Allosteric modulators interact with sites on the receptor different from the primary agonist binding site. This results in modulation of the conformation of the agonist binding site to impart higher (allosteric enhancers) or lower (allosteric inhibitors) affinity for the agonist. Some allosteric modulators are able to induce an active conformation of the receptor primary binding site to result in receptor activation in the absence of an agonist.
Three Classes of Allosteric Modulators:
- Allosteric Agonists: agonist by itself in absence of any other agonist
- Allosteric Enhancer (Agonist): enhances (potentiates) agonist biological response
- Allosteric Inhibitors (Antagonist): inhibits agonist biological response
As you can see in this image, allosteric modulators bind to an area/domain on the receptor that is topographically DISTINCT from the PRIMARY AGONIST BINDING SITE. Binding to this area results in modifications to the conformation of the primary site to either make it more or less favorable to bind the agonist (increase or decrease agonist affinity, respectively). This causes enhancement or dampening of agonist response.