Crystallization under an external electric field: A case study of glucose isomerase

Electric fields have been employed to promote macromolecular crystallization for several decades. Although crystals grown in electric fields seem to present higher diffraction quality, these methods are not widespread. For most configurations, electrodes are in direct contact with the protein solution. Here, we propose a configuration that can be easily extended to standard crystallization methods for which the electrodes are not in direct contact with the protein solution. Furthermore, the proposed electrode configuration supplies an external DC electric field. Glucose Isomerase from Streptomyces rubiginosus crystals were grown at room temperature using the microbatch method in the presence of 1, 2, 4, and 6 kV. Several crystallization trials were carried out for reproducibility and statistical analysis purposes. The comparison with crystals grown in the absence of electric fields showed that crystallization in the presence of electric fields increases the size of crystals, while decreasing the number of nucleations. X-ray diffraction analysis of the crystals showed that those grown in the presence of electric fields are of higher crystal quality.