Calcium-gated potassium channel blockade via membrane-facing fenestrations

Area of Science:

• Biophysics
• Structural Biology
• Molecular Pharmacology

Background:

• Large-conductance calcium-activated (BK) channels are crucial ion channels implicated in various physiological processes.
• Quaternary ammonium blockers are known to inhibit BK and MthK channels in both open and closed states.
• Previous models assumed blocker entry via the intracellular entryway, posing challenges for understanding closed-state channel block.

Purpose of the Study:

• To investigate alternative pathways for quaternary ammonium blocker access into closed potassium channels.
• To determine the role of membrane-facing fenestrations in blocker binding to BK and MthK channels.
• To explore novel strategies for selective drug targeting of BK channels.

Main Methods:

• Utilized atomistic free energy simulations to model blocker-channel interactions.
• Investigated a mutant MthK channel with narrowed fenestrations.
• Compared blocker sensitivity between wild-type and mutant channels.

Main Results:

• Demonstrated that intracellular blockers access the MthK channel pore through membrane-facing fenestrations.
• Showed that a mutant channel with narrower fenestrations exhibited no closed-state block by TPeA.
• Identified similar fenestrations in apo BK channels, suggesting a conserved access pathway.

Conclusions:

• Membrane fenestrations serve as a non-canonical pathway for blocker access into closed potassium channels.
• This finding challenges previous assumptions about blocker entry mechanisms.
• The fenestration pathway provides a novel target for developing selective drugs for BK channels.