SARS coronavirus, also known as SARS-CoV, is a virus which can cause severe acute respiratory syndrome (SARS). SARS coronavirus belongs to a family of enveloped coronaviruses. Coronaviruses are enveloped, single-stranded, positive-sense RNA viruses which belongs to the subfamily Coronavirinae. There are seven human coronaviruses: HCoV-229E, HCoV-OC43, HCoV-229E, HCoV-OC43, SARS-CoV, HCoV-NL63 and HCoV-HKU1, other novel human coronaviruses have also been discovered in recent years.

Coronaviruses can cause a range of symptoms varying from mild symptoms such as the common cold to more serious respiratory illnesses. They primarily cause respiratory and enteric diseases in mammals and birds. Coronavirus symptoms include rhinorrhea, sneezing, cough, nasal obstruction, bronchitis and so on. There are three main groups of coronaviruses: alpha, beta, and gamma. In 2012, a novel coronavirus was identified as the causative agent of rapidly progressive acute respiratory infection in two men from the Middle East.

SARS-CoV causes an atypical pneumonia that spread rapidly throughout parts of Asia, North America, and Europe during 2002-2003. SARS-CoV infection can cause bronchial epithelial cell peeling, cilia damage, the formation of multinucleated giant cells, squamous cell aplasia, alveolar interstitial fiber cell hyperplasia, and fibrotic lung disease. SARS-CoV has the same structure proteins as three previously known groups of coronaviruses: spike glycoprotein (S), membrane protein (M), envelope protein (E) and nucleocapsid protein (N). Coronavirus N protein is required for coronavirus RNA synthesis, and has RNA chaperone activity that may be involved in template switch.

SARS-CoV spike glycoprotein is 1255 amino acids long, with low (20-27 percent) amino acid similarity among other coronaviruses. Its carboxyl terminus (C-terminus) is comprised of the transmembrane region and the cytoplasmic tail. The extracellular domain of the SARS-CoV spike glycoprotein is comprised of two heptad repeat regions which are known as heptad repeat region 1 (HR1) and heptad repeat region 2.

SARS-CoV spike glycoprotein has two functional domains: S1 and S2. S1 is responsible for the binding with its receptor angiotensin-converting enzyme 2 (ACE2) on host cells and defines the host range of the virus. S2 is the transmembrane subunit that facilitates viral and cellular membrane fusion. Membrane fusion occurs when there is a conformational change in the HRs to form a fusion core. The HRs of the protein fold into coiled-coil structure-called the fusogenic state-causing the HR domains of the S protein to fold into a hairpin-like formation. This hairpin structure results in the cellular and viral membranes being pulled together and ultimately fusing.


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