Structural and Functional Basis of Antinociceptive Action of Χ-Conotoxin AoIA at the Noradrenaline Transporter

The χ-conotoxins are venom-derived peptides that specifically target the noradrenaline transporter (also known as norepinephrine transporter, NET). Regulation of noradrenergic signaling by NET affects neurophysiological processes, including pain. Therefore, the χ-conotoxin MrIA and its synthetic analogs have been previously investigated for their analgesic activity. Here we describe the synthesis and pharmacological characterization of χ-AoIA, a peptide that selectively inhibits NET with a higher potency compared to MrIA in in vitro radiotracer flux assays. Furthermore, we resolved the structure of the human NET:χ-AoIA complex by cryogenic electron microscopy, which revealed an atypical binding mode consisting of both the central binding site and the outer vestibule of the transporter. Lastly, χ-AoIA displays antinociceptive efficacy in a model of inflammatory pain after subcutaneous administration in mice. Our results demonstrate the efficacy of χ-AoIA as a highly selective ligand of NET and provide a mechanistic basis for its potential development as a nonopioid analgesic.