Structural basis of human Na_v1.5 gating mechanisms.

Area of Science:

• Cardiovascular Biology
• Structural Biology
• Ion Channel Biophysics

Background:

• Voltage-gated sodium channels, specifically Na_v1.5, are crucial for cardiac action potential generation and propagation.
• Dysfunction of Na_v1.5 channels is implicated in various cardiac diseases, including arrhythmias and heart failure.
• Limited structural information on intracellular regions of Na_v1.5 has hindered understanding of its gating mechanisms.

Purpose of the Study:

• To elucidate the structural basis of Na_v1.5 channel gating by determining high-resolution structures.
• To investigate the role of intracellular regions, particularly the C-terminal domain (CTD) and III-IV linker, in channel function.
• To correlate structural findings with functional electrophysiological data to understand disease mechanisms.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to obtain structures of human Na_v1.5 in open states.
• Molecular dynamics (MD) simulations to analyze ion conduction and structural stability.
• Electrophysiological studies to assess the functional impact of structural modifications.

Main Results:

• Two cryo-EM structures of human Na_v1.5 in open states revealed sequential conformational changes in voltage-sensing domains (VSDs) and intracellular regions.
• Structures showed repositioning, not dislodging, of the IFM motif in the open state; MD simulations confirmed Na⁺ ion conduction through the CTD.
• A dynamic interaction between the CTD and the III-IV linker was identified, regulating VSD conformation and pore opening.

Conclusions:

• The study provides unprecedented structural insights into the gating mechanisms of Na_v1.5 channels.
• The identified CTD-III-IV linker interaction is a key regulator of Na_v1.5 channel gating and fast inactivation.
• These findings lay the groundwork for understanding Na_v1.5 channelopathies and developing targeted therapies.