Proton-mediated conformational changes in an acid-sensing ion channel

Area of Science:

• Molecular biology
• Neuroscience
• Biophysics

Background:

• Acid-sensing ion channels (ASICs) are proton-gated ion channels.
• ASICs are involved in pain perception, neuronal signaling, and stroke pathology.
• Understanding ASIC gating mechanisms is vital for therapeutic development.

Purpose of the Study:

• To investigate the conformational changes in ASICs upon proton binding.
• To identify the specific amino acid residues critical for proton sensing and channel activation.

Main Methods:

• Luminescence resonance energy transfer (LRET) to detect conformational changes.
• Site-directed mutagenesis to alter specific amino acid residues (Asp-238, Glu-239, Asp-260).
• Electrophysiology to assess channel function and proton sensitivity (EC50).

Main Results:

• Proton binding induces a conformational change in the extracellular domain of ASICs, increasing LRET efficiency.
• Mutating key acidic residues (Asp-238, Glu-239, Asp-260) abolished or significantly altered proton-induced conformational changes.
• Mutations progressively reduced proton sensitivity, with a triple mutant showing no response despite surface expression.

Conclusions:

• Specific carboxylate residues in the finger domain are essential for proton detection.
• Proton-induced conformational changes in the extracellular domain are critical for ASIC activation.
• These findings elucidate the molecular mechanism of ASIC gating and proton sensing.