The Molecular Biology of Coronaviruses

  Biology Of Coronavirus

Coronaviruses are a family of enveloped RNA Viruses that are distributed widely among mammals and birds, causing respiratory or enteric diseases but in some cases neurologic illness or hepatitis. Individual coronaviruses usually infect their hosts during a species-specific manner, and infections are often acute or persistent. Infections are transmitted mainly via respiratory and fecal-oral routes. The-molecular-biology-of-coronaviruses the foremost quality of this viral family is genome size coronaviruses have the most important genomes among all RNA viruses. Also including those RNA viruses with segmented genomes.

This expansive coding capacity seems to both provide and necessitate a wealth of organic phenomenon strategies. And most of which are incompletely understood.
Virion Morphology, Structural Proteins, and Accessory Proteins

A. Virus and Nucleocapsid

• Coronaviruses are roughly spherical and moderately pleiomorphic. Virions have typically been reported to possess average diameters of 80–120 nm. But extreme sizes as small as 50 nm and as large as 200 nm. The surface spikes or peplomers of those viruses, variously described as clublike, and pear-shaped. And petal-shaped, project some 17–20 nm from the virion surface having a skinny base that swells to a width of about 10 nm at the distal extremity.
• For a few coronaviruses the second set of projections, 5–10nm long, forms an undergrowth beneath the main spikes. These shorter structures are now known to be the hemagglutinin esterase (HE) protein that’s found during a subset of group 2 coronaviruses.

B. Receptors:

• The pairings of coronaviruses and their corresponding receptors are generally highly species-specific, but the difference of SARSCOV -2 to the human population has reminded us that this allegiance is mutable. Well before the emergence of SARS. It had been clearly documented that another coronavirus, BCoV, was capable of sporadic cross‐species transmission.
• Viruses very closely associated with BCoV had been isolated from wild ruminants puppies and, in one case, a person’s child. Nevertheless, the interaction between S protein and receptor remains the principal, if not sole, determinant of coronavirus host species range and tissue.

C. Accessory Proteins:–

• Interspersed among the set of canonical genes, replicate, S, E, M, and N, all coronavirus genomes contain additional ORFs, during a wide selection of configurations. these “extra” genes can fall in any of the genomic intervals among the canonical genes and may vary from as few together (PEDV and HCoVNL63) to as many as eight genes (SARS-CoV).
• In some cases, accessory genes are often entirely embedded in another ORF, because the internal (I) gene found within the N gene of the many groups 2 coronaviruses. And they extensively overlapped with another gene because of the 3b gene of SARS-CoV. Many accessory genes don’t constitute the 5′most ORF within the largest subgenomic RNA during which they seem. And that they, therefore, must require nonstandard translation mechanisms for his or her expression.

D. Host Factors:

• RNA viruses often expropriate and redirect host cell components, to help in mechanisms of their own organic phenomenon. A variety of host factors propose to participate in coronavirus RNA synthesis. All of those discovered with either MHV or BCoV. And everyone originally identified on the idea of their ability to bind in vitro to RNA segments of functional importance.
• The most completely characterized coronavirus host factor is heterogeneous and nuclear Ribo nuclear protein (hnRNP A1). Which initially found as a member of a group of proteins that sure to the negative strand of the MHV TRS. Its RNA-binding property, its affinity for MHV N protein, and its propensity to dimerize, all made hnRNP A1 attractive as a possible mediator of the antigenome looping out event envisaged by the leader primed transcription model.

E. Genetics and Reverse Genetics:

• Numerous coronavirus mutants isolate over the past 25 years, mainly with MHV. Mutants identify as present viral variants (often on the idea of causing atypical pathogenesis). Alternatively, they obtain through selection criteria like shake neutralization by monoclonal antibodies.
• A number of sets of MHV mutants generate by chemical mutagenesis, followed by screening for temperature-sensitive phenotypes. In one case, for aberrant cytopathic effect or plaque morphologies. Although the latter search yielded a strangely high proportion of structural protein mutants viruses with conditionally lethal, RNA negative phenotypes were the predominant isolates altogether searches.
• The arrangement of the coronavirus genome dictates that the overwhelming majority of randomly generated mutations will fall within the replicate gene, due to its large target size. Despite assiduous efforts that applied classical genetic methods to the study of the progress limited by the technology available at the time. And exploitation of the complete value of those mutants would await the event of reverse genetic techniques.

Written By: Dr. Rashid Aslam (DVM, Pathologist Specialist)