SARS-related coronavirus
Severe acute respiratory syndrome-related coronavirus | |
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host cells cultured in the lab
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Virus classification | |
(unranked): | Virus |
Realm: | Riboviria |
Kingdom: | Orthornavirae |
Phylum: | Pisuviricota |
Class: | Pisoniviricetes |
Order: | Nidovirales |
Family: | Coronaviridae |
Genus: | Betacoronavirus |
Subgenus: | Sarbecovirus |
Species: | Severe acute respiratory syndrome-related coronavirus
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Strains | |
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Synonyms | |
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Severe-acute-respiratory-syndrome–related coronavirus (SARSr-CoV or SARS-CoV)
These
The SARS-related coronavirus was one of several viruses identified by the
Classification
SARS-related coronavirus is a member of the genus Betacoronavirus (group 2) and monotypic of the subgenus Sarbecovirus (subgroup B).[12] Sarbecoviruses, unlike embecoviruses or alphacoronaviruses, have only one papain-like proteinase (PLpro) instead of two in the open reading frame ORF1ab.[13] SARSr-CoV was determined to be an early split-off from the betacoronaviruses based on a set of conserved domains that it shares with the group.[14][15]
Bats serve as the main host reservoir species for the SARS-related coronaviruses like SARS-CoV-1 and SARS-CoV-2. The virus has coevolved in the
Genome
The SARS-related
The 5' methylated cap and 3' polyadenylated tail allows the
Function of SARSr-CoV genome proteins | |
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Protein | Function[21][22][23][24] |
ORF1ab P0C6X7 |
Replicase/transcriptase polyprotein (pp1ab) (nonstructural proteins) |
ORF2 P59594 |
Spike (S) protein, virus binding and entry (structural protein) |
ORF3a P59632 |
Interacts with S, E, M structural proteins; Bax, p53, and p38 MAP kinase
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ORF3b P59633 |
Upregulates cytokines and chemokines by RUNX1b; Inhibits Type I IFN production and signaling; Induces apoptosis and cell cycle arrest; |
ORF3c P0DTG1 |
Unknown; first identified in SARS-CoV-2 but also present in SARS-CoV |
ORF3d P0DTG0 |
Novel gene in SARS-CoV-2, of unknown function |
ORF4 P59637 |
Envelope (E) protein, virus assembly and budding (structural protein) |
ORF5 P59596 |
Membrane (M) protein, virus assembly and budding (structural protein) |
ORF6 P59634 |
Enhances cellular DNA synthesis; Inhibits Type I IFN production and signaling |
ORF7a P59635 |
Inhibits cellular protein synthesis; Induces inflammatory response by NF-kappaB and IL-8 promotor; Upregulate chemokines such as IL-8 and RANTES; Upregulates JNK, p38 MAP kinase; Induces apoptosis and cell cycle arrest |
ORF7b Q7TFA1 |
Unknown |
ORF8a Q7TFA0 |
Induces apoptosis through mitochondria pathway |
ORF8b Q80H93 |
Enhances cellular DNA synthesis, also known as X5. |
ORF9a P59595 |
Nucleocapsid (N) protein, viral RNA packaging (structural protein) |
ORF9b P59636 |
Induces apoptosis |
ORF9c Q7TLC7 |
Also known as ORF14; function unknown and may not be protein-coding |
ORF10 A0A663DJA2 |
Novel gene in SARS-CoV-2, of unknown function; may not be protein-coding |
SARS-CoV proteins unless they are specific to SARS-CoV-2
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The functions of several of the viral proteins are known.
