Visualizing ligand bias at the Mu-opioid receptor.

Different opioid ligands can result in biased μ-opioid signaling, differentially activating signal cascades which produce analgesia, tolerance, or adverse effects. In this issue of Cell, Xu et al. used cryo-EM and computational simulations to understand how different μ-opioid receptor selective-ligands interact with key residues to produce downstream signaling.