CCMV has a structure based on the truncated icosahedron (T=3 in the standard notation for triangulated icosahedral structures). In the native form, stable around pH 5, 180 chemically identical protein subunits form a shell of diameter 28.6 nm. The protein subunits form into either pentagonal or hexagonal capsomeres. At pH 7, the virus particles undergo a 10% increase in radius, thought to occur as a result of deprotonation of carboxyl moieties at the inter-capsomere contacts, leading to electrostatic repulsion that opens out the structure, but the process falls short of complete disassembly through preservation of interwoven carboxyl/protein links between capsomeres. Discrete swollen states have also been observed in many plant viruses, and similar phenomena have been inferred for animal viruses such as poliovirus.
The model consists of rigid plates representing the capsomeres, together with double-links — spherically jointed bars that represent a protein link between capsomeres. One important fact that we have elucidated is that a system of this type has a totally symmetric expansion mode whatever the detailed geometry of the links. The ability of the virus to expand only depends on evolution getting the topology, and not the geometry, correct.
Kovács, F., Tarnai, T., Fowler, P.W. and Guest, S.D. (2004), "Double-link expandohedra: a mechanical model for expansion of a virus." Submitted to the Proceedings of the Royal Society: Mathematical, Physical & Engineering Sciences. (pdf preprint)
Kovács, F., Tarnai, T., Fowler, P.W. and Guest, S.D. (2004), "A class of expandable polyhedral structures." International Journal of Solids and Structures. 41(3-4), 1119-1137. doi:10.1016/j.ijsolstr.2003.09.046
Last updated on the 7th of June, 2004S.D. Guest - firstname.lastname@example.org