Experimental Characteristics of Diffuse X-ray Scattering in Lysozyme Crystals

Abstract

X-ray crystallography, a popular and powerful technique for determining the atomic structures of proteins and other macromolecules, is traditionally limited to reporting static structures, whereas proteins in vivo are constantly shifting between conformations. Such conformational dynamics give rise to structured diffuse scattering, which is observable in protein crystallography experiments. Because the measurement of diffuse scattering involves numerous experimental challenges beyond those inherent to traditional crystallography, some basic questions about the behavior of diffuse intensities remain unanswered: how reproducible is the diffuse intensity between ostensibly identical crystals? What happens to diffuse intensity when the protein binds to an inhibitor molecule, when the crystal is cryocooled, or when it suffers radiation damage? Here, we present the results of diffuse scattering experiments on 23 different lysozyme crystals under a variety of experimental conditions. It is shown that diffuse intensity is highly consistent between ostensibly identical room temperature crystals. Binding to an inhibitor reduces the diffuse intensity non-uniformly, suggesting a change in the molecular motions that produce diffuse scattering. Cryocooling drastically changes the diffuse intensity pattern, indicating that cryocooled crystals are poor representatives of the correlated displacements in room temperature crystals. Radiation dose effects in a single image's diffuse scattering are also discussed.