Figure 5.

Three-dimensional structure of the agonist (adrenalin, epinephrine) bound active form of the β₂-adrenergic receptor (a type Aα GPCR). The structure [PDB ID 4LDO (Ring et al., 2013)] is shown from two different perspectives (the one on the right being a 90° rotated and somewhat enlarged view from the top). The receptor is covered with a semi-transparent gray surface and the secondary protein structure indicated; the ligand is highlighted as a darker solid CPK structure. The ligand is somewhat faded as it is buried inside the receptor and obscured by the covering semitransparent surface; this is intended to illustrate that this position is not accessible for direct binding from outside.