FIG 7.

Intrinsic tryptophan fluorescence assay for binding affinity between Cpc7 and CheY7. The fluorescence spectrum for purified epitope-tagged Cpc7 (0.5 μM) was obtained (see Materials and Methods). CheY7^WT (▼) or CheY7^F107A (●) was titrated in and spectra were normalized to a buffer control. The change in fluorescence is reported as relative fluorescence over the concentration of ligand. The fitted curve for CheY7^WT was calculated using nonlinear regression to reveal a K_d of 0.30 ± 0.05 μM. Each titration was done in triplicate and a representative experiment is presented.