwardly rectifying K+ channels are present in apical membranes of the distal nephron and play a major role in K+ recycling and secretion. The cloned renal K+ channel, ROMK1, is a candidate for the renal epithelial K+ channel, since it shares many functional characteristics with the native channel. Additionally, ROMK1 contains a putative carboxy-terminal ATP-binding site. Although ROMK1 channel activity could be reactivated by cytosolic Mg-ATP after rundown, the role of nucleotides in channel gating was less certain. We now show that an alternatively spliced transcript of the ROMK channel gene, ROMK2, which encodes a K+ channel with a truncated amino terminus, expresses an ATP-regulated and ATP-sensitive K+ channel (IKATP). Differences in the amino terminus of ROMK isoforms alters the sensitivity of the channel-gating mechanism to ATP. To test whether ATP sensitivity of renal IKATP is mediated by direct interaction of nucleotide, point mutation of specific residues within the ROMK2 phosphate loop (P-loop) were investigated. These either enhanced or attenuated the sensitivity to both activation and inhibition by Mg-ATP, thus demonstrating a direct interaction of nucleotide with the channel-forming polypeptide.

scholarly journals Mechanism of activation at the selectivity filter of the KcsA K+ channel

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Florian T Heer ◽  
David J Posson ◽  
Wojciech Wojtas-Niziurski ◽  
Crina M Nimigean ◽  
Simon Bernèche
Keyword(s):  
Conformational Changes ◽  
Selectivity Filter ◽  
K Channel ◽  
Ion Permeation ◽  
K Channels ◽  
Narrow Region ◽  
Gating Mechanism ◽  
Structural Fluctuations ◽  
Extracellular Side ◽  
Dynamics Simulations

Potassium channels are opened by ligands and/or membrane potential. In voltage-gated K+ channels and the prokaryotic KcsA channel, conduction is believed to result from opening of an intracellular constriction that prevents ion entry into the pore. On the other hand, numerous ligand-gated K+ channels lack such gate, suggesting that they may be activated by a change within the selectivity filter, a narrow region at the extracellular side of the pore. Using molecular dynamics simulations and electrophysiology measurements, we show that ligand-induced conformational changes in the KcsA channel removes steric restraints at the selectivity filter, thus resulting in structural fluctuations, reduced K+ affinity, and increased ion permeation. Such activation of the selectivity filter may be a universal gating mechanism within K+ channels. The occlusion of the pore at the level of the intracellular gate appears to be secondary.

scholarly journals Selectivity filter instability dominates the low intrinsic activity of the TWIK-1 K2P K+ channel

2019 ◽  
Vol 295 (2) ◽  
pp. 610-618
Author(s):  
Ehsan Nematian-Ardestani ◽  
Firdaus Abd-Wahab ◽  
Franck C. Chatelain ◽  
Han Sun ◽  
Marcus Schewe ◽  
...  
Keyword(s):  
Functional Activity ◽  
Selectivity Filter ◽  
Intrinsic Activity ◽  
K Channel ◽  
Open Probability ◽  
Gating Mechanism ◽  
Hydrophobic Barrier ◽  
K2p Channels ◽  
Voltage Dependent ◽  
Low Levels

Two-pore domain K+ (K2P) channels have many important physiological functions. However, the functional properties of the TWIK-1 (K2P1.1/KCNK1) K2P channel remain poorly characterized because heterologous expression of this ion channel yields only very low levels of functional activity. Several underlying reasons have been proposed, including TWIK-1 retention in intracellular organelles, inhibition by posttranslational sumoylation, a hydrophobic barrier within the pore, and a low open probability of the selectivity filter (SF) gate. By evaluating these potential mechanisms, we found that the latter dominates the low intrinsic functional activity of TWIK-1. Investigating this further, we observed that the low activity of the SF gate appears to arise from the inefficiency of K+ in stabilizing an active (i.e. conductive) SF conformation. In contrast, other permeant ion species, such as Rb+, NH4+, and Cs+, strongly promoted a pH-dependent activated conformation. Furthermore, many K2P channels are activated by membrane depolarization via an SF-mediated gating mechanism, but we found here that only very strong nonphysiological depolarization produces voltage-dependent activation of heterologously expressed TWIK-1. Remarkably, we also observed that TWIK-1 Rb+ currents are potently inhibited by intracellular K+ (IC50 = 2.8 mm). We conclude that TWIK-1 displays unique SF gating properties among the family of K2P channels. In particular, the apparent instability of the conductive conformation of the TWIK-1 SF in the presence of K+ appears to dominate the low levels of intrinsic functional activity observed when the channel is expressed at the cell surface.

scholarly journals Dissection of the Molecular Basis of pp60v-src Induced Gating of Connexin 43 Gap Junction Channels

