Structure of the macromolecular solutions that generate crystals
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- 作者：Tardieu ; Annette ; Finet ; Sté ; phanie ; et. al.
- 关键词：61.10.Eq ; 81.10.Dn ; 82.70.Dd ; 87.15.Da ; 87.15.Kg ; A1.Biocrystallization ; A1.Hofmeister effect ; A1.Phase diagrams ; A1.Small angle X-ray scattering ; B1.Proteins
- 刊名：Journal of Crystal Growth
- 出版年：2001
- 出版时间：November, 2001
- 年：2001
- 卷：232
- 期：1-4
- 页码：1-9
- 全文大小：169 K
文摘
Biomolecular interactions in solution include a variety of effects: hard sphere, electrostatic, van der Waals, hydrophobic, etc. The corresponding interaction potentials govern the macromolecular distribution in solution, the shapes of the phase diagrams and the crystallization process. Different techniques: small angle X-ray scattering (SAXS), light scattering, osmotic pressure, can be used to characterize these potentials. Here, SAXS was the tool of choice to follow the changes induced by the crystallizing agents in different physicochemical conditions. Moreover, the coupling of SAXS (experimental structure factors) and numerical simulations derived from statistical mechanics (calculated structure factors) allowed us to determine the best fit parameters of the relevant potentials. Several protein model systems have now been investigated, with different isoelectric points, sizes and compactness. After the studies performed on lysozyme, and on aspartate transcarbamylase (ATCase), we proceeded with lens gamma- and alpha-crystallins and with urate oxidase. We can now draw the following picture of the relevant potentials. With low molecular weight proteins, a coulombic, pH dependent, repulsive potential and a short range (a few Å), possibly van der Waals, attraction are sufficient to account for the behavior observed at low ionic strength. At higher ionic strength, the salt specific effects that follow the (direct or reverse) order of the Hofmeister series, correspond to an additional short range salt specific attraction. With increasing protein size, the van der Waals contribution becomes negligible. The addition of polymers like polyethylene glycol (PEG) induces a depletion mechanism, which is equivalent to a protein–protein attraction. Crystallization definitively appears to be under control of sufficiently strong and short range (a few Å) attractions, which means that, despite the diversity of protein sequences, it is possible to define a range of physicochemical conditions that may generate crystals. Yet, if salt addition appears to be sufficient to provide such conditions with small compact proteins, additives like PEG seem to be required at higher molecular weights. The success, of course, will also rely upon the protein purity and stability.