Voltage sensing in jellyfish Shaker K+ channels

Area of Science:

• * Ion channel biophysics
• * Molecular and cellular neuroscience
• * Marine invertebrate physiology

Background:

• * Shaker channels are voltage-gated potassium channels crucial for neuronal excitability.
• * The S4 segment's positive charges are critical for voltage sensing.
• * Jellyfish Shaker channels (jShak1, jShak2) exhibit unique S4 charge configurations and shifted activation/inactivation curves.

Purpose of the Study:

• * To investigate the role of S4 segment charge distribution in jellyfish Shaker channel gating.
• * To determine if the total charge or specific charge placement influences voltage activation and inactivation.
• * To identify key residues within the S4 segment that modulate channel function.

Main Methods:

• * Site-directed mutagenesis of the S4 segment in jellyfish Shaker channels (jShak1).
• * Electrophysiological recordings (two-electrode voltage clamp) to measure channel activation and inactivation kinetics.
• * Analysis of charge addition/removal effects on voltage-dependent gating parameters.

Main Results:

• * Mutating the N-terminal side of jShak1 S4 with an RIF motif caused a large positive shift in activation and inactivation without changing the slope.
• * Adding an IFR motif to the C-terminal side of K294 resulted in a small negative shift and prevented fast inactivation.
• * The residue K294 acts as a functional boundary within the S4 segment, separating distinct gating roles.

Conclusions:

• * The precise location of charges within the S4 segment, particularly around K294, is more critical than the total S4 charge for determining voltage thresholds.
• * K294 divides the S4 segment into functionally distinct regions influencing both activation and inactivation.
• * These findings refine our understanding of voltage-gated ion channel gating mechanisms and evolutionary divergence.