Fig. (1).

Allosteric GPCR models. A) The simple allosteric ternary complex model (ATCM), which describes the interaction between an orthosteric ligand, A, and allosteric modulator, B, in terms of their equilibrium dissociation constants (K_A, K_B) and the cooperativity factor, α, which describes the magnitude and direction of the allosteric effect on ligand binding affinity. B) The allosteric two state model (ATSM), which describes allosteric modulator effects on affinity, efficacy and the distribution of the receptor between active (R*) and inactive (R) states, in terms of distinct conformations selected by ligands according to their cooperativity factors for the different states.