Figure 7. CALP binds the C-terminus of CFTR with very low affinity.

(A) Direct binding analysis of a high affinity reporter: Fluorescence anisotropy was determined following titration of 30 nM F*C-SSR5₁₀ reporter peptide with increasing concentrations of CALP (diamonds) or CALP-D mutant (circles). Curve fitting (solid line) yields an estimate for K_d = 4.37 ± 0.31 μM. (B) Competition binding analysis: Fluorescence anisotropy data were obtained for 30 nM F*C-SSR5₁₀ and 5 μM CALP (~ 1 × K_d) incubated with increasing concentrations of either unlabeled C-SSR5₁₀ (filled diamonds, K_i = 37.6 ± 4.0 μM) or unlabeled C-CFTR₁₀ (open diamonds, K_i = 690 ± 120 μM). Fits are shown as solid lines. Values shown are mean ± SD, n=3.