E0660

SALT INFLUENCE ON PROTEIN SOLUBILITY AND CRYSTALLIZATION. Arnaud Ducruix, Pascal Retailleau, Madeleine Ries-Kautt, Laboratoire d'Enzymologie et Biochimie Structurale, Bât. 34, CNRS, 91198 Gif sur Yvette cedex, France

The solubility of proteins1 is related to many parameters and clearly associated to Hofmeister series2. In order to correlate ion effectiveness with "cristallisability" we selected acidic and basic model proteins and measured their solubility as a function of salt concentration. The results3,4,5 suggest that the anions have their effectiveness reversed depending on the net charge of the protein, i.e. if proteins are crystallized at a pH lower or higher than their isoelectric point. As a consequence it seems that Hofmeister series of anions are followed for acidic proteins, but reversed for basic proteins. We have used small angle X-ray scattering (SAXS) in order to correlate these observations with the influence of salts on protein-protein interactions of concentrated solutions6.

Solubility depending on the protein net charge, solubility diagrams at various pH from low to high ionic strength have been measured and will be presented.

In order to assess crystal quality, we have performed preliminary experiments using the quasi-planar wave from station D25B at LURE synchrotron. Direct measurements of rocking curves from crystals of the above model proteins have shown7 values as low as 1.510-3 degrees.

1M. Ries-Kautt & A. Ducruix, Methods in Enzymology, in press.

2 F. Hofmeister (1888), Arch. Exp. Pathol. Pharmakol., 24, 247.

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

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

5J.P. Guilloteau, N. Fromage, M. Ries-Kautt, S. Reboul, F.F. Clerc, D. Faucher, D. Bocquet, C. Colonna, A. Ducruix & J. Becquart. PROTEIN: Structure, Function and Genetics (1996) in press.

6A. Ducruix, J.P. Guilloteau, M. Ries-Kautt, A. Tardieu, J. Cryst. Growth, in press.

7R. Fourme, A. Ducruix, M. Ries-Kautt, B. Capelle, (1995) J. Synchrotron Rad. 2, 136-142.