Fig. 4.

Serial engagement of the last kinase can greatly influence signal output in a MAPK cascade. We consider the scenario where the first two kinases, A and B (MAP3K, MAP2K) bind tightly (E₂ = 20) and the binding affinity C (MAPK) is varied as follows: weak (E₂ = 4), intermediate (E₂ = 8), and strong (E₂ = 20) disassociation energies. The ordinate represents the fraction of activated C (MAPK) proteins (a measure of signal output), and the abscissa is the scaled strength of signal, σ, σ ≡ [S*]/[A]₀. The signal output is largest when kinase C (MAPK) is allowed to rapidly disassociate (E₂ = 4) from the scaffold. Data presented are for a 1:1:10:1 ratio of A/B/C/scaffolds.