Editing Capsid (section)

==Origin and evolution==
It has been suggested that many viral capsid proteins have evolved on multiple occasions from functionally diverse cellular proteins.<ref name=Krupovic2017>{{cite journal | vauthors = Krupovic M, Koonin EV | title = Multiple origins of viral capsid proteins from cellular ancestors | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 114 | issue = 12 | pages = E2401–E2410 | date = March 2017 | pmid = 28265094 | pmc = 5373398 | doi = 10.1073/pnas.1621061114 | bibcode = 2017PNAS..114E2401K | doi-access = free }}</ref> The recruitment of cellular proteins appears to have occurred at different stages of evolution so that some cellular proteins were captured and refunctionalized prior to the divergence of cellular organisms into the three contemporary domains of life, whereas others were hijacked relatively recently. As a result, some capsid proteins are widespread in viruses infecting distantly related organisms (e.g., capsid proteins with the [[jelly-roll fold]]), whereas others are restricted to a particular group of viruses (e.g., capsid proteins of alphaviruses).<ref name=Krupovic2017 /><ref name=Krupovic2019 />

A computational model (2015) has shown that capsids may have originated before viruses and that they served as a means of [[horizontal transfer]] between replicator communities since these communities could not survive if the number of gene parasites increased, with certain genes being responsible for the formation of these structures and those that favored the survival of self-replicating communities.<ref>{{cite journal | vauthors = Jalasvuori M, Mattila S, Hoikkala V | title = Chasing the Origin of Viruses: Capsid-Forming Genes as a Life-Saving Preadaptation within a Community of Early Replicators | journal = PLOS ONE | volume = 10 | issue = 5 | pages = e0126094 | date = 2015 | pmid = 25955384 | pmc = 4425637 | doi = 10.1371/journal.pone.0126094 | bibcode = 2015PLoSO..1026094J | doi-access = free }}</ref> The displacement of these ancestral genes between cellular organisms could favor the appearance of new viruses during evolution.<ref name=Krupovic2019 >{{cite journal | vauthors = Krupovic M, Dolja VV, Koonin EV | s2cid = 169035711 | title = Origin of viruses: primordial replicators recruiting capsids from hosts | journal = Nature Reviews. Microbiology | volume = 17 | issue = 7 | pages = 449–458 | date = July 2019 | pmid = 31142823 | doi = 10.1038/s41579-019-0205-6 | url = https://hal-pasteur.archives-ouvertes.fr/pasteur-02557191/file/Krupovic_NRMICRO-19-022_MS_v3_clean.pdf }}</ref>