What is Coronavirus? How Coronavirus can Enter into our Body?

What is Coronavirus?

Coronavirus is the family member of Coronaviridae. It causes a broad spectrum of animal and human diseases.  The name coronavirus is come from the Latin word corona, meaning “halo” or “crown” because they’re covered in a pointed shell like a noble crown.

Coronaviruses are enveloped viruses with a positive-sense RNA genome, but much more common for negative-sense RNA viruses and with a  nucleocapsid of helical symmetry.

Classification of Coronavirus:

Coronaviruses are divided into 3 groups:
Group 1: alpha-coronavirus (α)
Group 2: beta-coronavirus (β)
Group 3: gamma-coronavirus (ɣ)
There is some subgroups have been proposed for Group 2 and Group 3.
Two subgroups in group 2 coronavirus (Groups 2c and 2d) and
Two novel subgroups in group 3 coronavirus (Groups 3b and 3c).

Structure :

Coronavirus virus contains four main structural proteins. These are the spike (S), membrane (M), envelope (E), and nucleocapsid (N) proteins. The lipid bilayer envelope, membrane proteins, and nucleocapsid protect the virus when it’s outside the host cell. It also contains a shorter spike-like surface protein called hemagglutinin esterase. Hemagglutinin esterase is the fifth structural protein that is present in Beta-coronaviruses (β). The spike protein is also the principal player in determining the host cell. This protein acts as a hemagglutinin, binds sialic acids on surface glycoproteins and contains acetyl-esterase activity. These acetyl-esterase activities are supposed to boost spike protein-mediated cell entry and coronavirus spread over the mucosa.

Inside the envelope, there is the nucleocapsid, which is made from multiple copies of the nucleocapsid protein. This nucleocapsid protein is bound to the positive-sense single-stranded RNA genome. The genome size of these viruses ranges from approximately 27 to 34 kielbasas.

The virus attached to the host cell and initiated interactions between the S protein and its receptor. The S-protein/receptor interaction is the primary factor for a coronavirus to infect a host cell and also governs the tissue tropism of the virus. Some coronaviruses develop peptidases enzyme as their cellular receptor. It is not clear why peptidases are used, as entry occurs even in the absence of the enzymatic domain of these proteins.

Coronavirus Receptors:

Virus Receptor
Alphacoronaviruses  
HCoV-229E APN
HCoV-NL63 ACE2
TGEV APN
PEDV APN
FIPV APN
CCoV APN
Betacoronaviruses  
MHV mCEACAM
BCoV N-acetyl-9-O-acetylneuraminic acid
SARS-CoV ACE2
MERS-CoV DPP4

How Coronavirus can Enter into Host?

After the initial binding of the receptor, coronaviruses need to fuse their envelope with the target host cell membrane. After the fusion virus delivers its nucleocapsid into the target cell. The spike protein (Hemagglutinin esterase) plays a double role in entry by mediating receptor binding and membrane fusion. The fusion process includes large conformational modifications of the spike protein. Coronaviruses use a variety of receptors and triggers to activate fusion and the mechanisms of coronavirus entry are complex and differ between coronavirus species and strains. After entering into the host cell Uncoating happens when viral enzymes or host enzymes removed and destroyed the viral capsid. Then exposed the viral nucleic acid into the host cell. Now virus-cell start grows into the host cell by replication, transcription, and translation.

In the past 10-12 years, there are many new coronaviruses have been identified. Among all, They infect a wide range of hosts from mammals to birds, which may be a result of their species diversity, ability to fly, environmental pressures, and habits of roosting and flocking.

References: NCBI, US National Library of Medicine National of Health.

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