Figure 3. Effect of TnC mutations on TnI_128–180 binding affinity of TnC.

Figure shows the effect of TnC mutations on the TnI_128–180 binding properties of the Ca²⁺ saturated TnC. The concentration of TnC or its mutants was at 0.15 µM. The TnI_128–180 dependent changes in IAANS fluorescence are shown as a function of [TnI_128–180] for Ca²⁺ saturated ${\text{TnC}}_{\text{IAANS}}^{\mathrm{T}53\mathrm{C}}$ (black ■), $\mathrm{F}20{\text{QTnC}}_{\text{IAANS}}^{\mathrm{T}53\mathrm{C}}$ (blue ○), $\mathrm{V}44{\text{QTnC}}_{\text{IAANS}}^{\mathrm{T}53\mathrm{C}}$ (brown ●), $\mathrm{M}45{\text{QQTnC}}_{\text{IAANS}}^{\mathrm{T}53\mathrm{C}}$ (cyan ▲), $\mathrm{L}48{\text{QTnC}}_{\text{IAANS}}^{\mathrm{T}53\mathrm{C}}$ (red □) and $\mathrm{M}81{\text{QTnC}}_{\text{IAANS}}^{\mathrm{T}53\mathrm{C}}$ (green △). 100% IAANS fluorescence corresponds to the Ca²⁺ -saturated state, whereas 0% corresponds to the Ca²⁺-InI_128–180 saturated state for each individual TnC protein. In the case of $\mathrm{V}44{\text{QTnC}}_{\text{IAANS}}^{\mathrm{T}53\mathrm{C}}$, the IAANS fluorescence increased upon addition of TnI_128–180, so the plot of the data was inverted for comparison purposes. Each data point represents the mean ± S.E. of three to six titrations fit to the root of quadratic equation for binary complex formation.