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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.
SARS-CoV-2 is the seventh known coronavirus to infect people, after 229E, NL63, OC43, HKU1, MERS-CoV, and the original SARS-CoV. [105] Like the SARS-related coronavirus implicated in the 2003 SARS outbreak, SARS‑CoV‑2 is a member of the subgenus Sarbecovirus (beta-CoV lineage B). [106] [107] Coronaviruses undergo frequent recombination. [108]
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]
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]
Depending on the host cell protease available, cleavage and activation allows the virus to enter the host cell by endocytosis or direct fusion of the viral envelope with the host membrane. [58] Coronaviruses can enter cells by either fusing to their lipid envelope with the cell membrane on the cell surface or by internalization via endocytosis ...
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.
Throughout the COVID-19 pandemic, the genome of SARS-CoV-2 viruses has been sequenced many times, resulting in identification of thousands of distinct variants. In a World Health Organization analysis from July 2020, ORF1ab was the most frequently mutated gene, followed by the S gene encoding the spike protein .