Fig. 4
Switchable binding modulators can implement various response behaviors. The physiochemical properties of a modulator protein are controlled by the cooperativity α and the relative affinity of the two allosteric sites for their respective ligands β. In the cartoons, the regulator binding site is indicated by the open triangle, the signal binding site by the open square. Panels A–F show dose-response curves for the six different allosteric binding modulator proteins schematically depicted in the respective cartoons. Note, that α = 1 denotes a modulator molecule without cooperativity and thus it does not function as a signaling receptor (no response). For each receptor, a set of response curves is shown that results from varying total modulator concentration [MT] at fixed receptor concentration [RT]. Color intensity in each panel increases with stepwise increase in μ = [MT]/[RT] from 0.1, 0.32, 1, 3.2, 10. For all curves we set K1 = [RT] =1 μM. Blue lines denote inverse agonistic signaling schemes and the red lines agonistic schemes. The dotted lines indicate the shift in the EC50 as a function of μ. a α = 10, β = 0.1, b α = 0.1, β = 0.1, c α = 10, β = 1, d α = 0.1, β = 1 e α = 10, β = 10, f α = 0.1, β = 10