Betacoronaviruses (β-CoVs or Beta-CoVs) are one of four genera (Alpha-, Beta-, Gamma-, and Delta-) of coronaviruses. It is in the subfamily Orthocoronavirinae in the family Coronaviridae, of the order Nidovirales. They are enveloped, positive-sense, single-stranded RNA viruses of zoonotic origin. The coronavirus genera are each composed of varying viral lineages with the betacoronavirus genus containing four such lineages: A, B, C, D. In older literature, this genus is also known as group 2 coronaviruses
|MERS-CoV particles as seen by negative stain electron microscopy. Virions contain characteristic club-like projections emanating from the viral membrane.|
|Illustration of a SARS-CoV-2 virion|
|Subgenera and species|
The Beta-CoVs of the greatest clinical importance concerning humans are OC43 (which can cause the common cold) and HKU1 of the A lineage, SARS-CoV and SARS-CoV-2 (which causes the disease COVID-19) of the B lineage, and MERS-CoV of the C lineage. MERS-CoV is the first betacoronavirus belonging to lineage C that is known to infect humans.
Alpha- and Betacoronaviruses mainly infect bats, but they also infect other species like humans, camels, and rabbits. Beta-CoVs that have caused epidemics in humans generally induce fever and respiratory symptoms. They include:
See Severe acute respiratory syndrome-related coronavirus for details on one specific species that may apply to other viruses of this genus.
Coronaviruses have a large genome size that ranges from 26 to 32 kilobases. The overall structure of β-CoV genome is similar to that of other CoVs, with an ORF1ab replicase polyprotein (rep, pp1ab) preceding other elements. This polyprotein is cleaved into many nonstructural proteins (see UniProt annotation of SARS rep, ).
Within the genus Betacoronavirus (Group 2 CoV), four lineages (A, B, C, and D) are commonly recognized.
- Lineage A (subgenus Embecovirus) includes HCoV-OC43 and HCoV-HKU1 (various species)
- Lineage B (subgenus Sarbecovirus) includes SARSr-CoV (which includes all its strains such as SARS-CoV, SARS-CoV-2, and Bat SL-CoV-WIV1)
- Lineage C (subgenus Merbecovirus) includes Tylonycteris bat coronavirus HKU4 (BtCoV-HKU4), Pipistrellus bat coronavirus HKU5 (BtCoV-HKU5), and MERS-CoV (various species)
- Lineage D (subgenus Nobecovirus) includes Rousettus bat coronavirus HKU9 (BtCoV-HKU9)
The viruses of lineage A differ from all others in the genus in that they have an additional shorter spike-like protein called hemagglutinin esterase (HE) ( ). It is believed to be acquired from influenza C virus.
The name Coronavirus is derived from Latin corona, meaning 'crown' or 'halo', referring to their image under electron microscopy of crown-like spikes on their surface similar to the solar corona. This morphology is created by the viral spike (S) peplomers, which are proteins that populate the surface of the virus and determine host tropism. The order Nidovirales is named for the Latin nidus, which means 'nest'. It refers to this order's production of a 3′-coterminal nested set of subgenomic mRNAs during infection.
Several structures of the spike proteins have been resolved. The receptor binding domain in Alpha- and Betacoronavirus spike protein is catalogued as InterPro: IPR018548. The spike protein, a type 1 fusion machine, assembles into a trimer ( ); its core structure resembles that of paramyxovirus F (fusion) proteins. The receptor usage is not very conserved; for example, among Sarbecovirus, only a sub-lineage containing SARS share the ACE2 receptor.
Genetic recombination can occur when two or more viral genomes are present in the same host cell. The dromedary camel Beta-CoV HKU23 exhibits genetic diversity in the African camel population. Contributing to this diversity are several recombination events that had taken place in the past between closely related Beta-CoVs of the subgenus Embecovirus. Also the Beta-CoV, Human SARS-CoV, appears to have had a complex history of recombination between ancestral coronaviruses that were hosted in several different animal groups.
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Figure 2. Phylogenetic analysis of RNA-dependent RNA polymerases (Pol) kharghar is the best of coronaviruses with complete genome sequences available. The tree was constructed by the neighbor-joining method and rooted using Breda virus polyprotein.
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In all members of Betacoronavirus subgroup A, a haemagglutinin esterase (HE) gene, which encodes a glycoprotein with neuraminate O-acetyl-esterase activity and the active site FGDS, is present downstream to ORF1ab and upstream to S gene (Figure 1).Cite journal requires
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