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An electrostatic potassium channel opener targeting the final voltage sensor transition.

Börjesson SI, Elinder F - J. Gen. Physiol. (2011)

Bottom Line: However, molecular details for the interaction between PUFA and ion channels are not well understood.In this study, we have localized the site of action for PUFAs on the voltage-gated Shaker K channel by introducing positive charges on the channel surface, which potentiated the PUFA effect.Furthermore, we found that PUFA mainly affects the final voltage sensor movement, which is closely linked to channel opening, and that specific charges at the extracellular end of the voltage sensor are critical for the PUFA effect.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Clinical and Experimental Medicine, Division of Cell Biology, Linköping University, Sweden.

ABSTRACT
Free polyunsaturated fatty acids (PUFAs) modulate the voltage dependence of voltage-gated ion channels. As an important consequence thereof, PUFAs can suppress epileptic seizures and cardiac arrhythmia. However, molecular details for the interaction between PUFA and ion channels are not well understood. In this study, we have localized the site of action for PUFAs on the voltage-gated Shaker K channel by introducing positive charges on the channel surface, which potentiated the PUFA effect. Furthermore, we found that PUFA mainly affects the final voltage sensor movement, which is closely linked to channel opening, and that specific charges at the extracellular end of the voltage sensor are critical for the PUFA effect. Because different voltage-gated K channels have different charge profiles, this implies channel-specific PUFA effects. The identified site and the pharmacological mechanism will potentially be very useful in future drug design of small-molecule compounds specifically targeting neuronal and cardiac excitability.

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Possible interpretations of differential effects on different steps. (A) Three possible models for the S4 movement during the opening step. (B) The new PUFA action site compared with previously described sites. The Shaker channel is viewed from the extracellular side. The color coding follows that from Fig. 1 C. Green denote residues critical for the binding of quaternary ammonium compounds, magenta is for pore-blocking toxins, red is for voltage sensor–trapping toxins, yellow is for retigabine, and orange is for PUFA in the present investigation. The gating charges R362, R365, R368, and R371 are marked as blue sticks.
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fig8: Possible interpretations of differential effects on different steps. (A) Three possible models for the S4 movement during the opening step. (B) The new PUFA action site compared with previously described sites. The Shaker channel is viewed from the extracellular side. The color coding follows that from Fig. 1 C. Green denote residues critical for the binding of quaternary ammonium compounds, magenta is for pore-blocking toxins, red is for voltage sensor–trapping toxins, yellow is for retigabine, and orange is for PUFA in the present investigation. The gating charges R362, R365, R368, and R371 are marked as blue sticks.

Mentions: A tilted helical-screw motion in three steps (Keynes and Elinder, 1999; Tiwari-Woodruff et al., 2000; Lecar et al., 2003) is consistent with all of our experimental data (Fig. 8 A, top), but variations on the same theme could also explain the data: a helical-screw motion followed by a tilt of S4 in the final step (Pathak et al., 2005) (Fig. 8 A, middle), and a translational motion of a 310 helix followed by a 310-to-α-helix conversion in the final step (Shafrir et al., 2008; Bjelkmar et al., 2009; Schow et al., 2010) (Fig. 8 A, bottom). A small electrostatic PUFA effect on the early S4 movements (C0 to C4) can easily be understood from a simple surface charge theory, in which the PUFA carboxyl group provides additional fixed negative charges on the extracellular surface. If the charge is located close to the VSD, the modified transmembrane field will be sensed by the voltage sensor, and a smaller depolarizing step is needed to open the channel (Elinder and Århem, 2003). The mechanism is the same for all models. The larger PUFA effect on the opening step can be explained in a similar way if voltage sensor charges are moving closer to the PUFA action site during the opening step (C4→O). This occurs in all described models (Fig. 8 A). A gating charge movement in the plane of the membrane is also supported by the finding that a charge at R1 and R0 has profound effects on the PUFA potency. Such a model also implies the possibility that the PUFA affinity might be state dependent: a higher affinity in the open state than in a closed state. However, this has not been tested in the present investigation. These data are in concordance with fluorescence measurements suggesting that S4 moves laterally, with only a smaller transmembrane component, during the opening step (Pathak et al., 2005). The exact VSD rearrangement underlying the opening step is not known; therefore, it is difficult to differentiate between the models in Fig. 8 A. However, a recent investigation shows that the top charge of S4, R1, moves in an outward direction from the membrane during the final transition (Phillips and Swartz, 2010), thus supporting the helical-screw model in the top panel of Fig. 8 A.


