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Phase diagrams of biological macromolecules are governed by an appropriate combination of interaction potentials in solution. Repulsive regimes favor solubility, whereas the presence of attractive potentials may induce a variety of phase transitions, including the desired macromolecular crystallization. The forces at work may be analyzed with a combination of small angle X-ray scattering and of numerical treatments. From the results obtained with a variety of model systems, the respective advantages and drawbacks of using monovalent salts or PEGs as crystallizing agents are discussed.
research papers
The behavior of brome mosaic virus in solution as a function of physico-chemical conditions has already been characterized by Small Angle X-ray Scattering studies. The most striking result was that the precipitates induced by the addition of polyethylene glycol were in fact made of microcrystals. This result was reinvestigated on the ID2 beamline at ESRF (Grenoble, France) to determine whether there was an amorphous state before the organized one, and measure the necessary period of latency for the microcrystals to form. The stopped-flow device associated to the high brilliance of the beamline enabled us to characterize the growth of the diffraction peaks as a function of time.
