Evolutionarily conserved intracellular gate of voltage-dependent sodium channels

Area of Science:

• Molecular Biology
• Biophysics
• Neuroscience

Background:

• Voltage-gated ion channels (VGICs) control ion flow and electrical signaling in cells.
• The precise location of the gate in voltage-gated sodium channels is currently unknown.
• Understanding VGIC gating mechanisms is crucial for cellular electrophysiology.

Purpose of the Study:

• To determine the location of the pore gate in voltage-gated sodium channels.
• To investigate the role of the S6 helix in domain IV in channel gating.
• To explore conserved gating mechanisms within the VGIC superfamily.

Main Methods:

• Chemical modification of introduced cysteines along the S6 helix of domain IV.
• Utilizing an inactivation-removed sodium channel background.
• Assessing state-dependent accessibility of cysteines to charged thiol reagents.

Main Results:

• An S6 hydrophobic residue acts as a boundary for state-dependent accessibility.
• Cysteines above this residue are inaccessible to charged reagents in the closed state.
• Observed accessibility patterns align with structural data from prokaryotic sodium channels.

Conclusions:

• The intracellular S6 helix forms a hydrophobic gate regulating sodium channel pore access.
• This intracellular gate is a conserved feature among canonical VGIC superfamily members.
• The findings resolve the long-standing question of the sodium channel gate location.