Author: Divya Malhotra
Containing the largest RNA viruses ranging from 28 to 33kb in size, and having a viral envelope that can break down with the use of soap, the coronavirus is not new to anyone. Yet how much do we know about its anatomy?
In the core of the SARS-CoV-2 virion, proteins called Nucleocapsid proteins form a complex with a positive-sense single-stranded RNA. This RNA contains all of the genetic information, and collectively, they inhabit a lot of the host cells defence mechanisms. Particularly, the Nucleocapsid proteins assist the viral RNA to replicate itself, and together, they are enclosed by a protein shell called a capsid.
The capsid lays underneath a viral envelope. This viral envelope is derived from the host cell’s membranes and is made up of three proteins: envelope proteins, membrane proteins, and spike glycoproteins. The envelope proteins are the smallest structural proteins on the viral envelope and are the site of intracellular trafficking during replication. On the other hand, the membrane proteins are central organisers for assembly, interacts with all the other proteins, and supports the membrane curvature. Together these two proteins, help in setting up workshops where the virus and the host’s cells collaborate to make new viral particles. The third protein, the spike glycoproteins, are what scientists are currently using to map out vaccines, and are responsible for the characteristic crown-like spikes (corona means crown in Latin hence the name). The spikes can be distinguished into two functional subunits: s1 or s2. S1 helps in binding the host cell receptor and s2 helps infuse the virus’ membranes with the host’s membranes to make sure they are bonding.
Additionally, the Spike Glycoproteins have ten to twenty times more than the affinity than the last time the virus was present in 2002 (affinity is the strength of binding interaction between antigen and antibody molecules) which may explain why the virus is spreading faster than previous SARS virus. In particular, they bind to Angiotensin-converting enzyme 2 receptors or ACE-2 receptors. These can be found on the surface of epithelial cells in places like the lungs, heart, intestines, kidneys, or blood vessels.
Moreover, Spike Glycoproteins are the main targets of neutralising antibodies which is a type of antibody that is produced naturally as part of our immune system responses. These antibodies are triggered by infections or vaccinations and inhibit or destroy foreign substances that invade the body.
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