Explain mechanism of covishield spike protein incorporated

Priya sarda

The ongoing pandemic of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), poses a grave threat to global public health and imposes a severe burden on the entire human society. Like other coronaviruses, the SARS-CoV-2 genome encodes spike (S) glycoproteins, which protrude from the surface of mature virions. The S glycoprotein plays essential roles in virus attachment, fusion and entry into the host cell. Surface location of the S glycoprotein renders it a direct target for host immune responses, making it the main target of neutralizing antibodies. In the light of its crucial roles in viral infection and adaptive immunity, the S protein is the focus of most vaccine strategies as well as therapeutic interventions. In this review, we highlight and describe the recent progress that has been made in the biosynthesis, structure, function, and antigenicity of the SARS-CoV-2 S glycoprotein, aiming to provide valuable insights into the design and development of the S protein-based vaccines as well as therapeutics. Synthesis, Processing and Trafficking of the SARS-CoV-2 S Glycoprotein The SARS-CoV-2 S glycoprotein is synthesized as a 1273-amino acid polyprotein precursor on the rough endoplasmic reticulum (RER) . The unprocessed precursor harbors an endoplasmic reticulum (ER) signal sequence located at the N terminus, which targets the S glycoprotein to the RER membrane and is removed by cellular signal peptidases in the lumen of the ER . A single stop-transfer, membrane-spanning sequence located at the C terminus of the S protein prevents it from being fully released into the lumen of the ER and subsequent secretion from the infected cell . Co-translationally, N-linked, high-mannose oligosaccharide side chains are added during synthesis . Shortly after synthesis, the S glycoprotein monomers trimerize, which might be thought to facilitate the transport from the ER to the Golgi complex. Once in the Golgi complex, most of the high-mannose oligosaccharide side chains are modified to more complex forms , and O-linked oligosaccharide side chains are also added .