High-resolution electron crystallography of protein molecules.

Electron diffraction data and high-resolution images can now be used to obtain accurate, three-dimensional density maps of biological macromolecules. These density maps can be interpreted by building an atomic-resolution model of the structure into the experimental density. The Cowley-Moodie formalism of dynamical diffraction theory has been used to validate the use of kinematic diffraction theory (strictly, the weak phase object approximation) in producing such 3D density maps. Further improvements in the preparation of very flat (planar) specimens and in the retention of diffraction to a resolution of 0.2 nm or better could result in electron crystallography becoming as important a technique as X-ray crystallography currently is for the field of structural molecular biology.