Pleiomorphic viruses revealed by cryo tomography: the structure of coronaviruses

Cryo-electron microscopy has provided in the last decades a wealth of three-dimensional information on viral structures. However, most of this knowledge stems from single particle methods, which rely on averaging and are therefore restricted to viral homogenous structures such as icosahedral capsids [1]. This type of analysis excludes pleiomorphic viruses, that is, viruses that, having defined general architectures, arrange their components into different shapes or sizes. Cryo-electron tomography, which provides three-dimensional reconstructions of unique specimens, is now starting to shed light into the structure of this type of viruses [2].