Table 2.
Thermodynamic parameters for the titration of TodS mutants with agonists and antagonists
| Mutants* and compounds | KD, μM | ΔH, kcal/mol | KDmut/KDwt |
|---|---|---|---|
| F46A | |||
| Benzene | 10.0 ± 2 | −8.20 ± 2.2 | 12 |
| Toluene | 3.03 ± 0.2 | −14.6 ± 0.7 | 4.3 |
| o-Chlorotoluene | 3.48 ± 0.3 | −13.5 ± 1 | 4.5 |
| o-Xylene | 2.46 ± 0.1 | −5.66 ± 0.1 | 4.2 |
| I74A | |||
| Benzene | 5.81 ± 1.3 | −2.52 ± 0.8 | 7.7 |
| Toluene | 8.62 ± 1.0 | −5.49 ± 1.3 | 12 |
| o-Chlorotoluene | 2.29 ± 0.7 | −2.02 ± 0.5 | 3.1 |
| o-Xylene | 3.20 ± 0.6 | −3.52 ± 0.8 | 12 |
| F79A | |||
| Benzene | >200† | — | >263 |
| Toluene | >200† | — | >290 |
| o-Chlorotoluene | >200† | — | >274 |
| o-Xylene | >200† | — | >345 |
| I114A | |||
| Benzene | 2.32 ± 0.2 | −5.14 ± 0.3 | 3.0 |
| Toluene | 1.63 ± 0.3 | −9.75 ± 1.2 | 2.4 |
| o-Chlorotoluene | 2.33 ± 0.1 | −5.14 ± 0.3 | 3.2 |
| o-Xylene | 1.27 ± 0.2 | −20.0 ± 9.3 | 2.2 |
KDmut/KDwt shows the ratio of the determined KD to the corresponding value obtained for the wild-type (wt) protein.
*The location of the amino acids in the 3D model of the N-terminal PAS domain of TodS is shown in Fig. 4.
†A titration of this mutant with a series of 12-μl injections of 4–5 mM ligand solution gave rise to minor heats of binding, which did not permit data analysis. The KD is estimated to be >200 μM.