TABLE 1.
Thermodynamic parameters resulting from a two-state analysis of the thermal unfolding profiles of spc-SH3 at pH 3.0, followed by CD, NMR, and DSC
| Observable | Protein concentration (mg·mL−1) | Tm (°C) | ΔHm (kJ × mol−1) |
|---|---|---|---|
| CD wavelength (nm) | |||
| 222 | 0.2 | 54.0 ± 0.4 | 176 ± 5 |
| 222 | 1.0 | 53.5 ± 0.2 | 168 ± 4 |
| 294 | 1.0 | 52.8 ± 0.3 | 170 ± 9 |
| 270 | 5.0 | 51.9 ± 0.4 | 172 ± 12 |
| 294 | 5.0 | 51.3 ± 0.5 | 171 ± 13 |
| NMR native signal | |||
| Ala55-CβH3 | 4.9 | 51.3 ± 2.5 | 146 ± 31 |
| Leu33-CδH3 | 4.9 | 52.0 ± 3.5 | 159 ± 46 |
| Trp41-NɛH | 4.9 | 51.2 ± 3.3 | 202 ± 87 |
| Ala55-CβH3 | 38.9 | 47.1 ± 2.2 | 166 ± 34 |
| Leu33-CδH3 | 38.9 | 45.9 ± 3.6 | 160 ± 41 |
| Trp41-NɛH | 38.9 | 47.6 ± 2.0 | 223 ± 66 |
| DSC | |||
| 0.22 | 56.1 ± 0.1 | 182 ± 1 | |
| 1.1 | 55.9 ± 0.1 | 174 ± 1 | |
| 5.5 | 55.2 ± 0.1 | 164 ± 1 | |
| 15.5 | 54.6 ± 0.1 | 149 ± 1 | |
| 35.0 | 50.2 ± 0.3 | 127 ± 1 |
The heat-capacity change on the unfolding of SH3 has been fixed in the fittings of the CD and NMR profiles at a value of 1.7 ± 0.6 kJ × mol−1, as obtained from the DSC experiments. The uncertainties in the parameters correspond to the standard errors of the fittings.