Radiation-damage-induced phasing with anomalous scattering: substructure solution and phasing.

Substructure-solution and phasing procedures using a combination of anomalous scattering and radiation-damage-induced isomorphous differences have been investigated. The tyrosine residues in thaumatin were iodinated with N-iodosuccinimide in the crystalline form as well as prior to crystallization. Several data sets were collected from both forms and used for substructure solution and phasing using various protocols, employing anomalous, isomorphous or both these signals. It was shown that combination of the anomalous and isomorphous signals in the form of the RIPAS (radiation-damage-induced phasing with anomalous scattering) strategy is beneficial for both locating the substructure and subsequent phasing.