Structural plasticity of the selectivity filter in a nonselective ion channel

Area of Science:

• Biophysics
• Structural Biology
• Molecular Biology

Background:

• The sodium potassium (NaK) ion channel is a nonselective channel facilitating sodium and potassium ion transport across cell membranes.
• Understanding the structural basis of ion selectivity and conduction in NaK channels is vital for cellular physiology.

Purpose of the Study:

• To elucidate the structural and dynamic mechanisms underlying ion conduction in the NaK channel.
• To investigate the role of the selectivity filter and inner helix in NaK channel function.

Main Methods:

• X-ray crystallography to determine high-resolution structures of the NaK channel.
• Nuclear Magnetic Resonance (NMR) spectroscopy to study channel dynamics.
• Molecular dynamics (MD) simulations to complement structural and dynamic data.

Main Results:

• A novel crystallographic structure revealed conformational differences in the NaK channel's selectivity filter and inner helix.
• A unique side-entry pathway for Na+ permeation, specific to NaK, was identified.
• NMR and MD simulations confirmed the dynamic nature of the selectivity filter and inner helix.

Conclusions:

• The structural plasticity of the selectivity filter and the dynamics of the inner helix are essential for the efficient conduction of diverse ions through the NaK channel.
• These findings provide critical insights into the molecular mechanisms of nonselective ion channel function.