FIGURE 5.

Thermodynamic contributions to RGS14 GoLoco motif binding by WT and Gα_i1^Q147L subunits as determined by ITC. 30 μm solutions of each indicated Gα_i1 subunit were separately titrated with repeated additions of 350 μm RGS14 GoLoco motif peptide. Calorimetric traces of heat released and enthalpic binding curves (insets) fitted with a one-site binding model are shown for Gα_i1^WT (A) and Gα_i1^Q147L (B). The stoichiometry of binding was ∼1:1 in all experiments (three independent titrations were performed for each protein). C, average values and 95% confidence intervals for enthalpy of binding (ΔH) are given for the triplicate titration experiments (p = 0.006). Gibbs free energy (ΔG) is calculated from FP binding affinity measurements, and entropy of binding is derived by ΔS = (ΔH − ΔG)/T.