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Tris-dipicolinate lanthanide complex, Na3.[Ln(DPA)3], where DPA stands for pyridine-2,6 dicarboxylate, was used to obtain derivative crystals of hen egg-white lysozyme (HEWL). Derivative crystals were prepared by co-crystallization using conditions close to those leading to the native tetragonal HEWL crystals by adding in the crystallization drops solutions of Ce or Lu complexes to a final concentration of 50-100 mM. The crystals, belonging to a new monoclinic form of lysozyme, space group C2, were diffracting to a resolution never achieved with lysozyme crystals. Diffraction data for the Ce and Lu derivative crystals were recorded to resolutions of 0.80 and 0.85 A, respectively. Taking advantage of the anomalous signal of Lu (f'' = 7.8 e at λ = 0.85 A), experimental phases were determined by the SAD method using the program SHARP [1]. Most of the atoms in the structure could be individually observed in the experimental electron-density map, similar in quality to the final 2Fo-Fc map. |
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