Pretty Nasty: Symmetry in virus architecture

Abstract

Symmetry in virus architecture A piece of bad news, wrapped up in protein, is an often-quoted description of viruses eloquently made by Sir Peter Medawar. Putting aside the added complexity of the lipid envelopes found in many viruses, this describes most viruses very well. This catchy soundbite does not, however, convey exactly how the bad news is packaged, or the astonishingly intricate and dynamic nature of viral coat proteins. For reasons of genetic economy, viruses enclose their genomes in protective shells that are highly symmetrical and, consequently, these tiniest of pathogens can be strikingly beautiful structures. When confronted with images of viruses, it is tempting to view the virus particle (or virion) as a static entity, designed to do no more than protect its genetic payload in the harsh extra-cellular environment. Such a view is overly simplistic, however. The abstract beauty of these assemblies belies the complex morphogenetic pathways that ensure correct genome packaging and particle assembly. While remaining robust in the environment and evading host immunity, viruses must engage host cell receptors and other cellular components, traffic to specific compartments and only then release their genomes at precisely the correct moment to initiate infection. Viruses are marvels of nanoengineering, molecular machines superbly adapted to transmit their bad news and bring misery, illness and sometimes death to their unfortunate victims.