On the role of ball and chain interactions in recovery from the inactivation of the shaker potassium channel

AbstractWe describe a new factor in the recovery from inactivation in the ball and chain model. We propose a model in which the tension from the chain may help pull the ball away from its binding site, reducing the duration of the inactivation period. A corresponding model was built and analysed.

Download Full-text

Investigating the Putative Glycine Hinge in Shaker Potassium Channel

The Journal of General Physiology ◽

10.1085/jgp.200509287 ◽

2005 ◽

Vol 126 (3) ◽

pp. 213-226 ◽

Cited By ~ 67

Author(s):

Shinghua Ding ◽

Lindsey Ingleby ◽

Christopher A. Ahern ◽

Richard Horn

Keyword(s):

Potassium Channel ◽

Functional Expression ◽

Shaker Potassium Channel ◽

Glycine Residue ◽

Shaker Channels ◽

Channel Opening ◽

Activation Gating ◽

Voltage Dependent ◽

Shaker Potassium Channels

The crystal structure of an open potassium channel reveals a kink in the inner helix that lines the pore (Jiang, Y.X., A. Lee, J.Y. Chen, M. Cadene, B.T. Chait, and R. MacKinnon. 2002. Nature 417:523–526). The putative hinge point is a highly conserved glycine residue. We examined the role of the homologous residue (Gly466) in the S6 transmembrane segment of Shaker potassium channels. The nonfunctional alanine mutant G466A will assemble, albeit poorly, with wild-type (WT) subunits, suppressing functional expression. To test if this glycine residue is critical for activation gating, we did a glycine scan along the S6 segment in the background of G466A. Although all of these double mutants lack the higher-level glycosylation that is characteristic of mature Shaker channels, one (G466A/V467G) is able to generate voltage-dependent potassium current. Surface biotinylation shows that functional and nonfunctional constructs containing G466A express at comparable levels in the plasma membrane. Compared with WT channels, the shifted-glycine mutant has impairments in voltage-dependent channel opening, including a right-shifted activation curve and a decreased rate of activation. The double mutant has relatively normal open-channel properties, except for a decreased affinity for intracellular blockers, a consequence of the loss of the side chain of Val467. Control experiments with the double mutants M440A/G466A and G466A/V467A suggest that the flexibility provided by Gly466 is more important for channel function than its small size. Our results support roles for Gly466 both in biogenesis of the channel and as a hinge in activation gating.

Download Full-text

Role of hydrophobic and ionic forces in the movement of S4 of the Shaker potassium channel

Molecular Membrane Biology ◽

10.3109/09687688.2012.710343 ◽

2012 ◽

Vol 29 (8) ◽

pp. 321-332 ◽

Cited By ~ 1

Author(s):

David J. S. Elliott ◽

Edward J. Neale ◽

Tim S. Munsey ◽

John P. Bannister ◽

Asipu Sivaprasadarao

Keyword(s):

Potassium Channel ◽

Shaker Potassium Channel

Download Full-text

Role of the S4 in Cooperativity of Voltage-dependent Potassium Channel Activation

The Journal of General Physiology ◽

10.1085/jgp.111.3.399 ◽

1998 ◽

Vol 111 (3) ◽

pp. 399-420 ◽

Cited By ~ 116

Author(s):

Catherine J. Smith-Maxwell ◽

Jennifer L. Ledwell ◽

Richard W. Aldrich

Keyword(s):

Potassium Channel ◽

Amino Acid Sequences ◽

Channel Activation ◽

Shaker Potassium Channel ◽

Activation Pathway ◽

Activation Gating ◽

Voltage Dependent ◽

Rate Limiting ◽

Cooperative Transition

Charged residues in the S4 transmembrane segment of voltage-gated cation channels play a key role in opening channels in response to changes in voltage across the cell membrane. However, the molecular mechanism of channel activation is not well understood. To learn more about the role of the S4 in channel gating, we constructed chimeras in which S4 segments from several divergent potassium channels, Shab, Shal, Shaw, and Kv3.2, were inserted into a Shaker potassium channel background. These S4 donor channels have distinctly different voltage-dependent gating properties and S4 amino acid sequences. None of the S4 chimeras have the gating behavior of their respective S4 donor channels. The conductance–voltage relations of all S4 chimeras are shifted to more positive voltages and the slopes are decreased. There is no consistent correlation between the nominal charge content of the S4 and the slope of the conductance–voltage relation, suggesting that the mutations introduced by the S4 chimeras may alter cooperative interactions in the gating process. We compared the gating behavior of the Shaw S4 chimera with its parent channels, Shaker and Shaw, in detail. The Shaw S4 substitution alters activation gating profoundly without introducing obvious changes in other channel functions. Analysis of the voltage-dependent gating kinetics suggests that the dominant effect of the Shaw S4 substitution is to alter a single cooperative transition late in the activation pathway, making it rate limiting. This interpretation is supported further by studies of channels assembled from tandem heterodimer constructs with both Shaker and Shaw S4 subunits. Activation gating in the heterodimer channels can be predicted from the properties of the homotetrameric channels only if it is assumed that the mutations alter a cooperative transition in the activation pathway rather than independent transitions.

