title: Hydration dynamics of a halophilic protein in folded and unfolded states.
abstract: Proteins from halophilic microorganisms thriving at high salinity have an excess of charged carboxylate groups, and it is widely believed that this gives rise to an exceptionally strong hydration that stabilizes these proteins against unfolding and aggregation. Here, we examine this hypothesis by characterizing the hydration dynamics of a halophilic model protein with frequency- and temperature-dependent (17)O magnetic relaxation. The halophilic protein Kx6E was constructed by replacing six lysine residues with glutamate residues in the IgG binding domain of protein L. We also studied the unfolded form of Kx6E in the absence of salt. We find that the hydration dynamics of Kx6E does not differ from protein L or from other previously studied mesophilic proteins. This finding challenges the hypothesis of exceptional hydration for halophilic proteins. The unfolded form of Kx6E is found to be expanded, with a weaker dynamical perturbation of the hydration water than for folded proteins.
authors.affiliation: Department of Biophysical Chemistry, Center for Molecular Protein Science, Lund University, SE-22100 Lund, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Qvist
authors.forename: Gabriel
authors.initials: G
authors.lastname: Ortega
authors.forename: Xavier
authors.initials: X
authors.lastname: Tadeo
authors.forename: Oscar
authors.initials: O
authors.lastname: Millet
authors.forename: Bertil
authors.initials: B
authors.lastname: Halle
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019613:Haloarcula / Q000378:metabolism; D007074:Immunoglobulin G / Q000737:chemistry / Q000378:metabolism; D008280:Magnetics; D009154:Mutation; D010103:Oxygen Isotopes / Q000737:chemistry; D011485:Protein Binding; D017510:Protein Folding; D058767:Protein Unfolding; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D019843:Archaeal Proteins; D007074:Immunoglobulin G; D010103:Oxygen Isotopes; D011994:Recombinant Proteins; D014867:Water