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Biophys J, June 2001, p. 2751-2760, Vol. 80, No. 6

Hydration and Protein Folding in Water and in Reverse Micelles: Compressibility and Volume Changes

D. Valdez,* J -Y. Le Huérou,* M. Gindre,* W. Urbach,dagger and M. Waks*

 *Laboratoire d'Imagerie Paramétrique, UMR 7623 CNRS Université Pierre et Marie Curie,75270 Paris cedex 06, France;  dagger Laboratoire de Physique Statistique, UMR 8550 CNRS Ecole Normale Supérieure, 75231 Paris cedex 05, France

The partial specific volume and adiabatic compressibility of proteins reflect the hydration properties of the solvent-exposed protein surface, as well as changes in conformational states. Reverse micelles, or water-in-oil microemulsions, are protein-sized, optically-clear microassemblies in which hydration can be experimentally controlled. We explore, by densimetry and ultrasound velocimetry, three basic proteins: cytochrome c, lysozyme, and myelin basic protein in reverse micelles made of sodium bis (2-ethylhexyl) sulfosuccinate, water, and isooctane and in aqueous solvents. For comparison, we use beta -lactoglobulin (pI = 5.1) as a reference protein. We examine the partial specific volume and adiabatic compressibility of the proteins at increasing levels of micellar hydration. For the lowest water content compatible with complete solubilization, all proteins display their highest compressibility values, independent of their amino acid sequence and charge. These values lie within the range of empirical intrinsic protein compressibility estimates. In addition, we obtain volumetric data for the transition of myelin basic protein from its initially unfolded state in water free of denaturants, to a folded, compact conformation within the water-controlled microenvironment of reverse micelles. These results disclose yet another aspect of the protein structural properties observed in membrane-mimetic molecular assemblies.

Biophys J, June 2001, p. 2751-2760, Vol. 80, No. 6
© 2001 by the Biophysical Society   0006-3495/01/06/2751/10  $2.00


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