Macromolecular powder diffraction, though still in its nascence, is ideally suited for cases where no suitable single crystals are available.   In the past seven years, the viability of the approach for several protein structures has been demonstrated.  Among these initial powder studies, molecular replacement solutions of insulin and turkey lysozyme, themselves, into alternate space groups were accomplished by Von Dreele, et al., and Margiolaki, et al., respectively.  The first molecular replacement of an unknown protein structure, the SH3 domain of ponsin, was executed by Margiolaki, et al., which helped move the technique into uncharted territory.

To demonstrate that cross-species molecular replacement of larger structures is feasible, we present the solution of hen egg white lysozyme using the 60% identical human lysozyme (PDB code: 1LZ1) as the search model.  We have used extracted intensities from five data sets taken at different salt concentrations in a multi-pattern Pawley refinement, in an effort to reduce the impact of overlaps.  We also present a full-scale multi-species analysis, which demonstrates the reliability of the technique.  Extension to higher molecular weight structures, to test the limit of this technique is ongoing.  Use of the APS was supported by the DOE/OS/BES under contract number W-31-109-ENG-38

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1. Characterization of proteins by powder diffraction