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". The genus is in the subfamilyOrthocoronavirinae in the familyCoronaviridae, of the orderNidovirales.
The betacoronaviruses of the greatest clinical importance concerning humans areOC43 andHKU1 (which can cause thecommon cold) of lineage A,SARS-CoV-1 andSARS-CoV-2 (the causes ofSARS andCOVID-19 respectively) of lineage B,[2] andMERS-CoV (the cause ofMERS) of lineage C. MERS-CoV is the first betacoronavirus belonging to lineage C that is known to infect humans.[3][4]
The name "betacoronavirus" is derived fromAncient Greek βῆτα (bē̂ta, "the secondletter of theGreek alphabet"), and κορώνη (korṓnē, “garland, wreath”), meaning crown, which describes the appearance of the surface projections seen under electron microscopy that resemble asolar corona. Thismorphology is created by the viralspike (S)peplomers, which are proteins that populate the surface of the virus and determinehost tropism. The orderNidovirales is named for the Latinnidus, which means 'nest'. It refers to this order's production of a 3′-coterminal nested set ofsubgenomic mRNAs during infection.[5]
MERS-CoV: structure, attachment, entrance, and genomic composition
Several structures of the spike proteins have been resolved. The receptor binding domain in the alpha- and betacoronavirus spike protein is cataloged asInterPro: IPR018548.[6] The spike protein, atype 1 fusion machine, assembles into a trimer (PDB:3jcl,6acg); its core structure resembles that ofparamyxovirus F (fusion) proteins.[7] The receptor usage is not very conserved; for example, amongSarbecovirus, only a sub-lineage containing SARS share theACE2 receptor.
The viruses of subgeneraEmbecovirus differ from all others in the genus in that they have an additional shorter (8 nm) spike-like protein calledhemagglutinin esterase (HE) (P15776). It is believed to have been acquired frominfluenza C virus.[5][8]
Coronaviruses have a largegenome size that ranges from 26 to 32 kilobases. The overall structure of β-CoV genome is similar to that of other CoVs, with anORF1ab replicase polyprotein (rep,pp1ab) preceding other elements. This polyprotein is cleaved into 16nonstructural proteins (see UniProt annotation of SARSrep,P0C6X7).
As of May 2013,GenBank has 46 published complete genomes of the α- (group 1), β- (group 2), γ- (group 3), and δ- (group 4) CoVs.[9]
Genetic recombination can occur when two or more viralgenomes are present in the same host cell. Thedromedary camel Beta-CoV HKU23 exhibits genetic diversity in the African camel population.[10] Contributing to this diversity are several recombination events that had taken place in the past between closely related betacoronaviruses of the subgenusEmbecovirus.[10] Also the betacoronavirus, HumanSARS-CoV, appears to have had a complex history ofrecombination between ancestralcoronaviruses that were hosted in several different animal groups.[11][12]
Replication cycle of viruses of genusBetacoronavirus
Alpha- and betacoronaviruses mainly infect bats, but they also infect other species likehumans,camels, androdents.[13][14][15] Betacoronaviruses that have caused epidemics in humans generally induce fever and respiratory symptoms. They include:
Within the genusBetacoronavirus (Group 2 CoV), four subgenera or lineages (A, B, C, and D) have traditionally been recognized.[5] The four lineages have also been named using Greek letters or numerically.[9] A fifth subgenus,Hibecovirus, was added more recently.[16] Member subgenera and species include:[17][18]
.jpg)
