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Replication cycle of a coronavirus. The 5' and 3' ends of the genome have a cap and poly(A) tract, respectively.The viral envelope, obtained by budding through membranes of the endoplasmic reticulum (ER) or Golgi apparatus, invariably contains two virus-specified glycoprotein species, known as the spike (S) and membrane (M) proteins.
Transmission and life-cycle of SARS-CoV-2 causing COVID-19. Coronaviruses vary significantly in risk factor. Some can kill more than 30% of those infected, such as MERS-CoV, and some are relatively harmless, such as the common cold. [49] Coronaviruses can cause colds with major symptoms, such as fever, and a sore throat from swollen adenoids. [91]
For this reason the spike protein has been the focus of development for COVID-19 vaccines in response to the COVID-19 pandemic caused by the virus SARS-CoV-2. [11] [12] A subgenus of the betacoronaviruses, known as embecoviruses (not including SARS-like coronaviruses), have an additional shorter surface protein known as hemagglutinin esterase. [13]
Spike (S) glycoprotein (sometimes also called spike protein, [2] formerly known as E2 [3]) is the largest of the four major structural proteins found in coronaviruses. [4] The spike protein assembles into trimers that form large structures, called spikes or peplomers, [3] that project from the surface of the virion.
M is a glycoprotein whose glycosylation varies according to coronavirus subgroup; N-linked glycosylation is typically found in the alpha and gamma groups while O-linked glycosylation is typically found in the beta group. [8] [9] There are some exceptions; for example, in SARS-CoV, a betacoronavirus, the M protein has one N-glycosylation site.
The envelope (E) protein is the smallest and least well-characterized of the four major structural proteins found in coronavirus virions. [2] [3] [4] It is an integral membrane protein less than 110 amino acid residues long; [2] in SARS-CoV-2, the causative agent of Covid-19, the E protein is 75 residues long. [5]
Scanning electron micrograph of SARS virions. Severe acute respiratory syndrome (SARS) is the disease caused by SARS-CoV-1. It causes an often severe illness and is marked initially by systemic symptoms of muscle pain, headache, and fever, followed in 2–14 days by the onset of respiratory symptoms, [13] mainly cough, dyspnea, and pneumonia.
Certain studies revealed that coronavirus and toroviruses HE was originated from HEF glycoprotein that is found in influenza C viruses which resulted from alteration of hemagglutinin esterase from a trimer into a dimer glycoprotein. [1] During this process, the receptor destroying enzyme acetyl esterase domain stayed unchanged.