On the mechanism of cold denaturation

Abstract

A theoretical rationalization of the occurrence of cold denaturation for globular proteins was devised, assuming that the effective size of water molecules depends upon temperature [G. Graziano, Phys. Chem. Chem. Phys., 2010, 12, 14245-14252]. In the present work, it is shown that the latter assumption is not necessary. By performing the same type of calculations in water, 40% (by weight) methanol, methanol, and carbon tetrachloride, it emerges that cold denaturation occurs only in water due to the special temperature dependence of its density and the small size of its molecules. These two coupled factors determine the magnitude and the temperature dependence of the stabilizing term that measures the gain in configurational/translational entropy of water molecules upon folding of the protein. This term has to be contrasted with the destabilizing contribution measuring the loss in conformational entropy of the polypeptide chain upon folding.

On the effect of sodium salts on the coil-to-globule transition of poly(N-isopropylacrylamide)

“…9,10,12,13 It should be considered an entropy-driven collapse transition. 9,10,12,13 It should be considered an entropy-driven collapse transition.…”

“…9, 10 We would like to show that the same approach can account for the effect of sodium salts on the collapse transition of PNIPAM. 9, 10 We would like to show that the same approach can account for the effect of sodium salts on the collapse transition of PNIPAM.…”

“…The decrease in solvent-excluded volume upon collapse (reliably measured by the decrease in water accessible surface area, WASA 11 ) is the actual driving force of the coil-to-globule transition, 9,10,12,13 leading to a marked gain in the translational entropy of water molecules. The decrease in solvent-excluded volume upon collapse (reliably measured by the decrease in water accessible surface area, WASA 11 ) is the actual driving force of the coil-to-globule transition, 9,10,12,13 leading to a marked gain in the translational entropy of water molecules.…”

An optimized strategy to measure protein stability highlights differences between cold and hot unfolded states

“…Other authors have made use of artificial crowders such as dextran789, Ficoll101112, polyethylene glycol (PEG)913 or different proteins1415 that could potentially mimic the cellular environment. The role of soft interactions, evidenced by Pielak and co-workers414, is probably crucial inside cells, but the use of proteins as crowders may mask the true contribution of volume exclusion, the possible relationship between the dimensions of the protein under study and those of crowders and indirect effects mediated by water activity16. We focused on synthetic crowders, taking extra care to ascertain whether they interact with our protein before assessing their role in volume exclusion.…”

On the effect of hydrostatic pressure on the conformational stability of globular proteins

“…The approach assumes that there are two macro‐states accessible to a globular protein: the ensemble of folded conformations, N‐state, and the ensemble of denatured conformations, D‐state . A general statistical mechanical analysis and also a suitable thermodynamic cycle lead to the following expression for Δ G d , the Gibbs energy change associated with protein denaturation in water: where N represents the N‐state and D represents the D‐state; Δ G c (N|H 2 O) and Δ G c (D|H 2 O) represent the reversible work to create in water a cavity suitable to host the N‐state and the D‐state, respectively; E a (N|H 2 O) and E a (D|H 2 O) represent the energetic interactions (i.e., van der Waals attractions, H‐bonds and charge‐dipole interactions) among the N‐state or D‐state and surrounding water molecules; Δ E a (intra) = E a (D|intra) − E a (N|intra) accounts for the difference in intra‐molecular energetic interactions upon denaturation, and Δ S conf represents the conformational entropy gain of the polypeptide chain upon denaturation.…”