BK channel opening involves side-chain reorientation of multiple deep-pore residues

Area of Science:

• Molecular Biology
• Biophysics
• Ion Channel Function

Background:

• The BK channel (Ca(2+)-activated, large-conductance K(+) channel) plays a crucial role in regulating cellular excitability.
• Understanding the gating mechanisms of BK channels is vital for comprehending their physiological roles.

Purpose of the Study:

• To investigate the molecular mechanisms underlying the constitutive opening of BK channels.
• To identify specific residues within the S6 pore region that influence BK channel gating.

Main Methods:

• Scanning mutagenesis was employed to probe the BK channel S6 pore.
• Site-directed mutagenesis was used to substitute key residues with all 19 other amino acids.
• Electrophysiological recordings were performed to assess channel open probability and voltage/Ca(2+) dependence.

Main Results:

• Three deep-pore residues (L312, A313, A316) were identified as critical for BK channel gating.
• Charged or polar substitutions at these sites resulted in constitutively open BK channels.
• Mutant channels exhibited high open probability at negative voltages and lost voltage and Ca(2+) dependence.

Conclusions:

• Constitutive openness of BK channels is dependent on the hydrophilicity of side chains at specific deep-pore residues.
• BK channel opening likely involves structural rearrangements in the deep-pore region.
• Conformational changes in pore residues may lead to increased exposure of side chains to the polar pore environment.