Download Full-text

Tuning the tetraethylammonium sensitivity of potassium channel Kcv by subunit combination

The Journal of General Physiology ◽

10.1085/jgp.201110725 ◽

2012 ◽

Vol 139 (4) ◽

pp. 295-304 ◽

Cited By ~ 4

Author(s):

Qiulin Tan ◽

Brandon Ritzo ◽

Kai Tian ◽

Li-Qun Gu

Keyword(s):

Potassium Channel ◽

Binding Site ◽

Specific Interaction ◽

Site Directed Mutagenesis ◽

Molecular Probe ◽

K Channel ◽

Optimal Conformation ◽

Subunit Combination ◽

Insight Into

Tetraethylammonium (TEA) is a potassium (K+) channel inhibitor that has been extensively used as a molecular probe to explore the structure of channels’ ion pathway. In this study, we identified that Leu70 of the virus-encoded potassium channel Kcv is a key amino acid that plays an important role in regulating the channel’s TEA sensitivity. Site-directed mutagenesis of Leu70 can change the TEA sensitivity by 1,000-fold from ∼100 µM to ∼100 mM. Because no compelling trends exist to explain this amino acid’s specific interaction with TEA, the role of Leu70 at the binding site is likely to ensure an optimal conformation of the extracellular mouth that confers high TEA affinity. We further assembled the subunits of mutant and wt-Kcv into a series of heterotetramers. The differences in these heterochannels suggest that all of the four subunits in a Kcv channel additively participate in the TEA binding, and each of the four residues at the binding site independently contributes an equal binding energy. We therefore can present a series of mutant/wild-type tetramer combinations that can probe TEA over three orders of magnitude in concentration. This study may give insight into the mechanism for the interaction between the potassium channel and its inhibitor.

Download Full-text

A Mutation in S6 of Shaker Potassium Channels Decreases the K+ Affinity of an Ion Binding Site Revealing Ion–Ion Interactions in the Pore

The Journal of General Physiology ◽

10.1085/jgp.112.2.243 ◽

1998 ◽

Vol 112 (2) ◽

pp. 243-257 ◽

Cited By ~ 48

Author(s):

Eva M. Ogielska ◽

Richard W. Aldrich

Keyword(s):

Potassium Channels ◽

Potassium Channel ◽

Binding Site ◽

Sodium Current ◽

High Potassium ◽

Independent Evidence ◽

Channel Pore ◽

Shaker Potassium Channel ◽

Ion Interactions ◽

Barium Block

Under physiological conditions, potassium channels are extraordinarily selective for potassium over other ions. However, in the absence of potassium, certain potassium channels can conduct sodium. Sodium flux is blocked by the addition of low concentrations of potassium. Potassium affinity, and therefore the ability to block sodium current, varies among potassium channel subtypes (Korn, S.J., and S.R. Ikeda. 1995. Science. 269:410–412; Starkus, J.G., L. Kuschel, M.D. Rayner, and S.H. Heinemann. 1997. J. Gen. Physiol. 110:539–550). The Shaker potassium channel conducts sodium poorly in the presence of very low (micromolar) potassium due to its high potassium affinity (Starkus, J.G., L. Kuschel, M.D. Rayner, and S.H. Heinemann. 1997. J. Gen. Physiol. 110:539–550; Ogielska, E.M., and R.W. Aldrich. 1997. Biophys. J. 72:A233 [Abstr.]). We show that changing a single residue in S6, A463C, decreases the apparent internal potassium affinity of the Shaker channel pore from the micromolar to the millimolar range, as determined from the ability of potassium to block the sodium currents. Independent evidence that A463C decreases the apparent affinity of a binding site in the pore comes from a study of barium block of potassium currents. The A463C mutation decreases the internal barium affinity of the channel, as expected if barium blocks current by binding to a potassium site in the pore. The decrease in the apparent potassium affinity in A463C channels allows further study of possible ion interactions in the pore. Our results indicate that sodium and potassium can occupy the pore simultaneously and that multiple occupancy results in interactions between ions in the channel pore.

Download Full-text