SARS coronaviruses have been genetically engineered in several laboratories.[27]
Phylogenetics
SARSr‑CoV |
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A phylogenetic tree based on whole-genome sequences of SARS-CoV-1 and related coronaviruses is:
SARS‑CoV‑1 related coronavirus |
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SARS-CoV-2, 79% to SARS-CoV-1[37] | ||||||||||||||||||||||||||||||||||||||||
A phylogenetic tree based on whole-genome sequences of SARS-CoV-2 and related coronaviruses is:[38][39]
SARS‑CoV‑2 related coronavirus | |
SARS-CoV-1 , 79% to SARS-CoV-2
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Morphology
The morphology of the SARS-related coronavirus is characteristic of the coronavirus family as a whole. The viruses are large pleomorphic spherical particles with bulbous surface projections that form a corona around the particles in electron micrographs.[49] The size of the virus particles is in the 80–90 nm range. The envelope of the virus in electron micrographs appears as a distinct pair of electron dense shells.[50]
The
Inside the envelope, there is the nucleocapsid, which is formed from multiple copies of the nucleocapsid (N) protein, which are bound to the positive-sense single-stranded (~30 kb) RNA genome in a continuous beads-on-a-string type conformation.[54][55] The lipid bilayer envelope, membrane proteins, and nucleocapsid protect the virus when it is outside the host.[56]
Life cycle
SARS-related coronavirus follows the replication strategy typical of all coronaviruses.[19][57]
Attachment and entry
The attachment of the SARS-related coronavirus to the host cell is mediated by the spike protein and its receptor.[58] The spike protein receptor binding domain (RBD) recognizes and attaches to the angiotensin-converting enzyme 2 (ACE2) receptor.[7] Following attachment, the virus can enter the host cell by two different paths. The path the virus takes depends on the host protease available to cleave and activate the receptor-attached spike protein.[59]
The attachment of sarbecoviruses to ACE2 has been shown to be an
The first path the SARS coronavirus can take to enter the host cell is by endocytosis and uptake of the virus in an endosome. The receptor-attached spike protein is then activated by the host's pH-dependent cysteine protease cathepsin L. Activation of the receptor-attached spike protein causes a conformational change, and the subsequent fusion of the viral envelope with the endosomal wall.[59]
Alternatively, the virus can enter the host cell directly by proteolytic cleavage of the receptor-attached spike protein by the host's TMPRSS2 or TMPRSS11D serine proteases at the cell surface.[61][62] In the SARS coronavirus, the activation of the C-terminal part of the spike protein triggers the fusion of the viral envelope with the host cell membrane by inducing conformational changes which are not fully understood.[63]
Genome translation
Function of coronavirus nonstructural proteins (nsps)[64] | |
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Protein | Function |
nsp1 | Promotes host mRNA degradation, blocks host translation;[65] blocks innate immune response |
nsp2 | Binds to prohibitin proteins; unknown function |
nsp3 | Multidoman transmembrane protein; interacts with N protein; promotes cytokine expression; PLPro domain cleaves polyprotein pp1ab and blocks host's innate immune response; other domains unknown functions |
nsp4 | Transmembrane scaffold protein; allows proper structure for double membrane vesicles (DMVs) |
nsp5 | 3CLPro cleaves polyprotein pp1ab
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nsp6 | Transmembrane scaffold protein; unknown function |
nsp7 | Forms hexadecameric complex with nsp8; processivity clamp for RdRp (nsp12) |
nsp8 | Forms hexadecameric complex with nsp7; processivity clamp for RdRp (nsp12); acts as a primase |
nsp9 | RNA-binding protein (RBP) |
nsp10 | nsp16 and nsp14 cofactor; forms heterodimer with both; stimulates 2-O-MT (nsp16) and ExoN (nsp14) activity |
nsp11 | Unknown function |
nsp12 | RNA-dependent RNA polymerase (RdRp) |
nsp13 | RNA helicase, 5′ triphosphatase |
nsp14 | N7 Methyltransferase, 3′-5′ exoribonuclease (ExoN); N7 MTase adds 5′ cap, ExoN proofreads genome |
nsp15 | Endoribonuclease (NendoU) |
nsp16 | 2′-O-Methyltransferase (2-O-MT); protects viral RNA from MDA5 |
After fusion the nucleocapsid passes into the
The larger polyprotein pp1ab is a result of a -1 ribosomal frameshift caused by a slippery sequence (UUUAAAC) and a downstream RNA pseudoknot at the end of open reading frame ORF1a.[66] The ribosomal frameshift allows for the continuous translation of ORF1a followed by ORF1b.[67]
The polyproteins contain their own
The two SARS-CoV-2 proteases (PLpro and 3CLpro) also interfere with the immune system response to the viral infection by cleaving three immune system proteins. PLpro cleaves IRF3 and 3CLpro cleaves both NLRP12 and TAB1. "Direct cleavage of IRF3 by NSP3 could explain the blunted Type-I IFN response seen during SARS-CoV-2 infections while NSP5 mediated cleavage of NLRP12 and TAB1 point to a molecular mechanism for enhanced production of IL-6 and inflammatory response observed in COVID-19 patients."[68]
