Phase perturbation as a means of electron density map quality evaluation

Abstract

This paper describes a new means for evaluating the quality of crystallographic electron density maps. It has been found that a better data set possesses greater robustness against perturbations applied to the phases. Thus it allows recognition of a more precise phase set and provides a way to select the best or reject the worst from several noisy data sets derived from the same crystal structure. The results indicate that calculation of the correlations by the procedure described here can be useful in ranking electron density maps in this aspect of quality. The method suggested has potential use for selecting a better molecular replacement solution, as well as for evaluating trial phase sets in ab initio phasing procedures. ‡ Current address:

FEM: feature-enhanced map

“…The rationale behind map randomization followed by combination of the resulting perturbed maps is based on the hypothesis that map artifacts and noise are more affected by randomization than the signal in the map (Kirillova, 2008). In this way, the artifacts and noise might be reduced compared with the signal by map averaging or some other statistical treatment of the resulting maps.…”