title: New insights into urea action on proteins: a SANS study of the lysozyme case.
abstract: We present a study on lysozyme dissolved in mixtures of water and urea, which is ubiquitously used as a protein denaturant. Despite the wide use of urea, the basic molecular mechanisms inducing protein unfolding are not still clarified. Small-angle neutron scattering (SANS) experiments have been performed using little amounts of denaturant in solutions in order to investigate the urea effect on lysozyme preceding the unfolding process. A global fit strategy, applied to analyze SANS experiments, provides an estimation of the average composition of the solvent in the close vicinity of the protein surface and the change of the protein-protein interactions due to the presence of urea. In particular, the thermodynamic equilibrium constant responsible for cosolvent balancing between the bulk and solvation layer has been determined. It turns out that urea is preferentially driven to the protein surface, confirming literature results at infinite dilute conditions. SANS data also reveal a possible variation of the protein net charge as a function of urea concentration, opening new perspectives and questions about the protein surface architecture at the first stages of unfolding processes.
authors.affiliation: Dipartimento SAIFET and CNISM, Universita Politecnica delle Marche, Ancona, Italy.
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Ortore
authors.forename: Raffaele
authors.initials: R
authors.lastname: Sinibaldi
authors.forename: Francesco
authors.initials: F
authors.lastname: Spinozzi
authors.forename: Flavio
authors.initials: F
authors.lastname: Carsughi
authors.forename: Daniel
authors.initials: D
authors.lastname: Clemens
authors.forename: Adalberto
authors.initials: A
authors.lastname: Bonincontro
authors.forename: Paolo
authors.initials: P
authors.lastname: Mariani
mesh_terms: D000818:Animals; D008956:Models, Chemical; D009113:Muramidase / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011489:Protein Denaturation; D017510:Protein Folding; D053838:Scattering, Small Angle; D012996:Solutions; D012997:Solvents / Q000737:chemistry*; D013816:Thermodynamics; D014508:Urea / Q000737:chemistry*; D014867:Water
chemical_list: D012996:Solutions; D012997:Solvents; D014867:Water; D014508:Urea; C421864:hen egg lysozyme; D009113:Muramidase