Abstract

Cebranopadol is a first-in-class analgesic that combines agonism at the μ-opioid receptor (μOR) and the nociceptin/orphanin FQ receptor (NOPR), an approach proposed to improve the therapeutic index of opioid analgesia. Although Cebranopadol is highly potent at both μOR and NOPR, the structural basis by which a single small molecule productively engages these two opioid-family receptors has remained unclear. Here, we report cryo-electron microscopy structures of Cebranopadol bound to human μOR–G i and NOPR–G i complexes at 2.95 Å and 2.74 Å resolution, respectively. In both receptors, Cebranopadol adopts a conserved orthosteric recognition mode anchored by the canonical D 3.32 –tertiary amine interaction, whereas local differences in the extracellular pocket shift ligand position to accommodate receptor-specific microenvironments. Combined with functional mutagenesis and molecular dynamics simulations across the opioid receptor family, these structures identify nonconserved pocket features at positions 2.63 and 7.35 that contribute to potency and selectivity by modulating fluorophenyl-directed interactions and hydrophobic packing around the spiroindole moiety. Together, these findings define a structural framework for understanding the dual agonism of Cebranopadol at μOR and NOPR and provide a working model for improving selectivity over δOR and κOR while preserving the desired dual-target pharmacology.