Application of molecular replacement to protein powder data from image plates.

Macromolecular structures can be solved via molecular replacement from powder diffraction data collected not only on multi-analyzer diffractometers but also on image plates. Diffraction peaks recorded on image plates are generally broader than those collected using an array of crystal analyzer detectors, but the image-plate data often allow the use of powder data to lower d-spacings. Owing to the high incidence of overlaps in powder patterns, which is especially evident for larger structures, a multi-pattern Pawley refinement is necessary in order to distinguish intensity peaks. This work utilized various salt concentrations to produce small lattice distortions, which resulted in shifts of Bragg peak positions, in a suite of five powder patterns. Using reflection structure factors obtained from this combined refinement, the structure of hen egg-white lysozyme was determined by molecular replacement using the 60% identical human lysozyme (PDB code 1lz1) as the search model. This work also expands upon previous work by presenting a full-scale multi-species analysis combined with an investigation of the sensitivity with regard to discrimination between incorrect fold types. To test the limits of this technique, extension to higher molecular-weight structures is ongoing.