Second virial coefficient: variations with lysozyme crystallization conditions

Interparticle lysozyme interactions in solution have been studied by small angle X-ray scattering (SAXS) as a function of salt type (NaCl, NaNO3, NaSC N and NaOAc), salt concentration, and as a function of temperature between 30 degrees C and 10 degrees C. The choice of conditions was made to cover v ariations from (undersaturated) solutions to (supersaturated) crystallizati on conditions. The second virial coefficients (A(2)) were determined from t he X-ray structure factors extrapolated to the origin, as a function of pro tein concentration. The A(2) values which correspond to lysozyme crystalliz ation conditions were found to be in a range from about zero to -8.0 x 10(- 4) mol ml g(-2), in agreement with previous determinations by other groups. The variations of the second virial coefficient from positive (repulsive i nteractions) to negative (attractive interactions) were found to follow the efficiency of salts to induce crystallization. The choice of the second vi rial coefficient as a tool to predict crystallization conditions is discuss ed. (C) 1999 Elsevier Science B.V. All rights reserved.