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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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Localization the PUFA action site. (A) Extracellular view of the Shaker K channel in an open state (based on the Kv1.2/2.1 chimera; Long et al., 2007). Only one VSD and part of the pore domain are shown. The blue residues are the four most extracellular gating charges (R362, R365, R368, and R371). The selectivity filter is shown in cyan. Green residues (I325, A359, and I360) have the largest impact on the PUFA-induced shift of the G-V curve, the yellow residue (T329) has a smaller but significant effect on the PUFA-induced shift, and red residues have no significant effects on the PUFA-induced shifts. The negative charge denotes an approximate position of the PUFA carboxyl charge affecting the voltage sensitivity of the Shaker K channel. (B) Side view of the channel with I325, A359, and I360 in green, T329 in yellow, and residues with no significant effects on the PUFA-induced shifts in red. Not investigated residues in S3 are shown in cyan, and those in S4 are shown in blue. All residues in space fill.
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fig4: Localization the PUFA action site. (A) Extracellular view of the Shaker K channel in an open state (based on the Kv1.2/2.1 chimera; Long et al., 2007). Only one VSD and part of the pore domain are shown. The blue residues are the four most extracellular gating charges (R362, R365, R368, and R371). The selectivity filter is shown in cyan. Green residues (I325, A359, and I360) have the largest impact on the PUFA-induced shift of the G-V curve, the yellow residue (T329) has a smaller but significant effect on the PUFA-induced shift, and red residues have no significant effects on the PUFA-induced shifts. The negative charge denotes an approximate position of the PUFA carboxyl charge affecting the voltage sensitivity of the Shaker K channel. (B) Side view of the channel with I325, A359, and I360 in green, T329 in yellow, and residues with no significant effects on the PUFA-induced shifts in red. Not investigated residues in S3 are shown in cyan, and those in S4 are shown in blue. All residues in space fill.

Mentions: For I360C, located two residues outside the first gating charge in S4, and for I325C, in S3, 70 µM DHA at pH 7.4 shifts the G-V with −1.5 and −1.1 mV, respectively (Fig. 3, C and D, left, and Table I). For both mutations, modification with MTSEA+ clearly shifts the G-V with +7 and +19 mV, respectively (Fig. 3, C and D, middle, and Table I). The MTSEA+ modification significantly increased the DHA-induced shift to −8.5 and −5.9 mV, respectively (Fig. 3, C and D, right, and Table I), clearly more than for WT-IR. Therefore, both residues 325 and 360 are suggested to be located in or close to the voltage sensor (as also found in the structure) and to the PUFA action site. MTSEA+ modification of T329C in S3 and A359C in S4 also significantly affected the voltage sensitivity of the channel and the PUFA-induced shift (Table I). This is consistent with the cysteine mutagenesis data (see above); the three cysteine mutations that significantly altered the DHA sensitivity (325C, 329C, and 366C) are geographically close to or overlap with the residues that increase their DHA sensitivity when charge modified (325C, 329C, 359C, and 360C). Examination of the molecular structure showed that high-impact residues are clustered in a small region of the lipid-facing S3–S4 corner of the VSD (Fig. 4 A). An estimation of the PUFA action site locates the PUFA carboxyl charge in the lipid bilayer adjacent to S3 and S4 (Fig. 4, A and B). Intriguingly, this is the same motif on the channel as membrane phospholipids are suggested to interact with to alter channel gating (Milescu et al., 2009).


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

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

Localization the PUFA action site. (A) Extracellular view of the Shaker K channel in an open state (based on the Kv1.2/2.1 chimera; Long et al., 2007). Only one VSD and part of the pore domain are shown. The blue residues are the four most extracellular gating charges (R362, R365, R368, and R371). The selectivity filter is shown in cyan. Green residues (I325, A359, and I360) have the largest impact on the PUFA-induced shift of the G-V curve, the yellow residue (T329) has a smaller but significant effect on the PUFA-induced shift, and red residues have no significant effects on the PUFA-induced shifts. The negative charge denotes an approximate position of the PUFA carboxyl charge affecting the voltage sensitivity of the Shaker K channel. (B) Side view of the channel with I325, A359, and I360 in green, T329 in yellow, and residues with no significant effects on the PUFA-induced shifts in red. Not investigated residues in S3 are shown in cyan, and those in S4 are shown in blue. All residues in space fill.
© Copyright Policy - openaccess
Related In: Results  -  Collection

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

fig4: Localization the PUFA action site. (A) Extracellular view of the Shaker K channel in an open state (based on the Kv1.2/2.1 chimera; Long et al., 2007). Only one VSD and part of the pore domain are shown. The blue residues are the four most extracellular gating charges (R362, R365, R368, and R371). The selectivity filter is shown in cyan. Green residues (I325, A359, and I360) have the largest impact on the PUFA-induced shift of the G-V curve, the yellow residue (T329) has a smaller but significant effect on the PUFA-induced shift, and red residues have no significant effects on the PUFA-induced shifts. The negative charge denotes an approximate position of the PUFA carboxyl charge affecting the voltage sensitivity of the Shaker K channel. (B) Side view of the channel with I325, A359, and I360 in green, T329 in yellow, and residues with no significant effects on the PUFA-induced shifts in red. Not investigated residues in S3 are shown in cyan, and those in S4 are shown in blue. All residues in space fill.
Mentions: For I360C, located two residues outside the first gating charge in S4, and for I325C, in S3, 70 µM DHA at pH 7.4 shifts the G-V with −1.5 and −1.1 mV, respectively (Fig. 3, C and D, left, and Table I). For both mutations, modification with MTSEA+ clearly shifts the G-V with +7 and +19 mV, respectively (Fig. 3, C and D, middle, and Table I). The MTSEA+ modification significantly increased the DHA-induced shift to −8.5 and −5.9 mV, respectively (Fig. 3, C and D, right, and Table I), clearly more than for WT-IR. Therefore, both residues 325 and 360 are suggested to be located in or close to the voltage sensor (as also found in the structure) and to the PUFA action site. MTSEA+ modification of T329C in S3 and A359C in S4 also significantly affected the voltage sensitivity of the channel and the PUFA-induced shift (Table I). This is consistent with the cysteine mutagenesis data (see above); the three cysteine mutations that significantly altered the DHA sensitivity (325C, 329C, and 366C) are geographically close to or overlap with the residues that increase their DHA sensitivity when charge modified (325C, 329C, 359C, and 360C). Examination of the molecular structure showed that high-impact residues are clustered in a small region of the lipid-facing S3–S4 corner of the VSD (Fig. 4 A). An estimation of the PUFA action site locates the PUFA carboxyl charge in the lipid bilayer adjacent to S3 and S4 (Fig. 4, A and B). Intriguingly, this is the same motif on the channel as membrane phospholipids are suggested to interact with to alter channel gating (Milescu et al., 2009).

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