Human coronavirus HKU1 instance of taxon
Human coronavirus HKU1 (HCoV-HKU1) is a species of coronavirus in humans and animals. It causes an upper respiratory disease with symptoms of the common cold, but can advance to pneumonia and bronchiolitis. It was first discovered in January 2004 from one man in Hong Kong.  Subsequent research revealed it has global distribution and earlier genesis.
The virus is an enveloped, positive-sense, single-stranded RNA virus which enters its host cell by binding to the N-acetyl-9-O-acetylneuraminic acid receptor. It has the Hemagglutinin esterase (HE) gene, which distinguishes it as a member of the genus Betacoronavirus and subgenus Embecovirus.Virology
Woo and coworkers were unsuccessful in their attempts to grow a HCoV-HKU1 isolate but were able to obtain the complete genomic sequence. Phylogenetic analysis showed that HKU1 is most closely related to the mouse hepatitis virus (MHV), and is distinct in that regard from other known human betacoronaviruses, such as HCoV-OC43.When the RNA-dependent RNA polymerase (RdRp), spike (S), and nucleocapsid (N) genes were analyzed, incompatible phylogenetic relationships were discovered. Complete genome sequencing of 22 strains of HCoV-HKU1 confirmed this was due to natural recombination. HCoV-HKU1 likely originated from rodents.HCoV-HKU1 is one of seven known coronaviruses to infect humans. The other six are:
Human coronavirus 229E (HCoV-229E)
Human coronavirus NL63 (HCoV-NL63)
Human coronavirus OC43 (HCoV-OC43)
Middle East respiratory syndrome-related coronavirus (MERS-CoV)
Severe acute respiratory syndrome coronavirus (SARS-CoV-1)
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)The structures of HCoV-HKU1 spike (S) and hemagglutinin esterase (HE) proteins have been resolved by Cryo-EM in 2016 and 2020, respectively. The S protein (PDB: 5I08​) has been noted for its large size. The HE protein (PDB: 6Y3Y​) differs from conventional ones (such as the one in OC43) by having a much smaller vestigial lectin domain. This domain is shielded from recognition by the immune system via size changes and glycosylation.
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