title: Role of Internal Water on Protein Thermal Stability: The Case of Homologous G Domains.
abstract: In this work, we address the question of whether the enhanced stability of thermophilic proteins has a direct connection with internal hydration. Our model systems are two homologous G domains of different stability: the mesophilic G domain of the elongation factor thermal unstable protein from E. coli and the hyperthermophilic G domain of the EF-1α protein from S. solfataricus. Using molecular dynamics simulation at the microsecond time scale, we show that both proteins host water molecules in internal cavities and that these molecules exchange with the external solution in the nanosecond time scale. The hydration free energy of these sites evaluated via extensive calculations is found to be favorable for both systems, with the hyperthermophilic protein offering a slightly more favorable environment to host water molecules. We estimate that, under ambient conditions, the free energy gain due to internal hydration is about 1.3 kcal/mol in favor of the hyperthermophilic variant. However, we also find that, at the high working temperature of the hyperthermophile, the cavities are rather dehydrated, meaning that under extreme conditions other molecular factors secure the stability of the protein. Interestingly, we detect a clear correlation between the hydration of internal cavities and the protein conformational landscape. The emerging picture is that internal hydration is an effective observable to probe the conformational landscape of proteins. In the specific context of our investigation, the analysis confirms that the hyperthermophilic G domain is characterized by multiple states and it has a more flexible structure than its mesophilic homologue.
authors.affiliation: †Laboratoire de Biochimie Théorique, IBPC, CNRS, UPR9080, Univ. Paris Diderot, Sorbonne Paris Cité, 13 rue Pierre et Marie Curie, 75005, Paris, France.
authors.forename: Obaidur
authors.initials: O
authors.lastname: Rahaman
authors.affiliation: †Laboratoire de Biochimie Théorique, IBPC, CNRS, UPR9080, Univ. Paris Diderot, Sorbonne Paris Cité, 13 rue Pierre et Marie Curie, 75005, Paris, France.
authors.forename: Maria
authors.initials: M
authors.lastname: Kalimeri
authors.affiliation: ‡CNR-IPCF, Consiglio Nazionale delle Ricerche, Physics Dept., Univ. La Sapienza, P.le A. Moro 2, 00185, Rome, Italy.
authors.forename: Simone
authors.initials: S
authors.lastname: Melchionna
authors.affiliation: †Laboratoire de Biochimie Théorique, IBPC, CNRS, UPR9080, Univ. Paris Diderot, Sorbonne Paris Cité, 13 rue Pierre et Marie Curie, 75005, Paris, France.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Hénin
authors.affiliation: †Laboratoire de Biochimie Théorique, IBPC, CNRS, UPR9080, Univ. Paris Diderot, Sorbonne Paris Cité, 13 rue Pierre et Marie Curie, 75005, Paris, France.
authors.forename: Fabio
authors.initials: F
authors.lastname: Sterpone
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry*; D004548:Elasticity; D004926:Escherichia coli; D029968:Escherichia coli Proteins / Q000737:chemistry*; D007700:Kinetics; D056004:Molecular Dynamics Simulation; D010445:Peptide Elongation Factors / Q000737:chemistry*; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D048229:Sulfolobus solfataricus; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry*
chemical_list: D019843:Archaeal Proteins; D029968:Escherichia coli Proteins; D010445:Peptide Elongation Factors; D014867:Water