Assembly of Viruses: Enveloped Particles

Viruses can be broadly categorized based on the presence, or absence, of a lipid envelope in their structure. Enveloped viruses predominantly infect animal cells although a few are known to infect plants, bacteria, and Archaea. The lipid bilayer can be derived from a variety of cellular membranes with the plasma membrane being the most common source. The presence of the lipid envelope allows enveloped viruses to bud out of cells without disrupting the cell membrane and, therefore, require an intact cell for particle release. Viral glycoproteins are found embedded in the lipid bilayer, usually in the form of transmembrane proteins, which allows communication of viral components across the membrane. These glycoproteins play crucial roles in the virus life cycle including assembly, budding, receptor binding, and membrane fusion. The assembly of two groups of icosahedral enveloped viruses (the alphaviruses and the flaviviruses) is described in detail in this article in order to present common themes in enveloped virus assembly.