Protein Crystallization with a Physico-Chemical Point of View. M. Riès-Kautt, P. Retailleau and A. Ducruix, Laboratoire d'Enzymologie et Biochimie Structurales, Bât. 34, CNRS, 91198 Gif sur Yvette Cedex, France. Phone: 33 1 69 82 35 02 FAX : 33 1 69 82 31 39, e-mail: ries@lebs.cnrs-gif.fr

Changing the nature of the counter-ions of a charged protein implies changing the protein-protein interactions, thus the protein solubility, and may induce polymorphism¹. The more the pH of crystallization is away from the pI, the higher the protein net charge and its solubility, and the larger the number of counter-ions necessary for electrostatic compensation. Anions have been shown to affect the solubility of negatively charged proteins² according to the Hofmeister series, but in the reverse order for positively charged proteins³.The effect of anions on solubility has been correlated to their effect on protein-protein interactions in undersaturated lysozyme solutions by SAXS measurements⁴. Recently a particular behavior has been observed at very low ionic strength⁵ which will be discussed. Undertaking protein crystallization with a physico-chemical point of view has practical implications for preparing crystallization solutions⁶, defining the strategy to determine crystallization conditions⁷ and for handling the crystals.

¹M. Riès-Kautt & A. Ducruix (1997) Methods in Enzymology, Vol 276 Part A Chap 3, 23

²C. Carbonnaux, M. Ries-Kautt & A. Ducruix (1995) Protein Science, 4, 2123.

³M. Riès-Kautt & A. Ducruix (1989) J. Biol. Chem., 264, 745.

⁴A. Ducruix, J.P. Guilloteau, M. Ries-Kautt, A. Tardieu (1996) J. of Crystal Growth 168, 28.

⁵P. Retailleau, M. Riès-KAutt & A. Ducruix (in preparation)

⁶M. Riès-Kautt, A. Ducruix & A. Van Dorsselaer (1994) Acta Cryst . D50, 366.

⁷J.P. Guilloteau, N. Fromage, M. Riès-Kautt, S. Reboul, F.F. Clerc, D. Faucher, D. Bocquet, C. Colonna, A. Ducruix & J. Becquart (1996) Proteins: Structure, Function, and Genetics, 25, 112.