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Double gaps along Shaker S4 demonstrate omega currents at three different closed states
Tamer M Gamal El-Din1, Hansjakob Heldstab, Claudia Lehmann
1Institute of Physiology, University of Zurich, Switzerland.
Channels (Austin, Tex.)
|December 17, 2009
Summary
The Shaker potassium channel
Area of Science:
- Molecular Biology
- Biophysics
- Ion Channel Function
Background:
- Voltage-gated potassium channels are crucial for cellular electrical excitability.
- The Shaker potassium channel's gating mechanism has been debated, with the helical screw and paddle models proposed.
- The S4 segment's charged arginine residues are key to voltage sensing.
Purpose of the Study:
- To elucidate the movement of the voltage sensor (S4 segment) in the Shaker potassium channel during gating.
- To differentiate between the helical screw and paddle models of voltage sensor function.
Main Methods:
- Site-directed mutagenesis of arginine residues within the S4 segment.
- Introduction of systematic 'gaps' (substitutions with serine) in the arginine-containing thread.
- Analysis of induced 'omega' leak currents to infer S4 movement and pore interactions.
Main Results:
- Mutations R2S and R3S did not induce significant leak currents.
- Introducing double gaps (RR to SS) at sequential positions generated stable leak currents.
- Mutation of residue A359 to arginine blocked the omega current in the R1S mutant, suggesting A359 interaction with R1.
- Observed leak currents contradict the paddle model, where S4 would move with S3 within the lipid bilayer.
Conclusions:
- The S4 voltage sensor segment moves in discrete helical steps during channel gating.
- These movements occur through a fixed pore within the channel protein, supporting a refined helical screw mechanism.
- The findings provide critical insights into the molecular basis of voltage sensing in ion channels.
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