Deriving De Novo Atomic Models by Cryo Electron Microscopy

Cryo electron microscopy is a structural biology technique for determining three-dimensional structures of supramolecular complexes in solution. In cryoEM, samples in their physiological, non-crystalline state are embedded in vitreous ice during low dose imaging. A three-dimensional density map of the sample is obtained by combining tens of thousands of cryoEM images. In recent years, the resolution of cryoEM has improved steadily, reaching a resolution sufficient for building atomic models from the cryoEM density map alone.

In this video article, we illustrate how such atomic models can be derived by cryoEM. Others have described the detailed procedures for preparing frozen hydrated samples, image acquisition and the basic steps of data processing of cryoEM ^1,2. We will focus on several criticle technical aspects important for reaching 3-4 Å resolution and for building reliable atomic models. We use the tobacco mosaic virus (TMV) and cytoplasmic polyhedrosis virus (CPV) as representative complexes with helical and icosahedral objects, respectively. De novo atomic models of these objects have previously been determined by cryoEM and published, and their biological relevance is described in previous publications^3-6.