Topography and high resolution diffraction studies in tetragonal lysozyme

Two complementary approaches are used to enhance the usefulness of X-ray to pographies obtained from protein crystals. First, the use of thin plate-lik e crystals in conjunction with a high intensity, collimated and small sourc e size synchrotron beam produces a large beneficial effect on the level of detail and contrast of topographies for the quantification of local misalig nment in the crystal lattice. Second, the recording of topography series al ong the rocking curve of a diffraction peak is proposed as a technique to c ombine the benefits of both rocking curves and topographies and produce ver y detailed data ("rocking maps") on the spatial distribution of lattice mis alignments and mosaic spread ("local rocking curves"). The most important c rystal features controlling the observed contrast are growth sectors and in ter-sector boundaries, clearly observed in the topographies. Systems of par allel fringes are observed in many of the topographies. Two alternative exp lanations for these fringes are discussed: (a) as moire interference fringe s or (b) as Pendellosung fringes in a wedge shaped crystal volume. In both cases, growth sectors play a central role in the physics of fringe generati on. Many observations suggest the presence of a relatively large component of dynamical diffraction in these crystals; the consequences of this new sc enario are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.