Structural basis for the coupling between activation and inactivation gates in K(+) channels

Area of Science:

• Biophysics
• Structural Biology
• Molecular Physiology

Background:

• Potassium (K(+)) channels are crucial for cellular electrical signaling.
• Coupled activation and inactivation gating are key functional properties of K(+) channels.
• Previous studies demonstrated coupling via ion effects and cysteine accessibility.

Purpose of the Study:

• To elucidate the structural mechanisms linking K(+) channel activation and inactivation.
• To identify the specific residues and movements responsible for triggering inactivation.
• To investigate the role of Phe 103 in KcsA channel gating.

Main Methods:

• Analysis of multiple KcsA crystal structures in various open states.
• Molecular dynamics simulations to calculate interaction energies.
• Site-directed mutagenesis (F103A, F103C, F103W) to assess functional effects.
• Comparison with Shaker K(+) channel mutant (I470A).

Main Results:

• Inner bundle gate movements, specifically TM2 helix rotation, cause Phe 103 to tilt.
• Phe 103 tilting destabilizes the selectivity filter via interactions with pore-helix and neighboring residues.
• Mutations at position 103 show size-dependent effects on inactivation kinetics.
• Molecular dynamics confirm favorable interactions between Phe 103 and surrounding residues in the open state.

Conclusions:

• Phe 103 side-chain rearrangements mechanically couple activation and inactivation in KcsA.
• This mechanism likely extends to other K(+) channel families.
• Allosteric coupling relies on mechanical deformation propagated through steric contacts.