Probing protein hydration and conformational states in solution

摘要: The addition of polyethylene glycol (PEG), various molecular weights, to solutions bathing yeast hexokinase increases the affinity enzyme for its substrate glucose. results can be interpreted on basis that PEG acts directly protein or indirectly through water activity. nature effects suggests us PEG's action is indirect. Interpretation as an osmotic effect yields a decrease in number molecules, delta Nw, associated with glucose binding reaction. Nw difference PEG-inaccessible molecules between glucose-bound and glucose-free conformations hexokinase. At low concentrations, from 50 326 increasing MW 300 1000, then remains constant MW-PEG up 10,000. This solutes size are excluded ever larger aqueous compartments around protein. Three hundred twenty-six waters than estimated modeling solvent volumes crystal structures two conformations. For PEGs > falls about 25 concentration, i.e., alone appears "dehydrate" unbound conformation solution. Remarkably, work this dehydration would order only one k T per molecule. We conclude under thermal fluctuations, solution has conformational flexibility explores wide range hydration states not seen structure.