Open Access`Broken symmetries' in macromolecular crystallography: phasing from unmerged data
Author(s) -
Schiltz Marc,
Bricogne Gérard
Publication year - 2010
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
ISSN - 1399-0047
DOI - 10.1107/s0907444909053578
Subject(s) - symmetry operation , phaser , homogeneous space , rotational symmetry , symmetry group , symmetry (geometry) , molecular symmetry , point group , physics , global symmetry , diffraction , anisotropy , crystallographic point group , reciprocal lattice , polarization (electrochemistry) , symmetry breaking , theoretical physics , crystallography , crystal structure , spontaneous symmetry breaking , quantum mechanics , geometry , mathematics , optics , chemistry , molecule , mechanics
The space‐group symmetry of a crystal structure imposes a point‐group symmetry on its diffraction pattern, giving rise to so‐called symmetry‐equivalent reflections. Instances in macromolecular crystallography are discussed in which the symmetry in reciprocal space is broken, i.e. where symmetry‐related reflections are no longer equivalent. Such a situation occurs when the sample suffers from site‐specific radiation damage during the X‐ray measurements. Another example of broken symmetry arises from the polarization anisotropy of anomalous scattering. In these cases, the genuine intensity differences between symmetry‐related reflections can be exploited to yield phase information in the structure‐solution process. In this approach, the usual separation of the data merging and phasing steps is abandoned. The data are kept unmerged down to the Harker construction, where the symmetry‐breaking effects are explicitly modelled and refined and become a source of supplementary phase information.