Ligand-directed Labeling of Opioid Receptors for Covalent Attachment of Fluorophores or Small-Molecule Probes.

This protocol describes endogenous labeling of opioid receptors (ORs) using a ligand-directed reagent, naltrexamine-acylimidazole compounds (NAI-X). NAI acts by guiding and permanently tagging a small-molecule reporter (X)-such as fluorophores or biotin-to ORs. Here we detail syntheses and uses of NAI-X for OR visualization and functional studies. The NAI-X compounds overcome long-standing challenges in mapping and tracking endogenous ORs as the label-ing can be done in situ with live tissues or cultured cells.For complete details on the use and execution of this protocol, please refer to Arttamangkul et al.1, 2