Neutron scattering studies on dUTPase complex in the presence of bioprotectant systems

The aim of the present work is to investigate the chemical physics mechanisms of protein stabilization by homologous disaccharides (trehalose, maltose and sucrose). On this purpose the structural and dynamical properties of dUTPase-inhibitor candidate and dUTPase-inhibitor candidate/disaccharide mixtures have been investigated by elastic neutron scattering (ENS), quasi-elastic neutron scattering (QENS) and photon correlation spectroscopy (PCS). The decrease in the ENS intensity profiles vs temperature for the disaccharide-water mixtures is less marked in the case of trehalose/water mixture. This indicates that trehalose shows a larger structural resistance to temperature changes and a higher 'rigidity' in comparison with maltose/H2O and sucrose/H2O mixtures. In addition the protein/hydrated-disaccharide mixtures show a linear dependence between the solvent viscosity and the local mean-square displacement of hydrated dUTpase/disaccharide systems. This result shows that the protein dynamics is coupled with that of the surrounding matrix. Furthermore, QENS results on the binary disaccharide-H2O/D2O mixtures indicate that the water dynamics is affected by all the disaccharides and particularly by trehalose. Finally, PCS findings indicate that the protein hydrodynamic radius in solution does not change at low disaccharide concentrations, while reveal, at high disaccharide concentration, a breakdown of the Stokes-Einstein law. The experimental findings are discussed and interpreted in the frame of the current theories