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The results from this small-angle scattering study have been extended to the crystallization of large proteins in the presence of polyethylene glycol. The protein crystallization, the nucleation rate and the different morphological crystal shapes obtained were correlated with the second virial coefficient.
research papers
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
In the field of protein crystallization, a better knowledge of the nucleation process is essential to control the nucleation rate, the growth and therefore the size and the quality of crystals. With that aim, it becomes clear that the important stage is the determination of the protein phase diagram. We highlighted and investigated the bovine pancreatic trypsin inhibitor (BPTI) binary liquid-liquid phase separation in 350 mM KSCN solutions as a function of temperature. We measured the low concentration part of the binodal curve using light scattering and optical microscopy. We show, from small angle X-ray scattering experiments, that the high concentrated phase sediments in the bottom of the capillary and we analysed the low concentrated phase in terms of monomers/decamers equilibrium.
research papers
It has been shown for several years that the second virial coefficient, A2, can be helpfully used to describe the thermodynamic behavior of biological macromolecules in solution prior to crystallization. The coefficient, which reflects either repulsive or attractive interactions between particles, can allow a rapid determination of crystallization conditions. Different biological systems, from 14 kDa to 4600 kDa, were studied by small angle X-ray scattering. With large macromolecules, the A2 values were found at the low end of the crystallization slot described by George & Wilson [(1994) Acta Cryst. D50, 361-365]. This led us to investigate the physical meaning of the second virial coefficient and to propose the use of the dimensionless second virial coefficient independent of the molecular weight and the size of the particle, which only takes into account the interaction potential between macromolecules, to predict successful crystallization conditions for large macromolecules. With this normalized coefficient (a2), the effect of salt on small proteins becomes equivalent to the effect of PEG on large macromolecules in terms of interaction potentials.