Replication and transcription
A number of the nonstructural replication proteins coalesce to form a multi-protein replicase-transcriptase complex (RTC).[67] The main replicase-transcriptase protein is the RNA-dependent RNA polymerase (RdRp). It is directly involved in the replication and transcription of RNA from an RNA strand. The other nonstructural proteins in the complex assist in the replication and transcription process.[64]
The protein nsp14 is a 3'-5' exoribonuclease which provides extra fidelity to the replication process. The exoribonuclease provides a proofreading function to the complex which the RNA-dependent RNA polymerase lacks. Similarly, proteins nsp7 and nsp8 form a hexadecameric sliding clamp as part of the complex which greatly increases the processivity of the RNA-dependent RNA polymerase.[64] The coronaviruses require the increased fidelity and processivity during RNA synthesis because of the relatively large genome size in comparison to other RNA viruses.[69]
One of the main functions of the replicase-transcriptase complex is to transcribe the viral genome. RdRp directly mediates the
The other important function of the replicase-transcriptase complex is to replicate the viral genome. RdRp directly mediates the synthesis of negative-sense genomic RNA from the positive-sense genomic RNA. This is followed by the replication of positive-sense genomic RNA from the negative-sense genomic RNA.[70]
The replicated positive-sense genomic RNA becomes the genome of the progeny viruses. The various smaller mRNAs are transcripts from the last third of the virus genome which follows the reading frames ORF1a and ORF1b. These mRNAs are translated into the four structural proteins (S, E, M, and N) that will become part of the progeny virus particles and also eight other accessory proteins (orf3 to orf9b) which assist the virus.[71]
Recombination
When two SARS-CoV genomes are present in a host cell, they may interact with each other to form recombinant genomes that can be transmitted to progeny viruses. Recombination likely occurs during genome replication when the RNA polymerase switches from one template to another (copy choice recombination).[72] Human SARS-CoV appears to have had a complex history of recombination between ancestral coronaviruses that were hosted in several different animal groups.[72][73]
Assembly and release
Progeny viruses are released from the host cell by exocytosis through secretory vesicles.[74]
See also
- Bat SARS-like coronavirus WIV1 (SL-CoV-WIV1)
- Bat SARS-like coronavirus RsSHC014
- Bat coronavirus RaTG13
- Civet SARS-CoV
Notes
- ^ The terms SARSr-CoV and SARS-CoV are sometimes used interchangeably, especially prior to the discovery of SARS-CoV-2. This may cause confusion when some publications refer to SARS-CoV-1 as SARS-CoV.
References
- ^ "ICTV Taxonomy history: Severe acute respiratory syndrome-related coronavirus". International Committee on Taxonomy of Viruses (ICTV). Retrieved 27 January 2019.
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- ^ Branswell H (9 November 2015). "SARS-like virus in bats shows potential to infect humans, study finds". Stat News. Retrieved 20 February 2020.
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Most notably, horseshoe bats were found to be the reservoir of SARS-like CoVs, while palm civet cats are considered to be the intermediate host for SARS-CoVs [43,44,45].
- ^ PMID 24172901.
- ^ "Virus Taxonomy: 2018 Release". International Committee on Taxonomy of Viruses (ICTV). October 2018. Retrieved 13 January 2019.
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Figure 2. Phylogenetic analysis of RNA-dependent RNA polymerases (Pol) of coronaviruses with complete genome sequences available. The tree was constructed by the neighbor-joining method and rooted using Breda virus polyprotein.
- ^ Kieny MP. "After Ebola, a Blueprint Emerges to Jump-Start R&D". Scientific American Blog Network. Archived from the original on 20 December 2016. Retrieved 13 December 2016.
- ^ "LIST OF PATHOGENS". World Health Organization. Archived from the original on 20 December 2016. Retrieved 13 December 2016.
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See Figure 1.
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See Figure 1.
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Furthermore, subsequent phylogenetic analysis using both complete genome sequence and proteomic approaches, it was concluded that SARSr-CoV is probably an early split-off from the Betacoronavirus lineage [1]; See Figure 2.
- ^ "Coronaviridae - Figures - Positive Sense RNA Viruses - Positive Sense RNA Viruses (2011)". International Committee on Taxonomy of Viruses (ICTV). Archived from the original on 3 April 2020. Retrieved 6 March 2020.
See Figure 2.
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Betacoronaviruses-b ancestors, meaning SARSr-CoVs ancestors, could have been historically hosted by the common ancestor of the Rhinolophidae and Hipposideridae and could have later evolved independently in the lineages leading towards Rhinolophidae and Hipposideridae betacoronaviruses.
