The Structure of Elongated Viral Capsids

Abstract

There are many viruses whose genetic material is protected by a closed elongated protein shell. Unlike spherical viruses, the structure and construction principles of these elongated capsids are not fully known. In this article, we have developed a general geometrical model to describe the structure of prolate or bacilliform capsids. We show that only a limited set of tubular architectures can be built closed by hemispherical icosahedral caps. In particular, the length and number of proteins adopt a very special set of discrete values dictated by the axial symmetry (fivefold, threefold, or twofold) and the triangulation number of the caps. The results are supported by experimental observations and simulations of simplified physical models. This work brings about a general classification of elongated viruses that will help to predict their structure, and to design viral cages with tailored geometrical properties for biomedical and nanotechnological applications.

Self-assembly on a cylinder: a model system for understanding the constraint of commensurability

“…Our results may have broad implications for understanding the way tubular crystals assemble in nature. In particular, it has been pointed out that many biological materials exhibit the type of structure described here, and therefore the same commensurability constraint [25,26,35]. Because capsid proteins in helical viruses (tobacco mosaic virus, for example) are constrained to bind to the surface of a RNA strand, the situation described here might be informative in understanding their structure.…”

Charge Detection Mass Spectrometry Identifies Preferred Non-Icosahedral Polymorphs in the Self-Assembly of Woodchuck Hepatitis Virus Capsids

“…Moody 8,9 suggested elongation could be accomplished by adding rings of hexamers to the waist of the icosahedron. Luque and Reguera 14 generalized Moody’s rules to elongation along the two-fold and three-fold axes of an icosahedron. Moody’s model for elongation of the T =4 capsid along the 5-fold axis can account for the prominent species with 150 dimers (see Figure 4).…”

“…12,13 Capsids can also be extended along threefold and twofold axes by discrete steps of hexamers. 14,15 …”

A minimal representation of the self-assembly of virus capsids

“…The simple geometrical construction model introduced by Caspar and Klug (CK) 2 to explain the architecture of icosahedral viruses is a milestone in modern virology. Generalizations of the CK rules properly account for the geometry of some exceptional icosahedral capsids [3][4][5][6] and other elongated virus capsids that share coordination numbers with the icosahedral ones [7][8][9] . Recent work [10][11][12] provides important further development about the effect of the geometrical and topological constraints on the capsid structure.…”