International
Tables for
Crystallography
Volume F
Crystallography of biological macromolecules
Edited by E. Arnold, D. M. Himmel and M. G. Rossmann

International Tables for Crystallography (2012). Vol. F, ch. 4.1, p. 115   | 1 | 2 |

Section 4.1.7. The future of protein crystal growth

C. Sauter,a B. Lorber,b A. McPhersonc and R. Giegéd*

aInstitut de Biologie Moléculaire et Cellulaire (IBMC), Centre National pour la Recherche Scientifique (CNRS), 15 rue René Descartes, Strasbourg, F-67084, France,bUPR 9002, IBMC–CNRS, 15 rue René Descartes Cedex, Strasbourg, 67084, France,cDepartment of Molecular Biology and Biochemistry, University of California, 560 Steinhaus, Irvine, CA 92697–3900, USA, and dMachineries Traductionnelles, ARN, UPR 9002, IBMC du CNRS, 15 rue René Descartes, Strasbourg, 67084, France
Correspondence e-mail:  R.Giege@ibmc.u-strasbg.fr

4.1.7. The future of protein crystal growth

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The fact that high-quality X-ray diffraction data can frequently be obtained from a single crystal of dimensions in the range of 20 to 50 µm has changed the objectives considerably from 40 years ago, when many crystals in the millimetre size range were required for a structure analysis. A consequence of this is that attention is turning increasingly from the systematic growth of large protein crystals (Bailey, 1942[link]) to the nucleation and growth of any crystal. This direction has been further promoted by the development in the last 20 years of methods to use even the data from twinned or disordered crystals. One might be led to believe that the future of crystal growth is shrinking dramatically. Indeed, while smaller, fewer crystals are now the rule (with the exception of those required for neutron diffraction), this has not reduced the value of crystal perfection, nor the requirement that at least some sort of crystal be obtained. Thus, attention is now focused on nucleation, perhaps always the most problematic step in the crystallization process, and enhancing crystal perfection. These continue to remain formidable problems.

Furthermore, the objectives of crystallization, the entities to be crystallized, will continue to become more challenging. In addition to membrane proteins that pose difficult problems because of their solubility (see Chapter 4.2[link] ), interest has increasingly turned towards the solutions of the structures of RNA, glycoproteins (Chang et al., 2007[link]), lipoproteins, and larger protein or protein–nucleic acid complexes and assemblies. It is unlikely that crystals with unit cells much above 1200 Å can be solved with current X-ray technologies, but even those assemblies, such as large icosahedral viruses, that do yield crystals amenable to analysis are remarkably fragile in a mechanical sense, and the large unit-cell size requires that the crystals greatly exceed the small sizes of conventional protein crystals. Additional problems will arise from proteins conjugated with other entities of significant size such as lipids and oligosaccharides, which are often disordered, and with proteins that are unstructured, in whole or in part.

Finally, we have come to believe that the structure of a protein in the crystal is the same as the structure of the protein in solution. But when the protein has a spectrum of conformations in solution, as a consequence often of its function, then to visualize it in full one needs to see it in multiple crystal forms. Thus, it will be increasingly necessary to grow crystals not simply of the apo protein, but also of its possible ligand complexes, and possibly in several polymorphs. By studying the protein in a variety of crystal forms, its conformational variety may be appreciated and its dynamic range delineated.

References

Bailey, K. (1942). The growth of large single crystals of proteins. Faraday Soc. Trans. 38, 186–192.
Chang, V. E., Crispin, M., Aricescu, A. R., Harvey, D. J., Nettleship, J. E., Fennelly, J. A., Yu, C., Boles, K. S., Evans, E. J., Stuart, D. I., Dwek, R. A., Jones, E. Y., Owens, R. J. & Davis, S. J. (2007). Glycoprotein structural genomics: solving the glycosylation problem. Structure, 15, 267–273.
Sauter, C., Dhouib, K. & Lorber, B. (2007). From macrofluidics to microfluidics for the crystallization of biological macromolecules. Cryst. Growth Des. 7, 2247–2250.








































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