Thermal stability of proteins does not correlate with the energy of intramolecular interactions

Small monomeric proteins from mesophilic and thermophilic organisms were studied. They have close structural and physical and chemical properties but vary in thermal stability. A thermodynamic analysis of heat unfolding was made and integral enthalpy of unfolding (ΔHunf), heat capacity of hydration (ΔCphyd) and enthalpy of hydration (ΔHhyd) and of the buried surface area (ΔASA) of nonpolar and polar groups as well as the enthalpy of disruption of intramolecular interaction (ΔHint in gas phase) at 298 K were determined. The absence of correlation between protein thermostability and energetic components suggests that regulatory mechanism of protein thermal stabilization has entropic nature.