Dynorphin Neuropeptides Decrease Apparent Proton Affinity of ASIC1a by Occluding the Acidic Pocket.

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Prolonged acidosis, common in ischemic stroke, causes neuronal death by activating acid-sensing ion channel 1a (ASIC1a).
• Acidosis also desensitizes ASIC1a, making modulators of its acid sensitivity critical for understanding stroke pathophysiology.
• The opioid neuropeptide big dynorphin (Big Dyn) enhances ASIC1a activity during acidosis, but the molecular details of this interaction are unknown.

Purpose of the Study:

• To elucidate the molecular determinants and dynamics of the interaction between big dynorphin (Big Dyn) and acid-sensing ion channel 1a (ASIC1a).
• To understand how Big Dyn binding affects ASIC1a function and proton sensitivity.

Main Methods:

• Computational molecular modeling to visualize Big Dyn interaction with ASIC1a.
• Experimental validation of electrostatic forces driving the interaction.
• Utilizing noncanonical amino acids as photo-cross-linkers to identify ASIC1a binding residues.
• Covalent tethering of Big Dyn to ASIC1a to assess functional consequences.

Main Results:

• A molecular model revealed Big Dyn insertion into ASIC1a's acidic pocket.
• Electrostatic forces were confirmed as the primary drivers of the Big Dyn-ASIC1a interaction.
• Sixteen ASIC1a residues were identified as crucial for Big Dyn binding.
• Covalently linking Big Dyn to ASIC1a significantly reduced channel proton sensitivity.

Conclusions:

• Big dynorphin (Big Dyn) interacts with acid-sensing ion channel 1a (ASIC1a) via electrostatic forces, with specific residues mediating binding.
• Big Dyn binding stabilizes ASIC1a in a resting conformation, decreasing its sensitivity to protons.
• This interaction suggests a novel mechanism by which neuropeptides modulate ion channel activity in neurological conditions like stroke.