The Coronavirus

  

The genomic size of coronaviruses ranges from approximately 26 to 32 kilobases, the largest for RNA virus. The name “coronavirus” is derived from the Latin “corona” meaning crown or halo and refers to the characteristic appearance of virions under electron microscopy with a fringe of large, bulbous surface projections creating an image reminiscent of a royal crown or the solar corona. Most of the coronaviruses produce respiratory syndrome.

Coronaviruses are unique among enveloped viruses in that assembly of the viral envelope occurs at the ERGIC. From there, virions bud into the lumen, navigate their way through the host secretory pathway, and ultimately egress from the cell.

                Human coronavirus 229E

                Human coronavirus OC43

                SARS- CoV

                Human coronavirus NL63

                Human coronavirus HKU1

                Middle East Respiratory Syndrome coronavirus

Parts of the Coronavirus:

1.  Envelope Protein (E)

The E protein is the smallest of the major structural proteins, but also the most enigmatic involved in several aspects of the virus’ life cycle, such as assembly, budding, envelope formation, and pathogenesis. it has 76–109 amino acids, ranging from 8.4 to 12 kDa in size.

During the replication cycle, E is abundantly expressed inside the infected cell, but only a small portion is incorporated into the virion envelope.

The majority of the protein is localized at the site of intracellular trafficking, viz. the ER, Golgi, and ERGIC, where it participates in CoV assembly and budding.

To date, E has only been reported to interact with five host proteins:

a.   Bcl-xL

b.   PALS1

c.   Syntenin

d.   Sodium/Potassium (Na+/K+) ATPase α-1subunit

e.   Stomatin

2.  Membrane Protein (M)

The M protein is the most abundant structural protein and defines the shape of the viral envelope. It is also regarded as the central organizer of CoV assembly, interacting with all other major coronaviral structural proteins. Homotypic interactions between the M proteins are the major driving force behind virion envelope formation but, alone, is not sufficient for virion formation. Interaction of S with M is necessary for retention of S in the ER-Golgi intermediate compartment (ERGIC)/Golgi complex and its incorporation into new virions, but dispensable for the assembly process. Binding of M to N stabilizes the nucleocapsid (N protein-RNA complex), as well as the internal core of virions, and, ultimately, promotes completion of viral assembly. Together, M and E make up the viral envelope and their interaction is sufficient for the production and release of VLPs.

3.  Spike Protein (S)

The S protein mediates attachment of the virus to the host cell surface receptors and subsequent fusion between the viral and host cell membranes to facilitate viral entry into the host cell.

4.  Nucleocapsid protein (N)

N is the only protein that functions primarily to bind to the CoV RNA genome. Transient expression of N was shown to substantially increase the production of virus-like particles (VLPs) in some CoVs, suggesting that it might not be required for envelope formation, but for complete virion formation instead.

5.  Lipid Membrane (L)

The role lipids play in viral infection involves the fusion of the viral membrane to the host cell, viral replication, and viral endocytosis and exocytosis.

Lipid metabolism is an important component of the virus life cycle.  lipid metabolism pathways could constitute an early-intervention and exciting host-directed drug target.