Hydrophobic hydration processes. Thermal and chemical denaturation of proteins

E. Fisicaro , C. Compari , A. Braibanti

The hydrophobic hydration processes have been analysed under the light of a mixture model of water that is assumed to be composed by clusters (W), clusters (W) and free water molecules W. The hydrophobic hydration processes can be subdivided into two Classes A and B. In the processes of Class A, the transformation A(− ξW→ ξW+ ξW+ cavity) takes place, with expulsion from the bulk of ξ water molecules W whereas in the processes of Class B the opposite transformation B(− ξW- ξW → ξW-cavity) takes place, with condensation into the bulk of ξ water molecules W. The () principle is exploited to determine the number . The denaturation (unfolding) process belongs to Class A whereas folding (or renaturation) belongs to Class B. The enthalpy Δ and entropy Δ functions can be disaggregated in thermal and motive components, Δ = Δ + Δ, and Δ = Δ + Δ, respectively. The terms Δ and Δ are related to phase change of water molecules W, and give no contribution to free energy (Δ=0). The motive functions refer to the process of cavity formation (Class A) or cavity reduction (Class B), respectively and are the only contributors to free energy Δ. The folded native protein is thermodynamically favoured (Δ ≡Δ<0) because of the outstanding contribution of the positive entropy term for cavity reduction, Δ >>0. The native protein can be brought to a stable denatured state (Δ≡Δ <0) by coupled reactions. Processes of protonation coupled to denaturation have been identified. In thermal denaturation by calorimetry, however, is the heat gradually supplied to the system that yields a change of phase of water W, with creation of cavity and negative entropy production, Δ<

Mots clés: water clusters; cavity formation; cavity reduction; thermal enthalpy; termal entropy; motive free- energy

Domaines: Chimie-Physique [physics.chem-ph]

E. Fisicaro, C. Compari, A. Braibanti. Hydrophobic hydration processes. Thermal and chemical denaturation of proteins. Biophysical Chemistry, 2011, 156 (1), pp.51. ⟨10.1016/j.bpc.2011.02.009⟩. ⟨hal-00750640⟩