Isoenthalpic and isoentropic temperatures and the thermodynamics of protein denaturation.

Abstract

The standard enthalpy or entropy change upon transfer of a small nonpolar molecule from a nonaqueous phase into water at a given temperature is generally different for different solute species. However, if the heat capacity change is independent of temperature, there exists a temperature at which the enthalpy or the entropy change becomes the same for all solute species within a given class. Similarly, the enthalpy or the entropy change of protein denaturation, when extrapolated to high temperature assuming a temperatureindependent heat capacity change, shows a temperature at which its value becomes the same for many different globular proteins on a per weight basis. It is shown that the existence of these temperatures can be explained from a common formalism based on a linear relationship between the thermodynamic quantity and a temperature-independent molecular property that characterizes the solute or the protein. For the small nonpolar molecule transfer processes, this property is the surface area or the number of groups that are brought in contact with water. For protein denaturation, it is suggested that this property measures the polar/nonpolar mix of the internal interaction within the protein interior. Under a certain set of assumptions, this model leads to the conclusion that the nonpolar and the polar groups of the protein contribute roughly equally to the stability of the folded state of the molecule and that the solvent-accessible surface area of the denatured form of a protein is no more than about two-thirds that of the fully extended form.

Entropy and enthalpy convergence of hydrophobic solvation beyond the hard-sphere limit

“…7,10 To account for this, it is assumed that the solvation of hydrophilic groups contributes to the enthalpy but not to the entropy so that the solvation entropies of proteins and hydrophobic compounds are similar but not the enthalpies. 22 In contradiction to this assumption and not surprisingly, we find a continuous change of the solvation entropy as one goes from hydrophobic to hydrophilic solutes and in all cases the solvation entropy does not strictly vanish.…”

“…1 we show such a plot for the original set of proteins 6 used in the analysis of Murphy et al 7 (open triangles) including a linear fit to the data. The data in- 22 showed that convergence of some thermodynamic observable, e.g., the entropy of denaturation of a set of proteins or the entropy of dissolution S within a homologous series of compounds, can generally be expected if that observable is linearly dependent on the variable X (e.g., the number of hydrophobic groups in a homologous series of hydrocarbons) which distinguishes the elements of the series,…”

“…stirred an intense discussion about the interpretation and implications of these findings for the role of the hydrophobic effect in protein folding, 7,19,[21][22][23][24][25] which we will summarize briefly further below. Theoretically, the temperature dependence of hydrophobic hydration has been studied by various methods, [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] mostly focusing on the solvation of simple model solutes such as hard spheres 27, 28, 30-33, 35, 39 or Lennard-Jones particles.…”

Temperature Dependence of Dimerization and Dewetting of Large-Scale Hydrophobes: A Molecular Dynamics Study

“…It seems likely that the entropy change for these large-scale hydrophobic plates converges around T s , similar to the behavior observed for the hydration of small hydrophobic solutes and for the folding of proteins. 14,19,20 At this temperature, the driving force for plate association is only enthalpic. The entropic contribution increases as the temperature decreases.…”

Solvent effects on the molecular structures of crude gliadins as revealed by density and ultrasound velocity measurements

“…Kharakoz and Sarvazyan (1993) proposed that the compressible behaviour of a native protein is comparable to that of organic solids. However, proteins in compact intermediate states have liquid-like compressible behaviour (Lee, 1991;. The intrinsic core of a molecule at this stage is small but still preserved and more hydrophobic.…”