Wikipedia

Sputnik virophage

Mimivirus-dependent virus Sputnik(fromRussianспутник"satellite" ) is asubviral agentthat reproduces inamoebacells that are already infected by a certain helper virus; Sputnik uses thehelper virus's machinery for reproduction and inhibits replication of the helper virus. It is known as avirophage,in analogy to the termbacteriophage.[2]

Mimivirus-dependent virus Sputnik
Virus classificationEdit this classification
(unranked): Virus
Realm: Varidnaviria
Kingdom: Bamfordvirae
Phylum: Preplasmiviricota
Class: Maveriviricetes
Order: Priklausovirales
Family: Lavidaviridae
Genus: Sputnikvirus
Species:
Mimivirus-dependent virus Sputnik
Member virus
  • Sputnik 1
  • Sputnik 2
  • Sputnik 3
Amimiviruswith two satellite Sputnik virophages (arrows)[1]

Viruses like Sputnik that depend on co-infection of thehostcell by helper viruses are known assatellite viruses.At its discovery in a Paris water-cooling tower in 2008, Sputnik was the first known satellite virus that inhibited replication of its helper virus and thus acted as a parasite of that virus. In analogy, it was called avirophage.[2]

Sputnik virophages were found infecting giant viruses ofMimiviridaegroup A. However, they are able to grow in amoebae infected byMimiviridaeof any of the groups A, B, and C.[3]

Virology

edit

Sputnik was first isolated in 2008 from a sample obtained from humans; it was harvested from the contact lens fluid of an individual withkeratitis.[4]Naturally however, the Sputnik virophage has been found to multiply inside species of the opportunistically pathogenic protozoanAcanthamoeba,but only if that amoeba is infected with the largemamavirus.Sputnik harnesses the mamavirus proteins to rapidly produce new copies of itself.[2][5]

Mamavirusis formally known asAcanthamoeba polyphagamimivirus (APMV) and is a close relative of the previously knownmimivirus.The mimivirus is a giant in the viral world; it has more genes than many bacteria and performs functions that normally occur only in cellular organisms. The mamavirus is even larger than the mimivirus, but the two are very similar in that they form large viral factories and complex viral particles.[6]There are conditions in which Sputnik cannot produce new virions within these viruses however. It has been observed that when Mimivirus is cultured with germ-free amoeba, bald virions are produced that lack the surface fibers that are characteristic of this virus. For reasons unknown, Sputnik is unable to replicate and produce new virions in these bald viruses.[7]Virophage growth is deleterious to APMV and results in the production of abortive forms and abnormal capsid assembly of APMV. In one of the experiments done by inoculatingAcanthamoeba polyphagawith water containing an original strain of APMV, it was discovered that several capsid layers accumulate asymmetrically on one side of the viral particle causing the virus to become ineffective. Sputnik decreased the yield of infective viral particle by 70% and also reduced the amoebalysisby threefold at 24h.[2]

Sputnik has a circular double strandedDNAgenomeconsisting of 18,343 base pairs.[6]It contains genes able to infect all three domains of life:Eukarya,ArchaeaandBacteria.Of the twenty-one predicted protein-coding genes, three are apparently derived from APMV itself, one is a homologue of an archaeal virus, and four others are homologues of proteins in bacteriophages and eukaryotic viruses. The fact that three of these genes are derived from APMV indicates that Sputnik is able to participate in gene-transfer processes and mediate lateral gene transfer between giant viruses.[8]Thirteen areORFans,that is they do not have any detectable homologues in current sequence databases. The Sputnik genome has a highAT-content(73%), similar to that of APMV. It contains 16 predictedhairpin loops,all but two of which fall between ORFs.[9]

Several other homologues such as those of ahelicase-primase,a packagingATPase,an insertion sequence transposaseDNA-binding subunit,and a Zn-ribbon protein, were detected in theGlobal Ocean Surveyenvironmental data set, suggesting thatvirophagescould be a currently unknown family of viruses.[citation needed]

