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. 2018 Jun 21;175(21):4036–4046. doi: 10.1111/bph.14337

Figure 2.

Figure 2

Allosteric ligands bind to a topographically distinct receptor site to orthosteric ligands. The phenomenon of topographically distinct binding of orthosteric and allosteric ligands has been directly demonstrated for Family A GPCRs. For example, http://www.guidetopharmacology.org/GRAC/ObjectDisplayForward?objectId=14 crystal structures clearly show that the orthosteric antagonist, http://www.guidetopharmacology.org/GRAC/LigandDisplayForward?ligandId=3260 (QNB; yellow; PDB ID 3UON), and the orthosteric agonist, http://www.guidetopharmacology.org/GRAC/LigandDisplayForward?ligandId=6937 (cyan; PDB ID 4MQS), bind overlapping binding sites, whereas the PAM, http://www.guidetopharmacology.org/GRAC/LigandDisplayForward?ligandId=6938 (green; PDB ID 4MQT), recognizes a spatially discrete binding site within the extracellular vestibule. Top panel: side view; Bottom panel: top view.