From Lattice Distortion to Molecular Distortion: Characterising and Exploiting Crystal Deformation

While compensation for local displacements of unit cells is now an accepted part of any attempt to determine high-resolution molecular structures by electron crystallography, the rotation and deformation that accompanies such displacements has not yet been much examined; nor has the manner in which molecules respond to the associated stress. Deformation analysis provides a basis for selective averaging that makes it possible to recover new information on the mechanical properties of proteins. We summarise the relevant techniques; we report measurements of the various possible forms of distortion in several 2D crystals, and establish how these limit the resolution of averages obtained without distortion compensation; we present averages from two particular crystals that exhibit very different ways of accommodating the deformation, and finally consider how the resolution may in future be improved beyond what is currently achievable