Biology Reference
In-Depth Information
7
Crystallization of Proteins:
Principles and Methods
Lata Govada*
Crystallization of biological macromolecules is governed by a variety of vari-
ables. Since protein crystals are stabilized by rather weak interactions, they are
extremely sensitive to subtle variations in solution conditions; consequently,
protein crystal growth presents particularly challenging problems. In macromol-
ecular crystallography, the success of a project ultimately resides in the charac-
teristics of the crystals utilized for the study. The growth of suitable protein
crystals is therefore the most crucial step in the structure determination of a pro-
tein. Physico-chemical parameters such as protein and precipitant concentration,
pH, solubility, temperature, ionic strength, pressure and viscosity can play a cru-
cial role in determining the optimal conditions for perfect crystal formation.
Biochemical properties such as particle purity and conformational homogeneity
and the presence and nature of impurities and additives can also influence crys-
tallization. These parameters affect macromolecular solubility and are the major
factors behind the complexity of crystallization and therefore make predicting
suitable conditions laborious. A phase diagram is a useful tool to design experi-
ments for crystal growth. Applying a phase diagram can provide some guide-
lines on the various possible conditions that can influence crystallization
processes. This can be constructed by setting up many crystallization trials,
varying at least two conditions and plotting their outcomes, after a certain period
of time, on a two- or many-dimensional parameter grids.
Keywords:
Supersaturation; phase diagram; solubility and supersolubility curve;
batch and diffusion.
*Department of BioMolecular Medicine, Division of Surgery, Oncology, Reproductive
Biology and Anaesthetics (SORA), Faculty of Medicine, Sir Alexander Fleming Building,
Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, UK.
E-mail: l.govada@imperial.ac.uk.
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