In a recent article (1), the authors examined the temperature dependence of the interactions between two p382 isoforms (p38α and p38β) and two substrate proteins (MK2 and ATF) (Fig. 1A). Here, we show our analysis of the binding affinity data in the paper in terms of thermodynamics, which may provide further insight into the interactions.
Figure 1.
Thermodynamic analysis of the binding of p38 to substrate proteins. A, equilibrium reaction scheme for p38 binding and its association (KA) and dissociation (KD) constants. B, enthalpy–entropy compensation in the binding of p38 to substrate proteins. The values in Table 1 are plotted. Linear regression suggests a high degree of correlation between enthalpy and entropy values. Solid line, a linear fit to the data, ΔS° = 2.9 × 10−3ΔH° + 0.15 (R2 = 0.9988).
Using the van't Hoff relation, ln(KA) = −ΔH°/(RT) + ΔS°/R, where R is the ideal gas constant and T is the temperature in Kelvin (2), both ΔH° and ΔS° were obtained for each set of interactions (Table 1). These thermodynamic parameter values quantitatively explain two features of the interactions.
Table 1.
ΔH° and ΔS° values in the binding of p38 MAPK to substrate proteins
| p38 isoform | Substrate | ΔH° ± S.E.a | ΔS° ± S.E.a |
|---|---|---|---|
| kJ/mol | kJ/mol·K | ||
| α | MK2 | 122.0 ± 9.4 | 0.51 ± 0.03 |
| β | MK2 | 86.2 ± 18.4 | 0.39 ± 0.06 |
| α | ATF2 | −51.1 ± 10.7 | 0.25 × 10−3 ± 0.03 |
| β | ATF2 | −16.5 ± 1.1 | 0.11 ± 0.004 |
a S.E., standard error of the estimates.
1. The higher affinity of ATF2 (approximately nanomolar affinity) over MK2 (approximately micromolar affinity) to p38 is of enthalpy origin, as ΔΔH° values (equal to ΔHATF2° − ΔHMK2°) are −173.1 and −102.7 kJ/mol for p38α and p38β, respectively.
2. The temperature dependence of p38-binding affinity can be explained by the differential form of the van't Hoff equation, ∂ln(KA)/∂T = ΔH°/(RT2). MK2 has positive ΔH° values in binding to both p38α and p38β. This is the thermodynamic reason why its binding affinity increases as the temperature increases. In contrast, ATF2 has negative values of ΔH°, explaining the opposite trend in the temperature dependence of binding affinity.
One noticeable feature of the interaction is a compensatory behavior between ΔH° and ΔS° (Fig. 1B), which is known as enthalpy–entropy compensation (3–5). It will be interesting to examine whether the phenomenon is valid with other p38 substrate proteins, such as STAT1α.
The authors declare that they have no conflicts of interest with the contents of this article.
- p38
- p38 mitogen-activated protein kinase
- ATF
- activating transcription factor
- MK2
- MAPK-activating kinase-2
- STAT
- signal transducer and activator of transcription.
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