X-ray topography of a crystal of tetragonal lysozyme
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100th anniversary of the discovery of Xray diffraction
XRay Topography of a Crystal of Tetragonal Lysozyme A. E. Voloshina, S. I. Kovaleva, M. S. Lyasnikovaa, E. Kh. Mukhamedzhanovb, M. M. Borisovb, and M. V. Koval’chuka, b a
Shubnikov Institute of Crystallography, Russian Academy of Sciences, Leninskii pr. 59, Moscow, 119333 Russia email: [email protected] b National Research Centre “Kurchatov Institute,” pl. Kurchatova 1, Moscow, 123098 Russia Received April 27, 2012
Abstract—A crystal of the tetragonal modification of lysozyme grown under controlled conditions with in situ monitoring of the growth kinetics and morphology of the (110) face is studied by Xray topography using synchrotron radiation. The choice of a diffraction reflection with optimal dispersion allows us to obtain an informative Xray topographic image of the sample. It is found that the striations that are formed under changing supersaturation correspond to the type of zonality characteristic of crystals growing by the normal mechanism and differ from those observed in inorganic crystals growing by the layerbylayer mechanism. DOI: 10.1134/S1063774512050173
INTRODUCTION The crystallization of proteins is a necessary stage when determining their structure. Structural data with high spatial resolution can be obtained only for sam ples characterized by high structural perfection. How ever, growing protein crystals with a defect content that has no noticeable effect on the precision of Xray structure analysis is currently the main problem. In the last few years, a great number of publications concerning studies of the effect of the imperfection of protein crystals on the resolution of Xray structure analysis have appeared. In most of them (for example, [1–4]), the inhomogeneous (zonal or sectorial) distri bution of highmolecular impurities, in particular, dimers, trimers, and higher molecular complexes of protein molecules, is said to be the main type of defects. Different mechanisms of the effect of high molecular impurities on the precision of Xray struc ture analysis were studied in [5]. It was found that the influence of impurities becomes apparent only in the increase of crystal mosaicity because of the generation of elastic strains and the formation of cracks in a crys tal having an inhomogeneous composition. It was shown in [2, 3] that the level of strains that arise in pro tein crystals because of zonal inhomogeneity can reach the level of brittle fracture. For crystals grown in aqueous solutions, the most commonly encountered type of zonal inhomogeneity is morphological (or internal) zonality resulting from changes in the morphology of a growing face, i.e., changes of step sources, changes of slopes of vicinal growth hillocks, or the development of morphological instability [6]. In some cases, for example, in diamond crystals, kinetic (or external) zonality is also observed. It results from changes in the impurity content in the diffusion boundary layer of the liquid phase and in the
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