Virus Symmetry

VIRUS SYMMETRY

The orderly structural arrangement of similar protein to protein interface in viruses gives

rise to a symmetrical structure. With the help of electron microscopy, it has been found

that the morphology of nearly all viruses conforms to one of two basic symmetrical

patterns which could be:

1. Cubic/icosahedral

2. Helical

These are the two capsid symmetries described for all viruses

Cubic/Icosahedral symmetry

 Highly structured capsid in which capsomeres are arranged in form of an icosahedrons

 In the icosahedrons, there are 20 triangular faces and 12 apices/corners

 The capsomeres of each face form an equilateral triangle

 The capsomeres contribute to the rigidity of the capsid and help protect the nucleic acid

genome

 Each individual capsomere may consist of several polypeptides (in poliovirus, the

capsomere is madeup of three proteins)

 All DNA viruses of animals except poxviruses as well as some RNA viruses possess

icosahedral symmetry

 Viruses with icosahedral symmetry could be naked (without envelope) or enveloped

 Icosahedral capsids are generally assembled in the host cell prior to incorporation of the

viral nucleic acid. Some viral preparations may contain capsids devoid of nucleic acids.