title: Hofmeister ions control protein dynamics.
abstract: BACKGROUND
  Recently, we have elaborated a thermodynamic theory that could coherently interpret the diverse effects of Hofmeister ions on proteins, based on a single physical parameter, the protein-water interfacial tension (Dér et al., Journal of Physical Chemistry B. 2007, 111, 5344-5350). This theory, implying a "liquid drop model", predicts changes in protein conformational fluctuations upon addition of Hofmeister salts (containing either kosmotropic or chaotropic anions) to the medium.
  
  
  METHODS
  Here, we report experimental tests of this prediction using a complex approach by applying methods especially suited for the detection of protein fluctuation changes (neutron scattering, micro-calorimetry, and Fourier-transform infrared spectroscopy).
  
  
  RESULTS
  It is demonstrated that Hofmeister salts, via setting the hydrophobic/hydrophilic properties of the protein-water interface, control conformational fluctuations even in the interior of the typical membrane transport protein bacteriorhodopsin, around its temperature-induced, unusual α(II)→α(I) conformational transition between 60 and 90°C. We found that below this transition kosmotropic (COOCH3(-)), while above it chaotropic (ClO4(-)) anions increase structural fluctuations of bR. It was also shown that, in each case, an onset of enhanced equilibrium fluctuations presages this phase transition in the course of the thermotropic response of bR.
  
  
  CONCLUSIONS
  These results are in full agreement with the theory, and demonstrate that predictions based on protein-water interfacial tension changes can describe Hofmeister effects and interpret protein dynamics phenomena even in unusual cases.
  
  
  CONCLUSIONS
  This approach is expected to provide a useful guide to understand the principles governing the interplay between protein interfacial properties and conformational dynamics, in general.
authors.affiliation: Institute of Biophysics, Biological Research Centre of the Hungarian Academy of Sciences, H-6726 Szeged, Hungary. szalontai.balazs@brc.mta.hu
authors.forename: Balázs
authors.initials: B
authors.lastname: Szalontai
authors.forename: Gergely
authors.initials: G
authors.lastname: Nagy
authors.forename: Sashka
authors.initials: S
authors.lastname: Krumova
authors.forename: Elfrieda
authors.initials: E
authors.lastname: Fodor
authors.forename: Tibor
authors.initials: T
authors.lastname: Páli
authors.forename: Stefka G
authors.initials: SG
authors.lastname: Taneva
authors.forename: Győző
authors.initials: G
authors.lastname: Garab
authors.forename: Judith
authors.initials: J
authors.lastname: Peters
authors.forename: András
authors.initials: A
authors.lastname: Dér
mesh_terms: D002152:Calorimetry, Differential Scanning; D007477:Ions; D009502:Neutrons; D011506:Proteins / Q000737:chemistry*; D012542:Scattering, Radiation; D017550:Spectroscopy, Fourier Transform Infrared; D013816:Thermodynamics
chemical_list: D007477:Ions; D011506:Proteins
keywords: Bacteriorhodopsin; Differential scanning calorimetry; Fourier transform infrared spectroscopy; Hofmeister effect; Neutron scattering; Protein structural fluctuation