Sputnik was found to contain genes that were shared by APMV. These genes could have been acquired by Sputnik after the association of APMV with the host and then interaction between the virophage and the viral host. Recombination within the viral factory might have resulted in the exchange of genes. Sputnik is one of the most convincing pieces of evidence for gene mixing and matching between viruses.[citation needed]

The presence of these genes homologous to the mimivirus in Sputnik suggests that gene transfer between Sputnik and the mimivirus can occur during the infection ofAcanthamoeba.Therefore, it is hypothesized that the virophage could be a source of vehicle mediatinglateral gene transferbetween giant viruses, which constitute a significant part of theDNA viruspopulation in marine environments. Moreover, the presence of three APMV genes in Sputnik implies that gene transfer between a virophage and a giant virus is crucial to viral evolution.[10]

In 2016, for classification of Sputnik-like viruses, including Zamilon, genusSputnikvirusin the familyLavidaviridaehas been established by theInternational Committee on Taxonomy of Viruses.[11]

Structure

edit

The Sputnik virophage has a capsid 74 nm in diameter, withicosahedralsymmetry.[11]Within each asymmetric unit of the structure, there are 4 and 1/3hexoncapsomers. On the 3-fold axis lies one hexon which gives rise to the 1/3 hexon in each asymmetric unit.[12]There are flexible, mushroom-like fibers that protrude from each hexamer.[13]Each asymmetric unit also houses 1/5 of a penton which lies on each 5-fold axis.[12]In the middle of the pentamers are cavities that may allow for the entry or exit of DNA.[13]Sputnik has a triangulation number of 27 with 260 hexamers and 12 pentamers. This virus does not contain a lipid membrane which goes against what has been previously reported.[12]

Other viruses of Sputnik genus

edit

GenusSputnikvirushas two species, which can be divided further into strains:

  • SpeciesMimivirus-dependent virus Sputnik.All three Sputnik virophages share more than 99% of their DNA and can grow with viruses of any Mimiviridae group A, B, and C.[3]
  • SpeciesMimivirus-dependent virus Zamilon.Cannot infect group A due to aMIMIVIREdefense system.[15]
    • Zamilon 1 was discovered in 2013 in Tunisia.
    • Zamilon 2 was discovered in 2015 in North America.

Other virophages

edit
Main article:Virophage

In March 2011, two additional virophages were described: theMavirus virophagewhich preys on the giantCafeteria roenbergensisvirus,[16][3]and theOrganic Lake virophage(OLV), found in the saltyOrganic Lakein Antarctica, and which preys onphycodnavirusesthat attackalgae.[17][18][5]Zamilon virophagewas the first one found infecting a member of Mimiviridae group C (i. e.Mont1virus), being able to grow also in Mimiviridae group B, but not group A.[3]

All host viruses of the known virophages belong to the group ofnucleocytoplasmic large DNA viruses.Studies have been done to show similarities among the various virophages. Homologous genes among virophages include putative FtsK-HerA family DNA packaging ATPase (ATPase), putative DNA helicase/primase (HEL/PRIM), putative cysteine protease (PRSC), putative MCP, and putative minor capsid protein (mCP). These genes are also referred to as conserved core genes although there is sometimes no or very little sequence similarity among these virophages.[19]

