Effect of alcohols on protein hydration: crystallographic analysis of hen egg-white lysozyme in the presence of alcohols

Organic solvents are known to bring about dehydration of proteins, the molecular basis of which has remained uncharacterized. The dehydration effect in many cases leads to eventual unfolding of proteins through the macroscopic solvent effect. In some cases, the organic solvent molecules also bind to protein surfaces, thereby forcing local unfolding. The X-ray structure of hen egg-white lysozyme co-crystallized in the presence of alcohols with varying hydrophobicities has been studied. It was noticed that although the alcohols have very little effect on the conformation of the overall protein structure, they profoundly affect protein hydration and disorder of the bound waters. Systematic analysis of the water structure around the lysozyme molecule suggests that an increasing order of hydrophobicity of alcohols is directly proportional to the higher number of weakly bound waters in the protein. As anticipated, the water molecules in the native structure with high temperature factors (≥40 Ų) attain higher disorder in the presence of alcohols. It is believed that the disorder induced in the water molecules is a direct consequence of alcohol binding.