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Electron crystallography determines ordered molecular or atomic structure using electrons interacting with a crystalline specimen. Electron diffraction and suitably resolved electron images provide complementary constraints on a structural model. The periodic order supplies repeated information; interpreting that information still requires a model of scattering and image formation.

An important biological application resolved the alpha/beta tubulin heterodimer. Zinc-induced tubulin sheets provided an ordered specimen for a model reported at $3.7$ angstrom resolution. The resulting structure distinguished the two related protein subunits and their different nucleotide environments.^[ref]

The specimen geometry matters. An ordered sheet is not the same object as an isolated microtubule in a living cell, even when its molecules reveal features relevant to microtubule assembly. The structural experiment answers questions about the molecular arrangement under its preparation conditions; biological interpretation then connects that arrangement to other observations.

Resolution also differs from the size of the object. A sheet may extend over many molecular repeats while the data constrain features on the angstrom scale. Quoting a nominal resolution does not mean every atom is independently located with that exact uncertainty or that every flexible region is equally well resolved.

Electron crystallography belongs to the wider family of electron microscopy and crystallography methods, but should not be used as a synonym for every electron micrograph. A dark spot, an image of a cellular outline and a diffraction-constrained molecular model are different types of evidence.

E. Nogales is the first author of a 1998 study resolving the structure of the alpha–beta tubulin heterodimer, the building block of microtubules. The researchers used electron crystallography of zinc-induced tubulin sheets to obtain a density map at 3.7 angstrom resolution and fit an atomic model to it.^[ref]

The two related protein subunits had similar overall folds but occupied distinct positions in a heterodimer. The model identified a nucleotide-binding region and other structural regions relevant to interactions. It illustrates a practical strategy in structural biology: organize a difficult protein into a repeatable experimental specimen, measure its scattering or imaging signal, and test a molecular model against that evidence. The specimen here was an induced sheet, so interpreting it as the architecture of an intact cellular microtubule requires additional evidence.^[ref]