Identification of Sodium- and Chloride-Sensitive Sites in the Slack Channel

Area of Science:

• Neuroscience
• Molecular Biology
• Biophysics

Background:

• The Slack channel (KCNT1, Slo2.2) is crucial for regulating heart rate and nervous system excitability.
• Its sodium-activated and chloride-activated gating mechanisms are of significant interest, yet specific binding sites remain unidentified.

Purpose of the Study:

• To identify the specific sodium- and chloride-sensitive sites within the C-terminal domain of the rat Slack channel.
• To elucidate the molecular basis of Slack channel activation by sodium and chloride ions.

Main Methods:

• Electrophysiological recordings and systematic mutagenesis of cytosolic acidic residues in the rat Slack channel C terminus.
• Molecular dynamics (MD) simulations to predict ion-binding sites and interactions.
• Screening of predicted positively charged residues for chloride interaction.

Main Results:

• Identified E373 as a critical site that completely abolishes sodium sensitivity when mutated.
• Discovered an acidic pocket (D863/E865) also involved in sodium binding.
• Identified R379 as a specific chloride interaction site through MD simulations and mutagenesis.
• Two distinct sodium-binding sites and one chloride-binding site were pinpointed in the C-terminal domain.

Conclusions:

• The E373 site and the D863/E865 pocket are identified as key sodium-sensitive sites in the Slack channel.
• R379 is identified as a chloride interaction site, contributing to the channel's activation.
• These findings differentiate Slack channel gating from other BK channel family members and provide a foundation for future research.