Big Dynorphin and ASIC1a: How a Neuropeptide Triggers Pain Signals

Summary: Researchers at the University of Copenhagen have mapped how the neuropeptide Big Dynorphin binds to the acid-sensing ion channel receptor ASIC1a, revealing a molecular interaction that promotes pain signaling.

Source: University of Copenhagen

Fast communication between brain cells — neurotransmission — is essential for normal brain function. Neuropeptides, small protein-like messengers produced in the brain, are important modulators of neurotransmission, and some play key roles in pain signalling.

A new study from the University of Copenhagen identifies precisely how the neuropeptide Big Dynorphin interacts with the Acid-Sensing Ion Channel 1a (ASIC1a), a receptor known to contribute to pain transmission. The team mapped the binding site and mechanism by which Big Dynorphin alters the receptor’s conformation and activity, findings that could inform the development of new analgesics that act on this receptor.

Professor Stephan Pless of the Department of Drug Design and Pharmacology explains that Big Dynorphin is the most potent endogenous regulator of this receptor discovered so far. He notes that current painkillers target different receptor systems, and that a drug designed to interfere with Big Dynorphin–ASIC1a interactions might offer a novel therapeutic avenue with the potential to avoid some adverse effects associated with opioid treatments.

Relevance for inflammation and chronic pain

The study, published in PNAS, examines the interaction between Big Dynorphin and ASIC1a using a multi-disciplinary approach. Because both ASIC1a and Big Dynorphin are upregulated in conditions of inflammation and chronic pain, understanding how they interact is directly relevant to disease mechanisms and therapeutic strategies.

Using electrophysiology, voltage-clamp fluorometry, genetically encoded cross-linkers, synthetic Big Dynorphin analogs, noncanonical amino-acid-mediated photocrosslinking, and CRISPR-based manipulations, the researchers trapped and characterized receptor–peptide interactions that normally occur on very rapid timescales. These complementary methods allowed the team to determine how Big Dynorphin binds and how that binding shifts the receptor’s functional state.

Co-first author Dr. Nina Braun highlights that both the receptor and Big Dynorphin are present at higher levels in patients with inflammation and chronic pain than under normal conditions. This upregulation suggests a plausible link between increased Big Dynorphin–ASIC1a activity and heightened or prolonged pain, and it underscores the potential therapeutic importance of targeting this interaction.

Mechanism and site of action

The authors demonstrate that Big Dynorphin stabilizes ASIC1a in a closed resting conformation that differs from the open and desensitized states produced by protons. Analyses using alanine-substituted Big Dynorphin analogs indicate that the peptide’s modulation of ASIC1a depends largely on electrostatic interactions involving basic amino acids in Big Dynorphin’s N-terminal region. Complementary experiments showed that neutralizing acidic residues in the ASIC1a extracellular domain reduces the peptide’s effects, pointing to the acidic pocket as the binding site.

Photocrosslinking with a noncanonical amino acid, azidophenylalanine, provided direct evidence that the acidic pocket on ASIC1a is the locus of Big Dynorphin binding. Together, these findings define both the molecular mechanism by which Big Dynorphin modulates ASIC1a and the precise site of action on the receptor, highlighting the acidic pocket as a candidate target for drug development.

Therapeutic potential and next steps

Previous animal studies indicate that genetic deletion or inhibition of ASIC1a can reduce pain responses in mouse models, which supports the therapeutic promise of targeting this channel. The University of Copenhagen team plans to exploit the mechanistic insight from this study to screen and design compounds that can modulate the Big Dynorphin–ASIC1a interaction. Their goal is to identify molecules that reduce pain signaling in vulnerable patient groups without producing typical opioid side effects.

Source:
University of Copenhagen
Media contacts:
Stephan Pless – University of Copenhagen
Image source:
The image is in the public domain.

Original research (closed access):
“Mechanism and site of action of big dynorphin on ASIC1a”. Stephan Pless et al. PNAS. DOI: 10.1073/pnas.1919323117.

Abstract (summary):
Acid-sensing ion channels (ASICs) are proton-gated cation channels that contribute to neurotransmission and the initiation of pain, and they can mediate neuronal damage after ischemic stroke. The opioid neuropeptide Big Dynorphin is the most potent endogenous ASIC modulator identified and is upregulated in chronic pain, where it increases ASIC-mediated neuronal death during acidosis. Using electrophysiology, voltage-clamp fluorometry, synthetic peptide analogs, and photocrosslinking, the study defines how Big Dynorphin binds to and stabilizes ASIC1a in a distinct closed state, maps key electrostatic interactions, and locates the binding site to the acidic pocket — a promising target for the development of ASIC-targeting therapeutics aimed at pain and ischemic injury.