The impact of high hydrostatic pressure on structure and dynamics of beta-lactoglobulin

Methods Combining small-angle X-ray and neutron scattering measurements with inelastic neutron scattering experiments, we investigated the impact of high hydrostatic pressure on the structure and dynamics of ?-lactoglobulin (?LG) in aqueous solution. Background ?LG is a relatively small protein, which is predominantly dimeric in physiological conditions, but dissociates to monomer below about pH 3. Results High-pressure structural results show that the dimer-monomer equilibrium, as well as the protein-protein interactions, are only slightly perturbed by pressure, and ?LG unfolding is observed above a threshold value of 3000 bar. In the same range of pressure, dynamical results put in evidence a slowing down of the protein dynamics in the picosecond timescale and a loss of rigidity of the ?LG structure. This dynamical behavior can be related to the onset of unfolding processes, probably promoted from water penetration in the hydrophobic cavity. General significance Results suggest that density and compressibility of water molecules in contact with the protein are key parameters to regulate the protein flexibility.