Modelling and refining site-specific radiation damage in SAD/MAD phasing.
Site-specific radiation damage on anomalously scattering sites can be used to generate additional phase information in standard single- or multi-wavelength anomalous diffraction (SAD or MAD) experiments. In this approach the data are kept unmerged, down to the Harker construction, and the evolution of site-specific radiation damage as a function of X-ray irradiation is explicitly modelled and refined in real space. Phasing power is generated through the intensity differences of symmetry-related reflections or repeated measurements of the same reflection recorded at different X-ray doses. In the present communication the fundamentals of this approach are reviewed and different models for the description of site-specific radiation damage are presented. It is shown that, in more difficult situations, overall radiation damage may unfold on a time scale that is similar to the evolution of site-specific radiation damage or to the total time that is required to record a complete data set. In such cases the quality of the phases will ultimately be limited by the effects of overall radiation damage.
Schiltz
M
M
Ecole Polytechnique Fédérale de Lausanne (EPFL), Laboratoire de Cristallographie, CH-1015 Lausanne, Switzerland. marc.schiltz@epfl.ch
Bricogne
G
G
D003198:Computer Simulation; D018360:Crystallography, X-Ray / Q000379:methods*; D004307:Dose-Response Relationship, Radiation; D046911:Macromolecular Substances / Q000737:chemistry* / Q000528:radiation effects*; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation / Q000528:radiation effects; D011489:Protein Denaturation / Q000528:radiation effects; D011829:Radiation Dosage; D014965:X-Rays
D046911:Macromolecular Substances