Electrostatic interaction between charybdotoxin and a tetrameric mutant of Shaker K(+) channels

Area of Science:

• Molecular pharmacology
• Ion channel biophysics
• Neuroscience

Background:

• Voltage-gated potassium channels are crucial for neuronal excitability.
• Scorpion toxins, like Charybdotoxin (CTX), are potent modulators of these channels.
• CTX blocks potassium channels by binding to the outer pore entrance.

Purpose of the Study:

• To investigate the pH-dependence of Charybdotoxin (CTX) block on a Shaker potassium channel.
• To elucidate the binding orientation of CTX on the channel pore.
• To understand the role of specific amino acid residues in CTX-channel interactions.

Main Methods:

• Utilized site-directed mutagenesis to introduce histidine at position 425 of the Shaker potassium channel.
• Compared pH-dependent CTX block in channels with single and quadruple histidine mutations.
• Examined CTX block with mutated toxins lacking positive charges on their active face.

Main Results:

• Protonation of a single histidine at position 425 significantly altered CTX channel affinity.
• The observed pH-dependence indicated an electrostatic environment near position 425 is basic.
• Results suggested a CTX binding orientation where three positive charges on the toxin are near three Shaker 425 positions.

Conclusions:

• A single amino acid mutation profoundly impacts CTX binding affinity, suggesting a specific toxin-channel interaction.
• The study provides insights into the precise orientation of CTX within the potassium channel pore.
• Findings contribute to understanding the molecular mechanisms of ion channel modulation by toxins.