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The operational model of allosteric modulation of pharmacological agonism

The operational model of allosteric modulation of pharmacological agonism The cubic ternary complex model of allosteric modulation of receptor activation. Inactive, R, and active, R*, states of the receptor, K<sub>ACT</sub> receptor activation constant, K<sub>A,/sub> and K<sub>B</sub> affinities.

Proper determination of agonist efficacy is indispensable in the evaluation of agonist selectivity and bias to activation of specific signalling pathways. The operational model of pharmacological agonism is a useful means for achieving this goal.

Monod et al. (1963) originally introduced the concept of allosterism. Since then the concept of allosterism extended to many various fields of research spanning from DNA expression via metabolism to ion channels and G-protein coupled receptors. Allosteric ligands bind to a site that is distinct from the orthosteric site on a receptor. An orthosteric and allosteric ligand can bind to the receptor concurrently and form a ternary complex where they reciprocally modulate the binding affinity of each other. Moreover, the binding of an allosteric modulator may also affect the efficacy of an orthosteric agonist in eliciting a functional response.

Allosteric modulators are an intensively studied group of receptor ligands because of their selectivity and preservation of physiological space-time pattern of the signals they modulate. We analysed the operational model of allosterically-modulated agonism (OMAM) including modulation by allosteric agonists. Several parameters of OMAM are inter-dependent. We derived equations describing mutual relationships among parameters of the functional response and OMAM. We present a workflow for the robust fitting of OMAM to experimental data using derived equations.