Pore mutations alter closing and opening kinetics in Shaker K+ channels

Area of Science:

• Molecular Biology
• Biophysics
• Ion Channel Physiology

Background:

• Potassium (K+) channels are crucial for cellular electrical signaling.
• Shaker B K+ channels are extensively studied models for K+ channel function.
• Channel gating, including opening and closing, is modulated by pore structure and ion concentration.

Purpose of the Study:

• To investigate the impact of specific amino acid mutations in the Shaker B K+ channel pore on gating kinetics.
• To determine how extracellular potassium concentration ([K+]) influences channel closing and C-type inactivation.
• To elucidate the relationship between pore structure, ion occupancy, and channel gating mechanisms.

Main Methods:

• Site-directed mutagenesis of Shaker B K+ channel pore residues (positions 447 and 449).
• Transient expression of wild-type and mutant channels in Chinese hamster ovary (CHO) cells.
• Electrophysiological recordings to measure channel closing, C-type inactivation, and current-voltage relationships under varying extracellular [K+].

Main Results:

• Mutation D447E accelerated closing and C-type inactivation, effects reversed by elevated extracellular [K+], suggesting uniform K+ ion competition.
• Mutant T449K exhibited K+-dependent fast C-type inactivation but slower, [K+]-insensitive closing, indicating non-uniform K+ ion occupancy in the pore.
• Mutations affected channel opening kinetics, often coupled to C-type inactivation, and demonstrated that pore structure influences multiple gating parameters.

Conclusions:

• Channel pore structure significantly influences K+ channel closing and inactivation kinetics.
• Differential effects of mutations and extracellular [K+] suggest distinct molecular domains for closing and C-type inactivation gates.
• These findings provide deeper understanding of how ionic environment and pore architecture modulate K+ channel function.