On the relationship between diffraction patterns and motions in macromolecular crystals.

The quality of many macromolecular crystal structures published recently has been enhanced through the use of new methods for treating the effects of molecular motion and disorder on diffraction patterns, among them a technique called translation, libration, screw-axis (TLS) parameterization. TLS parameterization rationalizes those effects in terms of domain-scale, rigid-body motions and, interestingly, the models for molecular motion that emerge when macromolecular diffraction data are analyzed this way often make sense biochemically. Here it is pointed out that all such models should be treated with caution until it is shown that they are consistent with the diffuse scatter produced by the crystals that provided the diffraction data from which they derive.