Extended Data Figure 2: Superposition of M. musculus and human δ-OR receptor structures.

a, Comparison of the human BRIL–δOR(ΔN/ΔC)–naltrindole structure (green) with the previously determined 3.4 Å crystal structure of the M. musculus δOR-T4L (magenta; PDB 4EJ4). The ligand naltrindole in the BRIL–δOR(ΔN/ΔC)–naltrindole structure is shown as orange spheres and is omitted in the 4EJ4 structure. Water molecules and the sodium ion in the allosteric site of the BRIL–δOR(ΔN/ΔC)–naltrindole structure are shown as red and blue spheres, respectively. The grey box represents the approximate regions of the receptor 7TM domain embedded in the lipidic bilayer; yellow sticks represent lipids. ICL3 fusion protein in 4EJ4 (T4L) and N-terminal BRIL fusion protein in BRIL–δOR(ΔN/ΔC)–naltrindole structures are omitted. b, ECL3 conformation of human δ-OR and comparison with mouse δOR–T4L ECL3 structure. BRIL–δOR(ΔN/ΔC)–naltrindole is shown as green cartoon and side chains are depicted as green sticks. The ligand naltrindole is represented by orange carbon sticks and transparent spheres (BRIL–δOR(ΔN/ΔC)–naltrindole structure) and magenta carbon sticks (4EJ4 structure).