Effect of heavy water on the conformational stability of globular proteins

Abstract

It is well established from the experimental point of view that the native state of globular proteins is more stable in heavy water than in water. No robust explanation, however, has been provided up to now. The application of the theoretical approach, originally devised to rationalize the general occurrence of cold denaturation, indicates that the magnitude of the solvent-excluded volume effect is slightly smaller in heavy water than in water and cannot explain the observed protein stabilization. The latter has to be due to the strength of protein-water van der Waals attractions which are weaker in heavy water due to the smaller molecular polarizability of D O compared with that of H O molecules. Since protein-water van der Waals attractions occur more in the denatured than in the native state, this contribution leads to a stabilization of the latter through a destabilization of the former.

Effects of Hydrogen/Deuterium Exchange on Protein Stability in Solution and in the Gas Phase

“…Table reveals that D 2 O exposure causes Δ H U to increase by 40 and 60 kJ mol –1 for cyt c and lysozyme, respectively. This enthalpic stabilization of the native state in D 2 O is in line with earlier reports. − Interestingly, enthalpic stabilization is counteracted by a Δ S U increase in D 2 O of ca. 100 J K –1 mol –1 which destabilizes the native state.…”

“…At least 60 years after its discovery, the stabilization of proteins in D 2 O remains poorly understood. In agreement with earlier work, we found that this stabilization is rooted in enthalpic effects, i.e., a larger (more positive) value of Δ H U in D 2 O than in H 2 O. − Like those earlier studies, we attribute this stabilization to changes in the dissociation enthalpy of H-bonds. This effect is countered by entropy, as Δ S U is larger (more positive) in D 2 O than in H 2 O, thereby causing destabilization (Table ).…”

“…Thermodynamic stabilization of both proteins is evident from an upward displacement of the Δ G U profiles in D 2 O relative to H 2 O (Figure C, F), implying that the N ⇄ U equilibria were shifted toward the native state in D 2 O. This D 2 O-induced stabilization is consistent with earlier results. − , Overall, the results of Figure confirm that cyt c and lysozyme are more thermodynamically stable in D 2 O than in H 2 O. In contrast to some earlier studies, this result was obtained for samples that had well controlled (virtually complete) deuteration, as seen from the mass shifts in Figure .…”

Effects of Water Deuteration on Thermodynamic and Structural Properties of Proteins and Biomembranes

“…From the results presented in Figure 5, we see that the tightening of the protein structure upon water deuteration also leads to stabilization and increase of the protein melting temperature. This is in line with experimental observations, 27,28 and it is consistent with the sign of the free energies of transfer from H 2 O to D 2 O of individual amino acids in Figure 2.…”

“…This is in line with experimental observations, , and it is consistent with the sign of the free energies of transfer from H 2 O to D 2 O of individual amino acids in Figure .…”