title: SAXS/SANS on Supercharged Proteins Reveals Residue-Specific Modifications of the Hydration Shell.
abstract: Water molecules in the immediate vicinity of biomacromolecules, including proteins, constitute a hydration layer characterized by physicochemical properties different from those of bulk water and play a vital role in the activity and stability of these structures, as well as in intermolecular interactions. Previous studies using solution scattering, crystallography, and molecular dynamics simulations have provided valuable information about the properties of these hydration shells, including modifications in density and ionic concentration. Small-angle scattering of x-rays (SAXS) and neutrons (SANS) are particularly useful and complementary techniques to study biomacromolecular hydration shells due to their sensitivity to electronic and nuclear scattering-length density fluctuations, respectively. Although several sophisticated SAXS/SANS programs have been developed recently, the impact of physicochemical surface properties on the hydration layer remains controversial, and systematic experimental data from individual biomacromolecular systems are scarce. Here, we address the impact of physicochemical surface properties on the hydration shell by a systematic SAXS/SANS study using three mutants of a single protein, green fluorescent protein (GFP), with highly variable net charge (+36, -6, and -29). The combined analysis of our data shows that the hydration shell is locally denser in the vicinity of acidic surface residues, whereas basic and hydrophilic/hydrophobic residues only mildly modify its density. Moreover, the data demonstrate that the density modifications result from the combined effect of residue-specific recruitment of ions from the bulk in combination with water structural rearrangements in their vicinity. Finally, we find that the specific surface-charge distributions of the different GFP mutants modulate the conformational space of flexible parts of the protein.
authors.affiliation: University Grenoble Alpes, Grenoble, France; CNRS, Grenoble, France; CEA, IBS, Grenoble, France.
authors.forename: Henry S
authors.initials: HS
authors.lastname: Kim
authors.affiliation: Institut Laue-Langevin, Grenoble, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Martel
authors.affiliation: University Grenoble Alpes, Grenoble, France; CNRS, Grenoble, France; CEA, IBS, Grenoble, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Girard
authors.affiliation: Institut Laue-Langevin, Grenoble, France.
authors.forename: Martine
authors.initials: M
authors.lastname: Moulin
authors.affiliation: Institut Laue-Langevin, Grenoble, France.
authors.forename: Michael
authors.initials: M
authors.lastname: Härtlein
authors.affiliation: University Grenoble Alpes, Grenoble, France; CNRS, Grenoble, France; CEA, IBS, Grenoble, France; Institut Laue-Langevin, Grenoble, France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Madern
authors.affiliation: University Grenoble Alpes, Grenoble, France; CNRS, Grenoble, France; CEA, IBS, Grenoble, France.
authors.forename: Martin
authors.initials: M
authors.lastname: Blackledge
authors.affiliation: University Grenoble Alpes, Grenoble, France; CNRS, Grenoble, France; CEA, IBS, Grenoble, France; Institut Laue-Langevin, Grenoble, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Franzetti
authors.affiliation: University Grenoble Alpes, Grenoble, France; CNRS, Grenoble, France; CEA, IBS, Grenoble, France; Institut Laue-Langevin, Grenoble, France. Electronic address: frank.gabel@ibs.fr.
authors.forename: Frank
authors.initials: F
authors.lastname: Gabel
mesh_terms: D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli; D049452:Green Fluorescent Proteins / Q000737:chemistry* / Q000235:genetics; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D009154:Mutation; D033363:Neutron Diffraction; D053838:Scattering, Small Angle; D013499:Surface Properties; D014867:Water / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D014867:Water; D049452:Green Fluorescent Proteins