Fig. 1.

Locations of ¹⁹F-NMR labels in β₂AR and activation-related changes in GPCR crystal structures. (A) Side view of β₂AR in the active G protein-bound form (PDB ID 3SN6, shown in green). The trans-membrane helices I to VII and the C-terminal helix VIII are identified. The full agonist BI-167107 in the ligand-binding site is shown as a stick diagram. Green and yellow spheres highlight the three cysteine residues used for TET labeling, i.e., Cys265^6.27 and Cys327^7.54 at the cytoplasmic ends of helices VI and VII, respectively and Cys341 at the C-terminus. The bound G-protein heterotrimer is shown as red ribbons and surfaces. (B) Cytoplasmic view of the structure in (A), with the G-protein contact sites outlined by a broken red line. (C) Plot of distance root mean square deviations (RMSD) of individual residues between crystal structures of inactive and active-states of three GPCRs. Crystal structures used (from top to bottom): β₂AR (PDB IDs 2RH1 vs. 3SN6), rhodopsin (PDB IDs 1GZM vs. 3DQB), A_2A adenosine receptor (A_2AAR; PDB IDs 3EML vs. 3QAK). The horizontal axes represent the amino acid sequences (β₂AR residues 34–341, bovine rhodopsin residues 38–320, A_2AAR residues 6–302). The vertical axis shows all-heavy-atom RMSDs per residue, while the color code defined in the upper right corner of the panel indicates corresponding C^α deviations. For each protein, selected residues are identified (see text). The locations of the helices I to VIII are indicated at the top. Periplasmic loop regions are highlighted in red, while cytoplasmic loops and helix VIII are highlighted in blue. The cytoplasmic ends of helices VI and VII, which contain Cys265^6.27 and Cys327^7.54, are “hot spots” with large conformational rearrangements between the crystal structures of inactive and active states; other transmembrane helices and intracellular helix VIII, which includes Cys341, show only small displacements.