title: Protein stabilization by macromolecular crowding through enthalpy rather than entropy.
abstract: The interior of the cell is a densely crowded environment in which protein stability is affected differently than in dilute solution. Macromolecular crowding is commonly understood in terms of an entropic volume exclusion effect based on hardcore repulsions among the macromolecules. We studied the thermal unfolding of ubiquitin in the presence of different cosolutes (glucose, dextran, poly(ethylene glycol), KCl, urea). Our results show that for a correct dissection of the cosolute-induced changes of the free energy into its enthalpic and entropic contributions, the temperature dependence of the heat capacity change needs to be explicitly taken into account. In contrast to the prediction by the excluded volume theory, we observed an enthalpic stabilization and an entropic destabilization for glucose, dextran, and poly(ethylene glycol). The enthalpic stabilization mechanism induced by the macromolecular crowder dextran was similar to the enthalpic stabilization mechanism of its monomeric building block glucose. In the case of poly(ethylene glycol), entropy is dominating over enthalpy leading to an overall destabilization. We propose a new model to classify cosolute effects in terms of their enthalpic contributions to protein stability.
authors.affiliation: Department of Physical Chemistry II, Ruhr-Universität Bochum , 44780 Bochum, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Senske
authors.forename: Lisa
authors.initials: L
authors.lastname: Törk
authors.forename: Benjamin
authors.initials: B
authors.lastname: Born
authors.forename: Martina
authors.initials: M
authors.lastname: Havenith
authors.forename: Christian
authors.initials: C
authors.lastname: Herrmann
authors.forename: Simon
authors.initials: S
authors.lastname: Ebbinghaus
mesh_terms: D003911:Dextrans / Q000737:chemistry; D005947:Glucose / Q000737:chemistry; D046911:Macromolecular Substances / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D011189:Potassium Chloride / Q000737:chemistry; D055550:Protein Stability; D013816:Thermodynamics; D025801:Ubiquitin / Q000737:chemistry*; D014508:Urea / Q000737:chemistry
chemical_list: D003911:Dextrans; D046911:Macromolecular Substances; D025801:Ubiquitin; D011092:Polyethylene Glycols; D011189:Potassium Chloride; D014508:Urea; D005947:Glucose