See also

edit

References

edit
  1. ^Duponchel, S. and Fischer, M.G. (2019) "Viva lavidaviruses! Five features of virophages that parasitize giant DNA viruses".PLoS pathogens,15(3).doi:10.1371/journal.ppat.1007592.Material was copied from this source, which is available under aCreative Commons Attribution 4.0 International License.
  2. ^abcdBernard La Scola; et al. (2008). "The virophage as a unique parasite of the giant mimivirus".Nature.455(7205): 100–4.Bibcode:2008Natur.455..100L.doi:10.1038/nature07218.PMID18690211.S2CID4422249.
  3. ^abcdefMorgan Gaia et al.:Zamilon, a Novel Virophage withMimiviridaeHost Specificity,in: PLoS One. 2014; 9(4): e94923. Published online 2014 Apr 18.doi: 10.1371/journal.pone.0094923
  4. ^Desnues C (2012)."Provirophages and transpovirons as the diverse mobilome of giant viruses".Proc Natl Acad Sci U S A.109(44): 18078–83.Bibcode:2012PNAS..10918078D.doi:10.1073/pnas.1208835109.PMC3497776.PMID23071316.
  5. ^abcEd Yong:A Parasite’s Parasites,in: The Scientist, October 15, 2012
  6. ^abXie, Yun (September 2008)."Sputnik the virophage: a virus gets a virus".ARS technica.
  7. ^Boyer M (2011)."Mimivirus shows dramatic genome reduction after intraamoebal culture".Proc Natl Acad Sci U S A.108(25): 10296–301.Bibcode:2011PNAS..10810296B.doi:10.1073/pnas.1101118108.PMC3121840.PMID21646533.
  8. ^Sun, Siyang; La Scola, Bernard; Bowman, Valorie D.; Ryan, Christopher M.; Whitelegge, Julian P.; Raoult, Didier; Rossmann, Michael G. (2010-01-01)."Structural Studies of the Sputnik Virophage".Journal of Virology.84(2): 894–897.doi:10.1128/JVI.01957-09.ISSN0022-538X.PMC2798384.PMID19889775.
  9. ^Claverie J-M, Abergel C (2009), "Mimivirus and its Virophage",Annual Review of Genetics,43:49–66,doi:10.1146/annurev-genet-102108-134255,PMID19653859
  10. ^"Biggest Known Virus Yields First-Ever Virophage".Microbe Magazine.November 2008. Archived fromthe originalon 2011-07-22.
  11. ^abKrupovic M, Kuhn JH, Fischer MG (2016), "A classification system for virophages and satellite viruses",Archives of Virology,161(1): 233–47,doi:10.1007/s00705-015-2622-9,hdl:11858/00-001M-0000-0028-DC34-F,PMID26446887
  12. ^abcZhang X (2012)."Structure of Sputnik, a virophage, at 3.5-Å resolution".Proc Natl Acad Sci U S A.109(45): 18431–6.Bibcode:2012PNAS..10918431Z.doi:10.1073/pnas.1211702109.PMC3494952.PMID23091035.
  13. ^abSiyang Sun (2010)."Structural Studies of the Sputnik Virophage".Journal of Virology.84(2): 894–7.doi:10.1128/JVI.01957-09.PMC2798384.PMID19889775.
  14. ^Gaia M, Pagnier I, Campocasso A, Fournous G, Raoult D, et al:Broad spectrum of mimiviridae virophage allows its isolation using a mimivirus reporter.PLoS One 8: e61912 (2013)doi: 10.1371/journal.pone.0061912
  15. ^Levasseur A, Bekliz M, Chabrière E, Pontarotti P, La Scola B, Raoult D (2016), "MIMIVIRE is a defence system in mimivirus that confers resistance to virophage",Nature,531(7593): 249–252,Bibcode:2016Natur.531..249L,doi:10.1038/nature17146,PMID26934229,S2CID4382855
  16. ^Matthias G. Fischer and Curtis A. Suttle (2011). "A virophage at the origin of large DNA transposons".Science.332(6026): 231–4.Bibcode:2011Sci...332..231F.doi:10.1126/science.1199412.PMID21385722.S2CID206530677.
  17. ^Virginia Gewin:'Virus-eater' discovered in Antarctic lake,in: Nature, 28 March 2011,doi: 10.1038/news.2011.188
  18. ^Sheree Yau; et al. (2011)."Virophage control of antarctic algal host–virus dynamics".Proc Natl Acad Sci U S A.108(15): 6163–8.Bibcode:2011PNAS..108.6163Y.doi:10.1073/pnas.1018221108.PMC3076838.PMID21444812.
  19. ^Jinglie Zhou; et al. (2013)."Diversity of virophages in metagenomic datasets".Journal of Virology.87(8): 4225–36.doi:10.1128/JVI.03398-12.PMC3624350.PMID23408616.
edit
Retrieved from "https://en.wikipedia.org/w/index.php?title=Sputnik_virophage&oldid=1198266146"