Cooperativity decreases with the expression level of CheA.

(A,B) Model fit (A) and FRET data [12] (B) for different expression levels of CheA at 8 (red), 0.3 (orange) and 0.25 (yellow) times native level [A]0. (C) Hill curves were fitted to the model outcome to allow for comparison with experimental results. Hill coefficient pairs (model/experiment) in order of increasing [A] are (5.5/5.0), (5.5/5.0) and (3.4/2.0). (D) The corresponding Hill amplitudes in order of increasing [A] are (0.023/0.022), (0.026/0.026) and (0.030/0.031). (E) Distribution of complex types present at half-maximum ligand concentration for 8 (red) and 0.25 (yellow) times native concentration [A]0. Model parameters: Δϵ(QEQE) = −2.42, , , ρ = 3.13, , , and J = −3.81. Parameters are shared with model for variation in [W] (Fig 4).