TABLE 1.
Thermodynamic parameters of binding and unfolding
Thermodynamic parameters determined at To = 25 °C were obtained from global fitting of the model functions to the ITC binding data (Equation 6 and Fig. 4) and urea denaturation data (Equation 2 and Fig. 3).
| Process (i) | Parameter |
|||
|---|---|---|---|---|
| ΔGi(To)o | ΔHi(To)o | ΔCP,io | mi | |
| kcal mol−1 | kcal mol−1 | kcal mol−1K−1 | kcal mol−1m−1 | |
| CcdB binding | ||||
| GyrA12a | −11.2 (±0.2) | −8.0 (±0.2) | −0.41 (±0.05) | |
| GyrA14a | −11.8 (±0.3) | −7.3 (±0.3) | −0.42 (±0.05) | |
| GyrA59b | −14.5 (±1.5) | −11.0 (±4.4) | −0.54 (±0.60) | −1.0 (±0.3) |
| Urea unfoldingc | ||||
| GyrA59-CcdB | ||||
| Step I | 7.6 (±0.7) | 16.1 (±2.2) | 1.1 (±0.3) | 2.1 (±0.2) |
| Step IDd | 32.8 (±1.0)d | 35.2 (±2.6)d | 3.2 (±0.4)d | 3.2 (±0.1) |
| GyrA59 | 4.9 (±0.3) | 12.4 (±0.9) | 1.0 (±0.1) | 1.3 (±0.1) |
| CcdB | 21.0 (±0.9) | 27.9 (±2.6) | 2.7 (±0.4) | 2.9 (±0.2) |
a Model analysis of ITC binding data: ± values represent parameter errors estimated as 2× standard deviations obtained as square roots of diagonal elements of variance-covariance matrixes.
b Values of thermodynamic parameters obtained from model analysis of urea unfolding curves using the corresponding thermodynamic cycle.
c Average thermodynamic parameters obtained from fitting the model functions to two independent experimental datasets (Figs. 3 and Fig. 1-SM, supplemental materials). ± values represent parameter errors estimated as a square root of the sum of the corresponding variances.
d Values calculated from parameters describing CcdB binding to GyrA14 and CcdB unfolding.