CapsidThe capsid is the outer shell of the virus, and consists of monomeric subunits of protein. Its three primary purposes are to protect the virus's genetic material, detect cells suitable for infection, and initiate the infection by "opening" the target cell to inject DNA into the cytoplasm.
After infection, the capsid is synthesized using the protein biosynthetic mechanisms of the host cell. In addition to the capsid, some viruses will steal a portion of the host cell membrane. This is wrapped around the capsid, with viral proteins jutting through it, as extra protection for the virus.
Most viral structures are based on the structure of their capsids. These can come in helical, icosahedral or isometric, or enveloped forms. Helical symmetry has protein subunits arranged around the circumference of the virus, forming a disk. Icosahedrally symmetrical capsids form a quasi-spherical structure. And with enveloped viruses, protein subunits are exposed to the external environment.
It is the capsid of the virus that most antiviral medications are designed to attack. However, the capsid is remarkably strong in most viruses, and poses a significant challenge for disease researchers. Minor changes in the capsid pose significant challenges as well, as an antiviral specified for one structure won’t work on the new capsid structure and must be redeveloped.
Web Resources On Capsid
Viruses
Virus Capsid Images
Book Resources On CapsidParvovirus capsids by N. Young
The Virus and the Vaccine by Bookchin & Schumacher
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