Structure of the voltage-gated K+ channel Eag1 reveals an alternative voltage sensing mechanism

Current through voltage-gated K+ channels underlies the action potential encoding the electrical signal in excitable cells. The four subunits of a voltage-gated K+ channel each have six transmembrane segments (S1–S6), whereas some other K+ channels, such as eukaryotic inward rectifier K+ channels and the prokaryotic KcsA channel, have only two transmembrane segments (M1 and M2). A voltage-gated K+ channel is formed by an ion-pore module (S5–S6, equivalent to M1–M2) and the surrounding voltage-sensing modules. The S4 segments are the primary voltage sensors while the intracellular activation gate is located near the COOH-terminal end of S6, although the coupling mechanism between them remains unknown. In the present study, we found that two short, complementary sequences in voltage-gated K+ channels are essential for coupling the voltage sensors to the intracellular activation gate. One sequence is the so called S4–S5 linker distal to the voltage-sensing S4, while the other is around the COOH-terminal end of S6, a region containing the actual gate-forming residues.

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α-Helical Structural Elements within the Voltage-Sensing Domains of a K+ Channel

The Journal of General Physiology ◽

10.1085/jgp.115.1.33 ◽

1999 ◽

Vol 115 (1) ◽

pp. 33-50 ◽

Cited By ~ 133

Author(s):

Yingying Li-Smerin ◽

David H. Hackos ◽

Kenton J. Swartz

Keyword(s):

Secondary Structure ◽

K Channel ◽

Structural Elements ◽

Alanine Scanning Mutagenesis ◽

Voltage Sensing ◽

Tertiary Structures ◽

Voltage Gated ◽

Transmembrane Segments ◽

Membrane Spanning ◽

Pore Domain

Voltage-gated K+ channels are tetramers with each subunit containing six (S1–S6) putative membrane spanning segments. The fifth through sixth transmembrane segments (S5–S6) from each of four subunits assemble to form a central pore domain. A growing body of evidence suggests that the first four segments (S1–S4) comprise a domain-like voltage-sensing structure. While the topology of this region is reasonably well defined, the secondary and tertiary structures of these transmembrane segments are not. To explore the secondary structure of the voltage-sensing domains, we used alanine-scanning mutagenesis through the region encompassing the first four transmembrane segments in the drk1 voltage-gated K+ channel. We examined the mutation-induced perturbation in gating free energy for periodicity characteristic of α-helices. Our results are consistent with at least portions of S1, S2, S3, and S4 adopting α-helical secondary structure. In addition, both the S1–S2 and S3–S4 linkers exhibited substantial helical character. The distribution of gating perturbations for S1 and S2 suggest that these two helices interact primarily with two environments. In contrast, the distribution of perturbations for S3 and S4 were more complex, suggesting that the latter two helices make more extensive protein contacts, possibly interfacing directly with the shell of the pore domain.

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Omega Currents in Voltage-Gated Ion Channels: What Can We Learn from Uncovering the Voltage-Sensing Mechanism Using MD Simulations?

Accounts of Chemical Research ◽

10.1021/ar300290u ◽

2013 ◽

Vol 46 (12) ◽

pp. 2755-2762 ◽

Cited By ~ 15

Author(s):

Mounir Tarek ◽

Lucie Delemotte

Keyword(s):

Ion Channels ◽

Md Simulations ◽

Voltage Sensing ◽

Voltage Gated ◽

Sensing Mechanism ◽

Voltage Gated Ion Channels ◽

Gated Ion Channels

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The voltage-sensing domain of a phosphatase gates the pore of a potassium channel

The Journal of General Physiology ◽

10.1085/jgp.201210940 ◽

2013 ◽

Vol 141 (3) ◽

pp. 389-395 ◽

Cited By ~ 37

Author(s):

Cristina Arrigoni ◽

Indra Schroeder ◽

Giulia Romani ◽

James L. Van Etten ◽

Gerhard Thiel ◽

...

Keyword(s):

Electromechanical Coupling ◽

K Channel ◽

Modular Architecture ◽

Voltage Sensing ◽

Mode Shift ◽

Voltage Gated ◽

Kv Channels ◽

Pore Properties ◽

Voltage Sensing Domain

The modular architecture of voltage-gated K+ (Kv) channels suggests that they resulted from the fusion of a voltage-sensing domain (VSD) to a pore module. Here, we show that the VSD of Ciona intestinalis phosphatase (Ci-VSP) fused to the viral channel Kcv creates KvSynth1, a functional voltage-gated, outwardly rectifying K+ channel. KvSynth1 displays the summed features of its individual components: pore properties of Kcv (selectivity and filter gating) and voltage dependence of Ci-VSP (V1/2 = +56 mV; z of ∼1), including the depolarization-induced mode shift. The degree of outward rectification of the channel is critically dependent on the length of the linker more than on its amino acid composition. This highlights a mechanistic role of the linker in transmitting the movement of the sensor to the pore and shows that electromechanical coupling can occur without coevolution of the two domains.

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Localization and Molecular Determinants of the Hanatoxin Receptors on the Voltage-Sensing Domains of a K+ Channel

The Journal of General Physiology ◽

10.1085/jgp.115.6.673 ◽

2000 ◽

Vol 115 (6) ◽

pp. 673-684 ◽

Cited By ~ 99

Author(s):

Yingying Li-Smerin ◽

Kenton J. Swartz

Keyword(s):

K Channel ◽

Alanine Scanning Mutagenesis ◽

Voltage Sensing ◽

Alanine Scanning ◽

K Channels ◽

Voltage Gated ◽

Physical Location ◽

Molecular Determinants ◽

Central Pore ◽

Pore Domain

Hanatoxin inhibits voltage-gated K+ channels by modifying the energetics of activation. We studied the molecular determinants and physical location of the Hanatoxin receptors on the drk1 voltage-gated K+ channel. First, we made multiple substitutions at three previously identified positions in the COOH terminus of S3 to examine whether these residues interact intimately with the toxin. We also examined a region encompassing S1–S3 using alanine-scanning mutagenesis to identify additional determinants of the toxin receptors. Finally, guided by the structure of the KcsA K+ channel, we explored whether the toxin interacts with the peripheral extracellular surface of the pore domain in the drk1 K+ channel. Our results argue for an intimate interaction between the toxin and the COOH terminus of S3 and suggest that the Hanatoxin receptors are confined within the voltage-sensing domains of the channel, at least 20–25 Å away from the central pore axis.

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