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Direct incorporation of experimental phase information in model refinement

Pavol Skubak(1), Garib N. Murshudov(2) and Navraj S. Pannu(1)
(1) Biophysical Structural Chemistry, Leiden University, The Netherlands
(2) Structural Biology Laboratory, University of York, United Kingdom

The incorporation of prior phase information has been shown to strengthen model refinement. However, the current likelihood refinement target using prior phase information has shortcomings: the “phased” refinement target considers experimental phase information indirectly in the form of Hendrickson-Lattman coefficients and the refinement target implicitly assumes that the prior phase information is independent from the calculated model structure factor.

We have derived a multivariate likelihood function that overcomes these shortcomings and directly incorporates experimental phase information from a single-wavelength anomalous diffraction (SAD) experiment. We have implemented this function in the refinement program Refmac and have obtained promising results.