Role of hydrophobic interactions on the stabilisation of native state of globular proteins

The technique of intensity photon correlation spectroscopy has been utilised to investigate the native conformation of lysozyme in water/ethanol mixture as a function of alcohol concentration in the water-rich region of composition (cosolvent mole fraction x2<0.08). A non-trivial behaviour of the hydrodynamic radius is obtained, characterised by a minimum at x2=0.02 and a maximum at x2=0.06. This behaviour is similar to that of partial molar volume of ethanol in water and reflects changes in the alcohol/water structure. The results are discussed in connection to the effect of alcohol in modulating solvent-mediated interactions.