Tristromaviridae

Alphatristromavirus (formerly: Alphalipothrixvirus) is the sole genus of viruses in the family Tristromaviridae.[1] The thermophilic archaea of the genera Thermoproteus and Pyrobaculum serve as natural hosts. There are currently only two species in this genus: Thermoproteus tenax virus 1[2] and the type species Pyrobaculum filamentous virus 1[3] The genus was formerly classified into family Lipothrixviridae of order Ligamenvirales.[4] However, due to lack of sequence similarity of TTV1 and PFV1 to other members of the Lipothrixviridae, genus Alphalipothrixvirus was renamed to Alphatristromavirus and moved into a separate family, the Tristromaviridae.[1][5]

Tristomaviridae
Virus classification
(unranked): Virus
Realm: incertae sedis
Kingdom: incertae sedis
Phylum: incertae sedis
Class: incertae sedis
Order: incertae sedis
Family: Tristromaviridae
Genus: Alphatristromavirus
Type species
Pyrobaculum filamentous virus 1

Taxonomy

Group: dsDNA

[3]

Structure

Viruses in the genus Alphatristromavirus are enveloped, with rod-shaped geometries. The diameter is around 38 nm, with a length of 410 nm. Genomes are linear, around 15.9kb in length. The TTV1 virion contains four virus-encoded proteins, TP1-4.[2][6] The proteins do not display any sequence similarity to structural proteins of viruses from other families, including lipothrixviruses. Nucleocapsid protein TP1 has apparently evolved from a Cas4 endonuclease, a conserved component of the adaptive CRISPR-Cas immunity, presenting the first described case of exaptation of an enzyme for a virus capsid protein function.[7] High-resolution structure of the virion has been determined by cryo-EM for Pyrobaculum filamentous virus 2 (PFV2), a virus closely related to PFV1 which represents the type species.[8] The structure revealed that nucleocapsid is formed from two major capsid proteins (MCP1 and MCP2). MCP1 and MCP2 form a heterodimer, which wraps around the linear dsDNA genome transforming it into A-form. Interaction between the genome and the MCPs leads to condensation of the genome into the virion superhelix.[8] The helical nucleocapsid is surrounded by a lipid envelope and contains other viral proteins, with VP3 being the most abundant.[5] The fold of the MCPs as well as virions organization of tristromaviruses are similar to those of members of the families Rudiviridae[9] and Lipothrixviridae,[10][11] which together constitute the order Ligamenvirales. Due to these structural similarities, order Ligamenvirales and family Tristromaviridae were proposed to be unified within a class 'Tokiviricetes' (toki means ‘thread’ in Georgian and viricetes is an official suffix for a virus class).[8]

GenusStructureSymmetryCapsidGenomic arrangementGenomic segmentation
AlphatristromavirusRod-shapedHelicalEnvelopedLinearMonopartite

Life cycle

Viral replication is cytoplasmic. Entry into the host cell is achieved by adsorption to the host cell. DNA-templated transcription is the method of transcription. Hyperthermophilic and neutrophilic archaea of the genera Thermoproteus and Pyrobaculum serve as the natural hosts. The virions are released by lysis. Transmission routes are passive diffusion.[3][2]

GenusHost detailsTissue tropismEntry detailsRelease detailsReplication siteAssembly siteTransmission
AlphatristromavirusArchaea: Thermoproteus, PyrobaculumNoneInjectionLysisCytoplasmCytoplasmPassive diffusion

References
  1. Prangishvili, D; Rensen, E; Mochizuki, T; Krupovic, M; ICTV Report, Consortium (February 2019). "ICTV Virus Taxonomy Profile: Tristromaviridae". The Journal of General Virology. 100 (2): 135–136. doi:10.1099/jgv.0.001190. PMID 30540248.
  2. "Viral Zone". ExPASy. Retrieved 12 June 2015.
  3. "ICTV Report Tristromaviridae".
  4. Janekovic, D.; Wunderl, S.; Holz, I.; Zillig, W.; Gierl, A.; Neumann, H. (1 October 1983). "TTV1, TTV2 and TTV3, a family of viruses of the extremely thermophilic, anaerobic, sulfur reducing archaebacterium Thermoproteus tenax". MGG Molecular & General Genetics. 192 (1–2): 39–45. doi:10.1007/BF00327644.
  5. Rensen, EI; Mochizuki, T; Quemin, E; Schouten, S; Krupovic, M; Prangishvili, D (2016). "A virus of hyperthermophilic archaea with a unique architecture among DNA viruses". Proceedings of the National Academy of Sciences of the United States of America. 113 (9): 2478–83. Bibcode:2016PNAS..113.2478R. doi:10.1073/pnas.1518929113. PMC 4780613. PMID 26884161.
  6. Neumann, Horst; Schwass, Volker; Eckerskorn, Christoph; Zillig, Wolfram (1989). "Identification and characterization of the genes encoding three structural proteins of the Thermoproteus tenax virus TTV1". MGG Molecular & General Genetics. 217 (1): 105–110. doi:10.1007/BF00330948.
  7. Krupovic M, Cvirkaite-Krupovic V, Prangishvili D, Koonin EV (2015). "Evolution of an archaeal virus nucleocapsid protein from the CRISPR-associated Cas4 nuclease". Biol Direct. 10 (1): 65. doi:10.1186/s13062-015-0093-2. PMC 4625639. PMID 26514828.
  8. Wang, F; Baquero, DP; Su, Z; Osinski, T; Prangishvili, D; Egelman, EH; Krupovic, M (January 2020). "Structure of a filamentous virus uncovers familial ties within the archaeal virosphere". Virus Evolution. 6 (1): veaa023. doi:10.1093/ve/veaa023. PMC 7189273. PMID 32368353.
  9. DiMaio, F; Yu, X; Rensen, E; Krupovic, M; Prangishvili, D; Egelman, EH (2015). "Virology. A virus that infects a hyperthermophile encapsidates A-form DNA". Science. 348 (6237): 914–7. doi:10.1126/science.aaa4181. PMC 5512286. PMID 25999507.
  10. Kasson, P; DiMaio, F; Yu, X; Lucas-Staat, S; Krupovic, M; Schouten, S; Prangishvili, D; Egelman, EH (2017). "Model for a novel membrane envelope in a filamentous hyperthermophilic virus". eLife. 6. doi:10.7554/eLife.26268. PMC 5517147. PMID 28639939.
  11. Liu, Y; Osinski, T; Wang, F; Krupovic, M; Schouten, S; Kasson, P; Prangishvili, D; Egelman, EH (2018). "Structural conservation in a membrane-enveloped filamentous virus infecting a hyperthermophilic acidophile". Nature Communications. 9 (1): 3360. Bibcode:2018NatCo...9.3360L. doi:10.1038/s41467-018-05684-6. PMC 6105669. PMID 30135568.
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