Structural rearrangements underlying ligand-gating in Kir channels

Area of Science:

• Molecular biology
• Biophysics
• Structural biology

Background:

• Inward rectifier potassium (Kir) channels are crucial ion transporters regulated by various ligands.
• The precise molecular mechanisms and structural details of Kir channel gating remain incompletely understood.
• Ligand binding to Kir channels converges on a common gating mechanism, but its structural basis is unclear.

Purpose of the Study:

• To elucidate the molecular motions and structural rearrangements underlying ligand-induced gating in Kir channels.
• To investigate the gating mechanism of KirBac1.1 channels using biophysical techniques.
• To develop a general molecular model for Kir channel gating.

Main Methods:

• Utilized small molecule fluorescent probes attached to introduced cysteines in KirBac1.1 channels.
• Employed fluorescence resonance energy transfer (FRET) between probes attached to KirBac1.1 tetramers.
• Analyzed probe accessibility to map the inner cavity and conformational changes.

Main Results:

• Identified a significant barrier to fluorophore entry into the inner cavity of KirBac1.1 channels.
• Observed tilting and rotational motions of cytoplasmic domain secondary structures during channel closure.
• Demonstrated that phosphatidylinositol-4,5-bisphosphate binding induces channel closure via conformational changes.
• Linked ligand binding to a narrowing of the cytoplasmic vestibule.

Conclusions:

• The study provides direct visualization of molecular motions during Kir channel gating.
• A general model for ligand-induced Kir channel gating is proposed, involving conformational changes in the cytoplasmic domain.
• These findings offer insights into the structure-function relationship of Kir channels and their regulation.