Cowpea Chlorotic Mottle Virus

Cowpea Chlorotic Mottle Virus, known by the abbreviation CCMV, is a virus that specifically infects the cowpea plant, or black-eyed pea. The leaves of infected plants develop yellow spots, hence the name "chlorotic". Like the majority of viruses, it consists of a protein shell, that surrounds a central core of RNA. Its protein shell, or capsid, is composed of icosahedral arrangements of identical protein subunits. The symmetry at which this is done is exactly like the symmetry of a football: hexagons and pentagons are interchanged to give the final sphere. There are 20 hexagonal structures and 12 pentagons in each specimen of the virus, which gives in total 180 subunits. The virus is about 30 nm in size, and can be observed with transmission electron microscopy using negative staining. The subunits consist of 189 amino acid residues. The N-terminus of each subunit points toward the inside of the virus, where it has a stabilizing interaction with the RNA.

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History

Bancroft et al. in 1967 described the first experiments to isolate and characterise the virus. Since that time, due to the relative ease with which it is grown and isolated, many researchers have focused their attention on the virus. The interest of the scientific community for this virus is also due to a conspicuous property: it is possible to disassemble the virus and remove the genetic material, the RNA. Then, under slightly acidic pH and with relatively high amounts of salts, it is possible to stimulate the self-assembly of the protein subunits, into a shell of identical size to the virus. This yields an empty capsid which has a number of interesting properties. Several successful attempts are reported to incorporate other materials, such as inorganic crystals, inside the capsid.

References

• CCMV Overview
• Bancroft JB, Hiebert E. Formation of an infectious nucleoprotein from protein and nucleic acid isolated from a small spherical virus. Virology, 1967
• Douglas, T. & Young, M. Host–guest encapsulation of materials by assembled virus cages, Nature, 1998 [1]