The Beta-CoVs of the greatest clinical importance concerning humans are OC43 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:
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, 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.
Diagram of coronavirus virion structure showing spikes that form "crown" like the solar corona, hence the name.
Illustration of SARSr-CoV virion
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 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 assembles into a trimer (PDB: 3jcl, 6acg); 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.
^Memish, Z. A.; Zumla, A. I.; Al-Hakeem, R. F.; Al-Rabeeah, A. A.; Stephens, G. M. (2013). "Family Cluster of Middle East Respiratory Syndrome Coronavirus Infections". New England Journal of Medicine. 368 (26): 2487–94. doi:10.1056/NEJMoa1303729. PMID23718156.