An electrostatic potassium channel opener targeting the final voltage sensor transition.

Börjesson SI, Elinder F - J. Gen. Physiol. (2011)

Possible interpretations of differential effects on different steps. (A) Three possible models for the S4 movement during the opening step. (B) The new PUFA action site compared with previously described sites. The Shaker channel is viewed from the extracellular side. The color coding follows that from Fig. 1 C. Green denote residues critical for the binding of quaternary ammonium compounds, magenta is for pore-blocking toxins, red is for voltage sensor–trapping toxins, yellow is for retigabine, and orange is for PUFA in the present investigation. The gating charges R362, R365, R368, and R371 are marked as blue sticks.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3105513&req=5

fig8: Possible interpretations of differential effects on different steps. (A) Three possible models for the S4 movement during the opening step. (B) The new PUFA action site compared with previously described sites. The Shaker channel is viewed from the extracellular side. The color coding follows that from Fig. 1 C. Green denote residues critical for the binding of quaternary ammonium compounds, magenta is for pore-blocking toxins, red is for voltage sensor–trapping toxins, yellow is for retigabine, and orange is for PUFA in the present investigation. The gating charges R362, R365, R368, and R371 are marked as blue sticks.
Mentions: A tilted helical-screw motion in three steps (Keynes and Elinder, 1999; Tiwari-Woodruff et al., 2000; Lecar et al., 2003) is consistent with all of our experimental data (Fig. 8 A, top), but variations on the same theme could also explain the data: a helical-screw motion followed by a tilt of S4 in the final step (Pathak et al., 2005) (Fig. 8 A, middle), and a translational motion of a 310 helix followed by a 310-to-α-helix conversion in the final step (Shafrir et al., 2008; Bjelkmar et al., 2009; Schow et al., 2010) (Fig. 8 A, bottom). A small electrostatic PUFA effect on the early S4 movements (C0 to C4) can easily be understood from a simple surface charge theory, in which the PUFA carboxyl group provides additional fixed negative charges on the extracellular surface. If the charge is located close to the VSD, the modified transmembrane field will be sensed by the voltage sensor, and a smaller depolarizing step is needed to open the channel (Elinder and Århem, 2003). The mechanism is the same for all models. The larger PUFA effect on the opening step can be explained in a similar way if voltage sensor charges are moving closer to the PUFA action site during the opening step (C4→O). This occurs in all described models (Fig. 8 A). A gating charge movement in the plane of the membrane is also supported by the finding that a charge at R1 and R0 has profound effects on the PUFA potency. Such a model also implies the possibility that the PUFA affinity might be state dependent: a higher affinity in the open state than in a closed state. However, this has not been tested in the present investigation. These data are in concordance with fluorescence measurements suggesting that S4 moves laterally, with only a smaller transmembrane component, during the opening step (Pathak et al., 2005). The exact VSD rearrangement underlying the opening step is not known; therefore, it is difficult to differentiate between the models in Fig. 8 A. However, a recent investigation shows that the top charge of S4, R1, moves in an outward direction from the membrane during the final transition (Phillips and Swartz, 2010), thus supporting the helical-screw model in the top panel of Fig. 8 A.

Bottom Line: However, molecular details for the interaction between PUFA and ion channels are not well understood.In this study, we have localized the site of action for PUFAs on the voltage-gated Shaker K channel by introducing positive charges on the channel surface, which potentiated the PUFA effect.Furthermore, we found that PUFA mainly affects the final voltage sensor movement, which is closely linked to channel opening, and that specific charges at the extracellular end of the voltage sensor are critical for the PUFA effect.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Clinical and Experimental Medicine, Division of Cell Biology, Linköping University, Sweden.

ABSTRACT
Free polyunsaturated fatty acids (PUFAs) modulate the voltage dependence of voltage-gated ion channels. As an important consequence thereof, PUFAs can suppress epileptic seizures and cardiac arrhythmia. However, molecular details for the interaction between PUFA and ion channels are not well understood. In this study, we have localized the site of action for PUFAs on the voltage-gated Shaker K channel by introducing positive charges on the channel surface, which potentiated the PUFA effect. Furthermore, we found that PUFA mainly affects the final voltage sensor movement, which is closely linked to channel opening, and that specific charges at the extracellular end of the voltage sensor are critical for the PUFA effect. Because different voltage-gated K channels have different charge profiles, this implies channel-specific PUFA effects. The identified site and the pharmacological mechanism will potentially be very useful in future drug design of small-molecule compounds specifically targeting neuronal and cardiac excitability.

Show MeSH
Related in: MedlinePlus