A procedure for ab initio phasing of one-wavelength anomalous scattering data from proteins - Combining direct methods with the solvent flattening technique

Abstract

Both direct methods and the solvent flattening technique have been proved capable of breaking the phase ambiguity intrinsic in one-wavelength anomalous scattering (OAS) data. However, in theory, while direct methods are better in deriving starting phases from OAS data, the solvent flattening technique is more powerful in the subsequent phase refinement. A procedure is described in this paper which combines direct methods with the solvent flattening technique for phasing of OAS data. The procedure has been tested with the known protein RNase Sa. This protein is of moderate size, and the diffraction data were collected routinely without taking special care for the recording of Friedels. The test proved that the combination of the direct method and the solvent flattening leads to a much better result than that from either method alone.