Virus Particle Structure: Nonenveloped Viruses

Nonenveloped viruses provide model systems for high-resolution structural study of whole virus capsids (and their components) and the principles of large-scale nucleoprotein tertiary and quaternary interactions. The structures of viruses ranging from 200 to 5000 A in diameter have now been determined at moderate to near atomic resolution, revealing a complicated array of architectures that conform to both predicted theories and show previously unobserved and completely unexpected types of associations. We organize a selection of these structures into various classifications based on their overall symmetry and size, and begin by examining common and uncommon coat protein folds, followed by detailed exploration of a few of the particles into which they assemble. Both past and present studies have found common features between viruses infecting different domains of life; yet a number of their structural features are not only unique among viruses, but all known protein structures.