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. 2006 Mar 1;62(Pt 3):298-301.
doi: 10.1107/S1744309106006373. Epub 2006 Feb 28.

Large-scale purification and crystallization of the endoribonuclease XendoU: troubleshooting with His-tagged proteins

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Large-scale purification and crystallization of the endoribonuclease XendoU: troubleshooting with His-tagged proteins

Fabiana Renzi et al. Acta Crystallogr Sect F Struct Biol Cryst Commun. .

Abstract

XendoU is the first endoribonuclease described in higher eukaryotes as being involved in the endonucleolytic processing of intron-encoded small nucleolar RNAs. It is conserved among eukaryotes and its viral homologue is essential in SARS replication and transcription. The large-scale purification and crystallization of recombinant XendoU are reported. The tendency of the recombinant enzyme to aggregate could be reversed upon the addition of chelating agents (EDTA, imidazole): aggregation is a potential drawback when purifying and crystallizing His-tagged proteins, which are widely used, especially in high-throughput structural studies. Purified monodisperse XendoU crystallized in two different space groups: trigonal P3(1)21, diffracting to low resolution, and monoclinic C2, diffracting to higher resolution.

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Figures

Figure 1
Figure 1
Effect of chelating agents in the solubilization of aggregated His-tagged protein. HPLC gel-filtration analysis shows that 250 mM (red) and 100 mM (blue) imidazole yield monodisperse His-tagged protein. 20 mM (light green), 10 mM (dark green) and 5 mM (purple) EDTA also improve monodispersity in a concentration-dependent fashion. Addition of 20 mM Mn2+ salt with and without EDTA (brown and pink) causes the protein to aggregate again. Elution profiles were analyzed using the CSW program.
Figure 2
Figure 2
(a) Trigonal crystals in 40% (NH4)2SO4, 0.2 M sodium citrate pH 6, 17 mg ml−1 protein, 50 mM UMP at 293 K and (b) their diffraction image with an enlargement. (c) Monoclinic crystals in 40% NH4SO4, 0.2 M sodium phosphate pH 5.5, 17 mg ml−1 protein, 50 mM UMP at 293 K improved by seeding from aggregated (top) to single crystals (bottom) and (d) their diffraction image with an enlargement.

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