✍ Scribed by Basso, Sebastian ;Besnard, Céline ;Wright, Jonathan P. ;Margiolaki, Irene ;Fitch, Andrew ;Pattison, Philip ;Schiltz, Marc
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Protein powder diffraction is shown to be suitable for obtaining__de novo__solutions to the phase problem at low resolution__via__phasing methods such as the isomorphous replacement method. Two heavy-atom derivatives (a gadolinium derivative and a holmium derivative) of the tetragonal form of hen egg-white lysozyme were crystallized at room temperature. Using synchrotron radiation, high-quality powder patterns were collected in which pH-induced anisotropic lattice-parameter changes were exploited in order to reduce the challenging and powder-specific problem of overlapping reflections. The phasing power of two heavy-atom derivatives in a multiple isomorphous replacement analysis enabled molecular structural information to be obtained up to approximately 5.3 Å resolution. At such a resolution, features of the secondary structure of the lysozyme molecule can be accurately located using programs dedicated to that effect. In addition, the quoted resolution is sufficient to determine the correct hand of the heavy-atom substructure which leads to an electron-density map representing the protein molecule of proper chirality.
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The crystal structure of monoclinic thallium(III) hydrogendiphosphate, TlHP 2 O 7 , has been solved from laboratory X-ray powder diffraction data and refined by the Rietveld method. All atoms occupy general positions. The Tl III ions have a distorted octahedral coordination environment of O atoms fr