1999 ◽  
Vol 144 (5) ◽  
pp. 1033-1045 ◽  
Author(s):  
Lan Zhou ◽  
Eileen M. Kasperek ◽  
Bruce J. Nicholson
Keyword(s):  
Map Kinase ◽  
Gap Junction ◽  
Connexin 43 ◽  
Rat Kidney ◽  
Serine Phosphorylation ◽  
K Channel ◽  
Xenopus Laevis Oocyte ◽  
Gap Junction Channels ◽  
Gating Mechanism ◽  
Junctional Communication

Suppression of gap-junctional communication by various protein kinases, growth factors, and oncogenes frequently correlates with enhanced mitogenesis. The oncogene v-src appears to cause acute closure of gap junction channels. Tyr265 in the COOH-terminal tail of connexin 43 (Cx43) has been implicated as a potential target of v-src, although v-src action has also been associated with changes in serine phosphorylation. We have investigated the mechanism of this acute regulation through mutagenesis of Cx43 expressed in Xenopus laevis oocyte pairs. Truncations of the COOH-terminal domain led to an almost complete loss of response of Cx43 to v-src, but this was restored by coexpression of the independent COOH-terminal polypeptide. This suggests a ball and chain gating mechanism, similar to the mechanism proposed for pH gating of Cx43, and K+ channel inactivation. Surprisingly, we found that v-src mediated gating of Cx43 did not require the tyrosine site, but did seem to depend on the presence of two potential SH3 binding domains and the mitogen-activated protein (MAP) kinase phosphorylation sites within them. Further point mutagenesis and pharmacological studies in normal rat kidney (NRK) cells implicated MAP kinase in the gating response to v-src, while the stable binding of v-src to Cx43 (in part mediated by SH3 domains) did not correlate with its ability to mediate channel closure. This suggests a common link between closure of gap junctions by v-src and other mitogens, such as EGF and lysophosphatidic acid (LPA).

scholarly journals Bimodal regulation of an Elk subfamily K+ channel by phosphatidylinositol 4,5-bisphosphate

2015 ◽  
Vol 146 (5) ◽  
pp. 357-374 ◽  
Author(s):  
Xiaofan Li ◽  
Andriy Anishkin ◽  
Hansi Liu ◽  
Damian B. van Rossum ◽  
Sree V. Chintapalli ◽  
...  
Keyword(s):  
Voltage Gating ◽  
K Channel ◽  
Hcn Channels ◽  
Basic Residue ◽  
K Channels ◽  
Mode Shift ◽  
Kcnq Channels ◽  
C Terminus ◽  
Opposing Effects ◽  
Voltage Activation

Phosphatidylinositol 4,5-bisphosphate (PIP2) regulates Shaker K+ channels and voltage-gated Ca2+ channels in a bimodal fashion by inhibiting voltage activation while stabilizing open channels. Bimodal regulation is conserved in hyperpolarization-activated cyclic nucleotide–gated (HCN) channels, but voltage activation is enhanced while the open channel state is destabilized. The proposed sites of PIP2 regulation in these channels include the voltage-sensor domain (VSD) and conserved regions of the proximal cytoplasmic C terminus. Relatively little is known about PIP2 regulation of Ether-á-go-go (EAG) channels, a metazoan-specific family of K+ channels that includes three gene subfamilies, Eag (Kv10), Erg (Kv11), and Elk (Kv12). We examined PIP2 regulation of the Elk subfamily potassium channel human Elk1 to determine whether bimodal regulation is conserved within the EAG K+ channel family. Open-state stabilization by PIP2 has been observed in human Erg1, but the proposed site of regulation in the distal C terminus is not conserved among EAG family channels. We show that PIP2 strongly inhibits voltage activation of Elk1 but also stabilizes the open state. This stabilization produces slow deactivation and a mode shift in voltage gating after activation. However, removal of PIP2 has the net effect of enhancing Elk1 activation. R347 in the linker between the VSD and pore (S4–S5 linker) and R479 near the S6 activation gate are required for PIP2 to inhibit voltage activation. The ability of PIP2 to stabilize the open state also requires these residues, suggesting an overlap in sites central to the opposing effects of PIP2 on channel gating. Open-state stabilization in Elk1 requires the N-terminal eag domain (PAS domain + Cap), and PIP2-dependent stabilization is enhanced by a conserved basic residue (K5) in the Cap. Our data shows that PIP2 can bimodally regulate voltage gating in EAG family channels, as has been proposed for Shaker and HCN channels. PIP2 regulation appears fundamentally different for Elk and KCNQ channels, suggesting that, although both channel types can regulate action potential threshold in neurons, they are not functionally redundant.

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