THREE-DIMENSIONAL DIFFUSE X-RAY SCATTERING FROM STAPHYLOCOCCAL NUCLEASE. Michael E. Wall and Sol M. Gruner (Department of Physics, Princeton University, Princeton, NJ 08544, USA), Steven E. Ealick (Section of Biochemistry, Cell and Molecular Biology, Cornell University, Ithaca, NY 14853, USA).

The first full three-dimensional map of diffuse x-ray scattering from a protein crystal has been obtained using a CCD detector at the Cornell High-Energy Synchrotron Source (CHESS). The map was characterized and used to study the nature of disorder in crystals of Staphylococcal nuclease. Simulations indicate a correlation between the Staph. nuclease diffuse map and the calculated unit-cell structure factor. This result is consistent with a number of models of disorder, the most plausible being liquid-like motions of the protein [Caspar et al., Nature 332 (1988) 659] and thermal excitation of crystalline normal modes, both of which involve internal dynamics of the protein. Unit-cell substitutions and unit-cell rigid-body displacements, though unlikely, cannot be ruled out as models describing the disorder.