Table 1. Thermodynamic parameters for xylosaccharide and xylan binding to XT6(E159Q).
| Ligand | T, °C | Ka × 104, M-1 | Kd (1/Ka), μM | ΔHa, kcal/mol | TΔSa, kcal/mol | ΔGa, kcal/mol | ΔCp, cal/mol·K |
|---|---|---|---|---|---|---|---|
| Xylosaccharides | |||||||
| X2 | 20 | 4.1 ± 0.1 | 24 | -6.8 ± 0.1 | -0.6 | -6.2 | |
| 30 | 2.6 ± 0.3 | 38 | -6.7 ± 0.5 | -0.6 | -6.1 | -2 ± 5 | |
| 40 | 1.2 ± 0.1 | 83 | -6.9 ± 0.3 | -1.1 | -5.8 | ||
| 50 | 2.5 ± 0.3 | 40 | -6.8 ± 0.2 | -0.6 | -6.2 | ||
| X3 | 20 | 12 ± 0.5 | 8.3 | -9.0 ± 0.1 | -2.2 | -6.8 | |
| 30 | 11 ± 2 | 9.4 | -10.5 ± 0.1 | -3.5 | -7.0 | -94 ± 19 | |
| 40 | 4.9 ± 0.2 | 20 | -10.9 ± 0.1 | -4.2 | -6.7 | ||
| 50 | 2.9 ± 0.7 | 34 | -12.0 ± 0.2 | -5.1 | -6.9 | ||
| X4 | 20 | 50 ± 2.3 | 2.0 | -13.4 ± 0.1 | -5.8 | -7.6 | |
| 30 | 29 ± 5 | 3.5 | -14.4 ± 0.3 | -6.8 | -7.6 | -233 ± 24 | |
| 35 | 17 ± 1.7 | 5.9 | -15.6 ± 0.3 | -8.2 | -7.4 | ||
| 40 | 15 ± 1.7 | 6.7 | -17.9 ± 0.3 | -10.4 | -7.5 | ||
| 50 | 8.5 ± 0.6 | 12 | -20.0 ± 1.2 | -12.7 | -7.3 | ||
| X5 | 20 | 280 ± 27 | 0.36 | -13.2 ± 0.1 | -4.6 | -8.6 | |
| 30 | 110 ± 14 | 0.93 | -13.6 ± 1.0 | -5.3 | -8.3 | -257 ± 27 | |
| 40 | 84 ± 5 | 1.2 | -16.8 ± 0.1 | -8.3 | -8.5 | ||
| 50 | 41 ± 2.4 | 2.4 | -21.1 ± 0.2 | -12.8 | -8.3 | ||
| X6 | 20 | 760 ± 100 | 0.13 | -12.8 ± 0.1 | -3.6 | -9.2 | |
| 30 | 290 ± 23 | 0.35 | -15.0 ± 0.2 | -6.2 | -8.8 | -380 ± 35 | |
| 40 | 200 ± 23 | 0.5 | -20.3 ± 0.2 | -11.2 | -9.1 | ||
| 50 | 140 ± 2.3 | 0.74 | -23.7 ± 0.2 | -14.7 | -9.0 | ||
| Xylans | |||||||
| Beech wood | 20 | 160 ± 22 | 0.61 | -14.4 ± 0.2 | -6.1 | -8.3 | |
| 30 | 110 ± 19 | 0.89 | -15.9 ± 0.9 | -7.6 | -8.3 | -330 ± 32 | |
| 40 | 92 ± 5.8 | 1.1 | -20.3 ± 0.2 | -11.8 | -8.5 | ||
| 50 | 89 ± 1.6 | 1.1 | -23.2 ± 0.9 | -14.4 | -8.8 | ||
| Birch wood | 20 | 130 ± 16 | 0.79 | -10.0 ± 0.1 | -1.8 | -8.2 | |
| 30 | 150 ± 20 | 0.65 | -12.6 ± 1.0 | -4.2 | -8.4 | -360 ± 29 | |
| 35 | 160 ± 17 | 0.64 | -14.4 ± 0.1 | -5.6 | -8.8 | ||
| 40 | 98 ± 8 | 1.0 | -16.4 ± 0.2 | -7.8 | -8.6 | ||
| 50 | 130 ± 16 | 0.75 | -20.3 ± 0.2 | -11.3 | -9.0 |
Each set of results is based on the average of three independent measurements. The stoichiometry in all experiments with xylosaccharides was very close to 1 (±0.05). The size of a single “binding unit” for xylans was adjusted to fit n = 1 and was 17 xylose units for beech and birch wood xylans.