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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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Strategy to test if PUFA facilitates horizontal S4 movement. (A) Schematic illustration of the assumed charge-transfer motion used for distance calculations (Eq. 3). The only change in electric charges between each gating state is that one gating charge is moved from the intracellular side to the extracellular side. Gating charges within the membrane electric field pair up with conserved negative charges. (B) Structure of the Shaker K channel in the open state (based on the Kv1.2/2.1 chimera). One VSD and part of the pore domain are shown. The four most extracellular-positive charges in S4 are colored: red, R362; orange, R365; green, R368; blue, R371. The negative charge denotes the position for the effective PUFA molecule. Arrows denote the distances from the effective PUFA site to the charge of R362 and to the site where the positive charges of R365 and R368 emerge on the surface, respectively. (C) Structural comparison of an arginine, a MTSES−-modified cysteine, and a MTSET+-modified cysteine.
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fig6: Strategy to test if PUFA facilitates horizontal S4 movement. (A) Schematic illustration of the assumed charge-transfer motion used for distance calculations (Eq. 3). The only change in electric charges between each gating state is that one gating charge is moved from the intracellular side to the extracellular side. Gating charges within the membrane electric field pair up with conserved negative charges. (B) Structure of the Shaker K channel in the open state (based on the Kv1.2/2.1 chimera). One VSD and part of the pore domain are shown. The four most extracellular-positive charges in S4 are colored: red, R362; orange, R365; green, R368; blue, R371. The negative charge denotes the position for the effective PUFA molecule. Arrows denote the distances from the effective PUFA site to the charge of R362 and to the site where the positive charges of R365 and R368 emerge on the surface, respectively. (C) Structural comparison of an arginine, a MTSES−-modified cysteine, and a MTSET+-modified cysteine.

Mentions: If a charge is located at the border between a low dielectric medium (the lipid membrane) and a high dielectric medium (water), the potential ψ(r) at the distance r from an elementary charge e0 (e.g., the PUFA charge) can be calculated with a modified Coulomb’s law (McLaughlin, 1989; Elinder and Århem, 2003),(3)ψ(r)=2e0 exp(−κr)/(4πε0εar),where ε0 is the permittivity of free space (8.85 × 10−12 Fm−1), εa is the relative dielectric constant of the aqueous phase (80), and κ is the inverse of the Debye length in the aqueous phase (9.8 Å in the 1-K solution; see e.g., Elinder et al., 2001b). Eq. 3 was used to get a rough estimate of the distance between the PUFA carboxyl charge and the gating charges in S4 based on DHA-induced Q-V and G-V shifts for the ILT mutant. The calculation is based on the assumptions that the surface of the channel is smooth, and that the top S4 charges pop up on the channel’s surface one by one, leaving the interior of the channel unaffected with positive gating charges pairing with negative counter charges (see Fig. 6 A). This simple model has been evaluated previously (Elinder et al., 2001a) and proven surprisingly accurate (Elinder et al., 2001a; Broomand and Elinder, 2008).


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

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

Strategy to test if PUFA facilitates horizontal S4 movement. (A) Schematic illustration of the assumed charge-transfer motion used for distance calculations (Eq. 3). The only change in electric charges between each gating state is that one gating charge is moved from the intracellular side to the extracellular side. Gating charges within the membrane electric field pair up with conserved negative charges. (B) Structure of the Shaker K channel in the open state (based on the Kv1.2/2.1 chimera). One VSD and part of the pore domain are shown. The four most extracellular-positive charges in S4 are colored: red, R362; orange, R365; green, R368; blue, R371. The negative charge denotes the position for the effective PUFA molecule. Arrows denote the distances from the effective PUFA site to the charge of R362 and to the site where the positive charges of R365 and R368 emerge on the surface, respectively. (C) Structural comparison of an arginine, a MTSES−-modified cysteine, and a MTSET+-modified cysteine.
© Copyright Policy - openaccess
Related In: Results  -  Collection

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

fig6: Strategy to test if PUFA facilitates horizontal S4 movement. (A) Schematic illustration of the assumed charge-transfer motion used for distance calculations (Eq. 3). The only change in electric charges between each gating state is that one gating charge is moved from the intracellular side to the extracellular side. Gating charges within the membrane electric field pair up with conserved negative charges. (B) Structure of the Shaker K channel in the open state (based on the Kv1.2/2.1 chimera). One VSD and part of the pore domain are shown. The four most extracellular-positive charges in S4 are colored: red, R362; orange, R365; green, R368; blue, R371. The negative charge denotes the position for the effective PUFA molecule. Arrows denote the distances from the effective PUFA site to the charge of R362 and to the site where the positive charges of R365 and R368 emerge on the surface, respectively. (C) Structural comparison of an arginine, a MTSES−-modified cysteine, and a MTSET+-modified cysteine.
Mentions: If a charge is located at the border between a low dielectric medium (the lipid membrane) and a high dielectric medium (water), the potential ψ(r) at the distance r from an elementary charge e0 (e.g., the PUFA charge) can be calculated with a modified Coulomb’s law (McLaughlin, 1989; Elinder and Århem, 2003),(3)ψ(r)=2e0 exp(−κr)/(4πε0εar),where ε0 is the permittivity of free space (8.85 × 10−12 Fm−1), εa is the relative dielectric constant of the aqueous phase (80), and κ is the inverse of the Debye length in the aqueous phase (9.8 Å in the 1-K solution; see e.g., Elinder et al., 2001b). Eq. 3 was used to get a rough estimate of the distance between the PUFA carboxyl charge and the gating charges in S4 based on DHA-induced Q-V and G-V shifts for the ILT mutant. The calculation is based on the assumptions that the surface of the channel is smooth, and that the top S4 charges pop up on the channel’s surface one by one, leaving the interior of the channel unaffected with positive gating charges pairing with negative counter charges (see Fig. 6 A). This simple model has been evaluated previously (Elinder et al., 2001a) and proven surprisingly accurate (Elinder et al., 2001a; Broomand and Elinder, 2008).

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