Oral Presentation: 20 minutes 11th Asia-Pacific Congress of the International Society on Toxinology 2021

The isolated chicken ASIC1a thumb domain (ATD-c1a) retains the structure and ligand binding properties of the full length ASIC1a (#5)

Biswa Prasanna Mishra 1 , Elena-Laura Budusan 2 , Ben Cristofori-Armstrong 1 , Xinying Jia 1 , Yanni Chin 1 , Lachlan Rash 2 , Mehdi Mobli 1
  1. Centre for Advanced Imaging, The University of Queensland, St Lucia, QLD, Australia
  2. School of Biomedical Sciences, The University of Queensland, St Lucia, QLD, Australia

Acid-sensing ion channels (ASICs) are potential novel therapeutic targets in a range of pathologies including ischemic stroke, spinal cord injury, chronic pain, multiple sclerosis, rheumatoid arthritis, and migraine.1 Nonetheless, there are no drugs available on the market that target these channels selectively. A hurdle in the development of selective ASIC drugs is the lack of adequate and reliable structural data of these pH sensitive ion channels in their multiple conformational and protonation states. All ASIC structural data available to date are from a single isoform (1a) derived using X-ray crystallography and electron microscopy. This study proposes to study the thumb domain of the ASIC channel in isolation using solution state techniques. The ASIC thumb domain (ATD) is a cysteine-rich domain, and its two α-helices form a major part of the “acidic pocket” that collapses upon extracellular acidification.2 It is also known to be an important ligand binding domain, acting as the receptor site for four highly potent and selective venom peptide toxins PcTx1, MitTx, and mambalgins-1 and 2.3-6 Here, we present the first structure of the isolated thumb domain of the chicken ASIC1a (ATD-c1a) in solution determined by nuclear magnetic resonance (NMR) spectroscopy. Using a combination of NMR and ITC measurements, we characterise the structural and thermodynamic details of ligand binding of the ATD using endogenous and exogenous ligands. Ligand binding is performed across a range of pH values. This allows us to provide atomic resolution information on the pKa of protonatable residues, identifying residues that are important for the pH sensitivity of ligand binding. This information will help researchers screen for, design and optimise ASIC modulators as novel therapeutic lead compounds.

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