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Soft Matter and Biological Physics
Eur. Phys. J. E 9, 15-25 (2002)
DOI: 10.1140/epje/i2002-10047-7

Catching the PEG-induced attractive interaction between proteins

D. Vivarès1, L. Belloni2, A. Tardieu1 and F. Bonneté3

1  LMCP- UMR7590, case 115, 4 place Jussieu, F-75252 Paris Cedex 05, France
2  CEA-Saclay, Service de Chimie Moléculaire, F-91191 Gif-sur-Yvette, France
3  CRMC2 (Laboratory associated to Universities Aix-Marseille II and III.) -CNRS, Campus de Luminy, case 913, F-13288 Marseille Cedex 09, France

vivares@crmc2.univ-mrs.fr
bonnete@crmc2.univ-mrs.fr

(Received 29 April 2002 / Published online: 29 October 2002)

Abstract
We present the experimental and theoretical background of a method to characterize the protein-protein attractive potential induced by one of the mostly used crystallizing agents in the protein-field, the poly(ethylene glycol) (PEG). This attractive interaction is commonly called, in colloid physics, the depletion interaction. Small-Angle X-ray Scattering experiments and numerical treatments based on liquid-state theories were performed on urate oxidase-PEG mixtures with two different PEGs (3350 Da and 8000 Da). A "two-component" approach was used in which the polymer-polymer, the protein-polymer and the protein-protein pair potentials were determined. The resulting effective protein-protein potential was characterized. This potential is the sum of the free-polymer protein-protein potential and of the PEG-induced depletion potential. The depletion potential was found to be hardly dependent upon the protein concentration but strongly function of the polymer size and concentration. Our results were also compared with two models, which give an analytic expression for the depletion potential.

PACS
87.15.Nn - Properties of solutions; aggregation and crystallization of macromolecules.
87.15.Aa - Theory and modeling; computer simulation.
83.85.Hf - X-ray and neutron scattering.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002