What binds the proteins in a viral capsid together? Best answer on the web

Posted in: darrelrussell.com edit
07 Jan 2009
  • In other words, are there interactions between the proteins themselves that keep the capsid together, or is it something else?


  • Yes, interactions between the capsid proteins. Also, in some viruses, interactions between capsid proteins and the enclosed DNA or RNA matters as well.



    For enveloped viruses you can often remove the envelope with suitable detergents, and leave the protein capsid (with NA inside) relatively intact.



    [edited to correct typos]


  • The forces that drive the assembly of virus particles include hydrophobic and electrostatic interactions. Only rarely are covalent bonds used in holding together parts of the substructure. Now...why is this?



    Imagine a single virus particle being a hollow shell which encapsulates a genome. Easy to imagine, but it's impossible for the following reason: the triplet nature of the genetic code means that 3 nucleotides are necessary to encode 1 amino acid. This is as economical as it gets since anything less would not be usable by the host cell. Because the average molecular weight of a nucleotide triplet is 1000 and the weight of an amino acid is about 150, a nucleic acid can encode only about 15% of its own weight. Therefore, capsids must be made up of multiple protein molecules, called subunit construction, and also overcome how they arranged.



    In 1957, it was shown that tobacco-mosaic virus (TMV) could spontaneously form when all the component were just mixed together. This discovery showed that the particle was at a free energy minimum state and was the favored structure of the components. Which lead back to the initial paragraph of this piece.


  • Good question!! Some viruses are enveloped in a lipid membrane. I am not an expert on viruses, though, so, hopefully, some one will come along who is an expert on viruses.