Protonation controls ASIC1a activity via coordinated movements in multiple domains

Area of Science:

• Neuroscience
• Molecular Biology
• Biophysics

Background:

• Acid-sensing ion channels (ASICs) are crucial for neuronal function, mediating responses to changes in pH.
• ASICs are involved in pain, fear, and neurodegeneration, making them therapeutic targets.
• The precise mechanisms by which protonation controls ASIC activity remain largely unknown.

Purpose of the Study:

• To investigate the conformational changes in ASIC1a subunits upon extracellular acidification.
• To elucidate the role of specific residues and domains in ASIC gating and desensitization.
• To provide insights for the rational design of ASIC-targeting drugs.

Main Methods:

• Voltage-clamp fluorometry was employed to monitor real-time conformational changes in ASIC1a.
• Fluorophores were attached to residues in different domains of ASIC1a to detect protonation-induced movements.
• Comparison of fluorescence signals with ionic currents identified key residues and their movements during channel activity.

Main Results:

• Specific movements preceding desensitization were identified, potentially linked to channel opening.
• Other movements were closely associated with desensitization and recovery processes.
• The finger domain was observed to move away from the β-ball domain upon channel activation, as evidenced by fluorescence quenching changes.

Conclusions:

• Protonation triggers a sequence of interdependent conformational changes in ASICs.
• These movements directly influence channel gating, desensitization, and recovery.
• Understanding these dynamic structural changes is vital for developing targeted ASIC therapies.