Figure 4. Activation of β₂AR by formoterol.

STD-filtered HMQC spectra of a, unliganded β₂AR (≈60 μM), b, the same sample bound to a saturating concentration (320 μM) of agonist (R,R)-formoterol, and c, the same sample after exchanging formoterol for inverse agonist carazolol by dialysis. d, Model of β₂AR activation by formoterol (see Supplementary Fig. 16). Colored helices, loops, and side chains represent the carazolol-bound crystal structure (PDB: 2RH1). Gray helices and white side chains indicate the active state model. Green sticks indicate (R,R)-formoterol and yellow indicates ECL2. e, Overlay of spectra corresponding to dashed regions shown in panels a-c. The spectrum of unliganded β₂AR from panel a is shown in black, agonist-bound β₂AR from panel b in green, and inverse agonist-bound β₂AR from panel c in red.