International
Tables for Crystallography Volume F Crystallography of biological macromolecules Edited by M. G. Rossmann and E. Arnold © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. F. ch. 4.3, pp. 102-103
Section 4.3.7. Engineering crystal contacts to enhance crystallization in a particular crystal form
aLaboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0560, USA |
It is often the case that the structure of some related form of a protein is known, but the protein of interest crystallizes in a different space group. There have been attempts to use this knowledge to obtain crystals in a form that could be readily analysed. However, it may not be necessary to resort to molecular engineering approaches, since molecular replacement methods can often be successfully applied to determine the protein structure.
In one of the first applications of protein engineering to obtain crystals, Lawson et al. (1991) reported the crystal structure of ferritin H. Ferritin has two types of chains, H and L; the structure of rat L ferritin was known. Despite high sequence identity to L ferritin, human recombinant H ferritin did not crystallize satisfactorily. To obtain the structure of a human H ferritin homopolymer, the sequence in the subunit interface was modified to give crystals that were isomorphous with the rat L ferritin. The mutation
was introduced, which enabled metal bridge contacts to form, resulting in crystals that diffracted to 1.9 Å. Although the mutant was designed to crystallize from CdSO4, it did not do so. Rather, CaCl2 gave large crystals which were isomorphous with rat and horse L ferritin crystals. In these latter crystals, Ca2+ is coordinated between Asp84 and Gln86, providing the rationale for the mutation.
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