Colloidal properties of biomacromolecular solutions: Towards urate oxidase crystal design

Crystallization of biological macromolecules is governed by weak interaction forces, attractive and repulsive. Knowledge of solution properties, via second virial coefficient measurements, makes it possible to select physico-chemical parameters that govern and control phase diagrams and thus to grow crystals for specific applications (bio-crystallography or pharmaceutical processes). We highlight here with urate oxidase a salting-in effect that increases its solubility and the depletion effect of amphiphilic polymer, at a polymer concentration above its cmc, in order to grow diffracting crystals of urate oxidase. These two effects were used to grow crystals for high pressure crystallography and in a purification process.