SAD/MAD phasing

Abstract

Currently, the most common ways of solving novel macromolecular crystal structures are based on the anomalous signal provided by some atoms present in the investigated structures. They can be implemented as the Single- or Multi-wavelength Anomalous Diffraction (SAD or MAD) method. Instead of collecting diffraction data from the native crystal and a number of derivatives, as in the classic Multiple Isomorphous Replacement (MIR) approach, these techniques utilize one or more data sets, recorded from only one crystal containing suitable anomalous scatterers. Whereas with MIR the protein phases are estimated from the additional scattering of the heavy atoms present in the derivative crystals, in SAD and MAD they are calculated from the wavelength-dependent quantitative differences in the anomalous scattering contribution of certain atoms contained in the crystal. © 2013 Springer Science+Business Media Dordrecht.