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The SARS-CoV genome is ~29.7 kb long and contains 14 open reading frames (ORFs) flanked by 5′ and 3′-untranslated regions of 265 and 342 nucleotides, respectively (Figure 1).
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Virions acquired an envelope by budding into the cisternae and formed mostly spherical, sometimes pleomorphic, particles that averaged 78 nm in diameter (Figure 1A).
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Particle diameters ranged from 50 to 150 nm, excluding the spikes, with mean particle diameters of 82 to 94 nm; Also See Figure 1 for double shell.
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Nevertheless, the interaction between S protein and receptor remains the principal, if not sole, determinant of coronavirus host species range and tissue tropism.
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Different SARS-CoV strains isolated from several hosts vary in their binding affinities for human ACE2 and consequently in their infectivity of human cells76,78 (Fig. 6b)
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The SARS-CoV can hijack two cellular proteolytic systems to ensure the adequate processing of its S protein. Cleavage of SARS-S can be facilitated by cathepsin L, a pH-dependent endo-/lysosomal host cell protease, upon uptake of virions into target cell endosomes (25). Alternatively, the type II transmembrane serine proteases (TTSPs) TMPRSS2 and HAT can activate SARS-S, presumably by cleavage of SARS-S at or close to the cell surface, and activation of SARS-S by TMPRSS2 allows for cathepsin L-independent cellular entry (26,–28).
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S is activated and cleaved into the S1 and S2 subunits by other host proteases, such as transmembrane protease serine 2 (TMPRSS2) and TMPRSS11D, which enables cell surface non-endosomal virus entry at the plasma membrane.
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Finally, these results, combined with those from previous work (33, 44), suggest that CoVs encode at least three proteins involved in fidelity (nsp12-RdRp, nsp14-ExoN, and nsp10), supporting the assembly of a multiprotein replicase-fidelity complex, as described previously (38).
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Further reading
- Peiris JS, Lai ST, Poon LL, Guan Y, Yam LY, Lim W, et al. (April 2003). "Coronavirus as a possible cause of severe acute respiratory syndrome". Lancet. 361 (9366): 1319–25. PMID 12711465.
- Rota PA, Oberste MS, Monroe SS, Nix WA, Campagnoli R, Icenogle JP, et al. (May 2003). "Characterization of a novel coronavirus associated with severe acute respiratory syndrome". Science. 300 (5624): 1394–9. PMID 12730500.
- Marra MA, Jones SJ, Astell CR, Holt RA, Brooks-Wilson A, Butterfield YS, et al. (May 2003). "The Genome sequence of the SARS-associated coronavirus". Science. 300 (5624): 1399–404. PMID 12730501.
- Snijder EJ, Bredenbeek PJ, Dobbe JC, Thiel V, Ziebuhr J, Poon LL, et al. (August 2003). "Unique and conserved features of genome and proteome of SARS-coronavirus, an early split-off from the coronavirus group 2 lineage". Journal of Molecular Biology. 331 (5): 991–1004. S2CID 14974326.
- Yount B, Roberts RS, Lindesmith L, Baric RS (August 2006). "Rewiring the severe acute respiratory syndrome coronavirus (SARS-CoV) transcription circuit: engineering a recombination-resistant genome". Proceedings of the National Academy of Sciences of the United States of America. 103 (33): 12546–51. PMID 16891412.
- Thiel V, ed. (2007). Coronaviruses: Molecular and Cellular Biology (1st ed.). Caister Academic Press. ISBN 978-1-904455-16-5.
- Enjuanes L, Sola I, Zúñiga S, Almazán F (2008). "Coronavirus Replication and Interaction with Host". In Mettenleiter TC, Sobrino F (eds.). Animal Viruses: Molecular Biology. Caister Academic Press. ISBN 978-1-904455-22-6.
External links
- Media related to Severe acute respiratory syndrome-related coronavirus at Wikimedia Commons
- Data related to SARS-related coronavirus at Wikispecies
- WHO press release identifying and naming the SARS virus (archived 23 April 2003)
- The SARS virus genetic map Archived 18 August 2006 at the Wayback Machine
- Science special on the SARS virus (free content: no registration required)
- McGill University SARS Resources at the Wayback Machine (archived 1 March 2005)
- U.S. Centers for Disease Control and Prevention (CDC) SARS home (archived 12 April 2016)
- World Health Organization on alert